AN1 Mobile and Wireless Communication

8/4/2019 AN1 Mobile and Wireless Communication

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6: Wireless and Mobile Networks 6-1

89-850 CommunicationNetworks:Wireless and Mobile

Communication Networks

Prof. Amir HerzbergBIU, Dept. of CS

From ch.6 of Kurose and Ross,3rd edition; and [KMK], ch. 8.

Computer Networking:A Top Down ApproachFeaturing the Internet,3rd edition.

Jim Kurose, Keith RossAddison-Wesley, July2004.

All material copyright 1996-2004J.F Kurose and K.W. Ross, All Rights Reserved


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Background: Wireless and Mobile Networks

# wireless (mobile) phone subscribers now

exceeds # wired phone subscribers! Computer nets: laptops, palmtops, PDAs,

Internet-enabled phone promise anytimeuntethered Internet access

Internet telephony: a reality, an earthquake Two important (but different) challenges

Wireless link: no CD (e.g. hidden-terminal), reliability,security

Mobility of computers and users; provisioning Plus: limited computing power and energy


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Wireless and MobileCommunication Networks: Outline

6.1 Introduction

Wireless

6.2 Wireless links,

characteristics 6.3 IEEE 802.11

wireless LANs (wi-fi)

Sensor and personal-area networks

Mobility

6.5 Principles:addressing and routingto mobile users

6.6 Mobile IP

6.7 Cellular networks 6.8 Mobility and higher-

layer protocols

6.9 Summary


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Elements of a wireless network

network

infrastructure

wireless hosts laptop, PDA, IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility


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network

infrastructure

base station typically connected to

wired network relay - responsible

for sending packetsbetween wirednetwork and wireless

host(s) in its area e.g., cell towers,

802.11 accesspoints


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network

infrastructure

wireless link typically used to

connect mobile(s) tobase station also used as backbone

link multiple access

protocol coordinateslink access

various data rates,transmission distance


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Characteristics of selected wireless linkstandards

384 Kbps

56 Kbps

54 Mbps

5-11 Mbps

1 Mbps802.15

802.11b

802.11{a,g}

IS-95 CDMA, GSM

UMTS/WCDMA, CDMA2000

.11 p-to-p link

2G

3G

Indoor

10 30m

Outdoor

50 200m

Mid rangeoutdoor

200m 4Km

Long rangeoutdoor

5Km 20Km


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network

infrastructure

infrastructure mode base station connects

mobiles into wirednetwork handoff: mobile

changes base stationproviding connection

into wired network


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Wireless network characteristicsLower Signal/Noise ratio (cf. wired networks)Limited, shared spectrum: orthogonal signals

(FDMA/CDMA/TDMA) or `collisions as noise`

AB

C

Hidden terminal problem B, A hear each other

B, C hear each other A, C can not hear each other

A B C

As signalstrength

space

Cs signalstrength

Signal fading:

B, A hear each other B, C hear each other A, C can not hear each other

interfering at B


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Wireless Link CharacteristicsDifferences from wired link .

Energy and computing-power limitations Decreased signal strength

Obstacles and hidden-terminal problem

Collision detection hard or impossibleMore noise

Interference from other sources Multipath propagation different delaysinterferences between paths or (multipath) fading

Lower signal/noise Higher bit error rate

. more difficult


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Hi/Low BER States ModelWireless links often have two BER states

High, Low

E.g., due to (multipath) fading

Model by two-state Markov model:

Good Badg

(1g)

b

(1b)

Simplify: all packets Ok in `Good`, fail in `Bad`


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Wireless Link CharacteristicsDifferences from wired link .

Decreased signal strength: signal attenuates as itpropagates through matter (path loss) Obstacles: e.g. mountain; hidden-terminal problem Collision detection hard or impossible

More noise: Interference from other sources: frequencies (e.g., 2.4

GHz) shared by other devices (e.g., phone); also noise e.g.from motors

Multipath propagation: radio signal reflects off objectsground, arriving ad destination at slightly different times

Energy and computing-power limitations

. make communication across (even a point to point) wirelesslink much more difficult


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Wireless and Mobile

Communication Networks: Outline6.1 Introduction

Wireless

6.2 Wireless links,

characteristics 6.3 IEEE 802.11

wireless LANs (wi-fi)

Ad-hoc, sensor and

personal-areanetworks

Mobility

6.5 Principles:addressing and routingto mobile users

6.6 Mobile IP


layer protocols

6.9 Summary


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IEEE 802.11 Wireless LANs

802.11g802.11aUp to 54

Mbps

802.11blo-cost, goodpropagation;

but slow,interferences

Up to11Mbps

2.4-5 GHz(unlicensed)

5-6 GHz802.11WirelessLANs

All use CSMA/CA for multiple access

All have base-station and ad-hoc network versions


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IEEE 802.11 Wireless LAN 802.11b

2.4-5 GHz unlicensedradio spectrum

up to 11 Mbps

direct sequence spread

spectrum (DSSS) inphysical layer

all hosts use samechipping code

widely deployed, usingbase stations

802.11a

5-6 GHz range up to 54 Mbps

802.11g 2.4-5 GHz range

up to 54 Mbps

All use CSMA/CA formultiple access

All have base-stationand ad-hoc networkversions


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802.11 LAN architecture wireless host communicateswith base station

base station = access point

(AP) Basic Service Set (BSS) (aka

cell) in infrastructure modecontains:

wireless hosts (mobiles) access point (AP): base

station

ad hoc mode: hosts only =Independent BSS (IBSS)

Extended Service Set (ESS) One or more BSS

Connect by LANswitch or DS DS=Distribution System

BSS 1

BSS 2

Internet

LAN switchAP

AP

DS

router


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802.11: Channels, association 802.11b: 2.4GHz-2.485GHz spectrum divided into 11

channels at different frequencies

Non-overlapping only if at least 4 channels apart At most 3 non-overlapping channels (1, 6 and 11).

AP admin chooses frequency for AP

interference possible: channel can be same as thatchosen by neighboring AP!

host: must associatewith an AP scan channels, listening for beacon framescontaining

SSID (ESS/IBSS name) and MAC address of AP select AP; initiate association protocol

may perform authentication

will typically run DHCP to get IP address in APs subnet


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IEEE 802.11: multiple access

Like Ethernet, uses CSMA: random access

carrier sense: dont collide with ongoing transmission

Unlike Ethernet: Ack, no Collision Detection no collision detection transmit all frames to completion

ACK: to detect loss without collision detection

Why no collision detection? difficult to receive (sense collisions) when transmitting due

to weak received signals (fading)

cant sense all collisions in any case: hidden terminal, fading

And loss may be due to (higher) error rate of wireless

Goal: avoid collisions:CSMA/CA (Collision Avoidance)


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IEEE 802.11 MAC Protocol: CSMA/CA[simplified]

802.11 sender

1 if sense channel idle then- transmit entire frame (no Colli. Detect)

2 if sense channel busy then

- start random backoff timer

- timer counts down while channel idle

- transmit when timer expires

802.11 receiverif frame received OK

then return ACK else ignore (no NACK!)SIFS: Short Inter-Frame Space max time

to begin Ack [e.g., 16sec in 802.11a]

sender receiver

data

ACK

SIFS(e.g.16s)


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IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender (when trying to send)1 if sense channel idle for DIFS then

- transmit entire frame (no CD)[DIFS>SIFS+2Tprop for priority to ACK]

2 if sense channel busy then- count down the backoff timer

- but only while channel idle- transmit when timer expires

- If ACK, reduce backoff range by 1

- if no ACK, double backoff range, select

time randomly from range, repeat 2802.11 receiverif frame received OK

- return ACK (within SIFS)

sender receiver

DIFS

data

ACK

SIFS(e.g.16s)

DIFS


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Ack

Data

Next MPDU

Src

Dest

Other

Contention Window

Defer Access Backoff after Defer

DIFS

SIFS

DIFS

Acknowledgment should arrive within DIFS

Senders wait for DIFS no-carrier time, thenexponential backoff delay [slot=Tprop]

802.11 MAC OperationData Frames and their ACK


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Two Additional Mechanisms in 802.11

PCF (Point Coordination Function)

Polling to coordinate senders, e.g. to ensure QoS SIFS < PIFS < DIFS (priorities!)

RTS/CTS mechanism

Cant detect collision while sending Collision for long packet is wasteful

RTS (Request to Send): request to reserve

channel to send long packet w/o collisions CTS (Clear to Send): approve RTS

Optional mechanism


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RTS/CTS [optional in 802.11 MAC] Sender sends smallrequest-to-send (RTS)

RTSs may collide with each other (but are short)

Include indication of length of packet transmission AP broadcasts clear-to-send CTS in response to RTS CTS heard by all nodes

sender transmits data frame other stations defer transmissions for time

specified in CTS Q: if you hear RTS only (no CTS), should you wait?

Avoid data frame collisions completelyusing small reservation packets!


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Collision Avoidance: RTS-CTS exchange

APA B

time

RTS(A)

RTS(B)

RTS(A)

CTS(A) CT

S(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer


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Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till end

RTS

A B C D

CTSCTS

RTS

data

ACK ACK


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Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till end

Problem: maybe not granted?

Idea 2: defer only on CTSRTS

A B C D

CTSCTS

RTS

data

ACK ACK

RTS


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Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till end Problem: maybe not granted?

Idea 2: defer only on CTSWhat if unheard? RTS

A B C D

CTSCTS

RTS

data

ACK ACK


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Q: Defer on RTS, CTS or both? Idea 1: RTS contains length, defer till end Problem: maybe not granted?

Idea 2: defer only on CTSWhat if unheard?Solution:

Defer by CTS By length in CTS

Defer by RTSBut only 2 DIFS !

Ok if A hears eitherrecipient or sender

RTS

A B C D

CTSCTS

RTS

data

ACK ACK


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802.11 DCF MAC Example

ACKData

RTS CTS

DataACK

RTS CTS Data ACK

RTS

RTS

RTS CTS Data ACK

time

time

time

time

time

time

time

time

backoff period

1

2

3

4

1

2

3

4

....

node defers; backoff counter frozen


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Internetrouter

AP

H1 R1

AP MAC addr H1 MAC addr R1 MAC addr

address 1 address 2 address 3

802.11 frame

R1 MAC addr AP MAC addr

dest. address source address

802.3 frame

802.11 addressing & `switching`

AP identified in 802.11frame(Unlike regular switch!!)

AP


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framecontrol

duration address1

address2

address4

address3

payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seqcontrol

802.11 frame: addressing

Address 2: MAC addressof wireless host or APtransmitting this frame

Address 1: MAC addressof wireless host or APto receive this frame

Address 3: MAC addressof router interface towhich AP is attached

Address 4: used onlyin ad hoc mode

Why 3 addresses (with AP)?Is AP a switch or a router??


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frame

controlduration

address

1

address

2

address

4

address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seqcontrol

TypeFromAP

SubtypeToAP

Morefrag

WEPMoredata

Powermgt

Retry RsvdProtocolversion

2 2 4 1 1 1 1 1 11 1

802.11 frame: moreduration of reservedtransmission time (RTS/CTS)

frame seq #(for reliable ARQ)

frame type(RTS, CTS, ACK, data)


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hub orswitch

AP 2

AP 1

H1 BBS 2

BBS 1

802.11: mobility within same subnet

router H1 remains in same IP

subnet: IP addresscan remain same

Works fine for hub Switch: which AP is

associated with H1? self-learning switchwill see frame from H1and remember portto reach H1

Solution: when H1joins, AP2 sends switcha packet from H1


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MAC Management, Beacons and

Traffic Indication Map (TIM) 802.11 has several MAC management frames

(Re/De)Association req/response, Authentication Beacon (sent periodically by AP)

Timestamp, Beacon Interval, Capabilities, SSID,Rates, Parameters, Traffic Indication Map (TIM)

Allows host to select AP (or host can sendprobe) TIM: list of (associated but sleeping) hosts with

packets queued at the access point.

Even sleeping hosts (sometimes) listen to Beacon To check incoming messages in TIM, get broadcasts Sleeping to save energy when idle


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Ad Hoc NetworkingAd hoc networks no base stations transmit to other nodes

within link coverage nodes organize

themselves into a

network: route amongthemselves Supported in 802.11 but

still many open issues,research

WANET: Wireless Ad-Hoc NETwork

MANET: Mobile Ad-HocNet (they move, too!)


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Mradius ofcoverage

S

SS

P

P

P

P

M

S

Master deviceSlave device

Parked device (inactive)P

802.15: personal area network

less than 10 mdiameter

replacement for cables(mouse, keyboard,headphones)

ad hoc: noinfrastructuremaster/slaves:

slaves requestpermission to send (tomaster)

master grants requests

Evolved from Bluetooth

S N t k


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Sensor Networks

A special interesting type of Ad-Hoc network Idea: distribute low-cost `sensors` to perform

measurements, even do actions

Applications: Weather forecasts, natural disaster warnings

Detection of physical damages (leakage, fire,)

Military applications: intelligence, smart mines

Properties Wireless

Random location

Low cost, energy


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Which Transmission Range?When using AP/Bases, nodes must reach it

Large transmission range

But in sensor networks, WANET? Smaller transmission range

Saves energy, allows spectrum reuse (cellular?)

But: requires routing, forwarding by nodes


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Connectivity, Topology, RoutingAssume nodes distributed uniformly in area

One dimensional (line), two (surface), three (space)

Let nbe number of nodes Let r(n)be transmission range of nodeQuestions:

Probability that all/most nodes are connected Probability that entire area is `covered` by nodes

connected to `base`/`edge` Routing, scheduling, broadcast protocols for nodes

Using minimal resources (energy, storage) Minimize collisions


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Sensor Network Tasks/Protocols Routing, forwarding, broadcast

Neighbor/topology discovery, organization

E.g. setup spanning tree for efficient broadcast Optimization tasks

Optimize communication

Load balancing (also to save energy)

Location measurement Clock synchronization

Distributed computation

E.g. to detect image Handling mobility (MANET)


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Chapter 6 outline6.1 Introduction

Wireless 6.2 Wireless links,

characteristics

CDMA 6.3 IEEE 802.11

wireless LANs (wi-fi) 6.4 Cellular Internet

Access architecture standards (e.g., GSM)

Mobility 6.5 Principles:

addressing and routingto mobile users

6.6 Mobile IP

6.7 Handling mobility incellular networks 6.8 Mobility and higher-

layer protocols

6.9 Summary


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MobileSwitching

Center

Public telephonenetwork, andInternet

MobileSwitching

Center

Components of cellular network architecture

connects cells to wide area net manages call setup (more later!) handles mobility (more later!)

MSC

covers geographicalregion base station(BS)analogous to 802.11 AP

mobile usersattachto network through BS air-interface:physical and link layerprotocol between

mobile and BS

cell

wired network


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Cellular networks: the first hopTwo techniques for sharing

mobile-to-BS radio

spectrum combined FDMA/TDMA:

divide spectrum infrequency channels, divideeach channel into timeslots

CDMA: code division

multiple access

frequencybands

time slots


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Cellular standards: brief survey2G systems: voice channels

IS-136 TDMA: combined FDMA/TDMA (northamerica)

GSM (global system for mobile communications):combined FDMA/TDMA most widely deployed

IS-95 CDMA: code division multiple access

IS-136 GSM IS-95GPRS EDGE

CDMA-2000UMTS

TDMA/FDMA

Dont drown in a bowlof alphabet soup: use thisfor reference only


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Cellular standards: brief survey2.5 G systems: voice and data channels

for those who cant wait for 3G service: 2G extensions general packet radio service (GPRS)

evolved from GSM

data sent on multiple channels (if available)

enhanced data rates for global evolution (EDGE) also evolved from GSM, using enhanced modulation

Date rates up to 384K

CDMA-2000 (phase 1) data rates up to 144K

evolved from IS-95


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Cellular standards: brief survey3G systems: voice/data

Universal Mobile Telecommunications Service (UMTS) GSM next step, but using CDMA

CDMA-2000

.. more (and more interesting) cellular topics due tomobility (stay tuned for details)

Wi l d M bil


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Wireless and Mobile


Wireless

6.2 Wireless links,characteristics

6.3 IEEE 802.11wireless LANs (wi-fi)



6.6 Mobile IP


layer protocols

6.9 Summary

C d i [KR] i [KMK]


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What is mobility? spectrum of mobility, from the networkperspective:

no mobility high mobility

mobile wireless user,using same accesspoint

mobile user, passingthrough multipleaccess point while

maintaining ongoingconnections (like cellphone)

mobile user,connecting/disconnecting

from networkusing DHCP.

Covered in [KR], not in [KMK]


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Mobility: Vocabularyhome network:permanenthome of mobile(e.g., 128.119.40/24)

Permanent address:address in home

network, can alwaysbeused to reach mobilee.g., 128.119.40.186

home agent:entity that willperform mobility functions onbehalf of mobile, when mobileis remote

wide areanetwork

correspondent


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Mobility: more vocabulary

Care-of-address:addressin visited network.(e.g., 79.129.13.2)

wide areanetwork

visited network:networkin which mobile currentlyresides (e.g., 79.129.13/24)

Permanent address:remainsconstant (e.g., 128.119.40.186)

Foreign agent:entityin visited networkthat performsmobility functions onbehalf of mobile.

correspondent:wantsto communicate with

mobile


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How do youcontact a mobile friend:

I wonder whereAlice moved to?

Consider friend frequently changing

addresses, how do you find her? search all phone

books?

call her parents?

expect her to let youknow where he/she is?


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Mobility: approaches Let routing handle it:routers advertise permanent

address of mobile-nodes-in-residence via usualrouting table exchange. routing tables indicate where each mobile located

no changes to end-systems

Let end-systems handle it: indirect routing:communication from

correspondent to mobile goes through home

agent, then forwarded to remote direct routing:correspondent gets foreign

address of mobile, sends directly to mobile


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Mobility: approaches Let routing handle it:routers advertise permanent

address of mobile-nodes-in-residence via usual

routing table exchange. routing tables indicate where each mobile located

no changes to end-systems

let end-systems handle it: indirect routing:communication from

correspondent to mobile goes through home

agent, then forwarded to remote direct routing:correspondent gets care-of-

address of mobile, sends directly to mobile

not

scalableto millions of

mobiles


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Mobility: registration

End result: Foreign agent knows about mobile

Home agent knows location of mobile

wide areanetwork

home networkvisited network

1

mobile contactsforeign agent onentering visitednetwork

2

foreign agent contacts homeagent home: this mobile isresident in my network


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Mobility via Indirect Routing

wide areanetwork

homenetwork

visitednetwork

3

2

41

correspondent

addresses packetsusing home addressof mobile

home agent intercepts

packets, forwards toforeign agent

foreign agentreceives packets,forwards to mobile

mobile repliesdirectly tocorrespondent

d


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Indirect Routing: comments

Mobile uses two addresses:

permanent address: used by correspondent (hence

mobile location is transparentto correspondent) care-of-address: used by home agent to forward

datagrams to mobile

foreign agent functions may be done by mobile itself

triangle routing: correspondent-home-network-mobile

inefficient when

correspondent, mobileare in same network

d k


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Indirect Routing: moving between networks

suppose mobile user moves to anothernetwork registers with new foreign agent new foreign agent registers with home agent

home agent update care-of-address for mobile

packets continue to be forwarded to mobile (butwith new care-of-address)

mobility, changing foreign networks

transparent: ongoing connections can bemaintained!

M bili i Di R i


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Mobility via Direct Routing

wide areanetwork

homenetwork

visitednetwork

4

2

41correspondent

requests, receivesforeign address ofmobile

correspondent forwards

to foreign agent

foreign agentreceives packets,forwards to mobile

mobile repliesdirectly tocorrespondent

3

M bilit i Di t R ti t


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Mobility via Direct Routing: comments

overcome triangle routing problem

non-transparent to correspondent:

correspondent must get care-of-addressfrom home agent what if mobile changes visited network?

A d ti bilit ith di t ti


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wide areanetwork

1

foreign net visitedat session start

anchorforeignagent

2

4

new foreignagent

35

correspondentagent

correspondent

newforeignnetwork

Accommodating mobility with direct routing

anchor foreign agent: FA in first visited network data always routed first to anchor FA when mobile moves: new FA arranges to have data

forwarded from old FA (chaining)

R ( bil di )


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Response (mobilecorresponding)

Triangle routing: mobile corresponding Using mobile hosts IP address

Foreign network may block for `IP spoofing` (egressfiltering)

Indirect via foreign: mobileFA corresp. Requires FA (Foreign agent) to `spoof`

Indirect via home: mobile homecorresp. Overhead but works

Direct: mobile corresponding Use temporary IP address (and mobile IP)

Exercise: which are supported in mobile-IP? GSM?

Wireless and Mobile


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Wireless





6.6 Mobile IP

6.7 Cellular networks 6.8 Mobility and higher-layer protocols

6.9 Summary


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Mobile IP RFC 3220

has many features weve seen: home agents, foreign agents, foreign-agent

registration, care-of-addresses, encapsulation(packet-within-a-packet)

three components to standard: indirect routing of datagrams

agent discovery

registration with home agent

Mobile IP: indirect routing


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Mobile IP: indirect routing

Permanent address:128.119.40.186

Care-of address:

79.129.13.2dest: 128.119.40.186

packet sent bycorrespondent

dest: 79.129.13.2 dest: 128.119.40.186

packet sent by home agent to foreign

agent: apacket within a packet

dest: 128.119.40.186

foreign-agent-to-mobile packet


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Mobile IP: agent discovery agent advertisement: foreign/home agents advertise

service by broadcasting ICMP messages (typefield = 9)

R bit: registrationrequired

H,F bits: homeand/or foreign agent

RBHFMGV

bitsreserved

type = 16

type = 9 code = 0= 9

checksum= 9

router address

standardICMP fields

mobility agentadvertisement

extension

length sequence #

registration lifetime

0 or more availableCare-Of-Addresses (COA)

0 8 16 24

Mobile IP: registration example


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Mobile IP: registration example

visited network: 79.129.13/24home agent

HA: 128.119.40.7foreign agent

COA: 79.129.13.2COA: 79.129.13.2

.

ICMP agent adv.Mobile agent

MA: 128.119.40.186

registration req.

COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186Lifetime: 9999

identification:714.

registration req.

COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186

Lifetime: 9999identification: 714encapsulation format.

registration reply

HA: 128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714encapsulation format.

registration replyHA: 128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714.

time

Wireless and Mobile


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Wireless





6.6 Mobile IP 6.7 Cellular networks 6.8 Mobility and higher-

layer protocols

6.9 Summary

Components of cellular network architecture


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MobileSwitching

Center

Public telephonenetwork, andInternet

MobileSwitching

Center

p

connects cells to wide area net manages call setup (more later!) handles mobility (more later!)

MSC

covers geographicalregion base station(BS)analogous to 802.11 AP mobile usersattachto network through BS air-interface:physical and link layerprotocol betweenmobile and BS

cell

wired network


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Multiple operators (providers)

correspondent

MSC

MSCMSC MSC

MSC

wired publictelephonenetwork

different cellular networks,operated by different providers

recall:

Handling mobility in cellular networks


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Handling mobility in cellular networks

home network:network of cellular provider yousubscribe to (e.g., Sprint PCS, Verizon)

home location register (HLR):database in homenetwork containing permanent cell phone #,profile information (services, preferences,billing), information about current location

(could be in another network) visited network:network in which mobile currently

resides visitor location register (VLR):database with

entry for each user currently in network could be home network

GSM: indirect routing to mobile


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Publicswitchedtelephonenetwork

mobileuser

homeMobile

SwitchingCenter

HLRhomenetwork

visitednetwork

correspondent

MobileSwitching

Center

VLR

GSM: indirect routing to mobile

1 call routedto home network

2

home MSC consults HLR,gets roaming number ofmobile in visited network

3

home MSC sets up 2nd leg of call

to MSC in visited network

4

MSC in visited network completescall through base station to mobile

GSM: handoff with common MSC


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MobileSwitching

Center

VLR

old BSSnew BSS

oldrouting

newrouting


Handoff goal: route call vianew base station (without

interruption) reasons for handoff:

stronger signal to/from newBSS (continuing connectivity,less battery drain)

load balance: free up channelin current BSS

GSM doesnt mandate why toperform handoff (policy), only

how (mechanism) handoff initiated by old BSS



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MobileSwitching

Center

VLR

old BSS

1

3

24

5 6

78


new BSS

1. old BSS informs MSC of impendinghandoff, provides list of 1+ new BSSs

2. MSC sets up path (allocates resources)

to new BSS3. new BSS allocates radio channel for

use by mobile

4. new BSS signals MSC, old BSS: ready

5. old BSS tells mobile: perform handoff tonew BSS

6. mobile, new BSS signal to activate newchannel

7. mobile signals via new BSS to MSC:handoff complete. MSC reroutes call

8 MSC-old-BSS resources released

GSM: handoff between MSCs


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home network

HomeMSC

PSTN

correspondent

MSC

anchor MSC

MSCMSC


anchor MSC:first MSCvisited during cal call remains routed

through anchor MSC

new MSCs add on to endof MSC chain as mobilemoves to new MSC

Or: optional pathminimization step to

shorten multi-MSC chain



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home network

HomeMSC

PSTN

correspondent

MSC

anchor MSC

MSCMSC

(b) after handoff

GSM handoff between MSCs

anchor MSC:first MSCvisited during cal call remains routed

through anchor MSC

new MSCs add on to endof MSC chain as mobilemoves to new MSC

IS-41 allows optionalpath minimization step

to shorten multi-MSCchain

Mobility: GSM versus Mobile IP


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y

Care-of-address

Routable address for telephone call segmentbetween home MSC and visited MSC, visibleto neither the mobile nor the correspondent.

Mobile StationRoaming Number(MSRN), or roamingnumber

Foreign agentVisited MSC: responsible for setting up callsto/from mobile nodes in cells associated withMSC. VLR: temporary database entry invisited system, containing subscription

information for each visiting mobile user

Visited Mobileservices SwitchingCenter.Visitor Location

Record (VLR)

Visited networkNetwork other than home system where

mobile user is currently residing

Visited System

Home agentHome MSC: point of contact to obtain routable

address of mobile user. HLR: database inhome system containing permanent phonenumber, profile information, current location ofmobile user, subscription information

Gateway Mobile

Switching Center, orhome MSC. HomeLocation Register(HLR)

Home networkNetwork to which the mobile users permanentphone number belongs

Home system

Mobile IP elementComment on GSM elementGSM element

Wireless, mobility: impact on higher layer protocols


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logically, impact shouldbe minimal

best effort service model remains unchanged

TCP and UDP can (and do) run over wireless, mobile but performance-wise:

packet loss/delay due to noise, collisions, handoff

TCP interprets loss as congestion, will decreasecongestion window un-necessarily

delay impairments for real-time traffic

limited bandwidth of wireless links

Summary


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Wireless wireless links:

capacity, distance channel impairments CDMA

IEEE 802.11 (wi-fi) CSMA/CA reflects

wireless channelcharacteristics

cellular access

Mobility principles: addressing,

routing to mobile users home, visited networks direct, indirect routing care-of-addresses

case studies mobile IP mobility in GSM

impact on higher-layerprotocols

AN1 Mobile and Wireless Communication

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Transcript of AN1 Mobile and Wireless Communication