Wireless Ad Hoc and Sensor Networks

322 Wireless Ad Hoc and Sensor NetworksTheorem 7.3.4 and Theorem 7.3.5 can be used to determine delay guaranteeseven when a node has flows with different priorities and servicesthem in the priority order.THEOREM 7.3.6The end-to-end delay denoted byTEEDj( Pf), is given by( ) +mjEED ( jf )= ∑ jdi( f )− ai( f f j), , ,i=1T P T P T P ,φ Tprop ( Pjf )(7.81)jjwhere Tdi, ( Pf) and Tai, ( Pf, φ f,j)are the departure time and expected arrivaljtime of packet P f at hop i in the multihop network. T prop is the total propagationdelay experienced by the packet, from source to destination.REMARK 7As expected the end-to-end delay is a function of packet length, channeluncertainties, and backoff interval of the CSMA/CA protocol.7.3.6 Overhead AnalysisAnalysis is performed to estimate the overhead for data transmissionusing the proposed ADFS protocol. The additional overhead in ADFSprotocol is due to inclusion of the current weight value in the header fieldof the data packet. Note that the weight information is only transmittedfor the data packets but not for the request to send (RTS), clear to send(CTS) and acknowledgment (ACK) packets. For the overhead analysis,we denote the four bytes required for transmitting the weight, separatelyfrom the actual data packet. The term T x is defined as the size of the packettype x . The efficiency of the protocol is defined as the ratio of data portion(in bytes) in each data transmission to the total information transmittedincluding the control message overhead, and it is given byTdataη =T + T + T + T + Tdata weight RTS CTS ACK(7.82)The packet sizes specified in the IEEE 802.11 MAC protocol are used.The selected packet sizes are 24 bytes for RTS, 18 bytes for CTS, 20 bytesfor ACK, 6 backoff slots (each slot is set to be 5 B), 512 bytes for data, and4 bytes for weight. Then, the efficiency of the proposed ADFS protocolobtained from Equation 7.82 is around 84.2% with the additional overhead