-1- Georgia State UniversitySensorweb Research Laboratory CSC4220/6220 Computer Networks Dr. WenZhan...

-1- Georgia State UniversitySensorweb Research Laboratory

CSC4220/6220 Computer Networks

Dr. WenZhan Song

Associate Professor, Computer Science


About Me

Homepage: http://sensorweb.cs.gsu.edu/~song/

2010 – present, Associate Professor, Georgia State University Teaching evaluation: 4.8 (CSC 4220)

2005-2010, Assistant Professor, Washington State University - Vancouver

Teaching evaluation: Average: 4.5/5

Research experience: Sensorweb for environment monitoring, smart environments and smart

grid 6M+ research funding support from NSF, NASA, USGS, Boeing, including

NSF CAREER award http://sensorweb.cs.gsu.edu/news.html a dream: http://www.youtube.com/watch?v=WF-RKzqNtz0 (3:49)

Research has been featured in MIT technology review, National Geographic, Network World, etc

2001-2005, Ph.D. student, Illinois Institute of Technology 2004 Summer, Lucent Technologies 1999-2001, Alcatel Shanghai Bell


Several Notes Course website:

http://sensorweb.cs.gsu.edu/~song/csc4220/ Class mailing list through Google groups

Confirm email: have you received an email from me? Is it okay to add your email to it? Announcement and update will be sent through mailing

list. You may also ask questions through mailing list.

Homework submission needs a printed hard-copy, no hand-written!

Programming projects Count Java/C preferences in class – either one is fine


What to expect

Significant exposure to computer networking concepts and fundamental design principles.

Coverage of Internet protocol stacks. running example: TCP/IP

Details of network control algorithms. e.g. routing, congestion control, flow

control, ... Able to design network protocols and

systems.


What not to expect

End-user training. e.g. How to use FTP, NetWare, WWW or HTML, …

Trade school stuff. e.g. How to get Novel NetWare certified, how to setup

a Cisco router, how to administrate network system Detailed discussion of non-TCP/IP protocols.

e.g. OSI, Appletalk, ... Massively Parallel Processing

e.g. large numbers of interconnected, identical processors programmed to solve problems in parallel

Telecommunication networks and standards


Course roadmap

Introduction Application Layer: WWW, FTP, email, DNS,

multimedia Transport Layer: reliable end-end data transfer

principles, UDP, TCP Network Layer: routing, congestion control, QoS Data Link Layer: framing, error control, flow control

Medium Access Control (MAC) Layer: multiple-access, channel allocation

Physical Layer: wired, wireless, satellite Other Topics: network security, social issues, hot topics,

research directions


Get http://www.google.com/contact.html

Human Conversation vs Computer Communication

human conversation vs computer communication

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponse

<file>time


Communication is challenging

The two-army problem


Introduction Roadmap

Physical overview of Internet Physical architecture Network Edge - Internet access technologies Network Core – Switching technologies

Software overview of Internet Software architecture The OSI and TCP/IP Reference Models

Internet history Network standardization body


Physical overview of Internet

millions of connected computing devices: hosts = end systems

running network apps communication links

fiber, copper, radio, satellite

transmission rate = bandwidth

routers: forward packets (chunks of data)

Residential access

Companynetwork

Network Core

router workstation

servermobile


Physical overview of Internet

protocols control sending, receiving of msgs

e.g., TCP, IP, HTTP, FTP, PPP

Internet: “network of networks”

loosely hierarchical public Internet versus

private intranet Internet standards

Called RFC (Request for comments), developed by IETF (Internet Engineering Task Force)

Residential access

Companynetwork

Network Core

router workstation

servermobile


Metric Units

metric prefixes for data rateNote:

data rates – kbps (103), Mbps(106), Gbps(109) … bits per seconddata sizes – KB (210), MB(220), GB(230), … bytesms(msec): millisecond µs: microsecond ns: nanosecond



Physical overview of Internet Physical architecture Network Edge - Internet access technologies

Residential access Company access

Network Core – Switching technologies Software overview of Internet

Software architecture The OSI and TCP/IP Reference Models



Residential Internet Access

Phone Company Dialup ADSL

Cable TV Company HFC

Wireless Company WiMax


Residential access Phone Company

Dialup via modem up to 56Kbps direct access

to router (often less) Can’t surf and phone at

same time: can’t be “always on”

ADSL: asymmetric digital subscriber lineup to 1 Mbps upstream (today typically < 256

kbps)up to 8 Mbps downstream (today typically < 1

Mbps)


Dialup

Local loops Analog twisted pairs going to houses and businesses

Trunks Digital fiber optics connecting the switching offices

Toll Office (Switching offices) Where calls are moved from one trunk to another


ADSL: asymmetric digital subscriber line

Design goal:

(1) Work over exist 3 UTP twisted pair local loops.

(2) Not affect customers’ existing telephone and fax machine

(3) Much faster than 56kbps(4) Always on – monthly charge


ADSL

A typical ADSL equipment configuration.


ADSL

256 Channel over 1.1MHz: 0 (POTS), 1-5(unused), 6-255(data channels)

ANSI T1.413 and ITU G.992.1: up to 8 Mbps downstream and 1 Mbps upstream.

Standard service: 512 kbps downstream and 64 kbps upstream

Premium service: 1 Mbps downstream and 256 kbps upstream


Residential access Cable TV Company

HFC: hybrid fiber coax asymmetric: up to 27Mbps downstream, 9

Mbps upstream network of cable and fiber attaches homes to

ISP router homes in same community share bandwidth

deployment: available via cable TV companies


Community Antenna Television

An early cable television system.


HFC

Internet over TV Cable


Compare to ADSL

Internet over ADSL


Cable vs ADSL

FlexibleUsually notISP choices

1Mbps down256kbps up

Depends on # of shared users,Up to 27Mbps/9Mbps

Data rate

Security

Medium access

Physical

BetterOkay

IndependentShared

Twisted pairCoax

ADSLCable


Spectrum Allocation

Frequency allocation in a typical cable TV system used for Internet access


Signal Splitter


Cable Modems

Typical details of the upstream and downstream channels in North America.

Upstream: QPSK, slotted Aloha with binary exponential backoff

Downstream: QAM–64/QAM-256, time division multiplexing


Residential access Wireless Company

Wireless Local Loop

Example: IEEE 802.16 WiMax – Verizon Wireless

400~700kbps

Up to 2Mbps

- according to Verizon


Other ways for residential access?

How about other utility companies: Gas, Water, ……

Electricity company PLC (Power Line Communication)

BPL (Broadband over Power Line)http://en.wikipedia.org/wiki/Power_line_communication




Residential access Company access

Network Core – Switching technologies Software overview of Internet




Company access: local area networks

company/univ local area network (LAN) connects end system to edge router

Ethernet: shared or dedicated

link connects end system and router

10 Mbs, 100Mbps, Gigabit Ethernet


Wireless access networks

Shared wireless access network connects end system to router

via base station aka “access point”

wireless LANs: 802.11b (WiFi): 11 Mbps 802.11a, 802.11g …

wider-area wireless access WiMax – talked before 3G ~ 384 kbps 4G ~ 100Mbps – 1Gbps WAP/GPRS in Europe

wireless ad hoc networking Talk with each other directly

inside Through a gateway to visit

outside

basestation

mobilehosts

router

Ad hoc networkin

g




circuit switching packet switching




The Network Core

mesh of interconnected routers

the fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”


Network Core: Circuit Switching

End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required


Network Core: Circuit Switching

network resources (e.g., bandwidth) divided into “pieces”

pieces allocated to calls

resource piece idle if not used by owning call (no sharing)

dividing link bandwidth into “pieces”frequency

divisiontime division


Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 users

Example:


Numerical example

How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps = 1536 kbps Each link uses TDM with 24 slots 500 msec to establish end-to-end circuit

Solution: Each circuit transmission rate: 1.536Mbps/24

= 64kbps Time to transmit file: 640,000bits/64kbps =

10 sec Total: 10.5 sec


Network Core: Packet Switching

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

In TDM each host gets same slot in revolving TDM frame.

A

B

C10 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link


Network Core: Packet Switching

each end-end data stream divided into packets

user A, B packets share network resources

each packet uses full link bandwidth

resources used as needed

resource contention: aggregate resource

demand can exceed amount available

congestion: packets queue, wait for link use

store and forward: packets move one hop at a time Node receives complete

packet before forwarding

Bandwidth division into “pieces”

Dedicated allocationResource reservation


Packet-switching: store-and-forward

Takes L/R seconds to transmit (push out) packet of L bits on to link of R bps

Entire packet must arrive at router before it can be transmitted on next link: store and forward

delay = 3L/R

Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec

R R RL


Packet switching versus circuit switching

1 Mb/s link each user:

100 kb/s when “active” active 10% of time

circuit-switching: 10 users

packet switching: with 35 users,

probability of more than 10 active users is less than .0004

Packet switching allows more users to use network!

N users

1 Mbps link

probability of exact n of N users active:

9

0 1.0

35

10 1.0 )35|(1)35|(n pn p nPnP


Packet switching versus circuit switching

Great for bursty data resource sharing simpler, no call setup

Excessive congestion: packet delay and loss protocols needed for reliable data transfer,

congestion control Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

still an unsolved problem

Is packet switching a “slam dunk winner?”


Packet-switched networks: forwarding

Goal: move packets through routers from source to destination

we’ll study several path selection (i.e. routing) algorithms

datagram network: destination address in packet determines next hop routes may change during session analogy: driving, asking directions

virtual circuit network: each packet carries tag (virtual circuit ID), tag determines

next hop fixed path determined at call setup time, remains fixed thru

call routers maintain per-call state


Network Taxonomy

Networks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

• Datagram network is not either connection-oriented or connectionless.• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

e.g., telephone networks

e.g., ATM networks

e.g., Internet


Connection-oriented vs Connectionless

Key differences: Connection-oriented: packets arrives in the

order of sending out (e.g., FIFO), and need connection setup phase

Connectionless: packets may (or may not) arrive in different order of sending out, and does not need connection pre-setup

Example: Circuit Switch Network: connection-oriented Packet Switch Network

Virtual circuit network: connection-oriented Datagram network depends on layers and

protocols: TCP – connection-oriented UDP, IP - connectionless




Residential access: dialup, ADSL, cable, WiMax Company access: LAN, WLAN

Network Core – Switching technologies Circuit switching: setup path before communication,

have dedicated resource per call Packet switching: store and forward, share resource and

need contend for Software overview of Internet




Protocol “Layers”

Networks are complex!

many “pieces”: hosts routers links of various

media applications protocols hardware,

software

Question: Is there any hope of organizing structure

of network?

Or at least our discussion of

networks?


Internet protocol stack

application: supporting network applications

FTP, SMTP, HTTP, etc transport: host-host data transfer

TCP, UDP network: routing of datagrams

from source to destination IP, routing protocols

link: data transfer between neighboring network elements, including encapsulating bits into frames

PPP, Ethernet, etc physical: bits “on the wire”

application

transport

network

link

physical


Analogy scenario

The philosopher-translator-secretary architecture.


Services to Protocols Relationship

The relationship between a service and a protocol: each layer implements a service

via its own internal-layer actions or protocols relying on services provided by layer below


Why layering?

Dealing with complex systems: explicit structure allows identification,

relationship of complex system’s pieces layered reference model for discussion

modularization eases maintenance, updating of system change of implementation of layer’s service

transparent to rest of system e.g., changing common language of translators

does not affect the communication between the philosopher

layering considered harmful?


messagesegment

datagram

frame

sourceapplicatio

ntransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHnHl M

HtHn M

HtHnHl M HtHnHl M

router

switch

Typical network flow


General situation of end-end flow

Example information flow supporting virtual communication in layer 5.


The design principles of OSI Reference Models

A layer should be created when a different abstraction is needed

Each layer should perform a well-defined function

The function of each layer should be chosen with an eye toward defining internationally standardized protocols

The layer boundaries should be chosen to minimize the information flow across the interfaces

The number of layers should be large enough that functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy


OSI Reference Models

The OSI reference model.

Concern the syntax and semantics of information transmitted

Allow users on different machines to establish sessions


TCP/IP Reference Models

The TCP/IP reference model.


TCP/IP Reference Models

Major protocol and application components common to most commercial TCP/IP software packages and their relationship

123


A Critique of the OSI Model and Protocols

Bad timing Bad technology Bad implementations Bad politics


A Critique of the TCP/IP Reference Model

Service, interface, and protocol not distinguished

Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to

replace


Hybrid flow in the lecture

application: supporting network applications

FTP, SMTP, HTTP, DNS transport: host-host data transfer

TCP, UDP network: routing of datagrams

from source to destination IP, routing protocols

link: data transfer between neighboring network elements, including encapsulating bits into frames

MAC (Multiple Access Control) sublayer

physical: bits “on the wire”

application

transport

network

link

physical


Internet History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects

Agency 1969: first ARPAnet node operational

1961-1972: Early packet-switching principles

(a) Structure of the telephone system.

(b) Baran’s proposed distributed switching system.


Internet History

1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15+ nodes

1961-1972: Early packet-switching principles

Growth of the ARPANET

(a) December 1969. (b) July 1970.(c) March 1971. (d) April 1972. (e) September 1972.


Internet History

1970: ALOHAnet satellite network in Hawaii

1973: Metcalfe’s PhD thesis proposes Ethernet

1974: Cerf and Kahn - architecture for interconnecting networks

late70’s: proprietary architectures: DECnet, SNA, XNA

late 70’s: switching fixed length packets (ATM precursor)

1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles:

minimalism, autonomy - no internal changes required to interconnect networks

best effort service model stateless routers decentralized control

define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets


Internet History

Early 1990’s: ARPAnet decommissioned

1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

early 1990s: Web hypertext [Bush 1945,

Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later

Netscape late 1990’s:

commercialization of the Web

Late 1990’s – 2000’s: more killer apps: instant

messaging, P2P file sharing

network security to forefront

est. 50 million host, 100 million+ users

backbone links running at Gbps

1990, 2000’s: commercialization, the Web, new apps


Internet Usage

Traditional applications (1970 – 1990) E-mail News Remote login File transfer

Today in addition WWW: news, shopping, gaming, maps, trading,

etc Multimedia: Internet video, audio, radio P2P file sharing Blogs Messenger … …


Network Standardization

Telecommunications World ITU (International Telecommunication Union),

called CCITT during 1956-1993 International Standards World

ISO (International Standards Organization) U.S: ANSI (American National Standards Institute) Other countries …

IEEE (Institute of Electrical and Electronics Engineers)

Internet Standards World Internet Society

IAB (Internet Activities Board) IRTF (Internet Research Task Force): long-term research IETF (Internet Engineering Task Force): short-term

engineering issues – RFC documents


IEEE 802 Standards

The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.


Summary

Covered a “ton” of material!

Physical overview of Internet Physical architecture Network Edge - Internet

access technologies Network Core – Switching

technologies Software overview of Internet

Software architecture The OSI and TCP/IP Reference

Models Internet history Names and terms in network

society

You now have: context,

overview, “feel” of networking

more depth, detail to follow!


Suggestion

Read Chapter 1 Preview Chapter 2 (Application Layer) Install WireShark and read its manual:

http://www.wireshark.org/download.html Wireshark is a free and open-source packet analyzer.

It is used for network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, in May 2006 the project was renamed Wireshark due to trademark issues.

-1- Georgia State UniversitySensorweb Research Laboratory CSC4220/6220 Computer Networks Dr. WenZhan...

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