Performance of TCP over MANETS
Transmission Control protocol (TCP) is the widely used transmission protocol across the data services like file transfer and internet and thus its usage is spread towards MANETs as well. In general there could be multiple TCP connections over mobile adhoc networks and thus evaluating the performance of TCP is really a tedious job in case of multiple connections. In general performance of MANET depends on few attributes like scalability, traffic load and mobility. Extensive research has been done towards the performance of MANETs across the Constant Bit Rate (CBR) against file transfer protocol (FTP), TCP and User datagram protocol (UDP).
Scalability of the routing protocols across MANETs purely depends on the attributes as mentioned above. In most of the case TCP in the current form can’t support the MANETs in case of route failures and in terms of congestion control methodologies. There are many existing techniques which discuss the performance of TCP over MANETs, but still it is proved to be hard nut to crack and there is lot of research being done towards the performance of TCP across the mobile adhoc networks.
Performance of TCP can be improved in case of route failures by a feedback mechanism known as TCP-Feedback or TCP-F, where the intermediate node detects the link or route failures and sends a notification message known as Route Failure Notification (RFN) to the actual TCP source. Once the TCP senders receive this RFN notification, it quits sending the required packets and blocks the complete communication process. Now if the intermediate node is able to discover the path to destination, it immediately sends the Route Re-establishment notification (RRN) to the TCP senders and thus now the source will reactivate the state and continue with the data transmission process. Thus from this discussion it is clear that, the actual TCP throughput is completely related to the average repair time taken towards the link or route failures across the MANETs.
One more notification methodology was introduced later known as Explicit Link Failure Notification (ELFN) to improve the performance of TCP over mobile adhoc networks and is as discussed. Whenever an intermediate node intimates the TCP sender regarding the link failure, TCP sender will freeze its state along with the transmission window and the timer set. In this case the use of route re-establishment is not done; instead the TCP sender will constantly sends the packets and checks for the availability of route across the MANETs. Across many simulations using NS2 and OPNET, ELFN is proved to be the best notification procedure than RFN and can be considered as the better choice to improve the performance of TCP over MANETS.
In general TCP provides end-to-end data delivery across the wired networks and proved to be an efficient means of data transmission but it abruptly fails in case of wireless networks like MANETs and this is mainly due to the reason that TCP can’t work in few conditions like packet loss or delay, where in a general MANET packet delivery delay and packet losses are simply encouraged.
This paper is written and submitted by Sujana Priya V.