Wlan Mobile Ip

7/29/2019 Wlan Mobile Ip

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Wireless LANs: 802.11 and Mobile IP


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Outline

Overview of wireless networks Single-hop wireless: Cellular, Wireless LANs (WLANs)

multiple wireless hops Mobile ad hoc networks (MANETS)

Challenges of wireless communications

IEEE 802.11 spread spectrum and physical layer specification

MAC functional specification: DCF mode

role in WLANs infrastructure networks

role in MANETs

MAC functional specification: PCF mode

Mobile IPv4

Mobile IPv6


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Overview of

wireless networks


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Wireless networks

Access computing/communication services, on the move

Cellular Networks traditional base station infrastructure systems

Wireless LANs infrastructure as well as ad-hoc networks possible

very flexible within the reception area

low bandwidth compared to wired networks (1-10 Mbit/s)

Multihop Ad hoc Networks useful when infrastructure not available, impractical, or expensive

military applications, rescue, home networking


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Cellular Wireless

Single hop wireless connectivity to the wiredworld

Space divided into cells, and hosts assigned to a cell

A base station is responsible for communicating with

hosts/nodes in its cell

Mobile hosts can change cells while communicating

Hand-offoccurs when a mobile host starts

communicating via a new base station


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Evolution of cellular networks

First-generation: Analog cellular systems (450-900 MHz)

Frequency shift keying; FDMA for spectrum sharing AMPS (US)

Second-generation: Digital cellular systems (900, 1800MHz) TDMA/CDMA for spectrum sharing; Circuit switching

GSM (Europe)


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Wireless LANs

Infrared or radio links

Advantages

very flexible within the reception area

Ad-hoc networks possible (almost) no wiring difficulties

Disadvantages

low bandwidth compared to wired networks

many proprietary solutions

Bluetooth, HiperLAN and IEEE 802.11


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Wireless LANs vs. Wired LANs

Destination address does not equal destinationlocation

The media impact the design wireless LANs intended to cover reasonable

geographic distances must be built from basiccoverage blocks

Impact of handling mobile (and portable)stations Propagation effects

Mobility management

Power management


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Infrastructure vs. Ad hoc WLANs

infrastructure

network

ad-hoc network

APAP

AP

wired network

AP: Access Point

Source: Schiller


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Multi-Hop Wireless

May need to traverse multiple links to reachdestination

Mobility causes route changes


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Mobile Ad Hoc Networks (MANET)

Do not need backbone infrastructure support

Host movement frequent

Topology change frequent

Multi-hop wireless links

Data must be routed via intermediate nodes

AB A

B


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Applications of MANETS

Military - soldiers at Kargil, tanks, planes

Disaster Management Orissa, Gujarat

Emergency operations search-and-rescue, police and

firefighters

Sensor networks

Taxicabs and other closed communities

airports, sports stadiums etc. where two or more people

meet and want to exchange documents

Presently MANET applications use 802.11 hardware

Personal area networks - Bluetooth


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Challenges of

Wireless Communications


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Wireless Media

Physical layers used in wireless networks have neither absolute nor readily observable

boundaries outside which stations are unable toreceive frames

are unprotected from outside signals

communicate over a medium significantly less reliablethan the cable of a wired network

have dynamic topologies

lack full connectivity and therefore the assumption

normally made that every station can hear every otherstation in a LAN is invalid

have time varying and asymmetric propagationproperties


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Limitations of the mobile environment

Limitations of the Wireless Network limited communication bandwidth frequent disconnections

heterogeneity of fragmented networks

Limitations Imposed by Mobility route breakages

lack of mobility awareness by system/applications

Limitations of the Mobile Device short battery lifetime

limited capacities


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Wireless v/s Wired networks

Regulations of frequencies

Limited availability, coordination is required

useful frequencies are almost all occupied

Bandwidth and delays Low transmission rates

few Kbps to some Mbps. Higher delays

several hundred milliseconds

Higher loss rates susceptible to interference, e.g., engines, lightning

Always shared medium Lower security, simpler active attacking

radio interface accessible for everyone

Fake base stations can attract calls from mobile phones

secure access mechanisms important


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Difference Between Wired and

Wireless

If both A and C sense the channel to be idle at the same

time, they send at the same time. Collision can be detected at senderin Ethernet.

Half-duplex radios in wireless cannot detect collision atsender.

A B C

A

B

C

Ethernet LAN Wireless LAN


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A and C cannot hear each other.A sends to B, C cannot receive A.

C wants to send to B, C senses a free medium

(CS fails)

Collision occurs at B.A cannot receive the collision (CD fails).

A is hidden for C.

Hidden Terminal Problem

BA C


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Exposed Terminal Problem

A starts sending to B.

C senses carrier, finds medium in use and has to

wait for A->B to end. D is outside the range of A, therefore waiting is not

necessary.

A and C are exposed terminals

A B

CD


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Mobile IP


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Traditional Routing

A routing protocolsets up a routing table in routers

Routing protocol is typically based on Distance-Vector or

Link-State algorithms


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Mobile IP

A standard that allows users with mobile devices whose IPaddresses are associated with one network to stayconnected when moving to a network with a different IPaddress.

When a user leaves the network with which his device isassociated (home network) and enters the domain of aforeign network, the foreign network uses the Mobile IPprotocol to inform the home network of a care-of address towhich all packets for the user's device should be sent.

Mobile IP is most often found in wireless WAN environmentswhere users need to carry their mobile devices acrossmultiple LANs with different IP addresses.


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IP requires the location of any host connected tothe Internet to be uniquely identified by an

assigned IP address. This raises one of the most important issues in

mobility, because when a host moves to anotherphysical location, it has to change its IP address.

However, the higher level protocols require IPaddress of a host to be fixed for identifyingconnections.

The Mobile Internet Protocol (Mobile IP) is an

extension to the Internet Protocol proposed bythe Internet Engineering Task Force (IETF) thataddresses this issue.


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Overview of the Protocol

Mobile IP supports mobility by transparently binding

the home address of the mobile node with its care-of address. This mobility binding is maintained bysome specialized routers known as mobility agents.

Mobility agents are of two types

- home agents

- foreign agents. The home agent, a designated router in the home

network of the mobile node, maintains the mobilitybinding in a mobility binding table where each

entry is identified by the tuple .


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The basic Mobile IP protocol has four distinctstages. These are:

1. Agent Discovery:Agent Discovery consists of thefollowing steps: Mobility agents advertise their presence by periodically

broadcasting Agent Advertisement messages. An AgentAdvertisement message lists one or more care-of

addresses and a flag indicating whether it is a home agentor a foreign agent. The mobile node receiving the Agent Advertisement

message observes whether the message is from its ownhome agent and determines whether it is on the homenetwork or a foreign network.

If a mobile node does not wish to wait for the periodicadvertisement, it can send out Agent Solicitationmessages that will be responded by a mobility agent.


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2. Registration: Registration consists of the followingsteps: If a mobile node discovers that it is on the home network, it

operates without any mobility services.

If the mobile node is on a new network, it registers with theforeign agent by sending a Registration Request message whichincludes the permanent IP address of the mobile host and the IPaddress of its home agent.

The foreign agent in turn performs the registration process onbehalf of the mobile host by sending a Registration Request

containing the permanent IP address of the mobile node and theIP address of the foreign agent to the home agent. When the home agent receives the Registration Request, it

updates the mobility binding by associating the care-of addressof the mobile node with its home address.

The home agent then sends an acknowledgement to the foreign

agent. The foreign agent in turn updates its visitor list by inserting theentry for the mobile node and relays the reply to the mobilenode.


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Registration process in Mobile IP


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3. In Service: This stage can be subdivided into thefollowing steps: When a correspondent node wants to communicate with the

mobile node, it sends an IP packet addressed to the permanentIP address of the mobile node.

The home agent intercepts this packet and consults the mobilitybinding table to find out if the mobile node is currently visitingany other network.

The home agent finds out the mobile node's care-of address and

constructs a new IP header that contains the mobile node'scare-of address as the destination IP address. The original IPpacket is put into the payload of this IP packet. It then sends thepacket. This process of encapsulating one IP packet into thepayload of another is known as IP-within-IP encapsulation, ortunneling.

When the encapsulated packet reaches the mobile node'scurrent network, the foreign agent decapsulates the packet andfinds out the mobile node's home address. It then consults thevisitor list to see if it has an entry for that mobile node.


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If there is an entry for the mobile node on the visitor

list, the foreign agent retrieves the correspondingmedia address and relays it to the mobile node.

When the mobile node wants to send a message to a

correspondent node, it forwards the packet to the

foreign agent, which in turn relays the packet to thecorrespondent node using normal IP routing.

The foreign agent continues serving the mobile

node until the granted lifetime expires. If the

mobile node wants to continue the service, it hasto reissue the Registration Request.


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Tunneling operation in Mobile IP


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4. Deregistration: If a mobile node wants to drop its care-of address, it

has to deregister with its home agent. It achievesthis by sending a Registration Request with thelifetime set to zero.

There is no need for deregistering with the foreignagent as registration automatically expires whenlifetime becomes zero. However if the mobile nodevisits a new network, the old foreign network doesnot know the new care-of address of the mobilenode.

Thus datagrams already forwarded by the homeagent to the old foreign agent of the mobile node arelost.


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Security Considerations

During registration procedure the home agent should beconvinced that it is getting authentic Registration Requestfrom a mobile node and not receiving information from abogus node. Mobile IP solves this problem by specifying asecurity association between the home agent and the mobilenode.

This security association is at present manually configured.Every registration message should contain a mobile node-home agent aunthentication extension which contain anSecurity Parameters Index(SPI) followed by an authenticator..

The SPI is an index into the mobility security association and

it defines the security context (i.e., the algorithm and thesecret) used to compute and check the authenticator. Thedefault algorithm is keyed MD5 with a key size of 128 bits.Also each registration contains unique data to avoid validregistration recording by malicious nodes.


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Route Optimization

In the basic Mobile IP protocol, IP packets

destined to a mobile node that is outside its

home network are routed through the homeagent.

However packets from the mobile node to the

correspondent nodes are routed directly.

This is known as triangle routing.


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Triangle Routing


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This method may be inefficient in many cases.

Consider the case when the correspondent host

and the mobile host are in the same network,but not in the home network of the mobile host.

In this case the messages will experience

unnecessary delay since they have to be firstrouted to the home agent that resides in the

home network.

One way to improve this is Route Optimization.


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Route Optimization is an extension proposed to

the basic Mobile IP protocol . Here messages

from the correspondent node are routed directlyto the mobile node's care-of address without

having to go through the home agent. Route

Optimization provides four main operations.

These are: Updating binding caches,

Managing smooth handoffs between foreign

agents, Acquiring registration keys for smooth handoffs,

Using special tunnels.


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1. Updating binding caches:

Binding caches are maintained by correspondent

nodes for associating the home address of amobile node with its care-of address. A bindingcache entry also has an associated lifetime afterwhich the entry has to be deleted from the cache.

If the correspondent node has no binding cacheentry for a mobile node, it sends the messageaddressed to the mobile node's home address.

When the home agent intercepts this message, it

encapsulates it and sends it to the mobile node'scare-of address. It then sends a Binding Updatemessage to the correspondent node informing it ofthe current mobility binding.


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2. Managing smooth handoffs between foreignagents:

When a mobile node registers with a newforeign agent, the basic Mobile IP does notspecify a method to inform the previous foreignagent.

Thus the datagrams in flight which had alreadytunneled to the old care-of address of the mobilenode are lost.

This problem is solved in Route Optimization by

introducing smooth handoffs. Smooth handoffprovides a way to notify the previous foreignagent of the mobile node's new mobility binding.


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3. Acquiring registration keys for smoothhandoffs:

For managing smooth handoffs, mobile nodesneed to communicate with the previous foreignagent.

This communication needs to be done securely

as any careful foreign agent should requireassurance that it is getting authentic handoffinformation and not arranging to forward in-flightdatagrams to a bogus destination.

For this purpose a registration key is establishedbetween a foreign agent and a mobile nodeduring the registration process.


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4. Using special tunnels:

When a foreign agent receives a tunneleddatagram for which it has no visitor list entry, itconcludes that the node sending the tunneleddatagram has an out-of-date binding cache entryfor the mobile node.

If the foreign agent has a binding cache entry forthe mobile node, it should re-tunnel thedatagram to the care-of address indicated in itsbinding cache entry.

On the other hand, when a foreign agentreceives a datagram for a mobile node for whichit has no visitor list or binding cache entry, itconstructs a special tunnel datagram.


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Routing and Mobility

Finding a path from a source to a destination

Issues

Frequent route changes

amount of data transferred between route changes may be

much smaller than traditional networks

Route changes may be related to host movement

Low bandwidth links

Goal of routing protocols decrease routing-related overhead

find short routes

find stable routes (despite mobility)


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Mobile IP (RFC 3344): Motivation Traditional routing

based on IP address; network prefix determines the subnet change of physical subnet implies

change of IP address (conform to new subnet), or

special routing table entries to forward packets to new subnet

Changing of IP address

DNS updates take to long time TCP connections break

security problems

Changing entries in routing tables does not scale with the number of mobile hosts and frequent

changes in the location security problems

Solution requirements retain same IP address, use same layer 2 protocols

authentication of registration messages,


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Mobile IP: Basic Idea

Router

1

Router

3

Router

2

S MN

Home

agent


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Mobile IP: Basic Idea

Router

1

Router

3

Router

2

S MN

Home agent

Foreign agent

move

Packets are tunneled

using IP in IP


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Mobile IP: Terminology

Mobile Node (MN)

node that moves across networks without changing its IP address

Home Agent (HA)

host in the home network of the MN, typically a router

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

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

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

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

Correspondent Node (CN)

host with which MN is corresponding (TCP connection)


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Data transfer to the mobile system

Internet

sender

FA

HA

MN

home network

foreign

network

receiver

1

2

3

1. Sender sends to the IP address of MN,HA intercepts packet (proxy )

2. HA tunnels packet to COA, here FA,

by encapsulation

3. FA forwards the packet to the MN

Source: Schiller

CN


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Data transfer from the mobile system

Internet

receiver

FA

HA

MN

home network

foreign

network

sender

1

1. Sender sends to the IP address

of the receiver as usual,

FA works as default router

Source: Schiller

CN

M bil IP B i O ti


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Mobile IP: Basic Operation

Agent Advertisement

HA/FA periodically send advertisement messages into theirphysical subnets

MN listens to these messages and detects, if it is inhome/foreign network

MN reads a COA from the FA advertisement messages

MN Registration MN signals COA to the HA via the FA

HA acknowledges via FA to MN

limited lifetime, need to be secured by authentication

HA Proxy HA advertises the IP address of the MN (as for fixed systems)

packets to the MN are sent to the HA

independent of changes in COA/FA

Packet Tunneling

HA to MN via FA

M bil IP Oth I


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Mobile IP: Other Issues

Reverse Tunneling

firewalls permit only topological correct addresses

a packet from the MN encapsulated by the FA is

now topological correct

Optimizations

Triangular Routing

HA informs sender the current location of MN

Change of FA new FA informs old FA to avoid packet loss, old FA now

forwards remaining packets to new FA


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Registration

t

MN HAregistrationrequest

registra

tion

reply

t

MN FA HAregistrationrequest

registrationrequest

regist

ration

reply

registra

tion

reply


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Optimization of packet forwarding

Triangular Routing sender sends all packets via HA to MN higher latency and network load

Solutions sender learns the current location of MN

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, old FA nowforwards remaining packets to new FA

this information also enables the old FA to release resourcesfor the MN


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Reverse tunneling (RFC 3024)

Internet

receiver

FA

HA

MN

home network

foreign

network

sender

3

2

1

1. MN sends to FA

2. FA tunnels packets to HAby encapsulation

3. HA forwards the packet to the

receiver (standard case)

CN


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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 thehome network correct, but MN is too far away from the

receiver) Reverse tunneling does not solve

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

optimization of data paths, i.e. packets will be forwarded

through the tunnel via the HA to a sender (double triangularrouting)

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

with current implementations without these extensions

Mobile IPv4 Summary


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Mobile IPv4 Summary

Mobile node moves to new location

Agent Advertisement by foreign agent

Registration of mobile node with home agent

Proxying by home agent for mobile node

Encapsulation of packets

Tunneling by home agent to mobile node via

foreign agent

Optimizations for triangular routing

Reverse tunneling


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IPv6 Address Architecture

Unicast address

provider-based global address

link-local(at least one per interface), site-local

IPv4 compatible IPv6 address (IPv6 node)

IPv4 mapped IPv6 address (IPv4 node)

A single interface can have multiple addresses of any

type or scope

Multicast address identifies a group of stations/interfaces

(112-bit group ID)

No Broadcast addresses

Broadcast applications in IPv4 will have to be re-written in IPv6

A t fi ti


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Autoconfiguration

Plug & Play - a machine when plugged in willautomatically discover and register the required

parameters for Internet connectivity

Autoconfiguration includes

creating a link-local address verifying its uniqueness on a link

determining what information should be

autoconfigured, addresses and/or other info

In the case of addresses, they may be obtainedthrough stateless or stateful mechanism (DHCPv6), or

both

Wlan Mobile Ip

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