Wireless networks such as Bluetooth, WLAN and WiMax have transformed the way we access information and communicate seamlessly whether we are at home, in the office, or on the move on a train, bus or even aircraft. As mobile and embedded computing devices become more omnipresent, it will become increasingly difficult to interconnect them via wires and single-hop wireless links limited by radio transmission range. This has given rise to mobile ad hoc networks (MANET) where far away nodes communicate by requesting intermediate nodes to relay their information in order to reach the destination. MANETs self-organize, self-configure and self-heal themselves. MANETs are being used in many applications ranging from emergency response situations to wireless vehicular ad hoc networks. Many applications of MANETs such as Emergency Response and First Responders have strict Quality of Service (QoS) requirements for their communications systems, making MANET QoS provisioning mechanisms very crucial for supporting multimedia communications such as real-time audio and video. However, QoS provisioning in MANETs is quite tough in comparison to QoS provisioning in wireline IP networks. This is due to numerous reasons such as the dynamic network topology, unpredictable communication medium and limited battery power of mobile devices forming the network. This chapter describes the challenges and the current state of the art of QoS protocols and mechanisms in MANETs.
TopIntroduction
Only “best effort” communication services existed in the Internet in its early design, treating every kind of data traffic as equal and not having any provision for Quality of Service (QoS) support. In recent years, many real-time multimedia communication applications such as Voice over Internet Protocol (VoIP) and Video on Demand (VoD) have gained popularity. Such applications require stringent QoS requirements in terms of delay, jitter and throughput. Many QoS models have been developed to support the required communication QoS over the Internet. In order to satisfy the QoS requirements, the communication network has to meet certain QoS bounds such as delay, jitter, throughput and packet loss for a data flow (Crawley, 1998).
Wireless Networks have grown to be ever more popular in the recent years, creating the requirement for supporting real-time multimedia communication applications on highly mobile network environments. Within the wireless networks domain, Mobile Ad hoc networks (MANET) have received a lot of interest and numerous deployments. MANETs (Perkins, 2001) are formed by a collection of mobile nodes, such as PDAs and laptops; using wireless connections amongst the nodes in the network, without using any pre-existing wired or wireless network infrastructure, such as WLAN access points. Computing devices in MANET communicate with each other using wireless medium and route of data in a multi-hop fashion, if the wireless nodes are not within direct wireless transmission range of each other as shown in Figure 1.
Figure 1. Example of an ad hoc network
There are many applications of mobile ad hoc networking technology such as Satellite multi-hop networks (Vladimirova, 2008; Shen, 2004) as shown in Figure 2, public safety applications (Miller, 2005), planetary surface exploration (Alena, 2005), inter-planetary networks (Sekhar, 2004), intelligent transportation systems (Toh, 2007), metropolitan ad hoc networks (Conti, 2003), building automation (Reinisch, 2007) as well as providing connectivity to remote and inaccessible places (Wolff, 2005).
Figure 2 Multi-hop routing in satellite networks
MANETs have many advantages; they can be set-up very fast, they do not require any pre-existing network infrastructure such as wiring or base stations etc. MANETs can also configure and organize themselves without requiring any manual intervention, for example when new nodes join or leave the network or when two MANETs merge together. Furthermore, due to the mesh topology of MANETs, if a path breaks due to node mobility or battery exhaustion, alternate redundant paths can be discovered quickly. Having shorter wireless transmissions also increases the opportunity for frequency re-use.
In spite of the numerous advantages offered by MANET, there are still many challenges when it comes to supporting Quality of Service (QoS) on MANETs in comparison to supporting QoS in static wired networks due to many reasons as described in Section 3. Although initially most of the research on MANETs was focussed primarily on routing (Perkins, 1994; Perkins, 1999) and medium access control (Karn, 1990; Fullmer, 1995; Deng, 1998; & Tzamaloukas, 2001), in the past couple of years there has been an increased interest in QoS provisioning for MANETs with the aim to support real-time communication services such as voice and video (Ahn, 2002; Badis, 2006; Calafate, 2006; Reddy, 2007; Marwaha, 2008).
Many QoS protocols have been developed for MANETs and newer mechanisms are constantly being proposed. This chapter presents some of the important mechanisms and protocols for supporting QoS in MANETs. These range from QoS provisioning models to MANET QoS routing, signalling, admission control and MAC, as shown in Figure 3.