Analysis of AIMD protocols over paths with variable delay

Abstract

Abstract-The throughput of AIMD protocols in general and of TCP in particular, has been computed in many existing works by modeling the round-trip time as a constant and thus replacing the round-trip time by its expectation. There are however many scenarios in which the delays of packets vary, causing a variation of the round-trip time. Many typical scenarios occur in wireless and mobile networks. We propose in this paper an analytical model that accounts for the variability of delay, while computing the throughput of an AIMD protocol. We derive a closed-form expression for the throughput, that illustrates the impact of the variability of delay. We show by analysis and simulation, that an increase in the variability of delay improves the performance of an AIMD protocol. Thus, an analytical model that only considers the average delay could underestimate the performance of an AIMD protocol in scenarios where delay is variable.

An Accurate Link Model and Its Application to Stability Analysis of FAST TCP

“…This agrees with the description in the previous discussion as well as in the model (2). Moreover, the dynamics will be more distinguishable with increasing heterogeneity among the sources and cross traffic as in (1).…”

“…The solid gray line in Figure 1 shows the queue size when the system is simulated in NS-2. The black dashed, dotted and solid lines show the integrator model (1), the static model (2) and the joint model (3) static and the joint models is excellent (neglecting packet level "noise"); they are identical in this scenario. This suggests that the true dynamics in this case is indeed a pure delay.…”

“…Most existing literature on window based congestion control, see [2], [4], [11], [16], [17], [29], assumes that the sending rate is proportional to the window size divided by the round trip delay and may further model the queue as a simple integrator, integrating the excess rate at the link, i.e., Integrator link model:…”

“…To understand the difference between (and the accuracy of) the integrator model (1) and the static model (2), the key is to examine cases where flows have heterogeneous round trip delays or where non-window-based cross traffic such as UDP exist. Consider the case of N flows sending over the bottleneck link with constant window sizes, and consider the response to a change in window size by a system initially in equilibrium.…”

TCP-aware resource allocation in CDMA networks

“…References [1] and [12] modeled TCP in the presence of variable round trip times and packet losses on wireless links. However, they assume that the variability is independent of TCP dynamics which is at odds with the environment considered here as well as the commercial environment studied in [24].…”