Abstract
Mobile communication networks have become an integral part of our society, significantly enhancing communication capabilities. Mobile ad hoc networks (MANETs) extend this capability to any time/anywhere communication, providing connectivity without the need of an underlying infrastructure. The new coming realm of mobile ad hoc networks is first investigated, focusing on research problems related to the design and development of routing protocols, both from a formal and technical point of view. Then link stability in a high mobility environment is examined, and a route discovery mechanism is analyzed, together with a practical implementation of a routing protocol in ad hoc multi-rate environments which privileges link stability instead of traditional speed and minimum distance approaches.
TopIntroduction
Mobile ad hoc networks consist of interconnected mobile hosts with routing capabilities. Considerable work has been done in the development of routing protocols for ad hoc networks, starting from Internet protocols developed in the seventies. In recent years, the interest in ad hoc networks has grown due to the availability of wireless communication devices.
New research directions in theoretical computer science and in particular in protocol design make use of game-theory concepts and tools. From this “perspective”, protocols are viewed as games with players represented by network nodes which “play” (participate in) the game; each node (agent) has its own utility function, such as network flow (to be maximized) or energy consumption (to be minimized.) This approach thus is a natural point-of-view of a distributed computing architecture, the most interesting paradigm in actual computer science.
This is especially true since the advent of wireless networks based on IEEE 802.11 Protocol (IEEE, 1999, 2003) (and in particular with the definition of the new draft “n”) where it is possible to deal with a variable-speed link going from 1 to about 300 Mbps (Fan, 2004). Besides, considering that mobile networks (see Mobile landscape, 2009) have the peculiarity of movement (which makes the link speed highly variable and therefore very unstable), stability of routes becomes a difficult undertaking.
Furthermore, as for its intrinsic nature, the same protocol IEEE 802.11 introduces a considerable network overhead to control the transmission at the expense of throughput. So we think that choosing a stable routing – mainly considering stable links – is preferable to taking into account only the link speed and/or length.
Key Terms in this Chapter
Link Stability: transmission error rates (due to signal weakness or external environment factors such as white noise and wireless interference) can result in an unstable link. A link is stable if it has a low signal variation frequency with a minimum acceptable signal intensity.
Wireless: the term covers communication systems between electronic devices, which do not use cables (traditional cabled systems are called wired ). Generally, the wireless uses radio waves at typically low power, but also infrared radiation or laser.
Protocol: a set of rules formally described, defined in order to facilitate communication between one or more entities (network protocol, in case of remotely connected entities). All these rules are defined by specific standards (see ISO/OSI), of many different types, depending on the entities and communication means involved.
Route Discovery: a request to find the best available route to the destination, when sending a message.
Network: a system that allows the sharing of information and resources (both hardware and software) among several devices (hosts), providing an information transport service to a user population distributed over a more or less extensive area. Computer networks generate potentially high volume traffic, unlike the telephone, efficiently managed through the technology of packet switching.
Link: a hardware connection linking two or more electronic devices, normally using different types of cables each designed for a certain standard of data transmission. In addition to the electric cable is also possible to make a connection through fiber optics, radio waves and infrared (IrDA).
MANET: (Mobile Ad hoc NETwork): an independent system of mobile devices connected by ad hoc wireless links. All nodes in the system cooperate in order to correctly route packets in multihop forwarding mode. Due to the unpredictable mobility of nodes, the network topology may change constantly. Ad hoc networks are built and used as appropriate in extremely dynamic environments, not necessarily with the help of an already existing infrastructure, such as after natural disasters, military conflicts or during emergencies.
Routing: in packet-switching networks, routing is the function of a device (router) that decides the best path along which to send a received packet. Each packet is forwarded from the source to a router, and from this to the next, until reaching the desired destination. The router often uses a table with destination network addresses to decide where to send each packet. The format of this table and the way it is populated and possibly updated are specific to the different routing protocols adopted.
Multi-Rate: a transmission system in which speed (rate) can vary from point to point. The use of different sampling rates within the same system offers several advantages such as lower computational complexity, adequate transmission rate and less memory capacity requirements.