Formal modelling of TCP congestion control mechanisms ECN/RED and SAP-LAW in the presence of UDP traffic

Mazhar H Malik,Muhammad N Khan,Mubasher H Malik,Mohsin Jamil

doi:10.1186/s13638-016-0646-9

Abstract

Congestion avoidance mechanisms are used to prevent the saturation of the gateway which represents a bottleneck of the system. Recently, a new method for the congestion avoidance has been proposed: the smart access point with limited advertised window (SAP-LAW). The main idea is to hijack at the gateway the acknowledge packets in the transmission control protocol (TCP) connections in order to artificially reduce the advertised destination window according to some bandwidth allocation policy. Therefore, the flux control mechanism is artificially exploited to control the congestion at the bottleneck. The advantage of this approach is that it does not drop any packet and does not require any modification in the TCP implementations at the clients. While the most popular congestion avoidance mechanisms are the explicit congestion notification (ECN) and the random early detection (RED). In this paper, we propose stochastic models for the ECN/RED and SAP-LAW mechanisms in order to compare their performances under different scenarios. The models are studied in mean field regime, i.e. under a great number of TCP connections and UDP-based transmissions. Different from previous work for the ECN/RED, in this paper, we consider the presence of UDP traffic with bursts and the case of not greedy TCP connections. The models for SAP-LAW are totally new. The comparison is performed in terms of different performance indices including average queue length, system throughput, and expected waiting time.

Highlights

The wide use of Internet connectivity in modern communication networks has made the analysis of protocols designed to share one gateway among many devices more and more important
6.1 Greedy transmission control protocol (TCP) connections and smooth user datagram protocol (UDP) traffic we study the models for explicit congestion notification (ECN)/random early detection (RED) and smart access point with limited advertised window (SAP-LAW) under the scenario of greedy TCP connections, i.e. they tend to use all the size of their sending windows, and smooth UDP traffic
7 Conclusions In this paper, we have compared the performances of two mechanisms for the congestion control at a shared gateway in a TCP/IP-based network: the ECN/RED and the SAP-LAW

Summary

Introduction

The wide use of Internet connectivity in modern communication networks has made the analysis of protocols designed to share one gateway among many devices more and more important. The contributions of this paper are the extension of the mean field model presented in [14] in order to encompass the presence of UDP traffic and the introduction of a totally new model to analyse the SAP-LAW congestion mechanism Another novelty is the relaxation of the common assumption [6, 13, 14] that TCP connections are greedy, i.e. they always have packets to send so that the sender window is always completely used at each time slot. We will study models that allows TCP connections to send a geometrically distributed random number of packets and finish their life cycle We use these models to compare the performances of ECN/RED and SAP-LAW with presence of UDP traffic. Where UDPtraffic(t) is the amount of bandwidth occupied by the real-time applications at time t, C is the capacity of the bottleneck link, and #TCPflows(t) is the number of TCP connections at time t

Theoretical background

Modelling SAP-LAW with UDP and temporary TCP

Conclusions