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
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