Transport layer issues in ad hoc wireless networks

Induced traffic: Ad hoc wireless networks use multi-hop radio relaying, and a link-level transmission affects neighbor nodes of both sender and receiver of the link. This induced traffic affects throughput of the transport layer protocol. Induced throughput unfairness: Some MAC protocols, like IEEE 802.11 DCF, may add throughput unfairness to the transport layer. A transport layer protocol needs to take this into account to provide a fair throughput for contesting flows. Separation of congestion control, reliability, and flow control: The throughput may be improved if the transport control protocol handles congestion control, reliability and flow control separately. Congestion is usually a local activity that affects only neighboring nodes while reliability and flow control are end-to-end issues. Separation of these should not produce significant control overhead. Misinterpretation of congestion: Commonly used methods of detecting the congestion by measuring packet loss and retransmission timeout are not suitable for ad hoc wireless networks. Packet loss occurs in wireless networks relatively frequently for several reasons. Bit error rates are much higher than in wired networks and path breaks occur frequently because nodes are constantly moving and they may fail e.g. after draining a battery. Thus, a better method for detecting congestion must be used. Completely decoupled transport layer: In wired networks, transport layer is usually almost completely decoupled from lower network layers. In wireless networks, cross-layer interaction would help transport layer protocol to adapt to the changes in the network Power and bandwidth constraints: Ad hoc wireless networks are constrained by available power and bandwidth. These constraints affect the performance of transport layer protocol. Dynamic topology: Topology of ad hoc wireless network may change rabidly and this leads to path breaks and partitioning of network. A transport layer protocol should be able to adapt to these changes.