ADAPTIVE SIMULTANEOUS MULTIPATH TRANSMISSION SCHEMES

Abstract

The increase in the availability of multimode devices for ubiquitous network ac- cess and the need for larger bandwidth create thrust for utilization of simultaneous network connections. Unfortunately, the standard transport layer protocols like the transmission control protocol (TCP) and user datagram protocol (UDP) have architectural constraints due to which an Internet application can use only one interface at a time. The stream control transmission protocol (SCTP) provides support for concurrent multipath transfer (SCTP-CMT). Aggregated performance is analyzed with a number of experiments to measure the aggregated throughput of SCTP-CMT by using a very popular network simulator, NS-2. It is observed that the aggregated throughput is about 20% of the available aggregated band- width. The signi cant reduction in the aggregated throughput demands a careful scrutinization of its reasons. After carefully analyzing and carrying out some further experiments, it is di- agnosed that non-di erentiation of missing packets into intra and inter-path, usage of traditional congestion window management for these missing packets and using static fast retransmit threshold which is independent of available receiver bu er space, are the main reasons for the aggregated throughput degradation. Simulta- neous multipath transmission (SMT) schemes are proposed to handle the above mentioned issues with the intention to increase aggregated throughput by avoid- ing Rbuf blocking problem and e cient utilization of available Rbuf space. SMT- modi ed fast retransmit (SMT-MFR) and SMT-adaptive modi ed fast retransmit (SMT-AMFR) schemes are formulated for SCTP. To analyze the SMT-MFR in realistic network environments, a number of simulation scenarios are carried out. The initial results revealed that SMT-MFR has overcome Rbuf blocking with im- provement in aggregated throughput ranging from 164% to 72.4% (from normal to worst scenario respectively). SMT- MFR is composed of two sender side modules, i.e., inter-path missing packet di erentiation (IMPD) and multihomed congestion control (MCC). The IMPD module di erentiates the missing packets according to its cause of missing such as, packet missing due to network congestion or due to multiple path e ects. The MCC mechanism triggers the fast retransmit event with respect to the cause of the missing packet. The SMT-MFR has successfully over- come the Rbuf blocking problem, abnormal congestion window (cwnd) reduction and has improved the aggregated throughput.