SCTP-based Concurrent Multipath Transfer in the Contexts of Multihop Wireless Networks and TCP-friendliness PDF Download

Author: Ilknur Aydin
Publisher:
ISBN: 9781124240435
Category : Stream Control Transmission Protocol (Computer network protocol)
Languages : en
Pages :

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Book Description
A multihome-capable transport layer protocol allows an application to transmit data via multiple (disjoint) paths simultaneously, a scheme termed concurrent multipath transfer (CMT). SCTP is an IETF-standardized transport layer protocol with built-in multihoming capability. In prior work, a CMT protocol using SCTP multihoming (termed SCTP-based CMT) was proposed and investigated for improving application throughput in wired networks. In that effort, SCTP-based CMT was studied in (bottleneck-independent) wired networking scenarios with ns-2 simulations. This dissertation studies SCTP-based CMT in two specific contexts using QualNet simulations: (i) CMT over Multihop Wireless Networks (MWNs), and (ii) TCP-friendliness of CMT in the Internet. CMT over MWNs: Given the recent advances in multiple-radio nodes, multichannel radios, and multi-path routing, more multihomed nodes are deployed in the wireless networks. This trend motivated us to study two specific issues in the context of CMT over MWNs. The first issue concerns the performance of CMT over MWNs, where we studied how the contention-induced losses and the wireless channel characteristics impact the performance of CMT. We found that similar to the wired cases, CMT over MWNs showed better performance than one single-homed SCTP association and even the ideal AppStripe application, when the receiver buffer (rBuf) was unconstrained. For the cases of constrained rBuf, we showed that considering the bandwidth limitations of multihop wireless networks compared to their wired counterparts, rBuf sizes bigger than 128 KB can be sufficiently enough not to restrain the CMT performance. Overall, we concluded that applications will benefit from using CMT in the MWNs context when they have sufficiently large rBuf. The second issue concerns the acknowledgment (ACK) mechanism of CMT, where we investigated different design choices for the ACK mechanism of CMT in MWN to mitigate the effects of contention-induced losses in the multihop wireless channels among data and ACK traffic. According to the ACK policy of the original CMT, an ACK packet is sent to the path where the latest DATA packet arrives from. Therefore, a CMT receiver may send ACKs packets to any one of the (return) paths. In this dissertation, we surveyed historical developments of the TCP-friendliness concept and argued that the original TCP-friendliness doctrine should be extended to incorporate multihoming and SCTP-based CMT. Since CMT is based on (single-homed) SCTP, as a first step, we investigated TCP-friendliness of single-homed SCTP. We discovered that although SCTP's congestion control mechanisms were intended to be "similar" to TCP's, being a newer protocol, SCTP specification has some of the proposed TCP enhancements already incorporated which results in SCTP performing better than TCP. Therefore, SCTP can obtain larger share of the bandwidth when competing with a TCP flavor that does not have similar enhancements. We concluded that SCTP is TCP-friendly but achieves higher throughput than TCP, due to SCTP's better loss recovery mechanisms just as TCPSACK or TCP-Reno performs better than TCP-Tahoe. Then, we designed an experimental framework to investigate the TCP-friendliness of CMT according to the traditional doctrine of TCP-friendliness. Via QualNet simulations, we measured the sending rate of one two-homed CMT flow (containing two CMT subflows) and two SCTP flows and the impact of CMT and two SCTP flows on the other TCP flows in the network while sharing a tight link. We found out that one two-homed CMT association has similar or worse performance (for smaller number of competing TCP flows) than the aggregated performance of two independent, single-homed SCTP associations while sharing the link with other TCP connections, for the reason that a CMT flow creates a burstier data traffic than independent SCTP flows. When compared to the aggregated performance of two-independent TCP connections, one two-homed CMT obtains higher share of the tight link bandwidth because of better loss recovery mechanisms in CMT (as CMT inherits all the built-in TCP enhancements in SCTP). (Abstract shortened by UMI.).