Abstract
In this chapter, the authors present an improvement to the interactions between MAC (Medium Access Control) and TCP (Transmission Control Protocol) protocols for better performance in MANET. This improvement is called IB-MAC (Improvement of Backoff algorithm of MAC protocol) and proposes a new backoff algorithm. The principle idea is to make dynamic the maximal limit of the backoff interval according to the number of nodes and their mobility. IB-MAC reduces the number of collisions between nodes. It is also able to distinguish between packet losses due to collisions and those due to nodes’ mobility. The evaluation of IB-MAC solution and the study of its incidences on MANET performance are done with TCP New Reno transport protocol. The authors varied the network conditions such as the network density and the mobility of nodes. Obtained results are satisfactory, and they showed that IB-MAC can outperform not only MAC standard, but also similar techniques that have been proposed in the literature like MAC-LDA and MAC-WCCP.
TopIntroduction
A MANET (Mobile Ad Hoc Network) (Basagni, Conti, Giordano, & Stojmenovic, 2004) is a complex distributed system which consists of wireless mobile or static nodes. These nodes can freely and dynamically self-organize. In this way they form arbitrary and temporary “Ad hoc” networks topologies, allowing devices to be interconnected wirelessly in areas with no pre-existing infrastructures.
In such network, MAC (Medium Access Control) protocol (Karn, 1990; Bhargavan, Demers, Shenker, & Zhang, 1994; Parsa & Garcia-Luna-Aceves, 1999) must provide an efficient access to the wireless medium and reduces the data interference. Important examples of this protocol include Carrier-Sense Multiple Access CSMA with collision avoidance which uses a random backoff algorithm (IEEE, 1999). CSMA can use a virtual carrier sensing mechanism using Request-To-Send/Clear-To-Send (RTS/CTS) control packets (Mjeku & Gomes, 2008). Both techniques are used in IEEE 802.11 MAC protocol (IEEE, 1999) which is the current standard for wireless networks.
TCP (Transmission Control Protocol) (Holland & Vaidya, 1999; Hanbali, Altman, & Nain, 2005) is the transport protocol used in most IP networks (Kurose and Ross, 2005) and recently in MANETs (Kawadia & Kumar, 2005). It is important to understand the TCP behavior when coupled with IEEE 802.11 MAC protocol in such network.
When the interactions between the MAC and TCP protocols are not taken into account, this can degrade the MANET performance notably, by affecting to the performance of the TCP parameters, i.e. throughput and end-to-end delay (Jiang, Gupta, & Ravishankar, 2003; Nahm, Helmy, & Kuo, 2004; Papanastasiou, Mackenzie, Ould-Khaoua, & Charissis, 2006). In order to adapt the behavior of these protocols for better QoS (Li, 2006), it is very important to study their interactions. In Hamrioui, Bouamra, and Lalam (2007), we presented a study of the interactions between the MAC and TCP protocols. We showed that TCP performance (notably throughput parameter) is degraded while the number of nodes increases in a MANET using IEEE 802.11 MAC as access control protocol. In Hamrioui and Lalam (2008), we proposed a solution for the problem notified in Hamrioui et al. (2007), but we were just limited to a chain topology and also to the influence of the number of nodes on the TCP performance. In Hamrioui and Lalam (2010) we studied the validity of the solutions proposed previously with several routing and transport protocols and also with different static topologies. The results showed that the proposed solutions are not only influenced by the change of the network topology but also by the routing and the used transport protocols.
Key Terms in this Chapter
TCP Protocol: Is the The transport protocol used in most IP networks and recently in MANETs.
Mobility: The moving of the nodes in the network according to a given speed. It is used as second parameter to improve the interactions between the studied protocols.
Throughput: is given Given by the ratio of the received data, taking into account all data sent.
Interactions between Protocols: The exchange of data and information between the protocols belonging to different layers of the OSI model.
End-to-End Delay: Is given by the ratio of the time when the data is received minus the data transmission time divided by the number of data packets received.
Performance Evaluation: The goal of this process is to validate the proposed solutions by simulation using the networks simulator (NS).
Mobile Ad Hoc Network (MANET): Is a complex distributed system which that consists of wireless mobile or static nodes. These nodes can freely and dynamically self-organize.
Incidences of the Improvement: The impacts which that can have the proposed improvements for the interactions between protocols on the performance of the MANET.
Number of Nodes: The number of nodes belonging to the MANET. It is used as first parameter to improve the interactions between the studied protocols.
MAC Protocols: Is based on the Backoff algorithm that allows it to determine which node will access to the wireless medium in order to avoid collisions.
Transport Protocols: Transport services, which includes the lower-level data link protocol that moves packets from one node to another.
IEEE 802.11 Protocol: The IEEE protocol for wireless technology used in a wireless local area network.
Routing Protocols: Specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network.