ECE544: Communication Networks-II, Spring 2008

D. Raychaudhuri

Lecture 8

Includes tutorial materials from C. Perkins & D. Reininger

Today’s Lecture

• Mobility in networks• Mobile IP• Mobile ATM, 3G

Mobility in Cellular Networks

Cellular Concept of Mobility

• Users have a home system but can register at visited systems to make and receive calls – Single Number Service

• Users can roam among systems during a call and the call is handed-off without being dropped.

Functional Elements

Home System Visited System

HLR AC

VLR

AuthenticationCenter – Authenticates users

Visitor Location Register-Maintains temporary information onVisiting users.

Home Location Register –Maintains current customerLocation and service profile

GSM Registration

HLR/AC

VLR

Old VLR

Visited System

2) VLR queriesprevious VLR for user’s(actually the user’s smartcard) permanent ID.

Handset

1) Visited system detects handset,handset transmits temporary ID assignedby previous system.

3) The VLR sendsa registration messageto the HLR.

Mobile Data Networks

Name, Address, Routing

• Name: is a location independent identifier of a host

• Address: indicates where a given host is located.

• Route: tells how to get to a destination

Mobility Problem: The Internet Viewpoint

• Internet addresses are assigned in a topologically significant manner.– A mobile host must be assigned a new

address when it moves.• Change host address connection

breaks.• Retain host address routing fails.• Host address must be preserved

regardless of its location.

Constraints

• Inter-operability with TCP/IP protocol suite.• Existing networking apps should run

unmodified on mobile hosts.• System should provide Internet-wide

mobility.• No modification on existing routing

infrastructure should be required.• Solution should be independent of wireless

hardware technology.• Solution should have good scaling properties.

IP’s subnet model vs. Mobility

• Terminals move from one IP subnet to another, but have the wrong “subnet prefix” for the destination subnet.

• Solution: two-tier IP addressing– The mobile keeps its static IP address,

but borrows the service of a “care-of-address” on whatever IP subnet it happens to be visiting.

– A “care-of-address”, offered by a mobility agent, can be shared by visiting mobiles.

Basic Mobile IP

• How does it work?– Agent discovery:

advertisement/solicitation– MH registration– Use of Care-of-Address (COA)– Proxy ARP (Address Resolution Protocol)– Packet tunneling– Triangle routing

Key components

HN

R1 R3

FN FNR2

HA

MH

MHCH

FAMobile Host:a host or router capableof changing its point ofattachment to the Internet

Foreign Network:a network, other than MA’s homenetwork, that MH is currently attachedto.

Corresponding Host:a host or router communicationgwith a mobile node.

Home Network:the network identifiedwith a mobile node

Home Address:MH’s permanent IP address,network ID of this address identifiesthe mobile’s home network. Home Agent:

a router attached to the MH’s home networkmaintains current location information for the MHis responsible for forwarding packets destined for theMH when MH is away from home.

Foreign Agent (FA)a router in the foreign network that the MH is visitingprovides routing services to the MH while registredde-tunnels datagram to MHmay serve as default router for outgoing packet from MH

Route Optimization

Route Optimization

• Provides a means for nodes to– cache the bindings of a mobile node– tunnel their own datagrams directly to the

care-of-address– bypass mobile node’s home agent during

datagram delivery

• Allow datagrams sent based on an out-of-data cached binding, to be forwarded directly to the mobile node’s new care-of-address.

Terminology• Binding cache

– a cache of mobility bindings of mobile nodes– maintained by CH for use in tunneling

datagrams to those mobile nodes.

• Binding update– a message indicating a mobile node’s

current mobility binding and its care-of-address.

• Registration lifetime– the time duration for which a binding is

valid.

Route Optimization

• Key features– Binding cache update– Smooth handoffs between foreign

agents– New messages

• binding update• binding request• binding warning• binding ack

Binding Cache Creation/Update

• At CH, if no binding cache exists– datagrams will be routed to MH via basic

mobile IP routing– home agent should then send a Binding

Update message to the original source node– CH will then create a binding cache for the MH

• At an FA, if MH has moved to a new FA and the old FA still receives tunneled datagrams– old FA send Binding Warning message to

HA to advise the change.

Foreign Agent Smooth Handoff

• As part of registration procedure, the mobile node may request its new FA to notify its previous FA on its behalf– a Previous Foreign Agent Notification extension is

included in the Registration Request message

• The new FA builds a Binding Update message and transmits it to the mobile node’s previous FA as part of registration, requesting an ACK from the previous FA

• Security association between old FA and MH are used for authentication of the binding update message.

Mobile IPRefer to:

http://computer.org/internet/v2n1/perkins.htM

http://www.ietf.org/html.charters/mobileip-charter.html

http://wwwtgs.ctit.utwente.nl/Docs/education/advanced/mobile/

Tutorials/MobileIPv6.pdf

Slides on Mobile IP at: http://ing.ctit.utwente.nl/WU4/Documents/47

Mobile ATM Details

Mobile ATM: System Model• “M” UNI/NNI protocol extensions provide integrated &

efficient support for mobility within ATM access network Functions include: location mgmt, handoff control, mobile

QoS/routing

ATM Network

Mobile ATMAccess Network

ReroutedConnectionAfter handoff

Crossoverswitch

TerminalMovement

ConnectionBefore Handoff

Connect (ATM Addr A)

Initial Location AL1

Next Location AL2

Location Mgmt providesmapping of A-> AL1, AL2

Handoff supportsDynamic reroutingOf active connections

User Addr A (permanent)

HO (BS1->BS2)

BS1

BS2

User Addr A

Mobile ATM: Location Mgmt• Location management can be integrated into existing ATM

connection procedures.... (external servers can also be used) simple extensions to current CONNECT, RELEASE IE’s, etc. no need for a-priori partitioning of mobile & static address space

ATMHost

move

setup (home_addr)

release (foreign_addr)

setup (foreign_addr,home_addr)

update

Homeswitch

Current Foreignswitch

(1)

(2)

(3)(4)

Mobile ATM: Handoff• Handoff can be implemented via modest extensions to existing

ATM UNI/NNI signaling... new signaling messages/IE’s for handoff initiation, COS select, etc. provides high-performance, scalable solution (compared with

external MSC, BSC, etc.)

move

handoffrequest

(1)

COSselect

ATMHost

CrossoverSwitch (COS)

addsubpath

tear downsubpath

handoffconfirm

GSMNetwork

Mobile ATMAccess Network

TerminalMovement

GSM

GSM/ATMgateway

GSM

Proxy M UNI

GSMradiolink

M NNI

M UNI

M NNI

GSM

Handoff & locmgmt within mobileATM cloud providedBy “M” UNI/NNI

GSM

GSMradiolink

HLR/VLR

GSM radioair interface

Proxymigration

M NNI

GSMradiolink

GSM

Proxy M UNI

GSMradiolink

Mobile ATM: Use with Cellular• For mobile ATM infrastructure, a “proxy M-UNI” can be used

at the AP for interworking with a non-WATM radio protocol... GSM (or other cellular access protocol) converted to M-UNI at

AP Mobile ATM provides handoff and location mgmt to GSM user

GSM

25

Homework

- Read tutorial papers on mobile IP & ATM- Download and browse Mobile IP RFC