Wireless Ad Hoc and Sensor Networks

158 Wireless Ad Hoc and Sensor NetworksUsually, the target delay is specified as a percentage of the total transfertime. Using Equation 4.18 through Equation 4.20, the additional bandwidthrequired in the next measurement interval to satisfy the accumulatedtraffic, CLR, and delay constraints is given by⎛ ∆fˆ( x ( k )), Actual Cell losses ⎞ xk ( )∆Bw( k) = max⎝⎜ T TCLR*T ⎠⎟ + τ(4.21)where ∆ˆ( f x ( k )) = f ˆ( x( k)) − f ˆ( x( k−1))is the traffic accumulated in the measurementinterval. The bandwidth required at the next measurementinterval for all the existing sources is given byBw( k + 1) = Bw( k) + ∆Bw( k)(4.22)where Bw( k + 1), Bw( k)represents the bandwidth at the time instant k + 1and k, respectively. Equation 4.22 dictates that the bandwidth be assignedto the sources that are sending traffic to the ingress node/switch providedthe link bandwidth at the ingress switch meets the maximum availablecapacity requirement. If Bw(k + 1) exceeds S max , the maximum capacity ofthe outgoing link, the available bandwidth is set to S max . Otherwise, thebandwidth is calculated by using Equation 4.22.In the literature, in order to minimize short-term losses, the bandwidthsof all the sources are adjusted using an ad hoc factor chosen a priori andthe algorithm is referred to as the overallocation algorithm. Here, the factor( 08 . < ρ < 1) is chosen by trial and error and the bandwidth required isBWcalculated as ( k ) instead of BW( k)at the time instant k. If the overallocationfactor is not chosen carefully, bandwidth will be wasted. Inρthe literature, the PBR/PCR is used to reserve bandwidth for voiceand video traffic to minimize delays and packet losses as they arecategorized as real-time sources. However, assigning the bandwidthat PBR/PCR for a given source results in wastage of bandwidth andavailable resources, lowering the network utilization because PBR maynot provide a good indicator of the arrival rate of the sources. In orderto show the superiority of our scheme over the PCR and over allocationschemes, our proposed online bandwidth estimation scheme is comparedwith others.For the case of single source sending traffic onto a network switch, thebandwidth required for the next measurement interval is calculated byusing Equation 4.22. On the other hand, if multiple sources belonging toa particular class of traffic are sending traffic at the ingress node/switch,the bandwidth at the outgoing link has to be shared fairly among thesources. This problem is termed in the literature as bandwidth assignment,