MANET:
Mobile and Ad-Hoc Networks
Traditional Routing Methods
• Advantages of using routing protocols:
– Self-starting
– Multi-Hop
– Dynamic topology
• Single metric: number of hops to destination
• Link-State
– Each router broadcasts to all other routers in the network its distance to all its
neighbor
– Each router then computes the shortest distance to each host
– Complete topology stored
– OSPF (RFC 1583)
• Distance-Vector
– Each router broadcast to all its neighbors its distance to all hosts
– Updates routing table based on information from its neighbors
– One record per destination
– RIP version 2 (RFC 1723)
– Poisoned-Reversed/Split Horizon
– Count to infinity problem
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Ad-hoc Networking
3
• Allow an arbitrary collection of mobile nodes to create a network on demand,
without support from any base stations (or administrative support)
• Goal: Cooperative, interpersonal networking
• Works with modified mobile-IP
– Requires a foreign agent to allow multi-hop routing paths to a mobile node
• Model of operation (Instant Infrastructure)
– Computers with unrelated IP addresses
– Limited range broadcast media
– Dynamic interconnection
– No “administration” allowed
– Complete connectivity
– Sleep mode not taken into account
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MANET : Mobile
Ad-Hoc Network
Assymmetric link
Symmetric link
Dynamic Source Routing
4
• A host dynamically determines the best route based on:
– Cached information
– Route discovery protocol
• The sender explicitly lists this route in the packet’s header
• Comparison with conventional routing protocols
– Uses no periodic routing advertisement messages
• reduces network bandwidth overhead
• conserves mobile host battery power
– Scalable to increased number of links in ad-hoc networks; wired networks
have very small number of routers (usually 1) connecting any two networks
– Does not require bidirectional transmission between any two hosts; link
state routing assumes all links are bidirectional. Hosts may not be reachable
because wireless network transmission may not work in the opposite
direction
– Adapts quickly to host location changes; conventional algorithms converges
slowly to new network topology
• Assumption
– All host that wish to communicate with other hosts are willing to
participate in the routing protocol
Route Discovery
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• Sender broadcast a route request packet to hosts within a wireless
transmission range
• The route request packet is propagated through the ad-hoc network
• A route request packet contains:
– Request Id (eliminates duplicates)
– Target host
– Route record -- accumulated record of the sequence of hops taken by the
route request
• If the address of the host receiving the route request matches the target, then
the host returns a route reply
packet to the initiator containing the route
record
• Alternative routes used by the target host to return the route reply
– route entry in the route cache of the target host
– reversed route of the route record; may not work in non-bidirectional
wireless links
– piggyback the route reply packet on a route request targeted at the
initiator
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