Engineering Overview of Computer Networking

1Dr. Martin LandReviewProtocols and Networks — Hadassah College — Fall 2021

Engineering Overview

of Computer Networking


What is Computer Networking?Logical separation of tasks in digital systems

Data exchange between computation unitsCommunication:Local operations (ALU, load, store, branch, OS, …)Computation:

Local computationRequest information

Receive informationLocal computation

Accept requestProcess requestLocal computationSend response

communication

communication


Physical Transmission Serial data rate at physical layer

Bits per second = bps = b/sBytes per second = B/s1 B/s = 8 b/s

Capacity (bandwidth)Maximum data rate on mediumFixed by transmitter / medium / receiverLimits

Speed of circuitsSignal to noise ratio (SNR)

01


Physical Transmission Throughput

Takes account ofUtilization = % time transmitter sendingErrors re-transmission more data on same capacityDelays less data received on same capacity

2 3 1 4

utilization = 11 / 16 = 68.75%througput = 10 / 16 = 62.5%

0 16

1

bit errors

bits received

error-free data received per secondthroughputcapacity


Baud Rate

SymbolPhysical signal that encodes bits

Symbol rate (Baud rate)Symbols transmitted per second

Bit transmission rateBits transmitted per second = (symbols / second) (bits / symbol)

ExamplePulse amplitude modulation (PAM)Define 2N electrical levels from 0 to 11…1Each symbol (level) transmits N data bits

0001

1011

N = 2 (4 Level) PAM1.00 V

0.50 V0.75 V

0.25 V

Symbols per second


Baud Rate

33 kbps dial-up modemDefine 210 = 1024 electrical symbols (max for SNR on phone line)Baud rate = 3300 symbols / second

Bits transmitted per secondData rate = (3300 symbols / second) (10 bits / symbol)

= 33,000 bps

0000000000

00000000010000000010

1111111111

N = 10 (1024 Level) PAM

...

Symbols per second


Modeling InformationInformation

Set of possible answers (outcomes) to questions (tests)Finite set (yes/no, day of week, 256 pixel colors, etc)Infinite set ("Guess what happened today!")

Communication — transmission of symbol to receiverBefore transmission receiver has limited knowledge of symbol

Permitted range of symbols (universe of outcomes)Statistical distribution of symbols within range

After transmission receiver has better knowledge of outcomeReceiver tests message to decides on most likely symbol (outcome)Decision accuracy limited by noise

NoiseInterference, rounding-off errors, resolution of detector, etc.Communication does not determine unique outcome


Modeling NoiseReceiver detects

Signal from transmitterNoise sources

Other transmittersResolution errorsElectrical cables and devicesLightening

Input Electrical current or voltageSum of Signal and Noise

Transmitter Receiver

Signal

Noise

Input = Isignal + Inoise


Signal and Noise Inputs in 2‐Level Transmission

1 1 0 0 1 0 1 0 1 0 0 0

time0 2 3 4 5 6 7 8 9 10 11 12

AT

time

0 time

AA/2

Binary 2 level transmission

22 2 20noise noise noise noiseI I I I

2 21 12 2signal signalI A I A

Gaussian additive noise

DecisionSignal < A / 2 binary 0 Signal > A / 2 binary 1

Received signal = faded transmission + added noise

Signal to Noise Ratio

2 2

22 2signal

noise

I ASNRI


Probability of Error in 2 Level Transmission

2 22 2

22 2

2 22

| 0 0 |1 11 1| 0 |12 2

1 | 0 |1212 2 2

1 1 12 2 2

1 11 erf 12 22 2

error error error

error error

error error

noise noise

AI I

A

P P P P P

P P

P P

A AP I P I

e dI e dI

A

2

2 2

2 2

0

1 1 12erf 1 erf2 2 2

1 1 21 erf erf2 2

,

signal

noise

xy

A I

I

SNR x e dy

4

113

1 0.24

25 2.1 10

1023 1.2 10

error

error

error

SNR P

SNR P

SNR P


Quantifying InformationSet of possible outcomes (received symbols)

K = 2k different symbolsSymbol label = k-bit binary integers

Communication contentOne symbol of K possible symbolsOne label: k = log2 K bits

Information RatesSystem transmits one symbol in seconds

Shannon's theorem

b

W

= (W symbols / second) (k bits / symbol)= W k bits / second= W log2 K bps

Bit rate

= (1/) symbols / secondBaud rate

21 log 1maximum Maximum CapacityK SNR W SNR


Shannon's Theorem — Examples Average signal power = average noise power

V.34 modemCapacity (Bit Rate) = 33,000 bps Symbol rate W = 3,300 Hz

2 2log 1 log 1 1Capacity W SNR W W

2

102

log 1

log 1 10 2 1

33,000 3,300

Required 1023 SNR

SNR SNR


Probability of Error in DSSSDirect Sequence Spread Spectrum (DSSS)

Encode 1 data bit as an m-bit "chip" sequence 1 data bit error m/2 bit errors in one chip

bit = 8 Chips

Bit 1

Bit 0


DSSS Lowers Probability of Error

2

2

/ 2

/ 2 / 2 1

1

/ 2

bit error at least chip errors

chip errors chip errors

chip error chip error

chip error

m k m k

mk

m

P P m

P m P m

mP P

k

mP

m

2

4 42 2 6

810

810 1 10 ... 10

4

bits per chipchip error

bit error

mP

P

Example


Inter‐Symbol Interference

Transmitted signal undergoes multipath delayReceived signal is sum of delayed contributions

Inter-Symbol Interference (ISI)Interference caused by overlap between sequential bitsCauses bit errors

Jitter Delay varies from bit to bitDifficult to determine proper sampling clock

T1

T3 > T2 > T1

T2 > T10 1 0


Data Concentration High capacity link

No single node can utilize link capacityExample

Optical fiber cable with 4 fibers at 25 Gbps = 100 Gbps

Multiplexing Combine multiple nodes onto one linkExample

Optical fiber with 25 Gbps data rateCombine 25 nodes transmitting at 1 Gbps

25 inputsat 1 Gb/s

1 output at25 Gb/s

Multiplexor


Multiplexing MethodsFrequency Division Multiplexing (FDM)

Divide available frequencies (bandwidth) among nodesNodes transmit simultaneously on different frequencies

ExampleFM radio uses 88 MHz to 108 MHz = 20 MHz bandwidthDivide 20 MHz into 100 channels = 200 kHz per FM channel

88 91.3 93.9 95.5 96.6 97.8 101 104.8 MHz88 מוסיקה צ"גל ' ב צ"גל ' ג ירושלים ' ד


Multiplexing MethodsTime Division Multiplexing (TDM)

Divide capacity into time slotsNode transmits in assigned time slot

ExampleE1 digital line transmits at 2048 kbpsDivide 2048 kbps line into 32 time slots = 64 kbps per node

32 x 64 kbps = 2048 kbps = 2.048 Mbps

32 inputsat 64 kbps

1 output at2.048 Mbps

Multiplexor

32 outputsat 64 kbps

1 input at2.048 Mbps

Demultiplexor


E1 Multiplex

1125 s/sample

8000 samples/second

32 inputsat

8000samples/sec

1 output at32 x 8000 x 8 bps = 2.048 Mbps

byte from line 0

byte from line 1

byte from line 2

byte from line 31

0 1 2 ... 31

125 s

Every 125 sec multiplexor (MUX) receives 8‐bit sample from each line

(isochronous)

125 sec/frame3.91 sec/sample

32 samples/frame


Cellular telephoneMixed Multiplexing

Time Division Multiple Access (TDMA)Used on GSM (2G) and UMTS (3G) phonesCombines FDM and TDM

Frequency Division Multiplexing (FDM)GSM bands = 25 MHzDivide 25 MHz into 125 channels = 200 kHz per channelTransmit 270 kbps over 200 kHz channel

Time Division Multiplexing (TDM)Divide 270 kbps into 8 times slots = 33 kbps per user33 kbps = 23 kbps for voice + 10 kbps control


Data Statistics — CBRConstant Bit Rate (CBR)

Isochronous data Equal time interval between bitsBits per second = constant

Average data rateAverage data rate = peak data rate = minimum data rate

ExampleUncompressed digital audioSample analog signal every T seconds Round-off sample to n-bit numberDigital audio stream at n / T bps


Multiplexing StatisticsDeterministic multiplexing (CBR)

N Nodes = N time slotsNode reserves fixed time slot

Guaranteed transmission capacityNode transmits in assigned time slot

Example

N Nodesassigned

fixedtime slot

DeterministicMultiplexor

N time slots at B bps

N x B bps

39.81312 Gbps256 x E4STM‐256

9.95328 Gbps64 x E4STM‐64

SDHPDH

2.48832 Gbps

622.08 Mbps

155.52 Mbps

51.84 Mbps

16 x E4

4 x E4

E4

21 x E1

STM‐16

STM‐4

STM‐1

STM‐0

139.264 Mbps4 x E3E4

34.368 Mbps4 x E2E3

8.448 Mbps4 x E1E2

2.048 Mbps32 x DS0E1


Data Statistics — VBR Variable Bit Rate (VBR)

Bursty dataPeak data rate B > average data rate Assume packets are independent (Poisson statistics)

ExampleData sent by time-of-day client

Request time (1000 bits) once every hour (3600 seconds)Average data rate = 1000 bits / 3600 seconds = 0.28 bps

Peak data rate = 55 Mbps on 802.11g WiFiPeak data rate B = 55 Mbps > average data rate = 0.28 bps

, ,

, ,!

kT

P k T kT

TP k T e

k

probability of bits arriving

in seconds when average rate =

1 0.280.28, , 0.28 0.21

1!P e 1 bit 1 second


Multiplexing StatisticsStatistical multiplexing (VBR)

M nodes > N time slotsBursty data

Average data rate < peak data rate BAverage traffic = M x < capacity = N x B

Actual traffic < capacity OKActual traffic > capacity data delayed or lost

Example Internet routers

M Nodesrequest

time slots

StatisticalMultiplexor

M > N time slots at B bps

N x B bps


SwitchingSwitch

Multiplexor + DemultiplexorData at input_porti output portji,j = 0, 1, 2, ... , N - 1

Example

N inputs x B bps= N x B bps

N outputs x B bps= N x B bps

Capacity = C bps

switch

1

2

3

4 1

2

3

4


Circuit Switching — Circuit Mode ConnectionDeterministic multiplexing

Capacity C = N BDedicated (reserved) link

input_porti output portjNo competition (M nodes = N time slots)Guaranteed capacity B — if used or not

ExampleBezeq phone call64 kbps from telephone to telephone (even if no one speaks)



Capacity = C bps

switch


Packet Switching — Packet Mode ConnectionStatistical multiplexing

Capacity C = N B < total possible demand = M B Dynamical time slot assignment (on request)

input_porti output portjCompetition

More ports than capacity (M > N)Demand > capacity delay

ExampleInternet routerPacket queue — first come first served



Capacity = C bps

switch


Message Delay

Transmission delay TTTT = Time to inject bits into line = (bits in packet) / (bits per second)

Processing delay TprocPacket processing time in intermediate node

Propagation delay TpropTprop = (length of cable) / (signal speed)

Queuing delay TQTime packet waits in buffer for previous packets (congestion)TQ = (service time per packet) (packets waiting in buffer + 1)

Example: 1000 Mb / 100 Mbps = 10 sec

Example: 4 km / (2 108 km/s) = 2 10-8 sec << 10 sec

TT TpropTQ NodeTprocNode


Example of Queuing Delay

Queuing delay TQPackets waiting in buffer = utilization / (1 – utilization)TQ = (service time per packet) / (1 – utilization)

Queuing delay exampleService time per packet = 10 ms / packet

Service rate = 100 packets / secondAverage traffic = S = 85 packets / second

Utilization = (85 packets / second) / (100 packets / second) = 0.85Buffer level = 0.85 / (1 – 0.85) = 5.7

TQ = (10 ms / packet) / (1 – 0.85) = 67 msSwitch capacity C = 100 packets / second

Demand > 100 buffer overflow excess delay

85

1 1 101

85 0.05! !

demand demand k k

S

k C k C k

SP C P k e ek k

TT TpropTQ NodeTprocNode


Error ControlBit error

Data 1 received as 0 or data 0 received as 1

Packet LossCongestion or buffer overflow packet discarded

Error detectionError correction code / redundancy code / checksumChecksum transmitted with data in header / trailerReceiver compares independent hash with transmitted code

Error controlRequired

Discard corrupt packetOptional

Retransmit discarded / missing packets

bit errors in received dataBit Error Rate (BER)

bits in received data

packets lostPacket loss rate

packets transmitted


Flow Control and Congestion ControlFlow control

Sender avoids overflow of receiver bufferCongestion control

All senders avoid overflow of intermediate network buffersBuffer arrival rate

Bytes / second arriving from networkBuffer empty rate

Bytes / second leaving to network or application layerBuffer file time

Example

Full

EmptyArriving bytes

Leaving bytes

overflowbuffer size

Tbuffer arrival rate buffer empty rate

overflow

64 KB 64 KBT 16 seconds

8 KB/sec 4 KB/sec 4 KB/sec


Congestion Control

AssumptionsData packets arrive independently (Poisson statistics)

Random length (bytes)Average arrival rate in steady state

Data packets leave independently (Poisson statistics)Average emptying rate in steady state

Results

Queuing theory

arrival rateUtilization

empty rate

1 1 1Latency

empty rate arrival rate empty rate 1

Buffer Level Latency arrival rate1 0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Utilization

latencybuffer level


Congestion Control

(Over)-simplified throughput model

Realistic throughput behaviorHigh arrival rate at bufferLonger latency + overflowSender timeoutsRe-transmit more segments higher arrival rate at buffer

Buffer throughput

1

buffer utilization(from all senders)

latency


latency

1

throughput at receivers

1

1

receive rate

throughtputmaximum receive rate

arrival ratebuffer utilization

empty rate



Infrastructure layers

Physical layer (PHY)Physical transmission of bits

Data Link layer (DL)Management of PHYMake physical technology do what we want

Infrastructure managementDelivering data messages — 10% of effortMaking hardware work correctly — 90% of effort

OAM = Operations+Administration+MaintenanceApplication assumes infrastructure "just works""Just works"

Reliability, availability, stability, serviceability, growth

Data Link

physical bits


Layered Protocol ModelLayered communication

Communication task divided into layersProtocol stack

Specific peer-to-peer protocol defined at each layerLayer n protocol

Performs VIRTUAL COMMUNICATION between layer n peers Processes only layer n informationPasses request to layer n – 1 for communication serviceReceives response from layer n – 1

Layer 1

…

Layer n – 2

Layer n – 1

Layer n

Layer 1

…

Layer n – 2

Layer n – 1

Layer n Layer n protocolVirtual peer transaction

Layer 1 protocolPhysical peer transaction

ServiceTransactions Layer n – 2 protocol

Virtual peer transaction


Encapsulation — Protocol HeadersLayer n – 1 protocol

Receives service request from layer nRequest = message to layer n peer agent

Adds layer n – 1 HEADERHeader = message to layer n – 1 peer agent

Service Data Unit (SDU) at layer n – 1 Message received from layer nTreated as meaningless data by layer n – 1

Protocol Data Unit (PDU) at layer n – 1 Message sent by layer n – 1 protocolIncludes layer n – 1 SDU = layer n – 1 header + layer n PDU

Layer n – 1

Layer n

Layer n – 1

Layer n

Layer n – 1 SDU = Layer n PDULayer n –1 Header

Layer n PDU

Layer n – 1 PDU


Functional Analysis of CommunicationOpen System Interconnection Model (OSI)

DescriptionFunctionLayer

Physical

Data Link

Network

Transport

Session

Presentation

Application

Data transmission between neighboring hardware agents on physical channels (electrical, optical, radio, …)1

Control of data transmission between neighboring hardware agents (one hop)2

End-to-end data routing between host nodes via multiple hops3

Reliable end-to-end data exchange between host nodesPrevents data loss, errors, repetitions, ordering errors4

Identification, separation, and continuity of multiple ongoing data transactions between software agents5

Syntax and semantics of exchanged data6

Exchange of data between user applications7


Internet Functional Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

OSI Function CommentInternet

LayerOSI

Layer

Infrastructure

Network

Transport

Application

1

Internet protocols do not discuss physical data transmission

2

End-to-end data routing as in OSI3

4

Internet session management can be:Reliable — with transport serviceUnreliable — without transport service

5

6Application provides presentation service and some session service (transactions)

7

Ref: http://tools.ietf.org/html/rfc4949


Internet PDUsProtocol Data Unit (PDU)

Attachment Hardware Address

Network (IP) AddressPort

SocketIDPDUMessageLayer

Signal Frame

DatagramSegmentMessage

BitsHeader + Trailer

Header Header Data

PhysicalData LinkNetworkTransportApplication

T-DLApplication DataH-TH-NH-DL

Headers added by layers 2, 3, 4 Trailer

Host-to-host data framenetwork datagramtransport segment

EndpointNetwork Address + Port


Data Link SublayersLogical Link Control (LLC) sublayer

Multiplexing of data sources / destinationsPacket type identificationError correctionFlow control

Medium Access (MAC) sublayerNetwork topologyMedium access management

Sharing medium among nodesPermission to transmit

Data frame structureHardware (MAC) addressingError detection

1

2MAC

Sublayer

Physical Layer

Data Link Layer

LLC Sublayer


Data Link FunctionsSimilar to transport layer functions

FramingAssemble network PDUs into hardware packetsAttach header + trailer for Data Link and Physical layers

Medium access + flow control + congestion control When / how transmitter sends data onto linkTransmitter avoids overflow of receiver bufferTransmitters avoid interfering with other transmitters

Error controlDetect / correct transmission bit errors

Local addressingTransmit locally using hardware MAC addresses

Transport Reliability

Data LinkReliability

Data LinkReliability


Medium Access SharingTime division

Each host granted full bandwidth in allocated time slotTime slot allocated deterministically or statistically

ExamplesDeterministic — telephone switchingStatistical — Ethernet, WiFi, …

Frequency divisionEach host granted partial bandwidth in all time slotsExamples

Commercial radio / TVBluetooth

Code divisionEach host granted full bandwidth in all time slotsEach host transmits using different coding schemeExample

Cellular CDMA


Common Shared Medium Networks

ITU 2G / 3G cellular networkWireless code‐division access

CDMA / CDMA2000

ITU 2G / 3G cellular networkWireless time/frequency‐division access

GSM / UTMS

IEEE 802.16 metropolitan area networkWireless time/frequency‐division access

WiMAX

IEEE 802.15 personal area networkWireless frequency‐division access

Bluetooth

IEEE 802.11 local area networkWireless time‐division access

IEEE 802.3 local area networkWired time‐division access

WiFi

Ethernet


Connection TypesConnection

State machine associated with data exchangeSet-up channel before data exchangeMonitor channel state during data exchangeMultiple transactions associated with connection stateClose channel after data exchange

Connection-orientedExample — phone call

Connection at application layerEnter number answer call extended conversation disconnect

ConnectionlessExample — email message

No connection at application layerSend email hope message arrives hope message is found / read


High‐Level Data Link Control (HDLC)Family of data link protocols

Based on IBM SDLC Layer 2 protocol in mainframe SNA Originally for communication between CPUs and peripherals

Link Access Protocol (LAP)Versions of HDLC used in public network architectures

SLIP, PPPInternet point‐to‐point

IEEE 802.2Ethernet Logical Link Control (LLC)

LAPDISDN

LAPFFrame Relay

LAPBX.25


HDLC Frame StructureGeneral HDLC frame

Address8 bit address 256 hardware addresses

Control fieldSpecifies frame type / control

01111110 Address Control data CRC 01111110

8 8 8 0 16 / 32 8

7 6 5 4 3 2 1 0

Information (data) 0 SEQ N(S) p/f NEXT N(R)

7 6 5 4 3 2 1 0

Supervisory (flow control) 1 0 type p/f NEXT N(R)

7 6 5 4 3 2 1 0

Unnumbered (management / connectionless) 1 1 type p/f subtype


HDLC Internet ProtocolsSerial Line Internet Protocol (SLIP)

RFC 1055 (old and rarely used)

Point-to-Point Protocol (PPP)Layer 2 protocol used between

Internet routersHost and Internet service provider (ISP)

Address = 11111111 = broadcastHDLC control = 11000000 = Unnumbered (connectionless data)Protocol

Protocol in data fieldNetwork protocol or link negotiation protocol (layer 2 control sublayer)

0xC0IP datagram with byte stuffing (C0 DB DC, DB DB DB)0xC0

01111110 11111111 11000000 Protocol Data CRC 01111110 8 8 8 8 or 16 0 16 / 32 8


PPP Protocol OptionsStandard network protocols

IP, IPX, AppleTalk, …Datagram in data field

Control sublayersLink Control Protocol (LCP)

PPP optionsHeader compression (remove control / address fields)Size of protocol / CRC fields and data

Test Terminate

Network Control Protocol (NCP)Network layer options

ProtocolAddressHeader compression (encode header fields)

Authentication (ISP user / password exchange)

01111110 11111111 11000000 Protocol Data CRC 01111110 8 8 8 8 or 16 0 16 / 32 8


Ethernet Frame

4 bytes46 – 1500 bytes2 bytes6 bytes6 bytes1 byte7 bytes

CRCDataType or Length

SrcAddress

Dest AddressStartPreamble

IP = 0x0800 AppleTalk = 0x809BARP = 0x0806

Length of data field (<1500)Length

CRC‐32CRC

Code identifying protocol in data fieldUsed in most Ethernet systemsType codes > 1536 =0x600

Type

Hardware (MAC) address of node48‐bit MAC addresses assigned by OEM and fixed in hardwareBroadcast address FF:FF:FF:FF:FF:FF (frame read by all STAs)

Address

10101011Start

7 bytes of 10101010 for sync of receiversPreamble


Ethernet Switch (Hub)Implements Ethernet medium access (MAC) protocol

Simplest layer 1 + 2 packet switch architectureFrame at input port output port by DEST address

Learning modeSRC address in frame associates MAC address with port number

1

2

3

4 1

2

3

4



Capacity = C bps

switch

Switch Fabric: typically C = N x B no blocking or buffering


Asynchronous Transfer Mode (ATM)Complex layer 1 + 2 packet switch infrastructure

Path + Circuit SwitchingVPI — virtual path identifierVCI — virtual circuit identifier

Capacity2.5 Gbps (STM-16)

Small frames (cells) fast priority switching + low latency (delay)53 byte cell = 5 byte header + 48 byte data

GFC VPI

VPI VCI

VCI

VCI PTI CLP

HEC

PAYLOAD

PAYLOAD

8 bits

1

2

3

4

5

53

VPI

VPI VCI

VCI

VCI PTI CLP

HEC

PAYLOAD

PAYLOAD

8 bits

1

2

3

4

5

53

at User-to-Network Interface (UNI) at Network-to-Network Interface (NNI)

GFCGeneric Flow Control

PTIPayload Type Indicator

CLPCell Loss Priority

HECheader error check


Virtual Path:Virtual CircuitPath = set of circuits

VCI 1

VCI 2

VCI 1

VCI 2

VPI 4 VPI 7

VCI 3

VCI 4

VPI 2

VCI 1VPI 3

VCI 1

VCI 2

VPI 4

VCI 1 VPI 8

VP

VP

physicaltransmission

path

VP

VP

VC

VC

VC

VC


Quality of Service (QoS) ParametersService Level Agreement (SLA)

Defines parameters for each service flowService implemented in switching operations

Peak Cell Rate (PCR)Maximum instantaneous transmission rate

Sustained Cell Rate (SCR)Average transmission rate measured over time

Minimum Cell Rate (MCR) Minimum required cell rate

Cell Loss Ratio (CLR)Percentage of cells lost to error / congestion

Cell Transfer Delay (CTD)Total in system delay due to propagation + queuing + service delay

Cell Delay Variation (CDV)Variance of CTD (jitter)

Burst Tolerance (BT) Maximum burst size (cells) permitted at peak rate


Quality of Service (QoS)

Traffic categoriesConstant Bit Rate (CBR)

Emulates isochronous circuit mode

Variable Bit Rate (VBR)Statistical multiplexingSpecified QoS parameters

Available Bit Rate (ABR) Cheaper statistical multiplexingNo guaranteed minimum loss or delay

Unspecified Bit Rate (UBR) Cheapest statistical multiplexingNo guaranteed QoS


Protocol LayersATM Adaptation Layer (AAL)

Convergence sublayerSAP to higher layersProvides service specific functions

Segmentation And Reassembly (SAR) sublayerPackage higher layer data into / from ATM cellCell loss detection

ATM LayerAddressing / Switching QoS

7 Application Application 6 Presentation Presentation 5 Session Session 4 Transport Transport 3 Network ATM Switch Network 2a AAL AAL 2b ATM ATM ATM ATM 1 Physical Physical Physical Physical


ATM Adaptation Layer

SARSegmentation and Reassembly

messagehigher layer

AAL

convergencesublayer

AAL‐SDU

header payload trailer

SAR sublayer

SAR

header payload trailer

SAR‐PDU (48 bytes)

ATM Layer

header payload

ATM‐PDU (cell) (53 bytes)


Connection‐Oriented RoutingNetwork of switches and links

Circuit switching or packet switching

Switched Virtual Circuit (SVC) Set-up / close messages carry source and destination addresses

Example

Packet routing by VC ID in header (layer 2 or layer 3)Every packet follows same VC route Example

AB

C

E

F

D

1

2 3

4

5

6

Set-up VC – 1: B 1 4 6 F

dataVC – 1


Virtual Circuit LabelingSwitch topology

Mapping of node to interface numberExample

At Switch 1 Interface 1 = Node BInterface 2 = Node AInterface 3 = Switch 2

VC numberLabels src-to-dest pathAssigned at routersCan change at each switchExample

ATM network packet

Routing tableMapping between interface / VC pairs

A

B C

1

23 1 2

Switch 1 Switch 214

23 3442

59 72

Switch 1 Routing Table

422593141233593422233141

OutInVCIntfcVCIntfc

CRC DataPriorityType VCIVPI


Connectionless RoutingNetwork of routers and links

Packet switching

Each datagramRouted individually through networkHas source and destination address in header

Data Link header or Network headerDatagrams may follow separate routesExample

B 1 4 6 FB 1 5 6 F

AB

C

E

F

D

1

2 3

4

5

6

datasrc = B dest = F


Datagram ForwardingRouter topology

Mapping of node to interface numberExample

At Router 1 Interface 1 = Node BInterface 2 = Node AInterface 3 = Router 2

Node addressLabels nodeRouter handles next hopSrc + dest address in IP header

Routing tableMapping between dest addr and interface

A

B C

1

23 1 2

Router 1 Router 2

Switch 1 Routing Table

3other1B2A

OutInIntfcDest Addr Rangedataother fields destsrc


Internet Protocol version 4 (IPv4)IP datagram format

16 bits8 bits4 bits4 bits

Data

Options

Destination IP Address

Source IP Address

Header ChecksumProtocolTime to Live

Fragment Offset (13 bits)FlagsIdentification

Total Length (header + data in bytes)Service TypeHlen Version

MF (More Fragments — all frags but last)DF (Don't Fragment)0FlagsOffset in 8‐byte units from start of original datagram (fragmented)Fragment Offset

Protocol of data carried by datagram (usually TCP or UDP)ProtocolRouters perform: {if (--TTL == 0) delete datagram}Time To Live (TTL)

Provides a unique ID to each datagramIdentification

Differentiated Services Code Point (DSCP)Explicit Congestion Notification (ECN)

Service type(see chapter 5)

Header length in 32‐bit multiples Hlen


Internet address32-bit address Written as 4 octets (8-bit numbers in decimal) separated by dotsExample

www.hadassah.ac.il = 212.179.79.228

Networks / Subnets / HostsNetwork.Host

Network number = 212.179.79.0Host number = 228

Network.Subnet.HostSubnet 0 = 212.179.79.1 – 212.179.79.127Host address range = 212.179.79.X

X = 0xxxxxxx (binary)Subnet 1 = 212.179.79.128 – 212.179.79.254Host address range = 212.179.79.X

X = 1xxxxxxx (binary)

Internet Protocol version 4 (IPv4)IPv4 Addressing


3 main address classesA — small number of large networks (up to 224 = 16 Mhosts)C — large number of small networks (up to 28 = 256 hosts)

Internet Protocol version 4 (IPv4)Address classes

class octet 1 octet 2 octet 3 octet 4 network range

A 0 7 bits 8 bits 8 bits 8 bits 1.0.0.0 to 127.0.0.0

network host B 10 6 bits 8 bits 8 bits 8 bits 128.0.0.0 to

191.255.0.0 network host C 110 5 bits 8 bits 8 bits 8 bits 192.0.0.0 to

223.255.255.0 network host D 1110 4 bits 8 bits 8 bits 8 bits 240.0.0.0 to

247.255.255.255 multicast address


Length of network number = 1, 2, 3, … , 31Not restricted to 7, 16, 24

Address formatOctet1.Octet2.Octet3.Octet4/bits_in_network_number

Examples Class A address — 10.0.1.5/8

8-bit network number = 10.0.1.0Class C address — 192.168.0.37/24

24-bit network number = 192.168.0.0General node address — 192.168.0.33/27

Network address = 192.168.0.32Host addresses 192.168.0.32 — 192.168.0.63

Internet Protocol version 4 (IPv4)Classless Inter‐Domain Routing (CIDR)

00001330168192

host27-bit network address001000000001010100011000000


Forming subnet mask1 in all bits of network number0 in all bits of host numberEncodes same information as number of bits in network number

ExampleGeneral node address — 192.168.0.33/27

27-bit network numberMask

11111111.11111111.11111111.11100000255.255.255.224

Using maskMask AND IP address = network number

Example255.255.255.224 AND 192.168.0.33 = 192.168.0.32

Internet Protocol version 4 (IPv4)Subnet mask


Internet Protocol version 4 (IPv4)Subnet example

subnet 0

194.30.5.1 194.30.5.2

194.30.5.33

194.30.5.35

194.30.5.34

subnet 1

194.30.5.3

194.30.5.65

194.30.5.66 194.30.5.67

subnet 2

194.30.5.99

194.30.5.97

194.30.5.98

subnet 3

194.30.5.129

194.30.5.130 194.30.5.131

subnet 4

194.30.5.32/27255.255.255.224

194.30.5.0/27255.255.255.224

194.30.5.64/27255.255.255.224

194.30.5.128/27255.255.255.224

Octet4 = 3-bit_subnet _number.5-bit_host_number


Internet Protocol version 4 (IPv4)Reserved addresses

Reserved240.0.0.0/4

Multicast (Class D)224.0.0.0/4

Private network192.168.0.0/16


Loopback (destination = this node)127.0.0.0/8


Current network (source address)0.0.0.0/8

DescriptionCIDR address block

Broadcast on CIDR networkIP address = octet1.octet2.octet3.octet4/nw_bits

Network number = MASK AND IP Broadcast = MASK' OR IP

MASK 32 – nw_bitsnw_bits00...011...1

MASK' 32 – nw_bitsnw_bits11...100...0


Internet RoutingAutonomous System (AS)

Nodes managed by one organizationHierarchical routing

Interior Gateway Protocols (IGP) Routing protocols within one AS (Intra-AS)

Exterior Gateway Protocols (EGP)Routing protocols between ASs (Inter-AS)

Edge router (gateway router)Router within AS linked to router in different AS

AS‐1AS‐2Edge Routers

IGP IGPEGP

AS‐3

IGP


Relationship of Protocol LayersTypical network

Application Application 16‐bit

TCP Port 16‐bit TCP Port

32‐bit IP Address 32‐bit

IP Address 32‐bit

IP Address 32‐bit IP Address

32‐bit IP Address 32‐bit

IP Address 48‐bit

Ethernet Address

48‐bit

Ethernet Address

PPP PPP 48‐bit

Ethernet Address

48‐bit

Ethernet Address

Ethernet (PHY) Ethernet

(PHY) PHY PHY Ethernet (PHY) Ethernet

(PHY) Host Router Router Host

Locate router by IP address(uses default gateway)

Send to router by MAC addressEthernet always uses source / destination Ethernet addresses — not IP addresses

Host finds MAC address for router using an address resolution protocol (ARP)

Point‐to‐point Locate host by IP addressSend to host by MAC address


Network Address Translation (NAT)Router

Receives IP datagram Exchanges IP source / destination address in headerForwards datagramMaintains list of translations

Autonomous systemsAllocate private network addresses internally

10.0.0.0 and 192.168.0.0Only gateway and backbone devices require unique IP addresses

Local nodes on AS re-use private addressesExample

10.0.0.110.0.0.2

10.0.0.3 109.65.228.42

209.85.229.147

138.76.29.7

10.0.0.1

10.0.0.2

10.0.0.3


Network Address Translation (NAT)

No translation required on traffic internal to ASLocal addresses = real IP addresses

Local node to external nodeOutgoing packet

Source endpoint = local IP address + application source port numberDest endpoint = remote IP address + well-known port number

Gateway router NAT Replaces

Local IP address with gateway IP address Local application source port with unique unused NAT port

Records mappingNAT source port local IP address + source port number

Forwards packetExternal node to local node

Gateway router replaces NAT port local IP + app source port

Translation details


Host A HTTP request to Server SSource port = 1025 Source IP = 10.0.0.2Destination port = 80 Destination IP = 209.85.229.147

Outgoing NAT at Gateway router BSource port = 3745 Source IP = 109.65.228.42Destination port = 80 Destination IP = 209.85.229.147

Server S HTTP response to Host ASource port = 80 Source IP = 209.85.229.147Destination port = 3745 Destination IP = 109.65.228.42

Incoming NAT at Gateway router BSource port = 80 Source IP = 209.85.229.147Destination port = 1025 Destination IP = 10.0.0.2

Network Address Translation (NAT)Example

10.0.0.110.0.0.2

10.0.0.3 109.65.228.42

209.85.229.147

138.76.29.7

10.0.0.1

10.0.0.2

10.0.0.3

Host AServer Srouter B


ProblemHow to operate service behind NAT

SolutionsStatic router referral

Define service port on Server QRefer all incoming traffic at gateway for service port to Server Q

Relay serverServer Q connects to Server E with public address (no NAT)Host M requests service from Server Q via Server E Server Q replies via Server E

Universal Plug and Play (UPnP)Specialized protocols for NAT traversal

Network Address Translation (NAT)Traversal problem

10.0.0.110.0.0.2

10.0.0.3 109.65.228.42

209.85.229.147

138.76.29.7

10.0.0.1

10.0.0.2

138.76.29.18

Host M

Server Q Server E


Quality of Service (QoS) Network parameters

Bit error rate (BER)< 10-9 on fiber optic cable< 10-3 on wireless

Packet loss rateDepends on congestion control policy

Error control

Dynamic variations inData rate / propagation delay (jitter) TtransQueuing delay TQProcessing delay Tproc

Delay variation

End-to-end transmission time for one bitHigh data rate lower transmission delay TtransCongestion / priority longer queuing delay TQDatagram service longer processing delay Tproc

Delay

Physical transmission speed in bpsData rate


QoS and Network PoliciesData Rate

DelayTimeDelay

Variation

ErrorControl

TransmissionSpeed

AccessDelay

CongestionControl

PriorityControl

ConnectionType


QoS Requirements for Various Services

Service Speed Error Control Delay Delay

Variation

e‐mail — good — —

file transfer

NFS

database access

reasonable maximum reasonable reasonable

voice fast good very small very small

video

real time control very fast good very small very small


Internet Transport Layer ConnectionsReliable transport (TCP)

Connection-orientedTCP connection established before data transfer

Error-free deliveryData delivered

In original order No errors, duplications, omissions

Flow controlControl sender rate to prevent buffer overflow in receiver

Congestion controlControl sender rate to prevent buffer overflow in network

Unreliable transport (UDP)Connectionless Lower overhead faster but no guarantees Segments with errors discarded with no warning to application


Transport Layer —QoS Trade‐Off

Reliable TransportGenerally preferred when possible

Unreliable TransportUsed when

Some data loss tolerable Delay or jitter intolerableExample — video delivery

Datagram StreamSocket type

None Error correction, packet ordering, congestion control, session state

managementProcessing overhead

Connectionless Connection-orientedConnection No error correction Error-freeError control

UDPTCPProtocolUnreliable TransportReliable Transport


Source / Destination PortsClient

Opens socket to send requestsClient / OS binds port number to socket

1024 client port 65,535 identifies client applicationServer

Opens listen socket mapped to accept sockets for requestsBinds well-known port to service socket

0 well-known port 1023 identifies service application

Transport

Client ApplicationBind socket to port 1025Connect to port 80

Transport

Server ApplicationBind socket to service port 80Accept from 1025

Requestsrc: 1025 dest: 80

Responsesrc: 80 dest: 1025


Multiplexing / DemultiplexingApplications send / receive data on sockets

Multiple sockets multiple conversationsTransport layer segment

Transport header + application data (PDU)TCP / UDP headers carry source + destination ports

Multiplexing / demultiplexingSegments transmitted on same infrastructure Sorted by destination port at destination

Transport

Client Applications

Transport

Server Application

1025 80

10261025 80

1026 80

1025 80 1026 80

1025 80

1025 80

1026 80

1026 80

1025 801026 80

1025 801026 80


User Datagram Protocol (UDP)Internet unreliable transport protocol

Defined in RFC 768Used when low delay / jitter more important than error controlStreaming multimedia, multiplayer games, ...

UDP segment

UDP header

Length Number of bytes in UDP segment < 216 = 65,536Maximum length of data = 64 KB – lengths of all headers

application dataheader

checksumlength

destination portsource port

32 bits


TCP Header

Options

urgent pointerchecksum

window sizeflagsnot usedHLEN

acknowledgement number (ACK)

sequence number (SEQ)

destination portsource port

32 bits

Options fields + padding for multiple of 32 bits10 – 320 bitsOptions

Offset from SEQ points to last urgent data byte16 bitsUrgent pointerNumber of bytes receiver can receive now16 bitsWindow sizeControl bits9 bitsFlags Not used3 bitsReserved Length of TCP header in 32-bit words4 bitsHLEN (data offset)


TCP HeaderFlags

No more data from senderFIN

Synchronize sequence numbersSYN

Reset connectionRSTPush buffered data to receiving applicationPSHAcknowledgment field validACKUrgent pointer field validURG

ECN-EchoIf SYN = 1 peer is ECN capableIf SYN = 0 packet with Congestion Experienced flag in IP header received during normal transmission

ECE

Congestion Window Reduced (CWR) flag Sender indicates receiving segment with ECE flag setCWR

ECN-nonce concealment protectionNS


TCP Connection Set‐up

Client SYN segment SYN flag = 1SEQ = random number xNo data

Server SYN-ACK segmentSYN flag = ACK flag = 1SEQ = random number yACK = x + 1No data

Client ACK segmentSYN flag = 0ACK flag = 1SEQ = random number x + 1ACK = y + 1May contain data

Three-way handshake

Client Server

SYN flag = 1ACK flag = 0SEQ = xACK = 0

SYN flag = 1

ACK flag = 1

SEQ = y

ACK = x + 1

SYN flag = 0ACK flag = 1SEQ = x +1ACK = y + 1data

Connection request(synchronize)

Accept

ACK


Initial sequence number (ISN)Random SEQ in 3-way handshake

Prevents counterfeit segmentsAt end of handshake SEQ = ISN + 1

SEQ — byte sequencingSEQ = previous SEQ + length(data bytes in previous segment)

= ISN + 1 + data bytes sent in all previous segments

ACK — byte acknowledgementACK = next (expected) SEQACK = x + 1

Acknowledge x — now expect x+1

SEQ = x+501 ACK = y+1data = 400 bytes

TCP SEQ + ACK

Client Server

SEQ = y+1 ACK = x+501

First data segment after handshake

SEQ = y+1 ACK = x+901

SEQ = x+1 ACK = y+1data = 500 bytes


Send and Receive WindowsSend buffer

Holds sent segments until ACKedOn timeout resend segments from send buffer

Send windowAvailable space in send buffer

Receive bufferHolds received segments until requested by application

Receive window Available space in receive buffer

Full

Send Window

SendingApplication

Network Layer

Send Buffer

Full

Receive Window

ReceivingApplication

Receive Buffer


Simplified TCP Sender — 1// initialize

SEQ = ISN + 1SendBase = ISN + 1 // last byte ACKedInFlight = 0 // unACKed bytes sentRTO // timeout intervalSendWindow, RecvWindow // send & receive windows

// main loopif (new data from application)

Prepare data segmentsequence number for segment = SEQSEQ = SEQ + length(data)

if InFlight < min{SendWindow,RecvWindow)Pass segment to IP InFlight = InFlight + length(data)if !(timer running) timer = RTO


Simplified TCP Sender — 2if (receive ACK = y)

stop timerif (y > SendBase)

newACKs = y – SendBase // bytes ACKedSendBase = yInFlight = InFlight – newACKs if (InFlight > 0) timer = RTO

if (timeout)SEQ = SendBase = min{unACKed SEQ}resendtimer = RTO


Simplified TCP Receiver — 1// initialize

Set RecvWindow = receiver buffer sizeexpected = Sender ISN + 1ack_buffer = 0 // received unACKed segmentsack_max // delayed ACK triggerack_delay = 250 msec // local policy: < 500 msecStart ACK delay timer = ack_delay

if (ACK delay timer = 0 && ack_buffer > 0)Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0


Simplified TCP Receiver — 2if (receive SEQ = x)

if (x = expected && error-free)expected = expected + length(data)if (NACK = 1)

Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0NACK = 0

else if (ack_buffer < ack_max)nextACK = expectedack_buffer++

else if (ack_buffer = ack_max)Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0

elseSend ACK = expected with updated RecvWindowACK delay timer = ack_delayNACK = 1


TCP SEQ + ACK

Sender Receiver

ACK = 100

No errors

Timeo

utSEQ = 92 8 data bytes

ACK = 120

SEQ = 100 20 data bytes

ACK = 180

SEQ = 120 20 data bytes SEQ = 140 20 data bytes SEQ = 160 20 data bytes



TCP SEQ + ACK

Sender Receiver

ACK = 100

Bit errorsTimeo

ut


ACK = 120


ACK = 160

SEQ = 120 20 data bytes SEQ = 140 20 data bytes SEQ = 160 20 data bytes


Corruptpacket

discarded

error


TCP SEQ + ACK

Sender Receiver


ACK = 100

Timeout

Timeo

ut

error




TCP SEQ + ACK

Sender Receiver

ACK = 100

Lost ACKTimeo

ut

error




ACK = 100

Receiver discards duplicate packet


TCP SEQ + ACK

Sender Receiver

Missed ACKTimeo

ut SEQ = 100 20 data bytes



ACK = 100

ACK = 120

ACK = 120

SEQ = 92 8 data bytes Receiver discards duplicate packet

ACK 120 acknow

ledges all bytes <

120


TCP SEQ + ACK

Sender Receiver

ACK = 100

Cumulative ACK

Timeo

ut

error




ACK = 120

ACK all previous bytes


TCP Connection CloseSymmetric

Client or server may close connection

FIN segment SYN flag = 1SEQ = cumulative SEQ number

ACK segmentACK flag = 1ACK = SEQ + 1

FIN segmentFIN flag = 1SEQ' = cumulative SEQ number

ACK segmentACK flag = 1ACK = SEQ' + 1

Client Server

FIN flag = 1SEQ

FIN flag = 1

SEQ'

ACK flag = 1ACK SEQ'+1

ACK flag = 1

ACK SEQ+1


Socket Calls — Between App and OSSocket, Bind

OS creates resources for network connectionOS returns to App socket descriptor (socket ID)

Listen Server OS makes service available

ConnectClient OS attempts connection to service

AcceptServer OS creates new connection socketServer OS returns new descriptor to AppListen socket continues to listen

SendApp sends data to OS, pointed at socketOS transmits data on associated connection

ReceiveApp requests data from OS socket bufferOS returns data to AppPHY

OS

App

call

return

SocketCalls

OSActivity

Socket ID points to OS resources


Using UDPServerClient

Server UDP Agent

Perform checksum

ErrorDiscard segment

No errorPass data to socket by port

Application

Open socket

Bind service portListen on socketReceive data from listen socket

Client UDP Agent

Accept data

Add header with checksumSend to server

Application

Open socket

Send data on socket to endpoint (node address + service port)

If required — add reliability features at client / server application level


ConnectionServerClient

= socket(domain, type, protoc_ID col)

connect( , service_endpoc_ID int)

connection set‐up

address type service type = socket(domas_ in, type, protID ocol)

bind( , s_endpoint, s_endpoint_s_ID len)

s_IDlisten( , backlog)

= accept( , c_endpoint, endpoint_s s_ID len)

send( , data, len, s flags)

data

receive( , buffer, len, flc_ID ags)

bind( , c_endpoint, c_endpoint_c_ID len) If client skips bind()OS sets a default port


Perl Server Socket Example#!/usr/bin/perl$flag = "1";use IO::Socket; $sock = IO::Socket::INET->new(

LocalHost => '127.0.0.1',LocalPort => 1234, Listen => 1, Reuse => 1, Proto => 'tcp') || die "Error creating socket\n";

$client = $sock->accept(); while($flag == "1") { $line = <$client>;print $line; print $client "Received\n"; if ($line =~ /bye/) {$flag = "0";}

} close($sock);

Server Prints data from client EchoesReceivedCloses on data bye

In CLI run perl script$perl servlet.pl

In second CLI enter:$telnet 127.0.0.1 1234Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.

LOOPBACK ADDRESS (for testing)127.0.0.1

Local calls on this machine


Assistive Application Protocols used with IP LayerDomain Name System (DNS)

Convert between node name and network address

Address Resolution Protocol (ARP)Convert between network and hardware addressesDiscover local subnet topology

Dynamic Host Configuration Protocol (DHCP)IP address allocation on request from DHCP server

Server typically in gateway routerServer allocates IP address from pool of available addressesDHCP message types

DHCP server discovery (host broadcast)DHCP offer (server response)DHCP request (host request)DHCP ACK (server provides address)


Domain Name System (DNS)

Local Node

NameCache

Resolverrequest

response

Resolver

Default Name Server

Foreign Name Server

request

response

Forwarder Higher in hierarchy

Address Resolution Hierarchy$ nslookup www.hadassah.ac.ilServer: 10.0.0.11Address: 10.0.0.11#53

Non-authoritative answer:www.hadassah.ac.il canonical name = hathi.hadassah.ac.ilName: hathi.hadassah.ac.ilAddress: 212.179.79.228


Address Resolution Protocol (ARP)Look-up MAC address by IP address (RFC 826)

Q: Who has IP = a.b.c.d ? (MAC layer broadcast)A: I am IP = a.b.c.d with MAC = u:v:w:x:y:z

STAs store mappings in arp table

ARP packet fields

Target protocol addressTPA

Target hardware address (ignored in requests)THA

Sender protocol addressSPA

Sender hardware addressSHA

1= request / 2 = replyOperation

Protocol length — length in octets of network addressPLEN

Hardware length — length in octets of MAC addressHLEN

Protocol type — network protocolPTYPE

Hardware type —MAC protocolHTYPE


Internet Control Message Protocol (ICMP)Control protocol

Network management informationError reporting

Unreachable host / network / port / protocolEcho request / replyPackets carried in IP datagrams

Packet structure

Rest of Header — message specificPadding — data field

Padding64

Rest of Header32

ChecksumCode (subtype)Type0

24 – 3116 – 238 – 150 – 7Offset

Selected Message Types

bad IP header012TTL expired011

router discovery010

route advertisement09

echo request08

dest host unknown7

dest network unknown6

dest port unreachable3

dest protocol unreachable2

dest host unreachable1

dest network unreachable0

3

echo reply00descriptionCodeType


PingClient application program

Client sends echo request packets to destination IP addressType = 8 Code = 0 16-bit ID number 16-bit sequence number

OS dependentLinux ping

Default = continuous packets with 56 padding bytes Windows ping.exe

Default = 4 packets with 32 padding bytes Ping server (OS service)

Responds to each echo request packet with echo rely packetType = 0 Code = 0 16-bit ID number 16-bit sequence number

Ping clientMeasures round trip time (RTT)Reports packet losses, RTTs and average RTT

UDP pingUses UDP instead of ICMP


Ping Examplec:\>ping www.hadassah.ac.il

Pinging hathi.hadassah.ac.il [212.179.79.228] with 32 bytes of data:

Reply from 212.179.79.228: bytes=32 time=32ms TTL=119Reply from 212.179.79.228: bytes=32 time=70ms TTL=119Reply from 212.179.79.228: bytes=32 time=135ms TTL=119Reply from 212.179.79.228: bytes=32 time=83ms TTL=119

Ping statistics for 212.179.79.228:Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:Minimum = 32ms, Maximum = 135ms, Average = 80ms


Traceroute Client application program

Multiple echo request packets to destination IP addressFirst packet TTL = 1Each subsequent packet has TTL++

OS dependentLinux traceroute / tracepath

UDP to unlikely port number (port typically not defined)Windows tracert.exe

ICMP echo request packetsIntermediate routers

if (--TTL == 0){delete ; ICMP type 11 to client}ICMP packet carries router name + IP address

ICMP sequence = list of intermediate routers (hops = 1, 2, … )Destination node

UDP segment — ICMP port undefined (type 3 code 3) message ICMP packet — ICMP echo reply message


Traceroute Examplec:\>tracert www.hadassah.ac.il

Tracing route to hathi.hadassah.ac.il [212.179.79.228]over a maximum of 30 hops:

1 2 ms 1 ms 2 ms 10.0.0.1382 18 ms 19 ms 17 ms bzq-179-37-1.static.bezeqint.net [212.179.37.1]3 18 ms 17 ms 17 ms bzq-179-48-201.static.bezeqint.net [212.179.48.201]4 17 ms 17 ms 17 ms bzq-179-80-241.static.bezeqint.net [212.179.80.241]5 17 ms 18 ms 17 ms bzq-179-124-201.static.bezeqint.net [212.179.124.201]6 17 ms 17 ms 17 ms bzq-179-124-138.static.bezeqint.net [212.179.124.138]7 19 ms 18 ms 18 ms bzq-179-59-1.static.bezeqint.net [212.179.59.1]8 32 ms 36 ms 41 ms 10.20.110.189 105 ms 84 ms 71 ms bzq-179-79-228.static.bezeqint.net [212.179.79.228]

10 73 ms 88 ms 150 ms bzq-179-79-228.static.bezeqint.net [212.179.79.228]

Trace complete.

c:\>

1Dr. Martin LandAccess NetworkingProtocols and Networks — Hadassah College — Fall 2021

AccessNetworking

Connecting the Userto the World


Small Office / Home Office (SOHO)LAN (Local Area Network) to WAN (Wide Area Network)

Ethernet

WiFi

ADSL

WiFi Access PointEthernet Switch

IP RouterADSL Modem

Cable‐based transmission protocol defined at PHY layerG.992.5ADSL

802.11

802.3

Wireless LAN protocol defined at DATA LINK and PHY layersWiFi

Cable‐based LAN protocol defined at DATA LINK and PHY layersEthernet

Internet


Laptop Browser to Web Server — Simplified View

Access

IP

ADSL

WiFi Router

WiFi

IP

ADSL

Access

IP

ServerInternetLaptop

PHYPHY

Data LinkData LinkWiFi

IPIPIP

TCPTCP

HTTPHTTP


ADSL — Asymmetric Digital Subscriber LineHigh speed transmission on standard voice line

POTS — plain old telephone service24 Mbps downstream3.3 Mbps upstream

Ref: JDSU, ADSL Technology, JDS Uniphase Corporation, 2005


ADSL Access Network

Ref: Vodaphone, Wholesale Layer2 DSL (W‐DSL‐L2I), VTCW011 ‐ I 03/13


Typical Bezeq ATU‐R

ADSL33 Mbps

IP Routing

802.3Ethernet

802.11WiFi


Bezeq Fast Internet Access

usermanagement

and IP datagramforwarding

IP datagramforwarding

Bezeq ISP

Internet routing

ADSL modem onpoint-to-point

channel

Server

IPnetwork

telephonenetwork

Client

switchedATM

network


Fast Internet Protocols — Envisioned Campus CasePPP

Point to Point ProtocolLogon + connection management

PPPoEPPP over EthernetVirtual point‐to‐point connection over shared LANClient opens private session with ISP

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

Router

802.3

PPPoE

PPP


Fast Internet Protocols — Envisioned Campus CaseATM

Asynchronous Transfer ModeData Link protocol for broadband

telephone servicesPermits real time QoS

MPOA + AAL5Adaptation protocols for ATM

ADSLPhysical bit transmission

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq


Fast Internet Protocols — Envisioned Campus Case

Connection to ISPClient runs Network Control Protocol (NCP) over PPPCHAP (challenge handshake authentication protocol) —User Name + PasswordISP authorizes user and engages IP forwarding

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPPoE

PPP

ISP

Connection to ISP


Fast Internet Protocols — Envisioned Campus Case

IP forwardingISP forwards IP datagrams to server via Internet backbone

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPP

IP

PHY

PPPoE

PPP

ISP

PHY

Server

PPP

IP

TCP

App

Connection to ISPIP Routing


Fast Internet Protocols — Typical SOHO Case

Router/modem initiates connection to ISPRuns NCP over PPP over PPPoE over EthernetRouter provides always‐on Internet access over WiFi + Ethernet

Client

WiFi

802.11

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

PPP

Router

WiFi

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPP

IP

PHY

PPPoE

PPP

ISP

PHY

Server

PPP

IP

TCP

App

Connection to ISPIP Routing


Telephone Network Local loop (last mile)

Analog voice + dataVoice 64 kbps (DS0)

PDH / SDH digital hierarchyDS0 streams combined to hierarchy of data rates1.544 Mbps (T1) to 40 Gbps (STM-256)

ESS7Hierarchical tree of central office switches for DS0 streams

ATMGeneral packet switch mesh Switches 2.5 Gbps streams

(STM-16)

local loop

ESS ATM

Central Office

Router

local loop

ESS ATM

Central Office

Router

local loop

ESS ATM

Central Office

Router


Digital Voice on Telco Telephone Sample analog voice signal every 0.125 ms

0.125 ms per voice sample 8000 voice samples / second

Round-off sample to 8-bit dataData {0, 1, 2, ... , 255}Sample = {158.276, 158.879, 159.724, 159.821, 159.312, 158.791}Data = {158, 159, 160, 160, 159, 159}

DS-0 stream(8000 samples / second) (8 bits / sample) = 64 kbps64 kbps digitized voice (no compression)

158 159160 160 159 159

157

158

159

160

161

t


Data Concentration Multiplexing

Combine multiple nodes onto one link

32 inputsat 64 kbps

1 output at2.048 Mbps

Multiplexor

32 outputsat 64 kbps

1 input at2.048 Mbps

Demultiplexor

39.81312 Gbps256 x E4STM‐256

9.95328 Gbps64 x E4STM‐64

SDHPDH

2.48832 Gbps

622.08 Mbps

155.52 Mbps

51.84 Mbps

16 x E4

4 x E4

E4

21 x E1

STM‐16

STM‐4

STM‐1

STM‐0

139.264 Mbps4 x E3E4

34.368 Mbps4 x E2E3

8.448 Mbps4 x E1E2

2.048 Mbps32 x DS0E1


Cellular NetworkWireless to base station — uses Telco network for WAN service

Base System (BS)

Telco VoiceNetwork

CellController

ClusterController

Mobile SwitchingCenter (MSC)

Public Land Mobile Network

Mobile Station(MS)

HLRVLR

CellCluster

GPRS

Internet

SGSN

GGSN

Voice

Data


3G Cellular Network


Enormous investment in existing equipmentGlobal network of hardware nodes + transmission lines

Developed to provide many servicesInternet (IP-based unreliable connectionless) just one service

Most developed before Internet Telegraph — 1794Telephone — 1876Teletype modem — 1943Digital telephone — 1962Internet opened to public — 1992

Hardware updates Replacement of manufactured hardwareSlower than software updatesMore expensive than software updates

Network InfrastructureEconomic perspective


Enterprise NetworksEnterprise

The word (ref: http://www.etymonline.com)Past participle of entreprendre — "undertake, take in hand" From Old French — entre "between" + prendre "to take"

The pose

Enterprise networkLarger + more complex + more expensive + more awesome than SOHOIntegrated LAN + WAN technologies

Traditionally implemented in specifically‐designed hardware systemsIncreasingly implemented as Software Defined Networks (SDN)

SecurityHigh overall traffic volume


Traditional Network InfrastructureCisco Smart Business Architecture (SBA) Ref: WAN Design Overview, Cisco 2013


Technologies in the Cisco SBA Conventional Layer 3 routing

Permits universal access to any host / nodeNext‐hop IP datagram forwarding

Conventional Layer 2 switching —N x N non‐blocking switchingPermits access to nodes on same physical networkEthernet MAC physical port‐to‐port switchingESS7 64 kbps voice telephone switchATM cell switching for switched and permanent virtual circuitsFrame Relay switching for permanent virtual circuits

PHY

Data Link

IP

PHY

Router

PHY

Data Link

IP

Next Hop by IP

PHY

Data Link

Next Hop by MAC or VC

NodeSwitchNode

PHYPHY

Data LinkData LinkData Link

IPIP

TCPTCP

HTTPHTTP


Technologies in the Cisco SBAVirtual LAN (vLAN)

LAN switch configured to partition nodes into subnetsNo router needed for subnet partitions

Virtual Private Network (VPN)Private network implemented on public infrastructure

Router Network

Subnet Subnet

Internet

Private Network Private Network

Access Restricted by IP

Programmable Switch


Technologies in the Cisco SBAMultiprotocol Label Switching (MPLS)

Label header added to IP datagramLabel identifies end-to-end routeImplements end-to-end virtual circuit

MPLS enabled router Next hop by MPLS labelFaster than next hop IP routing

Saves time of layer 3 processingDatagram read / write, routing, TTL

Switch / Router InteractionPermits vLAN and VPN definitionOptimizes multimedia streaming

Application TCP IP DL PHY

DL PHY

Application TCP IP DL PHY

DL PHY

DL PHY

DL PHY


Technologies in the Cisco SBANexus 7000 Switch

100 Gbps Ethernet switchCopper or fiber access portsQoS control

Cut-through architecture (forward data without buffering)Low latency + jitter

Extensible through fabric extenders (FEX)Scalable to 15.76 Tbps (15,760 Gbps)

Supports virtual networking through MPLS

Nexus 2000Fabric extender (FEX)Add remote ports to Nexus 7000

Ref: http://www.cisco.com


Technologies in the Cisco SBACisco XR 12000 Router

For large enterprises and service providers1280 Gbps capacityInternet protocols

IPv4/v6, MPLSBGPv4/v6, IS-IS, OSPFv2.0, RIPv2, IGMP, DVMRP, PIM DX/SX

Infrastructure protocolsSONET/SDH, Ethernet, ATM, copper (DS-3/E3)

Cisco 7600 RouterWAN router240 Gbps capacityInfrastructure — Telco leased lines DS0 to OC-192

Cisco 3900 RouterFor branch office4 Gigabit Ethernet ports


Facts of Life for Telephone Business 2000 — 2008Enterprise

Business revolves around data center Access + storage + processing + service

Employees still talkMobility = standardVideo calls growing — voice calls still cost money

Network infrastructure providers (Telcos)Most installed infrastructure designed for voice callsProfit in leased lines not voice calls

Internet + private WAN + mobile backhaulStrategy

Scrap PSTNCash-in central office real estateBuild data-oriented mesh networkSupport voice as media streaming

local loop

ESS ATM

Central Office

Router

local loop

ESS ATM

Central Office

Router

Switching Hierarchy


Next Generation Networks (NGN)ITU initiative for long-term network planning

Standardizes current view of technology convergenceITU-T Recommendation Y.2001 (12/2004)

All-IP networkEvery service over IPIP over every infrastructure

Universal gateway pointDissolve traditional service

boundariesUniversal mobilityEvery service to every user

QoS controlIPv6MPLSSIP

Every Service

Every Infrastructure

IP

Transport

Network

Physical

Data Link

Session

Presentation

Application

OSI Layer


What is Cloud Computing?Outsourcing service model

Replace user hardware/software with "computing as service"Service Level Agreement (SLA)

Defines service provided to userGuarantees performance and quality of serviceProvider handles operations+administration+maintenance (OAM)

Business advantagesEconomies of scale to large provider lower cost to userUser cuts labor/capital costs from balance sheet happy investors

Customers Pizza Online

X86 Server

Delivery

Customers Pizza Online Cloud Inc.

Delivery

Virtual X86

Service


What is Cloud Computing?Cloud service organized from conventional resources

User chooses service level agreement (SLA) from menuProvider offers menu

Mix of hardware + software + network typesSLA implemented with dedicated or virtual system

Dedicated systemConstructed to perform only one specific taskExample — WiFi access point

Virtual systemImplemented in software on a generic systemExample — Java code running on Java VM over Linux

Unique technological issuesService reliability — provider financially committed to SLAProvider-side — seeks minimum configuration cost for SLAUser-side — seeks minimum contract cost for requirements


Service Hierarchy in Cloud ComputingInfrastructure as a service (IaaS)

User sees virtual hardware environment Real hardware or hypervisor / system virtual machine

User installs OS installs software runs jobs

Platform as a service (PaaS)User sees virtual OS environment

OS on single hardware platform or virtual OSUser installs software runs jobs

Software as a service (SaaS)User sees virtual application software environment

Applications running on private OS or "sandboxed" on shared OSSandbox — private execution environment per application instance

User runs jobsStorage as a service (STaaS)

User sees virtual mounted storage device


Considerations in Cloud ComputingCost

Provider issuesEconomies of scale lower cost per compute job

User issuesCapital + OAM costs operating costsLower start-up costs operating debt

Reliability Provider issues

Redundant infrastructure continuity + disaster recoveryCentralized management of OAM, security, performanceVirtualization serve multiple users on physical serverMultitenancy provide multiple sandboxed application instances on OS

User sees guaranteed serviceAgility

User / provider reconfigure service / infrastructure as needed Growth, load balancing, time-zone serving


Cloud OwnershipPublic cloud

Service provider as public utility — sells / rents computing serviceInitial providers leverage large existing infrastructureAmazon, Microsoft, Google, IBM

Menu of services at fixed prices

Private cloudCloud infrastructure for private organizationManaged internally or outsourcedIsolates service developers from implementation issues

Standard development platformRequirements for economic justification

Large organization Technology-based servicesFrequent new serviceExample — internet content provider


What's Different in Cloud NetworkingEnd user

Not muchAccesses service "somewhere" on network

Business service providerDefine business serviceOutsource implementationOAM limited to SLA-level virtual environment

Cloud service providerManage vast real environment mapped to virtual environmentsOAM requires effective picture of real system from SLA POV


Networking FunctionsForwarding function

Data transferImplement network protocolsHigh performance dedicated hardware

Control functionManagement of forwarding function

Configuration of network topology and policiesSupervision, measurement, maintenance

Traditional controlImplemented in dedicated hardware Switches, cable connections, programming at console interface

Software Defined Networking (SDN) control Implemented in system softwareGeneric control interface in hardwareSystem programmer configures modes, connections, policies


Software Defined Networking (SDN)SDN Application

Programs communicate network requirements to SDN Controller Receive abstracted view of network for planning

SDN ControllerTranslates requirements from SDN application to SDN Datapaths Provides SDN applications with view of network

SDN DatapathLogical network device controls data forwarding hardware

Single forwarding device Logical device defined from internal network of forwarding devices

FabricHardware associated into SDN


Cisco Software‐Defined Access DesignUnderlay network

Physical dedicated hardwareOverlay network

Virtual network implemented in SDNManagement

Identity Services Engine (ISE)Account database

DNA CenterHardware database

Border nodeConnects fabric to WAN

Edge nodeConnects fabric to user

References: https://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/Campus/CVD‐Software‐Defined‐Access‐Design‐Sol1dot2‐2018DEC.pdf

https://www.cisco.com/c/dam/en/us/solutions/collateral/enterprise‐networks/enterprise‐network‐security/data‐center‐design‐playbook.pdf


Layer 2 OverlayLayer 2 (Data Link) Logical network

Edge switchesEthernet, etcConnect users

Intermediate switchBorder switches

Physical networkPhysical switchesCables


Layer 3 OverlayLogical IP + switched network

Edge and border switchesIntermediate IP router

Physical networkSame as Layer 2Physical switchesCablesIP routing implemented

in software


Centralize Decentralize Centralize ?1950s — 60s

Centralized mainframe computer + multiple OS instances over hypervisorTimesharing OS serves multiple usersUser sees OS environment via dumb terminal (thin client)

1970s User applications offloaded to minicomputers + timesharing servicesUser sees timeshared OS environment via dumb terminal

1980sUser applications offloaded to personal workstations (PC)User sees single-user OS environment running locally

1990sNetwork single user workstations User sees single-user OS environment running locally

2000sCentralized control of local OS environment by IT departments

2010sCloud + netbook / tablet / smart phone — dumb terminal with high-res GUI


What Network Access Providers Do

https://www.rad.com/system/files/Media/rad‐catalog‐2019.pdf


VirtualizationHighly configurable network hardwareSoftware defined network (SDN) functions

NID—Network Interface DeviceNTU—Network Termination Unit

for Carrier Ethernet

Distributed Network Functions Virtualization (D‐NFV)


Carrier EthernetEthernet

802.3 CSMA/CD shared medium local area (~ 100 m) networkData rates — 10 Mbps to 100 Gbps on copper or optical fiber

Carrier EthernetBridge Ethernet LAN segments over WANOperates as single Ethernet broadcast domain

E-Line — point-to-point connectionE-LAN — general meshE-Tree — hierarchical tree


Cyber Security

EthernetETH

Terminal Protocol (?)TP

Remote Terminal UnitRTU

Intelligent Electronic DevicesIED

MAC layer security standard (802.1AE)MACsec

Supervisory Control and Data AcquisitionRemote Monitoring and Control

SCADA

Data Communications ChannelPort Based Network Access Control (802.1X)

DCC


vCPE (virtual customer premises equipment)

VNF — Virtualized Network FunctionGPON —Gigabit Passive Optical NetworkPDH — Plesiochronous Digital Hierarchy (standard telco multiplex hierarchy)GbE—Gigabit EthernetL2/L3 — layer 2 (data link) switching + layer 3 (IP) routing


Carrier Ethernet

ETXCarrier Ethernet demarcation and aggregation

MinID login system


TDM Over Packet Mode Networks

PSNPacket Switched Network

PBXPrivate Branch Exchange — telephone switchboard


Cellular Backhaul

Cell site2G BTS or 3G/4G Node B (NB/eNB) connects mobile device to cellular network

BackhaulCarry digital voice from mobile cell site to telephone central office

1Dr. Martin LandWirelessProtocols and Networks — Hadassah College — Fall 2021

IPv6


IPv4 & IPv6 Header Comparison

Fragment OffsetFlags

Total LengthType of ServiceIHL

PaddingOptions

Destination Address

Source Address

Header ChecksumProtocolTime to Live

Identification

Ver

Next Header

Hop Limit

Flow LabelTraffic Class

Destination Address

Source Address

Payload Length

Ver

IPv4 HeaderIPv4 Header IPv6 HeaderHeader


IPv6 Address ScopeAddress assigned to interface

Interface IDAddresses depend on scope

Link LocalLocal hardware connectionBroadcast domain

Site LocalAutonomous system (AS)Network of one organization

Global

Link-LocalSite-LocalGlobal


Types of IPv6 AddressesUnicast

One address on a single interfaceDelivery to single interface

MulticastAddress of a set of interfacesDelivery to all interfaces in set

AnycastAddress of a set of interfacesDelivery to closest single interface in set

No broadcast addresses


IPv6 Address128-bit address

340,282,366,920,938,463,463,374,607,431,768,211,456 addresses50,000 addresses per square meter of land on Earth

Colon-separated 16-bit hex2031:0000:130F:0000:0000:09C0:876A:130B

Leading zeros optional2031:0:130F:0:0:9C0:876A:130B

Successive 16-bit 0 fields written :: (once)legal 2031:0:130F::9C0:876A:130B

illegal 2031::130F::9C0:876A:130B

IPv4 compatible — used in tunneling IPv6 through IPv40:0:0:0:0:0:1.2.3.4 = ::0102:0304

IPv4 mapped — used by IPv6 source sending to IPv4 dest0:0:0:0:0:FFFF:1.2.3.4 = ::FFFF:0102:0304


IPv6 Prefix

Used in telephonyReserved for ATM0200::/70000 001

Assigned to a groupMulticast AddressFF00::/81111 1111

Addresses used with an AS (like 10.0.0.0 in IPv4)Site Local AddressFEC0::/101111 1110 11

HexBinary

FE80::/10

2000::/3

0::/8

Address hosts on LAN segmentLink Local Address1111 1110 10

Aggregation of host addresses into networks

and subnets

Aggregatable GlobalUnicast Address001

Not assignedReserved address0000 0000

ApplicationTypePrefix Format (PF)


Unicast Address FormatsLink Local

Site Local

Global

MAC derivedMUST be 01111111010FE80::/10

Interface ID (64 bits)Reserved (54 bits)FP (10 bits)

MAC derived

Interface ID (64 bits)

Locally Administered1111111011FEC0::/10

Subnet (16 bits)Subnet (38 bits)FP (10 bits)

Locally Administered

MAC derived or Locally Administered or Random

Interface ID (64 bits)

Provider Administered001

2000::/3

Subnet (16 bits)ISP assigned (45 bits)FP (3 bits)


Hierarchical Addressing & Aggregation

Authority Assigns 2001:0410::/32 to ISP

ISP Assigns 2001:0410:1:/48 to customer 1Assigns 2001:0410:2:/48 to customer 2

Customer 1Assigns subnets 2001:0410:1:1/64 , 2001:0410:1:2/64

ISP

2001:0410::/32

Customer 2 IPv6 Internet

2000::/32001:0410:0002:/48

2001:0410:0001:/48

Customer 1


Extension HeadersNext header field

Points to header following IPv6 header

Extension headersMultiple of 8 bytesSyntax depends on optionHeaders (except 60) appear only once

UDP Header17

TCP Header6

Upper Layer Protocol

IPv6 ICMP Packet58

Resource Reservation Protocol46

Interdomain Routing Protocol45

IPv6 Header41

IP Option Header

Destination Options Header60

No Next Header59

IPv6 Authentication Header51

Encapsulating Security Payload50

IPv6 Fragment Header44

IPv6 Routing Header43

Hop‐by‐Hop Options Header0


IPv6 Option HeadersTunneling

Option 41IPv6 datagram in data field of IPv6 datagramExample — used with fragmentation when router adds option field

Hop-by-hop header Options checked by every router and destination node

Destination options headerOptions checked by destination node

Routing headerSource sets route through network

Fragment headerHandles fragmentation

Authentication header / Encapsulating Security PayloadImplement IPsec


Option Header Examples

TCP Header + Data Fragment

Fragment HeaderNext = TCP

Hop‐by‐Hop HeaderNext = Fragment

IPv6 HeaderNext = Routing

TCP Header + Data Fragment

Fragment HeaderNext = TCP

Routing HeaderNext = Fragment


TCP Header + DataRouting HeaderNext = TCP


TCP Header + DataIPv6 HeaderNext = TCP


Traffic Class + FlowDSCP — 6 bits

Differentiated Services Code PointSets per-hop behavior according to service

ECN — 2 bitsExplicit Congestion NotificationRouter can set congestion indication

FlowStream of related packets from 1 source to 1 destination Require particular handling by routers

Requirements cached in routersExample — real time priority

24 bit flow labelChosen randomly from 1 to FFFFF0 — not part of a flow

Flow identified by label + src IP + dest IP


ICMPv6ICMP — Internet Control Message Protocol

ICMP Message32

ChecksumCode (subtype)Type0

16 – 318 – 150 – 7Offset

Redirect Message137

Neighbor Advertisement136

Neighbor Solicitation135

Router Advertisement134

Router Solicitation133

Group Membership Reduction132

Group Membership Report131

Group Membership Query130

Echo Reply129

Echo Request128

Parameter Problem4

Time (Hop Count) Exceeded3

Packet Too Big2

Destination Unreachable1


Neighbor DiscoveryIdentify hosts and routers on physical LAN segment

Replaces ARP

Address resolution Obtain MAC address for neighbors

Neighbor SolicitationNode sends ICMP neighbor solicitation message to host

Neighbor advertisementNeighbor sends ICMP neighbor advertisement with MAC address

Interface IDFF02::

64‐bit host address64‐bit local link multicast prefix


Router and Prefix DiscoveryRouter advertisements

Routers send ICMP messages to hosts on some scheduleAddressed to FF02::1

Multicast address — all systems on local linkProvides configuration parameters

MTUGlobal IP prefixIP address configuration method (ICMP / stateless)

Router solicitation messageHost sends ICMP message to request router serviceAddressed to FF02::2

Multicast address — all routers on local linkRouters respond with router advertisement


Stateful Auto‐ConfigurationDHCP service

Similar to IPv4DHCP messages

SolicitAdvertiseRequestReplyReleaseReconfigure

DHCP client Waits for DHCP advertisementSends DHCP request

DHCP server Sends DHCP replyProvides IP address + configuration parameters


Stateless Auto‐ConfigurationNode reads 48-bit MAC address from hardwareConverts 6-byte MAC address to 8-byte node address

48-bit MAC address 24 bits FFEE 24 bitsExample: 11 22 33 44 55 66 11 22 33 FF EE 44 55 66

Extends link-local prefix to 64 bitsFE80::/10 FE80::/64

Attaches link-local prefix to node address Creates temporary link-local unicast addressExample: FE80::1122:33FF:EE44:5566

Verifies unique address with neighbor solicitationNo response to link-level address assigns address to interface

Sends router solicitationRouters respond with router advertisement

No response node attempts DHCPResponse message provides parameters — MTU, global prefix

Replaces FE80::/64 global prefix to form global unicast address


Mobile IP (RFC 2002)Internet protocol supporting host mobility

Maintains TCP connections as host changes locationSupports authentication

Mobile host maintains single long-term IP addressVersion 4 IP address and address format are unaffected

Routing tunnel replaces standard IP routing

Router

132.4.16.X X=1, 2, 3, ..., 254

1 2 3

Router

138.27.192.Y Y=1, 2, 3, ..., 254

1 2 3

138.27.192.87


Mobile IP Basic IdeaSimilar to

Call forwardingMail forwarding at

post office

Mobile Node Permanent IP

addressUsual home service routerFinds mobile service routers when roaming

Home router and mobile service router coordinate

IP datagramsSent to usual home routerForwarded by home router to mobile service routerForwarded to Mobile Node

IP datagram

IP datagram

IP datagram


Mobile IP EntitiesMobile Node (MN)

Host or router that can change its point of attachmentHome Address

Permanent IP address assigned to MNCorrespondent Node (CN)

Node that sends datagrams to MN home addressHome Agent (HA)

Maintains table of registered mobile nodes Forwards datagrams addressed to mobile node

Foreign Agent (FA)Delivers datagrams between MN and HA

Mobility AgentHA or FA supporting mobility

Care-of-Address (COA)FA address used to identify current location of MN


Agent DiscoveryMobility Agents broadcast availability

Home Agents (HA) Foreign Agents (FA)

Mobile Node (MN) looks for Local router services when connected to home networkForeign Agent (FA) services when connected to foreign network

FA advertises services


Care‐of‐Address DiscoveryMobile Node (MN)

Requests service from Foreign Agent (FA)

Foreign Agent Assigns Care-of-Address (COA) to MN FA can have 1 or more available COAsUsually FA assigns same COA to all MNs

MN requestsservice from FA


RegistrationForeign Agent

Requests Mobile IP support from MN’s Home AgentHome Agent

Agrees to provide Mobile IP supportMN

Registers COA with its HAHA forwards datagrams to FA

Datagrams for MN arrive at HA

MN registerswith FA and HA

FA forwardsrequest to HA

HA acceptsor rejects

FA informsMN of status


Establishment of Service in Mobile IP

MN in home network

MN in foreign network


Mobile IP End‐to‐End Delivery

StandardIP datagram

From: CN IP addressTo: MN Home Address DATA

EncapsulatedIP datagram

From: HA IP addressTo: FA COA Address


StandardIP datagram


CN

MN

FA

HA


Roaming and Hand‐OffRoaming MN

Moves to new attachment point (network)Requires change of FA

Multiple bindings Multiple COAs — old + newAvoid datagram lossAvoid too frequent registrations

HA Forwards each packet to multiple COAs

MNReceives packet at one COA

Route optimization after reconnection


Change of Foreign AgentCN HA FAold FAnew MN

IPdatagram

EncapsulatedIP

datagram IPdatagram MN changes

location

registration

registration

updateACK

EncapsulatedIP

datagram

IPdatagram

EncapsulatedIP

datagram

IP datagram

IPdatagram

IPdatagram

ACK

EncapsulatedIPdatagram


Triangle RoutingHome agent is bottleneck

Increases network load


Route Optimization

(1)IP

datagramIP

datagrams (2b) Warning

(3) Binding Request(4) Binding Update

(5)IP datagram

HAFA

(2a) EncapsulatedIP datagram


Roaming Under Route Optimization


IPv6 Mobile IPImplements Mobile IP

1. Mobile node (MN) obtains local address using autoconfiguration Roaming address = care-of-address (CoA) No special Foreign Agent

2. MN registers with Home Agent by sending Binding Update3. HA forwards traffic for registered MN

Tunnels packets from CN to MN4. MN sends packets to CN directly5. Route optimization — HA provides CN with CoA

HA

MN

CN

12

34

5


IPv6 Mobility SupportNode writes home address in destination option header

Destination node can identify datagram by home address Tunneling

Using IPv6 routing extension headers instead of encapsulationReduces processing cost of delivering packets

HandoverNode moves from ESS to ESSLayer 2 handover — change AP and ESS IDNode detects change in on-link subnet prefix Updates CoA

IPv6 Mobility header messagesHome Test Init, Home Test, Care-of Test Init, and Care-of TestBinding Update / Acknowledgement

MN to notifies node or HA of current binding


Basics of

Wireless Networking


Energy and PowerEnergy

The ability to do workEnergy can be kinetic (movement) or potential (stored)

PowerEnergy transfer per secondTransfer can be kinetic (motion) or potential (moving stored energy)

UnitsPower is measured in WattsEnergy is measured in Joules = Watts seconds 1 kW-hour = 1000 Watts 3600 seconds/hour

= 3.6 106 Joules


Electricity and Magnetism

2 ,

0

Electric fieldMagnetic field

Power

charge at distance

RR

EB

E×B

E

B

A charged object may create

Radiation (transfer of power) from a charged object

Motionless charge does not radiate

Antenna accelerat0 0Accelerated charges induce fields and

Antenna radiates power as electromagnetic waves

=

E B

es charges electric current


Radio Communication

Moving electric charge is called electric currentCurrent depends on time charges must accelerate

Electromagnetic radiation satisfies wave equation Radiated power depends on time t and distance R from antenna

Transmitteraccelerates

chargesup and downon antenna

Informationsignal

controlsmotion

of charges

Power needed to accelerate charges getsradiated away as electromagnetic power

Radiation spreads in every directionlike expanding sphere

Radiated poweraccelerates

chargesup and downon receiver

antenna

Motionof chargeprovides

informationsignal toreceiver


Wave Motion

Wave height has peaks and troughsy = height of peak above center = depth of trough below center

At fixed distance from shore, wave rises and falls over timeT = time between two wave peaks (period) f = 1/T = number of wave peaks per second (frequency)

At fixed time, multiple wave peaks at various distances = distance between two wave peaks (wavelength)

Surfer rides peak of wavePeak depends on distance and time peak moves over timeSpeed of moving peak = f

R

yy

Ocean waves rolling onto a beach


Charge Moving on AntennaCharge on antenna accelerated up and down

Oscillates top to bottom (distance L) every T seconds

t0

T/4 T/2 3T/4 T y t

2L

2L

1

cos 2 cos 22 2

Frequency oscillation cycles per second

position of charge on antenna at time y

y

f Tt t

L t Lt ftT

L

movingcharge

y (t)


Field is Solution to Maxwell Equations

0 0

0 0

cos 2 cos 2, ,

1/,

distance from antenna to point of measurementtime (measured on some clock)frequency

are physical constantsspeed of light

R Rf t f tc cR t R tR R

Rtf T

c

E BE B

E B

Radiation fiel ds

R

R

P

20 02

0 020

cos 2

1 12

T

Rf tcR

P P t dtT R

E BP E B

E B

Radiated power

Average powe

r Fading


Wavelength

0 00

cos 2 cos 2cos 2,

cos 2 1 0,1,2,...

ccT f cf

f R R tftRf t c TcR tR R R

R t R tT T

R tT

E EEE

Define electromagnetic wavelength

Radiation field

Wave peaks

0 0 0R R t t R tT T

R f ct T

Wave peaks travel at speed of lightv

Speed


Spherical Waves in Space and TimeAt fixed distance wave rises and falls over time

t

T/4 T/2 3T/4 T

0

1 2

, cos 2

cos 2

constconst

const

ttT

ft

RR

R

C C

EE

2

0

1

, cos 2

cos 2

constconst

RRR T

C

t

R CR

t

EE

R

-1/R

4

2 3

4

1/R

At fixed time, multiple wave peaks at various distancesWave peaks decrease at larger distances from source


Electromagnetic Spectrum

Radio antennas are effective in the frequency rangefrom ~ 30 kHz ( = 10 km)to ~ 300 GHz ( = 1 mm)

Chemical reactions generate higher frequencies:Infra-Red (IR) Visible LightUltra-Violet (UV) X-rays (Roentgen)

Nuclear reactions generate gamma rays (γ)


Electromagnetic Spectrum

ExampleLine antenna most efficient when L = / 2GSM cellphones operate at f ~ 1 GHz = (31010 cm/sec)/(109 Hz) = 30 cm L ~ 15 cm = phone size

Wavelength(m) 104 102 100 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16

Frequency (Hz) 104 106 108 1010 1012 1014 1016 1018 1020 1022 1024

radio microwave IR visible UV X-ray gamma

1 MHz ~ 300 m 100 MHz ~ 3 m 10 GHz ~ 3 cm

VLF < 30 kHz LF 30 - 300 kHz MF 300 kHz - 3 MHz HF 3 - 30 MHz VHF 30 - 300 MHz UHF 300 MHz - 3 GHz SHF 3 - 30 GHz EHF > 30 GHz

103 10 cm/s f c


Radio Wave PropagationTransmitter generates radio waves

Waves propagate (spread out) through spacePart of radiated power may be obstructedPart of radiated power is detected by receiver

ionotropic wave

line of sight wave

ground wave

tropospheric wave

Transmitter Receiver


Interference with Radio Signals

absorption

reflection

refraction

medium


Multipath FadingObstacles reflect radio waves

Receiver gets signals from multiple pathsTime-to-arrive depends on path taken by signalReceiver gets signals transmitted at different times

ExampleThree signals sent at times t1 < t2 < t3

Antenna receives all three signals at time tSignal 1 sent first and followed longest path d1Signal 2 sent second and followed second longest path d2 < d1Signal 3 sent last and followed shortest path d3 < d2

Sum of waves can cancel out signals

d3

d1

d2


Cancellation of Signals in Wave MotionWave amplitudes

combine by adding

pulse

pulse

String receives two pulses at t = 0

String at t = 1

String at t = 2

String at t = 3

String at t = 4


Wave Interference

0 0

0 0

, ,

cos 2 cos 2

cos 2 c1

where and R t R R t t

R R t t

R R Rft f t tR R R

R ftRR R

R

E E E

E EE

E EE

Two waves arrive at antenna by slightly different paths

0

os 2

1

cos 2 cos 2 2

R R ft f t

RR

R R Rft ft f tR

EE

Ignoring


Wave Interference

0

1 12 2

0

cos 2 cos 2 2

cos cos 2cos cos

2co c2 ss o

R R Rft ft f tR

A B A B A B

R ftR

R c

R f t

t

EE

EE

Using identity

Transparent medium

0

1c

12

os

cos cos 02

R c tf t t f c f

R f

R ff t

t

R t

Total cancellation


IEEE 802.11 Protocol LayersPhysical Layer Convergence Sublayer

Specifies header for PHY Dependent SublayerDirect Sequence Spread Spectrum (DSSS)Frequency Hopping Spread Spectrum (FHSS)

Transmission typeModulation schemeData transmission rates

MAC layer Medium accessAddressingProcedures Data

Link Layer

LLC802.2

LLC frame for SEQ/ACK/ControlBridging Exchange of 802.2 PDUs

MAC

802.11

CSMA/CA, MACA, CFP

Physical Layer

Convergence PHY-Dependent Convergence Sublayer

PHY FHSS, DSSS, IR, Data rates

Wi‐FiTrademark of Wi‐Fi Alliance trade association


WiFi Ad Hoc ModeIndependent Basic Service Set (IBSS)

Any set of 802.11 STAs (wireless stations)All STAs transmit / receive on same frequencyPeer-to-peer serviceNo connection to a wired network

Simple unmediated communicationSTAs communicate directly with one anotherUseful for quick set upAuthentication or Registration not required

Multiple IBSSs are independentNo bridgingNo hand-off

Independent Basic Service Set

station

station

station

station


WiFi Infrastructure ModeBasic Service Set (BSS)

A set of wireless end stations (STA)An Access Point (AP)

Connected to the wired network infrastructure Acts as base station for the wireless networkAll traffic flows through AP by Contention or Polling (CFP)

Stations must Associate with APAuthenticationRegistration

Basic Service Set

station

station

accesspoint

station

Wired LAN

Internet


WiFi Extended Infrastructure ModeExtended Service Set (ESS)

Two or more BSSs Form single subnetwork (broadcast domain)Looks like one large BSS to LLC layer One Access Point (AP) in each BSS

BSSs connected via Distribution System (DS)DS is backbone networkDS performs MAC-level transport of MAC SDUs DS implementation not specified in 802.11

PortalSoftware gateway function in APBridges BSS to any non-802.11 DS protocol

DS services permit handoffStation moving from one BSS to another Requires coordination between APs

Basic Service Set

station

station AccessPoint

station

Basic Service Set AccessPoint

station

stationstation

DistributionSystem

Internet


Hidden Node ProblemA transmits to B

C cannot receive from A — out of range

C transmits — corrupts transmission from A to B

A B C D

transmit range

nowait

interfere


Exposed Node ProblemB transmits to A

C receives transmission from B — delays transmission to D

Inefficient — C transmission to D will not interfere with B to A

A B C D

wait


CSMA with Collision Avoidance (CSMA/CA)Carrier Sense Multiple Access (CSMA)

Stations listen for transmissionsDo not transmit if carrier is detectedCollision detection not possible

Hidden node problemAntenna cannot receive while transmitter active

Collision Avoidance (CA)Non-persistent accessRandom backoff

A B C D


Multiple Access with Collision Avoidance (MACA)Channel set-up before data transmission

RTS — Request To SendCTS — Clear To SendACK — Acknowledge error-free transmission

Net Allocation Vector (NAV)Transmitted in RTSEchoed in CTSPredicted data transmission time

Trade-off Adds overheadBetter throughput in hidden and exposed Nodes

RTS

CTS

DATA

ACK


Multiple Access with Collision Avoidance (MACA)C sends 30-byte RTS to D

Includes NAV for data transmissionB and D hear RTS

D responds with CTS to C Echoes NAVC and E hear CTS

B hears RTS but not CTSB can transmit to A — no interference with C to D

E hears CTS but not RTSE waits data transmit time before transmission to F

A B C D

RTS CTS

E F


MAC Sublayer Frame Structure

Frame Control

Duration/ ID

Address 1 Address 2 Address 3 Sequence Control

Address 4 Frame Body FCS

2 bytes 2 bytes 6 bytes 6 bytes 6 bytes 2 bytes 6 bytes 0-2312 bytes 4 bytes

Frame Control Control flags

Duration/ID Timing control

Addresses Various MAC entities

Sequence Control Sequence/Fragment number for error/flow control

Frame Body 0 or more data bytes (SDU)


Frame Control

Protocol Version Type Subtype To

DS From DS

More Fragments Retry Power

Management More data WEP Order

2 bits 2 bits 4 bits 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit

Type and Subtype Data, Control, Management with subtypes

To DS/From DS Access Point (AP) is destination/source

More Fragments Part of fragmented LLC packet

Retry Indicates re-transmission of bad packet

STA alerts AP of its mode

Value of 1 STA will be in power-save mode Power Management

Value of 0 STA will be in active mode

More Data AP alerts STA (in power-save mode) of buffered frames

WEP Indicates WEP encrypted data

Order Indicates Strictly Ordered service class


MAC Layer Address Fields4 Address Fields

5 possible MAC entities:BSS Identification Number (BSSID)

Source Address (SA)Station that initiated the message

Destination Address (DA)Final destination for the message

Transmitting Station Address (TA)Source station for the message on this hop

Receiving Station Address (RA)Destination station for the message on this hop


Address Field Definitions

To DS

From DS Address 1 Address 2 Address 3 Address 4

0 0 DA SA BSSID 0 1 DA BSSID SA 1 0 BSSID SA DA 1 1 RA TA DA SA

Source address for DS to DS messages (802.11 is also DS)Address 4Final destination or source when DS performs distributionAddress 3Immediate source addressAddress 2Immediate destination addressAddress 1

station accesspoint

Internet

stationstation

station

station


Addressing in an IBSS

Independent Basic Service Set (IBSS) No Access Point (AP) and no DSFields To DS and From DS are 0

To DS

From DS Address 1 Address 2 Address 3

0 0 DA SA BSSID

Independent Basic Service Set

station

station

station

station

Address 1 Immediate destination address (DA)Address 2 Immediate source address (SA)

Address 3BSSID Identifies Ad Hoc network Prevents message from reaching outside IBSS


Data Addressing in a BSS

Basic Service Set (BSS)All transmissions are sent To/From Access PointTo/From DS actually means To/From AP

To DS


0 1 DA BSSID SA 1 0 BSSID SA DA

Basic Service Set

station

station

accesspoint

station

Wired LAN

Address 1 Immediate destination address (DA)

Address 2 Immediate source address (SA)

Address 3 Final Destination or Source


BSS Addressing Example

Station A sends message to Station B via AP (BSSID)

To DS



Basic Service Set

stationA

stationB

accesspoint

To DS = 0From DS = 1

To DS = 1

From DS = 0

Wired LANAddress 1 = BSSID

Address 2 = Station AAddress 3 = Station B

Address 1 = Station BAddress 2 = BSSID

Address 3 = Station A


Control and Management Addressing in a BSS

Control and Management messages in a BSS: Only involve stations in the BSS and the APAre sent with To DS = From DS = 0Either the Source or the

Destination will be the AP (BSSID)

Address 3 in included as anerror check

Basic Service Set

station

station

accesspoint

station

Wired LAN

To DS


0 0 DA SA BSSID


Addressing in an ESS

Extended Service Set (ESS)All transmissions are sent via an APTo the stations, entire ESS looks like one BSSStations do not know if message passes via DS or not

To DS



Basic Service Set

station

station AccessPoint

station

Basic Service Set

AccessPoint

station

stationstation

DistributionSystem

Address 1 Immediate destination address (DA)Address 2 Immediate source address (SA)Address 3 Final Destination or Source


ESS Addressing Example

Station A sends message to Station B viaAP1 (BSSID1) DS AP2 (BSSID2)DS must forward Data, Sequence, SA, and DA

By some legal means

To DS



Basic Service Set

stationA

AccessPoint

1

Basic Service Set

AccessPoint

2station

B

DistributionSystem

Extended Service Set

To DS = 1From DS = 0

Address 1 = BSSID1Address 2 = Station AAddress 3 = Station B

Address 1 = Station BAddress 2 = BSSID2

Address 3 = Station ATo DS = 0

From DS = 1


Mobility ManagementRegistration

Performed when mobile station (MS) activated in Service AreaAuthentication

WiFi — managed by access point (AP)GSM / 3G / 4G

Home Location Register (HLR)Maintains account + location information for home customers

Visitor Location Register (VLR)Cache of HLR data on active roamers in each Service Area

Call EstablishmentPerformed when user initiates or receives call

SecurityProtects from fraud and eavesdropping

Handoff (handover)Performed when MS changes attachment point to network


Handoff (Handover)User moves between cells

Hard HandoffOld cell transfers control to new cell Break-Before-Make sequence

Transceiver in old cell stops transmitting to userTransceiver in new cell begins transmitting to user

New BS assigns user frequency pair from its frequency group

Soft HandoffCentral transceiver coordinates with nearest cellsDetermines which transmitter is receiving strongest signal from userMake-Before-Break sequence

Transceiver in old cell transmitting to userTransceiver in new cell begins transmitting to user Transceiver in old cell stops transmitting to user


1970 — 0G Mobile Phone System (MPS) One central transceiver (transmitter/receiver)

Mobile telephones communicate via central transceiverTransmit at high power for maximum distanceSystem covers 65 to 80 km

Modulation is standard analog FM Supports 12 simultaneous mobile phone calls If 12 channels busy, other calls are blocked

Requires 24 carrier frequencies2 frequencies per phone:

Dedicated transmit frequency Dedicated receive frequency


Cellular ConceptDivide coverage area into cells

In each cellCentral cell transceiver serves all clients in cellMobile Stations communicate via cell transceiverEach active device allocated frequency pair

Receive — downstream from base stationTransmit — upstream to base station

Transmit at low power (just enough to cover a cell)Use same frequencies in many cellsNo interference between cells

Handoff Telephone can move from cell to cell during a callRequires cell-to-cell infrastructure and coordination

B

C

A

C

C

B

A

B

A

B

A

C

B


Frequency (Channel) Reuse Patterns

B

C

DE

F

GA

B

C

DE

F

GA

B

C

DE

F

GA

B

C

A

C

C

B

A

B

A

B

A

C

B

7 cell reuse

3 cell reuse

4 cell reuse

B

D

A

C

B

C

D

D

C

A

B

A

A


Mobile Network Switching HierarchyMobile Service Provider

Service Areas or Registration AreasClusters

Cells

Mobile ServiceProvider

Mobile ServiceProvider

ServiceArea

ServiceArea

ServiceArea

ServiceArea

BC

DE

F

GA

BC

DE

F

GA

BC

DE

F

GA

B

C

DE

F

G

A

B

C

DE

F

G

A

B

C

DE

F

G

AB

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

ClusterCell


Mobility Elements in GSM

Base System(BS)

BTS BSC MSCPLMN

BSS

HomeSubscribers

BTS BSC MSCPLMN

BSS

Base System(BS)

Service Area

Service Area

Roamer

HLRVLR

HLRHome

Subscribers

Home SubscriberRegistration

Roaming SubscriberRegistration

Query to HomeMSC HLR

for VLR Entry

PLMN— public land mobile network, the portion of the cellular network that operates over cables.


Cellular Network: GSM (2G) UMTS (3G)

Radio Network System (RNS)Base Station Subsystem (BSS)

Radio Network Controller (RNC)Base Controller System (BSC)

Node‐BBase Transmitter System (BTS)

UMTS NameGSM Name


GSM Registration ProcessMS enters Service Area

Establishes low bit-rate control channel with service provider

MS requests serviceBTS allocates a frequency pair

MS reports to Mobile Switching Center (MSC)Location, Status, and Identity

Dedicated hardware ID code in phoneSubscriber Identity Module (SIM) card identifies customer in GSMMobile Station generates access code to network

Transmits code by public key encryption (PKE) algorithm

Mobile Switching Center (MSC)Authenticates customer identity with HLRFor roaming subscriber, creates VLR entry Updates Home Location Register (HLR) and billing database


GSM Registration

MS BTS BSC MSC VLR HLRChannel requestActivation responseActivation ACKChannel assignmentLocation update requestAuthentication requestAuthentication responseAuthentication checkTMSI assignmentTMSI ACKUpdate VLR / HLR entriesChannel release


GSM Call Establishment

MS BTS BSC MSCRequest control channelAssign control channelCall establishment requestAuthentication requestAuthentication responseEncryption keyEncryption responseDestination addressRouting responseTraffic channel requestAssign traffic channelAvailable or busyCall acceptedConnection establishedData exchange

MS Initiated


GSM Call Establishment

MS BTS BSC MSC VLR HLR GMSC PSTN CallerStandard call set-upRequest to Gateway MSCHLR user requestAssign roaming numberRequest to MSC (user location)Update user statusPage MSAuthenticationCall connection

Mobile Terminated


Handover Types

Intra-cellChange frequencies to avoid interference

Inter-cell — Intra-BSCMS moves between cells within control of one BSC

Inter-BSC — Intra-MSCMS moves between cells controlled by different BSCs MSC controls handover

Inter MSCMS moves between cells controlled by different MSCs

MSC MSC

BSC BSCBSC

BTS BTS BTSBTS

MS MS MS MS


GSM Inter‐BSC Handover Procedure

BTSold BSCnew

measurementreport

BSCold

Handoff link establishment

MSCMSmeasurement

report

Handoffrequired

BTSnew

Handoff request Channel

activation

Activation ACK

Handoff Request

ACKHandoff command

Handoff completeHandoff

completeclear commandclear command

clear completeclear complete

Handoff commandHandoff

command


3G RelocationServing RNC (SRNC) — RNC-1

Primary Node-B — 1Monitoring Node-B — 2

MSC

RNC-1 RNC-2

1 2 3 4Node-B Cells

Clusters



UE relocates to primary Node-B — 2Monitoring Node-B — 1

MSC

RNC-1 RNC-2

1 2 3 4Node-B Cells

Clusters



Active Node-B — 2Relaying RNC (RRNC) — RNC-2

Primary Node-B — 3 Monitoring Node-B — 4

MSC

RNC-1 RNC-2

1 2 3 4Node-B Cells

ClustersSRNC (RNC-1)

combines data from 2 and 3



No active Node-BRelaying RNC (RRNC) — RNC-2

Primary Node-Bs — 3 + 4

MSC

RNC-1 RNC-2

1 2 3 4Node-B Cells

ClustersRNC-2

combines data from 3 and 4

SRNC (RNC-1)receives combined datafrom RNC-2


3G RelocationServing RNC (RRNC) — RNC-2

Monitoring Node-B — 3Primary Node-B — 4

MSC

RNC-1 RNC-2

1 2 3 4Node-B Cells

Clusters


GSM Voice Transmission Summary

Voice 8000Samples/sec

3300 HzFilter

13-bitQuantization

8:1Compression

104 kbps

13 kbps 260-bitbuffer

104 kbps 20 msec = 2080 bits13 kbps 20 msec = 260 bits

CRCGenerator260:456

13 kbps 456 bits = 8 blocks 57 bits/block

57 57

24

1 2 3 4 5 6 7 8

16 17 18 19 20 21 22 238 9 10 11 13 14 150 1 2 3 4 5 6 7

57 user bits per field 2 fields per frame 24 frames per multiframe = 2736 user bits per multiframe

2736 bits per multiframe / 120 ms per multiframe = 22.8 kbps

22.8 kbps / (456/260) = 13 kbps

1 user time slot / frame

24 frames / multiframe


GSM Protocol Stack

BSSAPBSSAPRRMRRMSCCPSCCPBTSMBTSMRRM'RRM'

MSRadioLAPDm

MMCM

BTSRadioLAPDm

64 kbpsLAPD

BSC64 kbps

LAPD MTP

MSC64 kbps

MTP

MMCM

Message Transfer Part — standard PSTN signaling and managementMTPSignaling Connection Control Part (SCCP) — one SCCP connection per MSSCCPBSS Application Part (call setup + management)BSSAPBase Transceiver Station Management (BTS to BSC management messages)BTSMLink Access Protocol D — ISDN layer 2 protocol (Q.920/921) for LLC servicesLAPD

Radio Resource Management — allocates physical parameters for radio systemSeparate protocol instances at MS/BTS layer and MS/BSC layer

RRMRRM'

Mobility ManagementMMConnection ManagementCM


GSM Logical Channel Structure

TCH/FFull rate

TCH/HHalf rate

BCHBroadcast Channel

TCHTraffic Channel

CBCHCell Broadcast ChannelMSC to MS broadcasts

DCCHDedicated Control Channel

FACCHSACCH

FCCH SCH BCCH PCH AGCH RACH ACCH SDCCH

CCHControl Channel

CCCHCommon Control Channel


General Packet Radio Service (GPRS)Provides packet mode data access for GSM

IP-based architectureBegan as 2.5G enhancement

IP datagrams separated from circuit mode traffic at cluster Packet Control Unit (PCU)

Packet mode function in BSC to handle IP datagramsCircuit mode voice/data routed to MSC

Forwarded to other MSC or PSTNPacket mode data is routed to Serving GPRS Support Node (SGSN)

Forwarded to InternetPCU to SGSN runs IP over Frame Relay

Mobility managementCircuit mode traffic uses PSTN / PLMN routingPacket mode traffic uses IP routing


GPRS System Architecture

cell MSCBS

Internet

SGSN

GGSN

PSTN

PCU GPRSBackboneMS

PLMN - 1

GGSN

cell MSCBS

SGSN

PCUMS

cell MSCBS

SGSN

PCU GPRSBackboneMS

PLMN - 2

GPRSBackbone

BorderGateway

BorderGateway


GPRS Support NodesServing GPRS Support Node (SGSN)

Packet-switched version of MSCHandles packets to / from Mobile Stations (MS) Handles MS mobility management

Gateway GPRS Support Node (GGSN) Interfaces SGSNs to external IP networks Maintains routing information

Exterior gateway for GPRS networkDHCP — assigns IP addresses to MSRoutes incoming IP datagrams to appropriate PCU

PSTN

GGSNcell MSCBS

SGSN

PCU GPRSBackboneMS Internet


GPRS Architecture Protocol Stack

From Internet

MS to SGSN Tunnel SGSN to GSSN Tunnel

MS to BSS Tunnel BSS to SGSN Tunnel


Packet Data Protocol — PDP ContextPDP context

Data structure stored in SGSN and GPRS Subscriber session information during active GPRS session

Tunnel Endpoint ID (TEID) ID allocated by SGSN / GGSN Identifies SGSN — GGSN tunnel for sessionSimilar to VC number in SVC

RecordsSubscriber IP addressIMSITunnel Endpoint ID (TEID) at GGSNTunnel Endpoint ID (TEID) at SGSN


GPRS Protocol Structure — 1Fixed-system application sends data to MS

IP datagrams or X.25 packetsBasic hops

Internet GGSN SGSN BSS MSGGSN SGSN

L1L1

Standard user IP datagrams from InternetIP

GGSNSGSN

L2L2IPIP

Standard TCP/IP and infrastructure protocols

TCP/UDPTCP/UDP

GPRS Tunneling Protocol (GTP)GTP header added to user IP datagram

Call Data Records (CDR) for billingHandles call failure

GTPGTP


GPRS Protocol Structure — 2

SGSN-to-MS Tunnel

Logical Link Control (LLC)LLC headerFlow controlError controlLink control

Sub-Network Dependent Convergence Protocol (SNDCP)

SNDCP headerEncapsulates GTP + user IP datagrams Provides

Session servicesSAR (Segmentation and Reassembly)

Maps user IP datagrams to LLC channel

BSS SGSNL1bisNW

BSSGP

LLC

SNDCP

L1MS

L2IP

TCP/UDP

LLC

GTPSNDCP


GPRS Protocol Structure — 3SGSN to BSS

Frame Relay packetsMaps BSSGP signaling to Frame Relay signaling

Map LLC packets to BSSGPBase Station System GPRS Protocol (BSSGP) Processes routing and QoS information Routing layer for Frame Relay signaling Call setup / control signaling over Frame Relay

SGSNL1bisNW

BSSGP

LLCSNDCP

L1L1bisBSS

L2NW

IPBSSGP

TCP/UDP

GTP


GPRS Protocol Structure — 4BSS to MS

GSM Radio Frequency (RF)MS allocated 1 to 8 GSM time slots 18 kbps per time slot 18 kbps to 144 kbps

Media Access Control (MAC)Between MS and BSSControls access to GPRS

Radio Link Control (RLC)MS-to-BSS Logical Link Control Flow control, error control, link control

BSSGP

L1bis

NW

RLC

BSS

RF

MAC

LLC

RF

MS

MAC

RLC

SNDCPIP


GPRS Connection Process


GPRS Connection ProcessMS switches on and sends GPRS attach requestUser Registration — 1

Associate PLMN address with Packet Data Protocol (PDP) address PDP address — Static or dynamic IPPLMN address — International Mobile Subscriber ID (IMSI)

AuthenticationBSC queries Home Location Registers (HLR) — 2HLR updates Visitor Location Registers (VLR) — 3

Call Admission Control (CAC) — 4Determines required network resourcesGrants resources if available

Routing — hop-by-hop IP datagram deliveryRouting tables in GSN (GGSN or SGSN)

Address conversion / VC mappingGSN handles compression and encryption


Enhanced Data Rates for GSM Evolution (EDGE)Standard: GPRS-136HS

Formally defined as 3G enhancement to GPRS

Considered 2.75G enhancement

Uses enhanced modulation technique

Transmits 60 kbps in each time slot

8 slots 60 kbps/slot = 480 kbps

Uses 384 kbps for user data


High Speed Circuit Switched Data (HSCSD)Circuit Switched Data (CSD)

14.4 kbps circuit mode data connection in 2G GSM User data replaces digitized voice in 1 time slot

High Speed Circuit Switched Data (HSCSD)2.5G enhancementUp to 8 slots (full user frame) allocated to one data channelUp to 115.2 kbps

Transparent data transmissionUser data stream can contain signaling to network

Allows dynamic reconfiguration of data connection (data rate, QoS) HSCSD data frames carry data sub-stream numbers

Maintains order of transmission over GSMNon-transparent data transmission

Only user data in data streamNo signaling or reconfiguration

LLC functions performed by GSM protocols


High Speed Downlink Packet Access (HSDPA)Higher data rates for packet data

Downlink speeds of 1.8, 3.6, 7.2, 14.0, 337 MbpsHS-DSCH simplified for fast packet data

Power control and variable chip rate eliminatedHybrid automatic repeat-request (HARQ)

LLC layer added between PHY and MAC (not in RLC)Incremental redundancy

Corrupted packets not discardedRetransmitted packets combined until error-free packet assembledFaster than waiting for uncorrupted retransmitted packet

Fast packet scheduling2 ms scheduling granularity (instead of 10 ms)Transmission scheduled to UEs reporting highest power levels

Adaptive Modulation and Coding (AMC)Modulation scheme and code rate depend on channel quality


SMS in GSM Architecture

GMSCSMSC

IWMSC

SME

SMSC

SME: Short Messaging EntitySMSC: Short Message Service CenterGMSC: Gateway Message Service CenterIWMSC: Interworking Message Service Center


SMS NodesShort Messaging Entity (SME)

Any entity that can receive or send short messagesFixed network elementMobile StationAnother service center

Short Message Service Center (SMSC)Store and forwarding of SMS between SME and MS

Gateway Message Service Center (GMSC)Receives SMS in SMSCInterrogates HLR for routing informationDelivers SMS to MSC for destination SME

Interworking Message Service Center (IWMSC)Receives SMS from MSC Delivers SMS to appropriate SMSC for forwarding


SMS Delivery to MS

SME SMSC HLR MSC VLR BSSSMS

Submit RouteRequest

Route

SMSForward

MS

UserInfo

ACK

UserInfo Page

ACKACK

SMSForward SMS

ForwardACK

ACKDeliveryReportDelivery

Report


CDMACode Division Multiple Access

Commercial system developed by Qualcomm Operates on AMPS frequencies

Channelization25 MHz radio band per directionDivide band into 1.25 MHz RF channels25 MHz per cluster / 1.25 MHz per channel = 20 channels per cluster

DSSS digital transmissionTransmit 1.2288 Mcps in 1.25 MHz radio channelVoice and control modulation — QPSK

Code divisionUsers transmit simultaneously using independent chip sequences

Orthogonal (Walsh) Codes / Pseudorandom noise (PN) codesReceiver separates channels by decoding chip sequences

StandardsIS-95 — now called CDMAone


Orthogonal CDMA Codesm-dimensional vector space with inner product

m orthonormal basis vectors

Code schemeBasis vector Si is code assigned to station iStation i transmits ti Si with coefficientTotal transmission from all stations

1

1 mi ii

U Vm

U V

1

1 1 1

, 1, ... ,

,

0,,

1 1 1

with coefficient for any vector i

mi i ii

i j ij

m m mi i i j j j i j j ij ij j j

S i m

t S t

i jS S m

m i j

t S S t S t S S t m tm m m

T T

T

1 ,0 ,

1 ,

data 0no transmissiondata 1

it

1

mi iit S

T


Example 4‐Chip CDMACode vectors for m = 4 stations

4-bit transmission levels (chips)

Radio signal amplitudes added together

1 2 3 4

1 1 1 11 1 1 11 1 1 11 1 1 1

S S S S

Binary 1 Binary 0 Station 1 –1 –1 –1 –1 +1 +1 +1 +1 Station 2 –1 +1 +1 –1 +1 -1 -1 +1 Station 3 –1 –1 +1 +1 +1 +1 -1 -1 Station 4 –1 +1 -1 +1 +1 -1 +1 -1


Example 2‐bit Transmission

Data 0 1Station 1 Signal +1 +1 +1 +1 -1 -1 -1 -1

Data 0 1 Station 2 Signal +1 -1 -1 +1 -1 +1 +1 -1

Data no data 1 Station 3 Signal 0 0 0 0 -1 -1 +1 +1

Data 0 1 Station 4 Signal +1 -1 +1 -1 -1 +1 -1 +1 Total Transmission Signal +3 -1 +1 +1 -4 0 0 0


Example 2‐bit Transmission

1

2

3

4

T

+3 -1 +1 +1 -4 0 0 0

Data

Chip


Example DecodingInner Product

4

1

14 i ii

U V

U V T Sj jt

1 11 4 4

1 12 4 4

1 13 4 4

1 14 4 4

3, 1, 1, 1 1, 1, 1, 1 3 1 1 1 1 0

3, 1, 1, 1 1, 1, 1, 1 3 1 1 1 1 0

3, 1, 1, 1 1, 1, 1, 1 3 1 1 1 0

3, 1, 1, 1 1, 1, 1, 1 3 1 1 1 1 0

no data

t

t

t

t

1 11 4 4

1 12 4 4

1 13 4 4

1 14 4 4

4,0,0,0 1, 1, 1, 1 4 1 1

4,0,0,0 1, 1, 1, 1 4 1 1

4,0,0,0 1, 1, 1, 1 4 1 1

4,0,0,0 1, 1, 1, 1 4 1 1

t

t

t

t

First bitT = (+3, -1,+1,+1)

Second bit T = (-4,0,0,0)


Orthogonal Walsh CodesWalsh 0

Walsh 1

Walsh 2

Walsh 3

Walsh N

W0 = 1 W0' = - 1

W1 =W0 W0

W0 W0'=

1 11 -1

=1 1 1 11 -1 1 -11 1 -1 -11 -1 -1 1

W2 =W1 W1

W1 W1'

W3 =W2 W2

W2 W2'

WN =WN-1 WN-1

WN-1 WN-1'

=S1

S4

S3

S2

Walsh N is 2N 2N matrix


Pseudo‐Noise (PN) CodingPseudorandom Bernoulli sequence of 1 or –1

Equivalent to sequence of m coin tossesNearly equal number of 1 and –1 in each code

By central limit theorem

Codes are "nearly orthogonal"For codes A and B with chip patterns Ci

(A) and Ci(B)

2

1 1

1 1 1 1m mA Bi ii i

A B C Cm m

1

21 1 1 -1 -1 1 -1 -11

1

1 44

m A Bi ii

m

i

A B C Cm

P P P P P P P Pm m

1 11 1 11 12 2

P P P Pm


Channel CodingForward channels

64 orthogonal Walsh codes to 64 usersTheoretically perfect separation between users

All signals in same cell scrambled using PN sequence Reduces interference between same Walsh code in neighboring cellsShort PN sequence uses cell ID as seedPaging and traffic scrambled with long PN sequence before Walsh

Reverse channels Orthogonal codes not applicable in uplink

Orthogonality requires time synchronizationMSs transmit asynchronously

Long PN sequenceStream is scrambled using short PN sequence Carries cell ID


4G CellularInitial planning for 4th generation cellular systems

ITU working group planning IMT-2000 IMT-AdvancedConceived as network supporting mobility — not telephones + dataConvergence with NGN

4G objectivesHigher network capacity than 3GSpectral efficiency (high bps / Hz and bps / Hz /site)100 Mbps for moving client and 1 Gbps for stationary client100 Mbps between any two points in worldSmooth handoff across heterogeneous networksGlobal roaming across multiple networksQoS for multimedia support — audio, HDTV, etcInteroperability with existing wireless standardsAll IPv6 packet switched network — eliminate circuit mode entirely


Long Term Evolution (LTE)3.5G service

Early introduction of certain 4G enhancementsMarketed as 4G — does not meet 4G standards

Improved radio interface + data rates299.6 Mbps downstream75.4 Mbps upstream

Improved mobilitySupports MS moving at 500 km/h

Voice over LTE (VoLTE)Packet switched voiceLong-term replacement for circuit switched voice networkEnhanced voice encoding as VBR stream

Circuit-switched fallback (CSFB)Intermediate migration pathData over LTE + circuit switched voice

1Dr. Martin LandCongestion / Flow Control in TCPProtocols and Networks — Hadassah College — Fall 2021

Congestion and Flow Control

inTCP


Flow Control and Congestion ControlFlow control

Sender avoids overflow of receiver bufferCongestion control

All senders avoid overflow of intermediate network buffersBuffer fill rate

Bytes / second arriving from networkBuffer empty rate

Bytes / second leaving to network or application layerBuffer file time

Example

Full

EmptyArriving bytes

Leaving bytes

overflow

buffer sizeT

buffer fill rate buffer empty rate

overflow

64 KB 64 KBT 16 seconds

8 KB/sec 4 KB/sec 4 KB/sec


Congestion ControlFlow control

Avoid overflow in TCP receiver bufferCongestion control

Avoid overflow in router buffers

Flow Control TCPBuffer

RouterBuffer


Queuing TheoryAssumptions

Segments arrive independently (Poisson statistics)Random length (bytes)Average arrival rate in steady state — Packets/sec, Bytes/sec, or bps

Segments leave independently (Poisson statistics)Average emptying rate in steady state — Packets/sec, Bytes/sec, or bps

Results

ExampleArrival rate = 90 packets / sec Empty rate = 100 packets / secUtilization = (90 packets / sec) / (100 packets / sec) = 0.9 = 90%Buffer level = 0.9 / (1 – 0.9) = 9 packets in bufferLatency = 1 / (100 packets / sec) 9 packets in buffer = (9 / 100) sec = 0.09 sec

arrival rateUtilization

empty rate

1 1 1Latency

empty rate arrival rate empty rate 1

Buffer Level Latency arrival rate1

0

2

4

6

8

10

12

14

16

18

200 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Utilization

latencybuffer level


Buffer Throughput(Over)-simplified throughput model

Realistic throughput behaviorHigh arrival rate at bufferLonger latency + overflowSender timeoutsRe-transmit more segments higher arrival rate at buffer

1


latency


latency

1


1

1

receive rate

throughtputmaximum receive rate

arrival ratebuffer utilization

empty rate


receive rate (error‐free in‐order)

goodputmaximum receive rate


TCP Flow ControlSource window

Initial source window = maximum number of "unACKed" bytesDetermined by congestion + flow control

Destination windowNumber of bytes receiver can acceptDetermined by available space in receiver bufferBuffer level = Previous level + arriving bytes – bytes read by AppApplication reads too slowly decrease destination window

Sliding windowWindow field in TCP header Number of bytes receiver will acceptReceiver discards bytes above window size Full

EmptyArriving bytes

Bytes read by App


Flow Control Example

04 KB

Persist Timeout4 KB4 KB

App reads 4 KB

00

08 KB6 KB00 KB6 KB

App reads 4 KB6 KB2 KB

04 KB

2 KB6 KB2 KB2 KB

4 KB4 KB4 KB64 KB6 KB2 KB4 KB64 KB8 KB02 KB64 KB8 KB0—64 KB

Dest Window

Buffer LevelIn FlightSource

Window

2 KB2 KB

ACK 4 KB window = 4 KB

2 KB


6 KB


ACK 12 KB + 1B window = 4 KB1 B

2+2 = 4

2+4 = 6

6+6 = 12

ACK 12 KB window = 4 KB6+6 = 12error


Receive Window Bugs — 1Bug — deadlock

Receiver advertises window = 0Window update with window > 0 is lost deadlock

Fix — persist timeoutSender attempts small segmentACK contains new window size

Sender Receiver

win = 0

win > 0

error

1 byte

ACK

win > 0

1 byte

win = 0


Receive Window Bugs — 2Silly Window Problem

Application reads received data slowlyReceiver advertises small window Data bytes ~ header bytesMore segments / file transfer larger total traffic (data + headers)

Nagle Algorithm — bug fix for Silly WindowSender accumulates application data — sends large segmentsWorks badly with Telnet (requires small segments)

Receiver side bug fixReceiver keeps 0 window size until it can advertise large window


TCP Congestion ControlEnd-to-end congestion control

Based on host estimatesNo feedback from intermediate network nodes

Slow-startBegin session with low transmission rateIncrease rate until timeouts begin

Fast retransmitDo not wait for timeoutRe-transmit after duplicate ACKs (dupACKs)

Congestion avoidanceLimit transmission rate after duplicate ACKsGrowth rate of transmission rate slows


Slow‐StartCongestion window (cwnd)

Source windowMaximum number of "unACKed" bytes

Initial cwnd = 1 MSS (maximum segment size)Data rate = 1 MSS / RTT

RTT = round trip time = time from send to ACK Maximum cwnd = destination window

Exponential growthOn (ACK)

cwnd cwnd + size of data ACKedif (cwnd > maximum cwnd)

cwnd max cwndOn (ACK timeout)

cwnd initial cwnd = 1 MSS

Sender Receiver

RTT

Timeout

ACK 1 MSS

ACK 2 MSS

ACK 3 MSS


Computing TCP's Retransmission Timer — RFC 2988Initialize

RTO 3 secondsG clock granularity (typically 500 ms)R first RTT measurement (round trip time)SRTT RRTTVAR R/2RTO max(1 sec, SRTT + max(G, 4 * RTTVAR))

Update after measurements R'RTTVAR (1 - ) * RTTVAR + * |SRTT – R'|SRTT (1 - ) * SRTT + * R'RTO max(1 sec, SRTT + max (G, 4 * RTTVAR))

= 1/8

= 1/4

Sender Receiver

SEQRTT

ACK


Fast RetransmitBetter performance with RTO >> RTT

3 duplicate ACKs (dupACKs) for segment re-send segment

Sender Receiver

Timeo

ut

error

SEQ = 100

SEQ = 200

SEQ = 300

SEQ = 400

SEQ = 200 (duplicate)

ACK = 200

ACK = 200 (duplicate)

SEQ = 500



ACK = 600


Congestion Avoidance

Slow start phaseOn (ACK && cwnd < ssthresh)

cwnd cwnd + size of data ACKedOn (ACK timeout)

ssthresh cwndcwnd initial cwnd = 1 MSSRTO 2 * RTO

Congestion avoidance phaseOn (ACK && cwnd > ssthresh)

cwnd cwnd + 1 MSSFast retransmit with fast recovery

On (3 dupACKs)ssthresh cwnd / 2 cwnd ssthresh + 3retransmit, wait 1 RTT continue

Reno protocol

If dupACKs > 3cwnd++ on each dupACK


TCP Sender with Reno — 1// initialize

SEQ = ISN + 1SendBase = ISN + 1InFlight = 0cwnd = 1 MSSSet ssthreshold large (local policy)RTO = timeout interval

on (new data from application)Prepare data segment:sequence number = SEQif InFlight < min{cwnd,SendWindow,RecvWindow)

Pass segment to IP SEQ = SEQ + length(data)InFlight = InFlight + length(data)if !(timer running) timer = RTO


TCP Sender with Reno — 2if (receive ACK = y)

stop timerif (y > SendBase)

dupACK = 0newACKs = y – SendBase // bytes ACKedSendBase = yInFlight = InFlight – newACKsif (cwnd < ssthresh) cwnd = cwnd + newACKs else cwnd = cwnd + 1 MSSif (InFlight > 0) timer = RTO


TCP Sender with Reno — 3// if (y > SendBase)else

dupACK++if (dupACK = 3)

SEQ = SendBase = min{unACKed SEQ} and retransmittimer = RTOssthresh = cwnd / 2cwnd = ssthresh + 3wait 1 RTT // wait for ACK of resent packet

if (dupACK > 3)cwnd = cwnd + 1 MSS and resend again

if (timeout)SEQ = SendBase = min{unACKed SEQ} and retransmitssthresh = cwndcwnd = initial cwnd = 1 MSSRTO = 2 * RTOtimer = RTO


TCP Receiver with Reno — 1// initialize

Set RecvWindow = receiver buffer sizeexpected = Sender ISN + 1ack_buffer = 0ack_max (local policy: delayed ACK trigger)ack_delay = 250 msec (local policy: < 500 msec)Start ACK delay timer = ack_delay

if (ACK delay timer = 0 && ack_buffer > 0)Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0


TCP Receiver with Reno — 2if (receive SEQ = x)

if (x = expected && error-free)expected = expected + length(data)if (NACK = 1)

Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0NACK = 0

else if (ack_buffer < ack_max)nextACK = expectedack_buffer++

else if (ack_buffer = ack_max)Send ACK = expected with updated RecvWindowACK delay timer = ack_delayack_buffer = 0

else Send ACK = expected with updated RecvWindowACK delay timer = ack_delayNACK = 1


Reno Example — 1Counting in bytes: SEQ = SEQm (1 MSS) ACK = ACKm (1 MSS)ssthresh = 32 Receiver sends ACK for every 4 packets (or ACK delay)

ReceiverSender

48+4 = 12

412

8 – 15 (8)888

04+4 = 8

4 – 7 (4)

2 – 3 (2)

1 (1)

Packets Sent

48

444

02+2 = 4

24

222

01+1 = 2

12

111

New ACKsACKm SentSEQm Sentin‐flightcwnd


Reno Example — 2

New ACKsACKm SentPackets SentSEQm Sentin‐flightcwnd

48 – 63 (16)483232

1628+4 = 32

432

2024+4 = 28

428

40 – 47 (8)402424

1620+4 = 24

424

32 – 39 (8)322020

1216+4 = 20

420

16 – 31 (16)161616

012+4 = 16

416

412


Reno Example — 3


1237+1 = 38

456

1636+1 = 37

452

2035+1=36

448

2434+1 = 35

444

2833+1 = 34

440

64 – 67 (4)643233

2832+1 = 33

436

48 – 63 (16)483232


Reno Example — 4


76 – 98 (23)762323

023

1676 (cumulative)

Retransmit 1 packet60601622

16ssthresh 1919 + 3 = 22

0603rd dupACK

1639

060

1639

060

1638+1 = 39

460

68 – 75 (8)682038


Reno: First Alternative Scenario

01+1 = 2

cwnd = in‐flight no more packets no 3 dupACKs Timeout


14

3 (1)311

01

03

33+0 = 3

03

4 – 5 (2)433

12+1 = 3

13

2 – 3 (2)222

01+1 = 2

12

1 (1)111


Reno: Second Alternative Scenario – 1

8ssthresh 33 + 3 = 6

7 (1)77retransmit

07

073rd dupACK


07

7 packets can cause 7 dupACKs8 – 13 (6)877

14+3 = 7

37

4 – 7 (4)444

02+2 = 4

24

2 – 3 (2)222

01+1 = 2

12

1 (1)111


Reno: Second Alternative Scenario – 2

7 (1)799

89

076th dupACK

88

87

14 – 23 (10)101410

09+1 = 10

074th dupACK

714 (cumulative)


075th dupACK


Selective Acknowledgment OptionSelective ACK (SACK)

Permits ACK for segments with gapsOption negotiated between hostsDefined in RFC 2018

ExampleLast ACK = 5000Send 8 segments 500 data bytes / segmentCase 1

First 4 segments received and last 4 droppedReceiver returns normal ACK = 5000 + 4 * 500 = 7000No SACK option field

Case 2First segment lost and 7 segments receivedFor each segment receiver returns segment with

ACK = 5000 SACK option field with start + end ACK

Option Field

8999550050008500849955005000800079995500500075007499550050007000699955005000650064995500500060005999550050005500———5000EndStartACKData


Active Queue Management (AQM)Standard Queue

At receiver Full buffer drop excess packets

At senderNo ACK timeout signal congestion

Random Early Detection (RED)Router

Detects congestion earlyDrops random packets

Sender Sees dupACKs or timeoutAssumes congestionLowers cwnd

Full

EmptyArrivingpackets

Leavingpackets

buffer utilization(all senders)

latency1

0.85 1



RED AlgorithmAlgorithm

for each packet arrivalcalculate avg = average queue size

if minth avg < maxthcalculate probability pawith probability pa:

mark arriving packet for dropelse if maxth avg

mark arriving packet for dropParameters

maxp = maximum mark probability (0.1 to 0.5)minth ~ 5 maxth ~ 30

pb maxp (avg − minth) / (maxth − minth)pa pb / (1 − count pb)count = number of consecutive dropped packets


AQM with ECNExplicit Congestion Notification (RFC 3168)

1. IP router predicts congestion — RED with mark (no drop)2. IP router indicates congestion to receiver in IP header3. Receiver indicates congestion to sender in TCP ACK header

App

TCP

IP

DL

PHY

IP datagram 85%Full

IP datagramwith ECN

TCP segmentwith ECN

App

TCP

IP

DL

PHY

1 2

3


Explicit Congestion Notification (ECN)

Differentiated Services Code Point (DSCP)QoS requirements

Explicit Congestion Notification (ECN)

2 bitsECN

16 bits6 bits4 bits4 bits

DataOptions

Destination IP AddressSource IP Address

Header ChecksumProtocolTime to LiveFragment Offset (13 bits)FlagsIdentification

Total Length (header + data in bytes)DSCPHlen Version

IP datagram

To allow protocol error checking

For retransmissions

CE (Congestion Experienced)11

ECT(1) — ECN Capable Transport (1)10

ECT(0) — ECN Capable Transport (0)01

Not ECN capable00


Explicit Congestion Notification (ECN)TCP header flags

ECN‐EchoECE

Congestion Window Reduced (CWR) flagCWR

ECN‐nonce concealment protectionNS

Options urgent pointerchecksumwindow sizeflagsnot usedHLEN

acknowledgement number (ACK)sequence number (SEQ)

destination portsource port32 bits

No more dataFIN

SynchronizeSYN

ResetRST

Push bufferPSH

AcknowledgmentACK

Urgent pointerURG


ECN NegotiationTCP client

SYN ECE = CWR = 1 in SYNTCP server

ECE = 1 in SYN-ACKIP

ECT(0) , ECT(1) in SYN and SYN-ACK

client serverSYN with ECE = CWR = 1

SYN‐ACK with ECE = 1 C

WR = 0

ACK


ECN Operation — 1No congestion

Measure long term average buffer level nCompare with threshold level th

App

TCP

IP

DL

PHY

IP datagramECN = 01 (ECT) n < th

IP datagramECN = 01 (ECT)

TCP segmentECE = CWR = 0

App

TCP

IP

DL

PHY


ECN Operation — 2No congestion

App

TCP

IP

DL

PHY

TCP ACKECE = CWR = 0

App

TCP

IP

DL

PHY




ECN Operation — 3Incipient congestion

Router Sees ECN = ECT in incoming IP headerSets ECN = CE in outgoing IP headerNotifies receiver of incoming congestion

App

TCP

IP

DL

PHY

n > th


App

TCP

IP

DL

PHY


IP datagramECN = 11 (CE)



Receiver Sets ECE = 1 in TCP headerNotifies sender of congestion

App

TCP

IP

DL

PHY


TCP ACKECE = 1 CWR = 0

App

TCP

IP

DL

PHY




Sender Lowers congestion window (once per RTT)Sets CWR = 1 in TCP header (ACK of ECE to receiver)

App

TCP

IP

DL

PHY

TCP segmentECE = 0 CWR = 1

App

TCP

IP

DL

PHY

n > thIP datagramECN = 01 (ECT)




Receiver Sees CWR = 1 in sender TCP headerCE in IP header new incoming ECE = 1 in ACK TCP header

App

TCP

IP

DL

PHY



App

TCP

IP

DL

PHY



ECN Operation — 7Continued congestion

Sender Lowers congestion window once per RTTSets CWR = 1 in TCP header (ACK of ECE)

App

TCP

IP

DL

PHY


App

TCP

IP

DL

PHY

n > thIP datagramECN = 01 (ECT)



ECN Operation — 8Continued congestion

Receiver Sees CWR = 1 in sender TCP headerCE in IP header new incoming ECE = 1 in ACK TCP header

App

TCP

IP

DL

PHY



App

TCP

IP

DL

PHY



ECN Operation — 9End of congestion

Sender sets CWR = 1 in TCP header (ACK of ECE)Router sends ECN = 01 in IP header (signals no congestion)

App

TCP

IP

DL

PHY




App

TCP

IP

DL

PHY



Receiver sends ECE = 0 in TCP header (signals no congestion)

App

TCP

IP

DL

PHY

TCP ACKECE = CWR = 0

App

TCP

IP

DL

PHY





Sender clears CWR and begins raising congestion windowRouter sends ECN = 01 in IP header

App

TCP

IP

DL

PHY




App

TCP

IP

DL

PHY


RED and ECN GoodputParameters

minth = 5 maxth = 30

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

0 100 200 300 400 500 600Number of flows

Goo

dput

(Mbp

s)

ECN (max_p=0.1)RED (max_p=0.1)ECN (max_p=0.5)RED (max_p=0.5)

Ref: Kinicki and Zheng, A Performance Study of Explicit Congestion Notification (ECN) with Heterogeneous TCP Flows


RED and ECN DelayParameters

minth = 5 maxth = 30 maxp =0.5

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 100 200 300 400 500 600

Number of flows

One

-way

del

ay (S

econ

ds) ECN (Fragile flows)ECN (Average flows)ECN (Robust flows)RED (Fragile flows)RED (Average flows)RED (Robust flows)


Goodput with 120 flowsParameters

minth = 5 maxth = 30

55.5

66.5

77.5

88.5

99.510

0 0.2 0.4 0.6 0.8 1

max_p

Goo

dput

(M

bps)

ECN (max_th=15)RED (max_th=15)ECN (max_th=30)RED (max_th=30)


ECN Nonce (RFC 3540)Problem

Unscrupulous or poorly implemented receiverClears ECN-Echo — no congestion signals to senderGives receiver advantage over connections that behave properly

SenderIP header with ECN = 01 = ECT(0) or ECN = 10 = ECT(1)

Except retransmissions (Not ECN Capable) and CE packetsKeeps per-packet map of SEQ to nonce (0 or 1)

RouterForwards packet or overwrites ECT with ECN = 11 = CE

ReceiverKeeps cumulative ACK number (standard TCP)Keeps cumulative sum % 2 of received nonces for ACKed packetsNS flag in TCP header = sum of nonces for ACKed packetsCE packets — use nonce = 0


Nonce ExampleHonest Receiver

Sender Receiver

SEQ_1 ECT(0)

SEQ_2 ECT(0)

SEQ_3 ECT(1)

SEQ_4 ECT(0)

ACK_3 NS = 0

SEQ_5 ECT (1)

ACK_6 NS = 0 ECE = 1

SEQ_5 CEnonce = 0 0

0

0

1

1

Nonce Sum

NS initialized to 1 Sent in SYN‐ACK and ACK of handshake

Sender sees correct NS

Sender sees correct NS


Nonce ExampleCheating Receiver

Sender Receiver

SEQ_1 ECT(1) sum = 0SEQ_2 ECT(0) sum = 0

SEQ_3 ECT(1) sum = 1


ACK_3 NS = 0 (guess)

SEQ_5 ECT (1) sum = 0

ACK_6 NS = 1 (guess)

SEQ_3 CEnonce = 0


Receiver ignores CEDoes not set ECEGuesses nonce sum after CE

1

1

0

0

0

0

Guess

Sender sees wrong NS

Sender sees wrong NS

Engineering Overview of Computer Networking

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