tailieunhanh - Mobile Ad Hoc Networks Applications Part 13

Tham khảo tài liệu 'mobile ad hoc networks applications part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TCP-MAC Interaction in Multi-hop Ad-hoc Networks 411 collision _ probi t 1 - non _collision _ probit 2 It should be noted that all the calculated values are considered for the data packets and the transmission of RTC CTS control frames is not taken into account. The pseudo-code depicted in Fig. 4 describes the whole process at one node. collision_prob 0 transmitted_pkts 0 retransmitted_pkts 0 1. for each data packet Packet is received at a node 2. if 1st node of the path 3. non_collision_prob t l 4. else 5. noncollisionprob is read from the packet header 6. collision_prob retransmitted_pkts transmitted_pkts 7. non_collision_probtot non_collision_probitc1t l-collision_probi 8. end if 9. if last node of the path 10. collision_prob t l-non_collision_prob ot 11. end if 12. if retransmitted packet 13. retransmitted_pktSj 14. end if 15. transmitted-pktSj 16. end for Fig. 4. Packet processing at a single node to collect the collision probability Delaying window strategy The ACK processing in TCP-MDA is dependent on the calculated collision probability total_collision_prob in different channel traffics. Withholding ACK responses is done by maintaining a dynamic delaying window dwin at TCP receiver to define the number of data packets that would arrive before generating an ACK. Like TCP-DAA dwin size is initialized to one and it is gradually enlarged to its limit of 4 data packets. When the achieved total_collision_prob from MAC layer is less than a threshold collision_ thresh the channel is considered in the good condition and dwin is incremented by one for every received data packets. This means that dwin would become 4 faster and the receiver would generate less ACKs. It would be advantageous then to keep dwin at 4 as long as the channel is stable. When facing losses however dwin should be reduced due to the fact that during these periods the channel may have less packets than 4 in flight to trigger the fast retransmit mechanism at the sender. As a result the channel