An end-to-end freeze TCP for ad-hoc networks.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
SACK TCP, as the baseline, performs promisingly in the wireline network where major control point is of the network buffer utilization. Basically, the reactive based congestion window progression causes high network buffer utilization due to the likelihood of large bursts of data, and it deteriorates the network bandwidth utilization: the resultant end-to-end RTT inflation results in large retransmission timouts (RTOs), thus long timeouts, and reduced TCP throughput. In this thesis, we have evaluated that through a series of simulations performed in ns-2, the baseline, of such large bursts of data transfer and the resultant large RTOs, is not suited for ad hoc networks in terms of power and badwidth limitations. We investigated a receiver-oriented rate controller (rater) dominated by the resource-constraint ad hoc links, where the link availability changes not gracefully but transiently. Assuming that end clocks are both synchronized in a passive or active way and TCP takes into account the TTL field of the IP header each time when data packet is received, the forward link delay (FLD) and the current hop length give the instantaneous throughput available. Then, in order to throttle the sender congestion window by using the advertised window field, the receiver employs the congestion window delimiter that is characterized by the 802.11 MAC protocol. In addition, the transient nature of the medium availability due to medium contention proposes the freezing timer (freezer) to be equipped at the receiver-end that periodically freezes the sender in cases of heavy contention present. In this sense, two other metrics, i.e., buffer occupancy and contention factor have been introduced to perceive the degree of the buffer utilization and the medium contention, respectively, for supporting the delimiter and the freezer. Finally, an elaborate sender-end, namely ad hoc sender enhancements, was proposed for achieving the optimized behaviors of the receiver-end enhancements, as an optional deployment. It implemented an add-on probing mechanim to deal with the route disconnection problem by means that the probing backoff supersedes the RTO backoff. The combination of the schemes, i.e., delimiter + freezer + ad hoc sender enhancements, is called the ad hoc TCP. It outperformed the baseline in perspective of both throughput and, especially, goodput. The primary merit of our ad hoc TCP is that such propositions are based on solely end-to-end, so do not require the network originated feedback.