MOBILE TCP

The M-TCP (mobile TCP)1 approach has the same goals as I-TCP and snooping TCP: to prevent the sender window from shrinking if bit errors or disconnection but not congestion cause current problems. M-TCP wants to improve overall throughput, to lower the delay, to maintain end-to-end semantics of TCP, and to provide a more efficient handover. Additionally, M-TCP is especially adapted to the problems arising from lengthy or frequent disconnections (Brown, 1997).

 M-TCP splits the TCP connection into two parts as I-TCP does. An unmodified TCP is used on the standard host-supervisory host (SH) connection, while an optimized TCP is used on the SH-MH connection. The supervisory host is responsible for exchanging data between both parts similar to the proxy in ITCP

The advantages of M-TCP are the following: 

● It maintains the TCP end-to-end semantics. The SH does not send any ACK itself but forwards the ACKs from the MH. 

Proactive Routing Protocols

Destination-Sequenced Distance-Vector (DSDV)
•When X receives information from Y about a route to Z
–Let destination sequence number for Z at X be S(X), S(Y) is sent from Y
–If S(X) > S(Y), then X ignores the routing information received from Y
–If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z
–If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y)
DSDV Protocol
•Packets are transmitted between the nodes using route tables stored at each node.
•Each route tablelists all available destinations and the number of hops to each destination.
•For each destination, a node knows which of its neighbours leads to the shortest path to the destination.
•Consider a source node Sand a destination node D.
•Each route table entry in S is tagged with a sequence number that is originated by the destination node.
•For example, the entry for D is tagged with a sequence number that Sreceived from D (may be through other nodes).
•We need to maintain the consistency of the route tables in a dynamically varying topology.

DSR Optimization: Route Caching

•Each node caches a new route it learns by any means

•When node S finds route [S,E,F,J,D]to node D, node S also learns route [S,E,F] to node F

•When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S

•When node F forwards Route Reply RREP[S,E,F,J,D],node F learns route [F,J,D] to node D

•When node E forwards Data [S,E,F,J,D]it learns route [E,F,J,D] to node D

Dynamic Source Routing: Advantages

•Routes maintained only between nodes who need to communicate

–reduces overhead of route maintenance

•Route caching can further reduce route discovery overhead

•A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches

Reactive Routing Protocols

Dynamic Source Routing (DSR)
•When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery
•Source node S floods Route Request (RREQ)
•Each node appends own identifierwhen forwarding RREQ

Route Discovery in DSR
•Destination D on receiving the first RREQ, sends a Route Reply (RREP)
•RREP is sent on a route obtained by reversingthe route appended to received RREQ

•RREP includes the routefrom S to D on which RREQ was received by node D

•Node S on receiving RREP, caches the route included in the RREP
•When node S sends a data packet to D, the entire route is included in the packet header
–hence the name source routing
•Intermediate nodes use the source routeincluded in a packet to determine to whom a packet should be forwarded

Routing Protocols

•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)

Routing Protocols
•Proactive protocols
–Traditional distributed shortest-path protocols
–Maintain routes between every host pair at all times
–Based on periodic updates; High routing overhead
–Example: DSDV (destination sequenced distance vector)
•Reactive protocols
–Determine route if and when needed
–Source initiates route discovery
–Example: DSR (dynamic source routing)
•Hybrid protocols
–Adaptive; Combination of proactive and reactive
–Example : ZRP (zone routing protocol)

MANETs Applications

•Industrial and commercial networks
•‘Anywhere’ communication
•Military applications
•Robust alternatives to cellular networks
•Wearable and Ubiquitous computing
•Remote satellite -based communication

Many Applications
•Personal area networking
–cell phone, laptop, ear phone, wrist watch
•Military environments
–soldiers, tanks, planes
•Civilian environments
–taxi cab network
–meeting rooms
–sports stadiums
–boats, small aircraft
•Emergency operations
–search-and-rescue
–policing and fire fighting

MOBILE AD HOC NETWORKS

Interconnected collection of wireless nodes
•Nodes enter and leave over time
•Nodes also act as routers; forward packets
•No pre-established network infrastructure
•No centralized administration
•Communication using BlueTooth and WAP

Characteristics Of MANETs

• Dynamic Topologiesand node memberships
• Host movement frequent
• Topology change frequent
• Data must be routed via intermediate nodes
• Bandwidth constraints
• Many Transmission Errors
• Energy-constrained operation