The Research And Implementation Of Reliable Multicast Protocol In The Wireless Multi-Hop Networks

Recently,both wired and wireless network use UDP in the transport layer,but UDP can not cope with the problems of packet loss or network congestion.As a result,it provides little guarantee for the transport reliability.To deal with such problems,research concerning Reliable Multicast Transport protocols is catching more and more attention.There are some common means of achieving reliable multicast,such as response control,congestion control,error detection and recovery.There are some protocols for Reliable Multicast Transport applying to the wireless multihop network,one of which is NORM.NORM is proposed by reaearchers of RMT belonging to IETF in 2009.This prorocol puts mechanisms into practice,like FEC for transport,NACK response and recovery,congestion control,but it has poor adaptability of link dynamic characteristics in the wireless multi-hop network.Based on the NORM protocol,this paper has completed FEC coding blocks to transmit adaptively and fixing through levels.The detailed work is described as folows:Firstly,the paper analyses the operation mechanism of NORM protocol and finds some defects while applying it in the wireless multihop network.The NORM protocol uses combine FEC with NACK to cope with the probles of random packet loss and congestion control mechanism to limit the sending rate for the source,so as to reduce the congestion of the network.But the pre-fixed redundancy for transport may waste the bandwith for transport and the receivers may not finish decoding.So this mechanism isn't sutiable for the dynamic of wireless network.Besides,NORM only use the source to recover the packet loss,it will bring about problesm of leap for the transmission delay and greate burden for the source when there are quite a few receiving nodes or the hop count is too long.Secondly,to sovle the problems above,this paper designs and implements the NORM-adv protocol.The protocol adapts the mechanism of FEC conding block to transmit adaptively,combing PFEC(proactive FEC)and RFEC(reactive FEC)transmission together.This mechanism will calculate the loss probability for the whole multicast network,and the numbers of RFEC segemnts of this period as PFEC segments for the next period,so as to reduce the numbers of NACK messages and improve the throughout rate for the data in the network.In addition,this passage also designs an algorithm indepent of routing protocols in the undrlying network,which makes full use of data cached by the upper group members distributed in the multicast tree and the group members will send request to their upper group members until the source when they find it impossible to meet the NACK requests they received.At last,we developed protocol software NORM-adv based on the linux operating system and builded wireless multihop multicast network in the real world,and we have made an expriment on FEC coding blocks to transmit adaptively.In the passage,we describe the platform,tools and method for testing used in the expriment in detail.The result shows that NORM-adv can adjust the numbers of the fixing packages according to the network condition.In both one hop and multihop condition,NORM-adv with mechanism of transmiting adaptively has achieved better throughput of useful data and the rate of useful data in the whole data than NORM protocol with fixed redundancy.