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CCM 4300 Lecture 8Computer Networks: Wireless and Mobile Communication

Systems

Dr E. EverSchool of Computing Science

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Mobility and IP …… more information

Mobile Wireless Internet Forum

• http://www.ipv6forum.com/

http://playground.sun.com/pub/ipng/html/ipng-main.html

IPv6 work including mobility support

•"The 3G IP Multimedia Subsystem" by Gonzalo Camarillo and Miguel A. Garcia Martin (available in google books)

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Facts about Mobile IP• More than 2 billion subscribers

•More than 70% of all digital mobile phones use GSM

•7.3 million people accesses the net via their mobile phones, during the second and third quarters of 2008. (BBC news channel)

•An increase of 25% compared to growth of juts 3% for the PC based net audience-(BBC news channel)

• IPv4 can do it all, it will be at a tremendous (unimaginable) cost and complexity

•Only IPv6 offers enough addresses •IPv6 offers features needed for mobile networking

•IPv6 utilises features to offer seamless roaming

•Network layer roaming enables cost reduction and improve deploy ability

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Lesson objectives To acquire a basic understanding of the basics of Mobile IPv4 and IPv6, you will:

- Understand principles of network MIP and HMIP: HA, CN, MN, FN, HN, FA, binding updates, CoA, RCoA.Triangular ruleRoute optimisation Availability and access control.

-Security in MIPKey distribution

Home Agent (HA)

Correspondent Node (CN)

Mobile Node (MN)

Foreign Network(FN)

Home Network(HN)

Foreign Agent (FA)

Care-of Address (COA)

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Mobile Network layer

• Mobile phone

• Mobile IP (Internet Protocol)

• Hand-off effects:

• addressing and routing

• operation of upper layer protocols

• Mobile IPv6

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Why Mobile IP• Routing

– Both ends of TCP (connection) need to keep the same IP address for the life of the session (home address, end-end)

– change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables (care-of-address, routing

• Specific routes to end-systems?– change of all routing table entries to forward

packets to the right destination– does not scale with the number of mobile hosts and

frequent changes in the location, security problems• Changing the IP-address?

– adjust the host IP address depending on the current location (managing a binding)

– almost impossible to find a mobile system, DNS updates take a long time (dynamic tunnel between CoA & HA)

– TCP connections break, security problems!!!!

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Requirements for Mobile IP• Transparency

– mobile end-systems keep their IP address– continuation of communication after interruption of link

possible– point of connection to the fixed network can be changed

• Compatibility– support of the same layer 2 protocols as IP– no changes to current end-systems and routers required– mobile end-systems can communicate with fixed systems

• Security– authentication of all registration messages

• Efficiency and scalability– only little additional messages to the mobile system required

(connection typically via a low bandwidth radio link)– world-wide support of a large number of mobile systems in

the whole Internet

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Mobile IP: TerminologyMobile Node (MN)

system (node) that can change the point of connection to the network without changing its IP address

Home Agent (HA)system in the home network of the MN, typically a router

registers the location of the MN, tunnels IP datagrams to the COA

Foreign Agent (FA)system in the current foreign network of the MN, typically a router

forwards the tunneled datagrams to the MN, typically the default router for the MN

Care-of Address (COA)address of the current tunnel end-point for the MN (at FA or MN)temporary IP address for a mobile deviceallows a home agent to forward messages to the mobile device. separate address is required because the IP address of the device that is used as host identification is topologically incorrect

actual location of the MN from an IP point of view, can be chosen, e.g., via DHCP

Correspondent Node (CN)communication partner

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Key Question

How do mobile hosts maintain IP connectivity

when mobility is supported at layer 3?

Here we investigate two extensions to IPv4.

•As mobile computing devices increase in capability mobile communication becomes increasingly wide-spread.

THE BIG QUESTION IS: How can IP support mobile connectivity?

Mobile IP: An Overview

CN

routerHA

routerFA

Internet

router

1.

2.

3.home

networkMN

foreignnetwork

4.

CN

routerHA

routerFA

Internet

router

homenetwork

MN

foreignnetwork

COA

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Mobile Phone network routingCall set-up

• MS emits beacon:

• IMSI/IMEI unique ID

• beacon heard by BTS

• BTS BSC MSC

• MSC:

• HLR

• VLR• updates HLR/VLR• if VLR updated, sends info

to home network for MS

• Network always knows location of MS

During call

• Hand-off:

• within area: BTS BTS

• between areas: BSC BSC, MSC informed of move to different area

• MSC MSC: updates to

HLR/VLR

• Call maintained during hand-off:

• only last-hop link

• Transparent to user:

• momentary signal loss(?)

IMSI: international mobile subscriber identity

IMEI: international mobile equipment identity

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Data transfer to the mobile system

Internethome network

foreignnetwork

FA

HA

MN

receiver

1

2

3

sender

CN

1. Sender sends to the IP address of MN, HA intercepts packet2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN

Triangular

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foreignnetwork

home network

Data transfer from the mobile system

Internet

HA

MN

sender

receiver

CN

1. Sender sends to the IP address of the receiver as usual, FA works as default router

FA

1

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Internet

sender

FA

HA

MN

home network

foreignnetwork

receiver

1

2

3

1. Sender sends to the IP address of MN, HA intercepts packet (proxy ARP)2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN

CN

Mobile phone network routing

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Mobile IP (1)• Need to support mobile users:

• Transparency:

• to upper layers

• to remote end-systems

• IPv4: IP address indicates

point of attachment to Network

• Movement of host means:

• new IPv4 address?

• update routing information?

• Mobile host (MH):

• home network (HN), home agent (HA)

• foreign network (FN),

foreign agent (FA)

• care-of-address (CoA)

• Communication:

• HA sends packets to CoA:

IP-in-IP encapsulation

• must reply to ARP for MH

• CoA:

• may be new IP address

• foreign agent

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Mobile IP (2)1) MH arrives at FN, and locates FA (using agent advertisements from FA or by solicitation).

2) MH completes registration procedure with FA.

3) MH updates HA with its new CoA (i.e. the FA).4) Host A now tries to contact MH. Packets for MH are intercepted by HA

5) HA tunnels the packets from Host A to the CoA for MH (i.e. the FA)

6) The FA de-encapsulates the inner IP packet and transmits the packet locally to MH.

7) The packets from MH to Host A are sent directly from the FN.

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Mobile IP (2)

HA

home network

Host A

remote network

FA

foreign network

Internet

MH 1

23

45

6

7

Data src = Host A

dst = MH

Data src = Host A

dst = MH

src = Host A

dst = MN

IP-in-IP encapsulation

Encapsulation

original IP headeroriginal data

new datanew IP header

outer headerinner headeroriginal data

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Mobile IP (3)X Security:

• firewalls have to be (dynamically) configured

• authentication:

MH FN(?), FA HA(?)

MH HA

• end-to-end security?

X Hand-off between FAs or FA/HA:

• lost packets(?)

Transparent to non-mobile hosts

Does not break/change existing IP addressing and routing

Can be introduced into the network as required

Normal (unicast) routers do not need to be modified

X Asymmetric routing:

Packets flowing in i.e. TCP connections flow through different routes to different directions.

• could be inefficient

• QoS

• higher layer protocol operation (e.g. TCP)

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Registration

t

MN HAregistrationrequest

registration

reply

t

MN FA HAregistrationrequest

registrationrequest

registration

reply

registration

reply

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Handoffs: layer 2 versus Layer 3 Layer 2

• No global changes:

• only local last hop

• No routing at layer 2

• No global addressing

significance at layer 2

• Need to have same layer 2

technology across network

• Mobility within network:

• no hand-off between network technologies

Layer 3 • Global, end-system to end-system connectivity

• Addresses have global significance

• Change in layer 3 address is change to network

• Layer 3 address valid across different layer 2 technologies

• Mobility across networks:

• internetworking!

Register an FA only

Register a new IP

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TCP behaviour (1)

Problems• Layer 2 cell hand-off:

• data loss /corruption (also due to high BER in general)

• no ACK for data

• TCP:

• no ACK slow start

• TCP has degraded performance

• High BER on wireless link (~10-3 - ~10-4 common):

• corrupt data requires end-to-end re-tx (use layer 2 FEC)

• Affects other transport-layer or application-layer protocols:

• real-time applications – errors and packet loss are harmful

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TCP behaviour (2)Possible solutions• TCP SACK option: (selective acknowledgment)

• retransmission of missing “holes” in byte stream

• not always implemented

• Use ECN in IP: (explicit congestion notification)

• need to modify TCP interface and applications

• Link-local re-tx:

• on wireless hop

• need to hold TCP, e.g. at base station

• need re-tx protocol

• Soft hand-off at layer 2: (a cell phone is simultaneously connected to two or more cells during a call.)

• need to use CDMA, which has its own problems

Network integration Agent Advertisement

HA and FA periodically send advertisement messages into their physical subnets

MN listens to these messages and detects, if it is in the home or a foreign network (standard case for home network)

MN reads a COA from the FA advertisement messages Registration (always limited lifetime!)

MN signals COA to the HA via the FA, HA acknowledges via FA to MN

these actions have to be secured by authentication Advertisement

HA advertises the IP address of the MN (as for fixed systems), i.e. standard routing information

routers adjust their entries, these are stable for a longer time (HA responsible for a MN over a longer period of time)

packets to the MN are sent to the HA, independent of changes in COA/FA

Encapsulation I Encapsulation of one packet into another as payload

e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast (Mbone) here: e.g. IP-in-IP-encapsulation, minimal encapsulation or GRE (Generic

Record Encapsulation) IP-in-IP-encapsulation (mandatory, RFC 2003)

tunnel between HA and COA

Encapsulation II Minimal encapsulation (optional)

avoids repetition of identical fields e.g. TTL, IHL, version, DS (RFC 2474, old:

TOS) only applicable for unfragmented packets,

no space left for fragment identification

Generic Routing Encapsulation

originalheader

original data

new datanew header

outer headerGRE

headeroriginal data

originalheader

Care-of address COAIP address of HA

TTLIP identification

GRE IP checksumflags fragment offset

lengthDS (TOS)ver. IHL

IP address of MNIP address of CN

TTLIP identification

lay. 4 prot. IP checksumflags fragment offset

lengthDS (TOS)ver. IHL

TCP/UDP/ ... payload

routing (optional)sequence number (optional)

key (optional)offset (optional)checksum (optional)

protocolrec. rsv. ver.CRK S s

RFC 1701

RFC 2784

reserved1 (=0)checksum (optional)protocolreserved0 ver.C

An example:

Optimisation of packet forwarding Triangular Routing

sender sends all packets via HA to MN higher latency and network load (for each RTT)

“Solutions” sender learns the current location of MN (give away your

position!) direct tunneling to this location HA informs a sender about the location of MN big security problems!

Change of FA packets on-the-fly during the change can be lost new FA informs old FA to avoid packet loss (chaining), old FA

now forwards remaining packets to new FA this information also enables the old FA to release resources for the MN

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Change of the foreign agent with the optimized mobile IP

CN HA FAold FAnew MN

t

requestupdate

ACKdata data

MN changeslocationregistration

updateACKdata

data datawarning

update

ACKdata

data

registration

Direct tunneling is used. HA only provides information about FA

Change of foreign agent

CN HA FAold FAnew MN

MN changeslocation

t

Data Data DataUpdateACK

Data Data

RegistrationUpdateACK

Data Data DataWarningRequest

UpdateACK

Data Data

Reverse Tunneling (RFC 2344)

•Mobile Internet Protocol (IP) uses tunneling from the home agent to the mobile node's care-of address, but rarely in the reverse direction.

•Usually, a mobile node sends its packets through a router on the foreign network, and assumes that routing is independent of source address.

•When this assumption is not true (it is not feasible or desired to have the mobile node send datagrams directly to the internetwork using FA), it is convenient to establish a topologically correct reverse tunnel from the care-of address to the home agent.

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Reverse tunneling:

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

3

2

1

3. HA forwards the packet to the receiver (standard case)

CN

1. MN sends to FA

2. FA tunnels packets to HA by encapsulation

Reverse tunneling (RFC 3024, was: 2344)

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

3

2

1

1. MN sends to FA2. FA tunnels packets to HA by encapsulation3. HA forwards the packet to the receiver (standard case)

CN

Mobile IP with reverse tunneling Router accept often only “topological correct“

addresses (firewall!) a packet from the MN encapsulated by the FA is now

topological correct furthermore multicast and TTL problems solved (TTL in the

home network correct, but MN is to far away from the receiver) Reverse tunneling does not solve

problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking)

optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing)

The standard is backwards compatible the extensions can be implemented easily and cooperate with

current implementations without these extensions Agent Advertisements can carry requests for reverse tunneling

Mobile IP and IPv6 Mobile IP was developed for IPv4, but IPv6 simplifies

the protocols security is integrated and not an add-on, authentication of

registration is included COA can be assigned via auto-configuration (DHCPv6 is one

candidate), every node has address auto configuration no need for a separate FA, all routers perform router

advertisement which can be used instead of the special agent advertisement; addresses are always co-located (any router can act like an FA)

MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimsation)

“soft“ hand-over, i.e. without packet loss, between two subnets is supported

MN sends the new COA to its old router the old router encapsulates all incoming packets for the MN and

forwards them to the new COA authentication is always granted

Once a MN moves into a foreign network, acquiring a new IP address - (CoA)

The MN is required to register this address with its HA via a binding update.

This binding update is issued over an IPSec tunnel, using an IPv6 security association, to protect its integrity and authenticity.

Mobile IP and IPv6 (2)

Advertisement from local router contains routing prefix•Seamless Roaming: MN always uses home address•Address configuration for care-of-address•Binding Updates sent to home agent & correspondent nodes (home address, care-of address, binding life time)•Mobile node ALWAYS ON by way of Home agent

Mobile IPv6 Protocol: an overview Home agent

Local router

Correspondent node

Correspondent node with binding

lasebae@mdx.ac.uk

• Enough address (340 undecillion 1036 addresses)•Addresses in IPv6 are 128 bits long, compared to 32-bit addresses in IPv4.The very large IPv6 address space supports a total of 2128 (about 3.4×1038) addresses340,282,366,920,938,463,463,374,607,431,768,211,456In China alone, there are 8 million IPv4 addresses and 70+ million handsets •Enough security (almost, not quite!)

• KDC, symmetric key, managing 10 million security associates, authentication header, security payload

•Address Autoconfiguration • Movement detection, Monitoring advertisement

•Route Optimisation (binding updates part of IPv6)•Destination Options (binding updates and acks) no reg and reg reply

Mobile IPv6 Design Points (why?)

•Seamless Mobility • Paging, context transfer, micro-mobility (localised

binding management)•Robust Header Compression

• Reducing 40/60 bytes of header overhead to 2-3 byte

•Authentication, Authorisation, and Accounting (AAA)•Smooth handover == low loss•Fast handover == low delay (approx 30 ms)•Seamless handover == smooth and fast

Other relevant issues with IP

•Scenario I: mobile sends special Router Solicitation (RS)

• Previous Access Router replies with proxy Router Advert (RA)

• Previous Access Router sends Handover Initiate (HI)• New Access Router sends Handover Acknowledge

(HACK)

• kjhasj

Mobile-controlled seamless handover

RS

RA

HI

HAck

•Previous access router sends Proxy Router Advertisement on behalf of the new access router – contains prefix and lifetime information …•Previous access router sends Handover Initiate message to new access router•Mobile node May finalise context transfer at new access router

Network Controlled Handover

Proxy router adv

HI

HAck

Problems with mobile IP Security

authentication with FA problematic, for the FA typically belongs to another organisation

no protocol for key management and key distribution has been standardised in the Internet

patent and export restrictions Firewalls

typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)

QoS many new reservations in case of RSVP tunneling makes it hard to give a flow of packets a special

treatment needed for the QoS Security, firewalls, QoS etc. are topics of current research and

discussions!

RSVP (Resource reSerVation Protocol)

Security in Mobile IP Security requirements (Security Architecture for the

Internet Protocol, RFC 1825) Integrity: any changes to data between sender and

receiver can be detected by the receiver Authentication: sender address is really the address

of the sender and all data received is really data sent by this sender

Confidentiality: only sender and receiver can read the data

Non-Repudiation: sender cannot deny sending of data Traffic Analysis: creation of traffic and user profiles

should not be possible Replay Protection: receivers can detect replay of

messages

not encrypted encrypted

IP security architecture I Two or more partners have to negotiate

security mechanisms to setup a security association typically, all partners choose the same

parameters and mechanisms Two headers have been defined for

securing IP packets: Authentication-Header

guarantees integrity and authenticity of IP packets if asymmetric encryption schemes (Public, Private

Keys) are used, non-repudiation can also be guaranteed

Encapsulation Security Payload protects confidentiality between communication

partners

Authentification-HeaderIP-Header UDP/TCP-Paketauthentication headerIP header UDP/TCP data

ESP headerIP header encrypted data

Mobile Security Association for registrations parameters for the mobile host (MH), home agent

(HA), and foreign agent (FA) Extensions of the IP security architecture

extended authentication of registration

prevention of replays of registrations time stamps: 32 bit time stamps + 32 bit random number Nonces (number for once pseudo random number): 32 bit

random number (MH) + 32 bit random number (HA)

registration reply

registration requestregistration request

IP security architecture II

MH FA HAregistration reply

MH-HA authenticationMH-FA authentication FA-HA authentication

Key distribution

Home agent distributes session keys

foreign agent has a security association with the home agent

mobile host registers a new binding at the home agent

home agent answers with a new session key for foreign agent and mobile node

FA MH

HA

response:EHA-FA {session key}EHA-MH {session key}

IP Micro-mobility support Micro-mobility support (Change FA):

Efficient local handover inside a foreign domainwithout involving a home agent

Reduces control traffic on backbone Especially needed in case of route optimisation

Example approaches: Cellular IP HAWAII Hierarchical Mobile IP (HMIP)

Important criteria: Security Efficiency, Scalability, Transparency, Manageability

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Support for Mobility in IPv6 • Route optimisation:

• send CoA to remote end-system

• Security:

• authentication and privacy

• Stateless address auto-configuration:

• find an address (CoA) for use at the FN

• Neighbour discovery:

• find default router

• No FA required to support mobility:

• MH takes care of home

address and foreign address

• Need dynamic DNS update support

Cellular IP (CIP) Operation:

“CIP Nodes“ maintain routing entries (soft state) for MNs

Multiple entries possible Routing entries updated

based on packets sent by MN CIP Gateway:

Mobile IP tunnel endpoint Initial registration processing

Security provisions: all CIP Nodes share

„network key“ MN key: MD5(net key, IP addr) MN gets key upon registration

CIP Gateway

Internet

BS

MN1

data/controlpackets

from MN 1

Mobile IP

BSBS

MN2

packets fromMN2 to MN 1

Cellular IP: Security Advantages:

Initial registration involves authentication of MNsand is processed centrally by CIP Gateway

All control messages by MNs are authenticated Replay-protection (using timestamps)

Potential problems: MNs can directly influence routing entries Network key known to many entities

(increases risk of compromise) No re-keying mechanisms for network key No choice of algorithm (always MD5, prefix+suffix mode) Message-Digest algorithm 5 is a widely used cryptographic hash function

Cellular IP: Other issues Advantages:

Simple and elegant architecture Mostly self-configuring (little management needed) Integration with firewalls / private address support

possible

Potential problems: Not transparent to MNs (additional control messages) Public-key encryption of MN keys may be a problem

for resource-constrained MNs Multiple-path forwarding may cause inefficient use of

available bandwidth

HAWAII

Operation: MN obtains co-located COA

and registers with HA Handover: MN keeps COA,

new BS answers Reg. Requestand updates routers

MN views BS as foreign agent Security provisions:

MN-FA authentication mandatory

Challenge/Response Extensions mandatory

BS

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BackboneRouter

Internet

BS

MN

BS

MN

CrossoverRouter

DHCPServer

HA

DHCP

Mobile IP

Mobile IP

1

2

3

4

HAWAII: Security Advantages:

Mutual authentication and Challenge/Response extensions mandatory

Only infrastructure components can influence routing entries Potential problems:

Co-located COA raises DHCP security issues(DHCP has no strong authentication)

Decentralised security-critical functionality(Mobile IP registration processing during handover)in base stations (BS)

Authentication of HAWAII protocol messages unspecified(potential attackers: stationary nodes in foreign network)

MN authentication requires PKI or AAA infrastructure

PKI: Public Key InfrastructureAAA: authentication, authorization and accounting

HAWAII: Other issues Advantages:

Mostly transparent to MNs(MN sends/receives standard Mobile IP messages)

Explicit support for dynamically assigned home addresses

Potential problems: Mixture of co-located COA and FA concepts may not be

supported by some MN implementations

No private address support possiblebecause of co-located COA

Hierarchical Mobile IPv6 (HMIPv6) Operation:

Network contains mobility anchor point (MAP)

mapping of regional COA (RCOA) to link COA (LCOA)

Upon handover, MN informsMAP only

gets new LCOA, keeps RCOA HA is only contacted if MAP

changes Security provisions:

no Hierarchical Mobile IPv6 -specific security provisions

binding updates should be authenticated

MAP

Internet

AR

MN

AR

MN

HA

bindingupdate

RCOA

LCOAoldLCOAnew

Problem: how to reduce latency due to signalling Agent

Solution: localise signalling to visited Domain

How, "method": Regional Registration/Regional Binding Update

Hierarchical Mobility Agents

Hierarchical Mobile IP: Security Advantages:

Local COAs can be hidden,which provides some location privacy

Direct routing between CNs sharing the same link is possible (but might be dangerous)

Potential problems: Decentralised security-critical functionality

(handover processing) in mobility anchor points MNs can (must!) directly influence routing entries

via binding updates (authentication necessary)

Hierarchical Mobile IP: Other issues Advantages:

Handover requires minimum number of overall changes to routing tables

Integration with firewalls / private address support possible

Potential problems: Not transparent to MNs

Handover efficiency in wireless mobile scenarios: Complex MN operations

All routing reconfiguration messages sent over wireless link

Other features (for IPv6 or seamless h/o)

• integration of Regional Registration with GPRS•Header compression•Buffer management•UDP Lite•AAA HLR adaptation layer•Challenge generation (optionally from HLR)•Privacy considerations•QoS handover•Smooth handover mechanisms for keys