ECE544: Communication Networks-II, Spring 2009

H. LiuLecture 10 (Mobility)

Includes tutorial materials from D. Raychaudhuri, C. Perkins, D. Reininger

Today’s Lecture

• Announcements: Final Exam• Mobile IP• Network Security

Announcements

• Final: Monday, May 11, 8:00 PM-11:00 PM, Location: SEC 210– OPEN BOOK: Only the textbook, Peterson & Davie,

"Computer Networks: A Systems Approach“ plus 2 pages of notes are permitted.

– Textbook Chapters 1 – 6, Chapter 8, and Lecture Slides (Chapters 1 and 2 are not the main focus of this final exam but are needed as background knowledge)

– Calculator is permitted

• Course Survey: end on Monday, May 4

Review

• Ethernet switching, wireless LAN• MPLS basic, ATM• IP Routing (RIP, OSPF, BGP)• IP Addressing (Subnetting, CIDR, IPV6)• Mobile IP• End-to-End Protocols (UDP, TCP, RTP)• Congestion control and QoS (queuing

disciplines, TCP congestion control, congestion avoidance, IntServ, DiffServ)

• Network Security

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 IP 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 capable of changing its point of attachment to the Internet

Foreign Network:a network, other than MA’s homenetwork, that MH is currently attached to.Care-of-address: the IP address of the foreign agent

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 (HA):

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-date cached binding, to be forwarded 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 host 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 IP in IPv6

• Mobile IPv6 shares many features with Mobile IPv4,

• but:– Mobility protocol fully integrated into IPv6– Provides many improvements over Mobile

IPv4.• No Foreign Agent: all care-of-address are collocated• Intrinsic "Route Optimization" mechanism• Automatic procedures for acquiring CoA: stateless

addr autoconfig, DHCP (stateful)

Mobile IPv6• MH uses Binding Update and Binding Ack to inform its

HA or a CH of its new care-of-address • HA and CH can send Binding Request to MH to request

Binding Update • Binding Update, Binding Ack, and Binding Request uses

IPv6 optional header (Destination Option Header) and can be piggybacked with data payload

• Use of IPv6 Routing Header option for avoiding triangular routing– Destination addr in IPv6 header = MH care-of address– “type 0” routing header: addr = MH home address

• HA possibly tunnels first few IP packets using IPv6-in-IPv6 encapsulation– MH sends Binding Update to CH

Mobile IPv4 vs Mobile IPv6

Mobile IPv4• Advantages:

– a lot of mobile IPv4 implementations are available on different OS

• Limitations– too small address

space.– lack of support for

Integrated Route Optimization

– Control messages not included inside IPv4 data packet header

Mobile IPV6• Advantages

– Address space (128 bit)

– Route optimization– Optional header

structure to support mobility

– QoS treatment

• Limitations – IPV6 is not popular yet