But this presumption of congestion by sender TCP while using constant threshold technique is not an impeccable procedure and may cause several problems. The TCP design vehemently relies on in-order packet delivery despite the fact that the reordering process is quite possible in the network. The static nature of segment retransmission totally undermines the possibility of delay in the network which have result late delivery of the packet which has actually been assumed as a lost packet. The lack of dynamicity in the behavior of the protocol may cause unnecessary retransmission and rate reduction as well further improvement in the technology involving routing algorithms, network components and link-layer retransmission mechanisms.
The solution proposed by this paper provides a set of modifications at sender level applying Non-congestion Robustness (NCR) to TCP. The ACK based system is modified to selective ACK i.e., SACK. This SACK based segment recovery technique while getting out of in-order segment transmission strategy, will inform the sender about all segment that have been received and hence the sender will have to retransmit only those segments which have actually been lost. The TCP-NCR withdraws the TCP from ACKs based retransmission technique to congestion window (cwnd) of data that has left the network. ...Show more