Reliable Transport Protocol In Mobile Ad Hoc Networks

As a complex distributed networks, ad hoc networks are composed of wirelessmobile or static nodes which can self-organize. In this way, they can form arbitrary andtemporary network topologies allowing devices to interconnect seamlessly in areas withno pre-existing infrastructures. Thus they can be used for communications in hazardousenvironments, such as disaster relief operations and military environment.Mobile ad hoc networks are different from the wired networks, which arecharacterized with limited bandwidth, dynamic network topology, instability channeland shared channel competition. All of these characteristics will lead to relatively lownetwork performance. Therefore, some researches about transport layer protocol inmobile ad hoc networks have been done in this thesis. One of the biggest problems formobile ad hoc networks using the transport protocol is that its misinterpretation ofpacket loss to network congestion. Thus, once the transfer protocol detects that packetloss occurs, it will execute the congestion control algorithms in an attempt to alleviatethe congestion on the network. While it does not work well for ad hoc network sinceroute failures and wireless channel errors are indeed the dominating factors that causepacket loss. Erroneously execution of the congestion control algorithms to reduce thesending rate unnecessarily will lead to the available network bandwidth heavilyunderutilized. To solve these problems, this paper proposes two improvedmechanisms-TCP-CROSS and MTCP-CODE.On the basis of cross-layer design principle, TCP-CROSS can detect anddifferentiate all possible network events that might cause packet loss in ad hoc networkby utilizing the physical and data link layer information. Using the event detected bylower layer, it will let transport layer protocol work well. The results of severalcomputerized simulations verify the goodput and delivery ratio of TCP-CROSS.MTCP-CODE is a novel transport protocol that effectively utilizes availablebandwidth and diversity gains provided by the heterogeneous and high-loss path.MTCP-CODE distinguishes between congestion and link losses through ECN and usesRS coding recover from data losses. Also, it uses a dynamic packet mapping based on the current path characteristics to choose a path for packet. It can be seen throughsimulation analysis, MTCP-CODE is suitable for a large variety of applications thatseek reliable delivery under lossy conditions and allow us to attain a desirable tradeoffbetween goodput and delay.