Wireless Ad Hoc and Sensor Networks

80 Wireless Ad Hoc and Sensor NetworksWe derive design rules mathematically for selecting the parameters ofthe NN algorithm such that the desired performance is guaranteed duringcongestion, and potential trade-offs are shown. Simulation results areprovided to justify the theoretical conclusions. The nonlinear-systemtheory-basedmethodology can be readily applied to designing routingalgorithms, transmission-link bandwidth estimation and allocation, and soon. An ATM network uses hop-by-hop feedback whereas the Internet usesan end-to-end network. First, we present the issue of congestion control forATM networks and then end-to-end congestion control for the Internet.3.1 ATM Network Congestion ControlATM is a key technology for integrating broad-band multimedia services(B-ISDN) in heterogeneous networks, where data, video, and voicesources transmit information. ATM provides services to these sources withdifferent traffic characteristics, by statistically multiplexing cells in termsof fixed length packets of 53 bytes long. The uncertainties of broadbandtraffic patterns, unpredictable statistical fluctuations of traffic flows, andself-similarity of network traffic can cause congestion in the networkswitches, concentrators, and communication links.The ATM forum has specified several service categories in relation totraffic management in an ATM network. Two major classes, guaranteedservice and best-effort service, resulted from the service categories (Kellyet al. 2000). The best-effort service category is further divided into twosubclasses, namely, unspecified bit-rate (UBR) and ABR. The UBR sourceneither specifies nor receives a bandwidth, delay, or loss guarantee. Incontrast, the ABR service type guarantees a zero-loss cell rate if the sourceobeys the dynamically varying traffic management signals from the network.The network uses resource management (RM) cells to inform theABR source about the available bandwidth. If the source obeys thesesignals, it is guaranteed zero loss.In a B-ISDN, the traffic and congestion controls describe differentaspects of ATM operation. Congestion is defined as a condition of an ATMnetwork, where the network does not meet a stated performance objective.By contrast, a traffic control, such as the connection admission control(CAC), defines a set of actions taken by the network to avoid congestion.Because of the uncertainty in the traffic flows of multimedia services,network congestion may still occur, despite the fact that an appropriateconnection admission control scheme is provided. To prevent the QoSfrom severely degrading during short-term congestion, a suitable congestioncontrol scheme is required.