This paper discusses the use of Explicit Congestion Notification (ECN) mechanisms in the TCP/IP protocol. The first part proposes new guidelines for TCP’s response to ECN mechanisms (e.g., Source Quench packets, ECN fields in packet headers). Next, using simulations, we explore the benefits and drawbacks of ECN in TCP/IP networks. Our simulations use RED gateways modified to set an ECN bit in the IP packet header as an indication of congestion, with Reno-style TCP modified to respond to ECN as well as to packet drops as indications of congestion. The simulations show that one advantage of ECN mechanisms is in avoiding unnecessary packet drops, and therefore avoiding unnecessary delay for packets from low-bandwidth delay-sensitive TCP connections. A second advantage of ECN mechanisms is in networks (generally LANs) where the effectiveness of TCP retransmit timers is limited by the coarse granularity of the TCP clock. The paper also discusses some implementation issues concerning specific ECN mechanisms in TCP/IP networks.

Performance evaluation of TCP over ATM has been the focus of much research recently. A number of studies have analysed observed performance degradation, suggested ways to improve throughput, compared the performance of ABR and UBR as suitable class of ATM service in transporting TCP traffic. With this explosion of studies exploring various combinations of scenarios (LANs versus WANs, backbone ATM versus native ATM to mention few), there is a need for a framework for a coherent formulation of the design space and analysis of the results. The aim of this paper is to characterise the major research issues and draw upon the published work to illustrate some of the proposed solutions. The aim is to move towards a framework for building a taxonomy, and this paper is the first step towards achieving this. The characterisation of the performance evaluation of TCP over ATM is undertaken by identifying and evaluating the research problems, the experimental designs to address the prob...

Key issues in the current development of Internet seem to be its capability to scale and to support new real-time or near realtime applications like video- and audio conferencing. There are two factors that affect these qualities: one is the ability to distinguish which connections should be switched and the other is the effective control over network resources. ATM is a serious attempt to standardize global multiservice networks. This attempt seems to suit well for the future Internet. ATM was originally meant to be an easy and an efficient protocol but it is now turning to be `yet another ISDN'. More and more features are implemented to ATM resulting in the overloading of the network with management procedures. Therefore a new approach needs to be taken. In this approach a strong reminder of `what is necessary' needs to be kept in mind. This paper presents an alternative, simpler approach to the ATM traffic management and introduces some suggestions how to map Internet applications to simplified ATM environment using an advanced IP switching concept.

To evaluate the provision of data service support in ATM networks, complex interactions between different protocol layers have to be considered. These interactions are originated by concurrent operation of flow control mechanisms at several layers. In this paper, we propose a new modelling approach for performance evaluation of these kind of systems. The proposal is based on a modular and object-oriented SDL description. Using this approach, a generic ATM network model is described. Finally, a simulation model is built to illustrate its use. The study case shows a comparison between ABR vs. UBR supporting bursty data traffic carried over TCP. Our conclusion is that detailed modelling of all the relevant mechanisms operating at several layers is necessary to significantly evaluate the performance of data service support in ATM networks.