CCM 4300 Lecture 18Computer Networks, Wireless and Mobile

Communication Systems

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Mobility – Mobile IP Part-I

Dr S Rahman

Lesson objectives� To acquire a basic understanding of the basics of Mobile

IPv4 and IPv6, you will:

- Understand principles of MIP & HMIP: (Part-I) mHA, CN, MN, FN, HN, FA, binding updates, CoA, RCoA.

mTriangular rule

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mTriangular rule

mRoute optimisation

mAvailability and access control.

-Security in MIP (Part-II)mKey distribution

-HMIP (Hierarchical MIP) (Part-II)

-CIP (Cellular IP) (Part-II)

Home Agent (HA)

Correspondent Node (CN)

Mobile Node (MN)

Foreign Network(FN)

Home Network(HN)

Foreign Agent (FA)

Care-of Address (COA)

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)

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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

Mobile Network layer

• Mobile phone

• Mobile IP (Internet Protocol)

• Hand-off effects:

• addressing and routing

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• addressing and routing

• operation of upper layer protocols

• Mobile IPv6

Interworking

TheInternet

IP backbone

BillingVHE

Signalling Gateway

WAP Accounting

Broadcast Networks

Satellite FES

The

Context-aware informationCentre

ISPSIP Proxy Server

The

UMTS

Broadcast Networks(DAB, DVB-T)

GSM / GPRS

IP-based micro-mobility Wireless

LANs

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Hierarchical Coverage Layers

Global coverage

DAB and DVB-T, DVB-S

Satellite

Regional coverage

IP-based backbone

National coverage

Local area coverageWireless LANs

2G, 3G and 4G Cellular

Personal area coverageWireless PANs

Vertical Handover

Horizontal Handover 6

Vertical Handover (Next Generation Mobility)

WiFiWiFi

UMTS

1. Wired connection at the working desk2. Moving Indoor3. Moving Outdoor4. Moving into a hot-spot

Tor K Moseng, Handoff in Wireless Internet Access

EthernetEthernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

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Mobile IP - Introduction

•Mobile IP protocol allows location-independent routing of IP datagrams on the Internet. •Each mobile node is identified by its home address disregarding its current location in the Internet. •While away from its home network, a mobile node is associated with a care-of address which identifies its current location and its home address is associated with the local endpoint of a tunnel to its home agent.

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endpoint of a tunnel to its home agent. •Mobile IP specifies how a mobile node registers with its home agent and how the home agent routes datagrams to the mobile node through the tunnel.•A mobile node has two addresses - a permanent home address and a care of address(CoA), which is associated with the network the mobile node is visiting.

(Ref.: Wikipedia notes)

Mobile IP – Introduction..cont..

Two kinds of entities comprise a Mobile IP implementation:•A home agent - stores information about mobile nodes whose permanent home address is in the home agent's network.•A foreign agent - stores information about mobile nodes visiting its network. Foreign agents also advertise care-of addresses, which are used by Mobile IP. Home agent redirects packets towards the remote address through an IP tunnel by encapsulating the datagram with a new IP header using

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IP tunnel by encapsulating the datagram with a new IP header using the care of address (CoA) of the mobile node.When acting as transmitter, a mobile node sends packets directly to the other communicating node, without sending the packets through the home agent, using its permanent home address as the source address for the IP packets. This is known as triangular routing.

If needed, the foreign agent could employ reverse tunneling by tunneling the mobile node's packets to the home agent, which in turn forwards them to the communicating node.

Why Mobile IP

� Routing

� based on IP destination address, network prefix (e.g. 129.13.42) determines physical subnet

� 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

� Specific routes to end-systems?

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� 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

� almost impossible to find a mobile system, DNS updates take to long time

� TCP connections break, security problems

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

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– 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

Mobile IP: Terminology� Mobile Node (MN)

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

� Home Agent (HA)� provides several services for the MN and is located in the home network

� 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)

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

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

� Care-of Address (COA)� address of the current tunnel end-point for the MN (at FA or MN)

� actual location of the MN from an IP point of view

� can be chosen, e.g., via DHCP

� Correspondent Node (CN)� at least one partner is needed - communication partner, it represents the

partner for the MN.

•Home network – is the subnet the MN belongs to with respect to its

IP address. Home address of a mobile device is the IP address

assigned to the device within its home network.

•Foreign network is the current subnet the MN visits and which is

not the home network.

•Care-of address of a mobile device is the network-native IP

address of the device when operating in a foreign network.

Mobile IP: Terminology....cont...

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address of the device when operating in a foreign network.

•Home agent is a router on a mobile node’s home network which

tunnels datagrams for delivery to the mobile node when it is away

from home. It maintains current location (IP address) information for

the mobile node. It is used with one or more foreign agents.

•Foreign agent is a router that stores information about mobile

nodes visiting its network. Foreign agents also advertise care-of-

addresses which are used by Mobile IP.

•Binding - association of the home address with a care-of address.

Example network

router

HA

MN

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mobile end-systemInternet

router

routerend-system

FA

home network

foreign

network

(physical home network

for the MN)

(current physical network

for the MN)

CN

Data transfer to the mobile system

HA

MN2

Triangular

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1. Sender sends to the IP address of MN,

HA intercepts packet

2. HA tunnels packet to COA, here FA,

by encapsulation

3. FA forwards the packet to the MN

Internethome network

foreign

networkFA

receiver

1

3

sender

CN

Data transfer from the mobile system

HA

MN

home network sender

1

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1. Sender sends to the IP address

of the receiver as usual,FA works as default router

Internet

receiver

FA

home network

foreign

network

sender

CN

CN

router

HA

router

FA

Internet

router

home

networkMN

foreign

network

COA 1. CN wants to send an IP packet to the MN. CN does not need to know anything about the MN’s current location.

2. It sends the packet as usual to the IP address of MN

3. Internet routes the packet to the router responsible for the home network of

MN

Data transfer to the mobile system

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CN

router

HA

router

FA

Internet

router

1.

2.

3.

home

networkMN

foreign

network

4.

MN4. HA intercepts the packet

and encapsulates and tunneled to the CoA. A new header is put in front of the old IP header

5. FA decapsulates the packet and forwards the original packet with CN as source address and MN as destination address to the MN

Mobile Phone network routingCall set-up

• MS emits beacon:

• IMSI/IMEI unique ID

• beacon heard by BTS

• BTS → BSC → MSC

• MSC:

During call

• Hand-off:

• within area: BTS → BTS

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

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• MSC:

• HLR

• VLR

• updates HLR/VLR

• if VLR updated, sends info

to home network for MS

• Network always knows location of MS

• 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, MS – Mobile station

IMEI: international mobile equipment identity, MSC – Mobile Services Switching Centre

Mobile IP (1)• Need to support mobileusers:

• Transparency:

• to upper layers

• to remote end-systems

• IPv4: IP address indicates

• Mobile host (MH):

• home network (HN), home agent (HA)

• foreign network (FN),

•foreign agent (FA)

• care-of-address (CoA)

• Communication:

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• IPv4: IP address indicates

point of attachment toNetwork

• Movement of host means:

• new IPv4 address?

• update routing information?

• Communication:

• HA sends packets to CoA:

IP-in-IP encapsulation

• must reply to ARP for MH

• CoA:

• may be new IP address

• foreign agent

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

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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.

Mobile IP (3)

X Security:

• firewalls have to be (dynamically) configured

• authentication:

MH ⇔ FN(?), FA ⇔ HA(?)

√ 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

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MH ⇔ HA

• end-to-end security?

X Hand-off between FAs or FA/HA:

• lost packets(?)

√ 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)

� 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

Network Integration

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� 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

Registration

MN HAMN FA HA

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t

t

Handoffs: layer 2 versus Layer 3

Layer 2• No global changes:

• only local last hop

• No routing at layer 2

• No global addressing

Layer 3

• Global, end-system to end-system connectivity

• Addresses have global significance

• Change in layer 3 address is change

Register an FA only

Register a new IP

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• 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

• Change in layer 3 address is change to network

• Layer 3 address valid across different layer 2 technologies

• Mobility across networks:

• internetworking!

TCP behaviour (1)

Problems

• Layer 2 cell hand-off:

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

• no ACK for data

• TCP:

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• 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

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

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• 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

Encapsulation

original IP header original data

new datanew IP header

inner header original dataouter header inner header original data

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Encapsulation is the mechanism of taking a packet consisting of packet header and data and putting it into the data part of a new packet.The reverse operation, taking a packet out of the data part of another packet, is called decapsulation.

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

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Care-of address COAIP address of HATTLIP identification

IP-in-IP IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

IP address of MNIP address of CNTTLIP identification

lay. 4 prot. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

TCP/UDP/ ... payload

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 identificationspace left for fragment identification

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care-of address COAIP address of HATTLIP identification

min. encap. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

IP address of MNoriginal sender IP address (if S=1)

Slay. 4 protoc. IP checksum

TCP/UDP/ ... payload

reserved

Generic Routing Encapsulation (GRE)

originalheader

original data

new datanew header

outer headerGRE header

original dataoriginalheader

TTLIP identification

GRE IP checksumflags fragment offset

lengthDS (TOS)ver. IHL

RFC 1701

An example:

Care-of address COA

IP address of HATTL GRE IP checksum

IP address of MNIP address of CN

TTL

IP identification

lay. 4 prot. IP checksum

flags fragment offsetlengthDS (TOS)ver. IHL

TCP/UDP/ ... payload

routing (optional)sequence number (optional)

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

protocolrec. rsv. ver.C R K S s

RFC 2784

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

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Optimisation of packet forwarding� Triangular Routing

� CN to HA, HA to CoA/MN, and MN back to CN

� 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 MNrequest

updateACK

Direct tunneling is used. HA only provides information about FA

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t

ACK

data data

MN changes

locationregistration

updateACKdata

data datawarning

update

ACKdata

data

registration

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 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:

HA

MN2

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Internet

receiver

FA

home network

foreign

network

sender

3

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

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� 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 tunneling35

Triangular Routing(Recap)

Home Network

CNCN

Foreign Network

MNMN 36

Routing Optimization(Recap)

Foreign Network

Home Network NetworkNetwork

Internet

CNCN

MNMNFirst attempt

Binding Information

Direct Transmission

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Routing Optimization (Recap)

Home CNCN

TransmissionBinding Information

Foreign Network

Home Network

MNMN

Optimized route

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Reverse Tunnelling (Recap)

Foreign Network

Home Network

2

3

NetworkNetworkInternet

CNCN

MNMN14

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Summary

•Mobile IP:

• Why Mobility required and how is it achieved?

• Mobile IP terminology and use

• Encapsulation and Network integration

• Routing techniques in mobile IP

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• Routing techniques in mobile IP

� Triangular Routing

� Reverse Tunnelling

� Routing Optimisation