Ž. In this paper, we review the basic mechanisms used in packet networks to support Quality-of-Service QoS guarantees. We outline the various approaches that have been proposed, and discuss some of the trade-offs they involve. Specifically, the paper starts by introducing the different scheduling and buffer management mechanisms that can be used to provide service differentiation in packet networks. The aim is not to provide an exhaustive review of existing mechanisms, but instead to give the reader a perspective on the range of options available and the associated trade-off between performance, functionality, and complexity. This is then followed by a discussion on the use of such mechanisms to provide specific end-to-end performance guarantees. The emphasis of this second part is on the need for adapting mechanisms to the different environments where they are to be deployed. In particular, fine grain buffer management and scheduling mechanisms may be neither necessary nor cost effective in high speed backbones, where ‘‘aggregate’ ’ solutions are more appropriate. The paper discusses issues and possible approaches to allow coexistence of different mechanisms in delivering end-to-end

Active networking offers a change in the usual network paradigm: from passive carrier of bits to a more general computation engine. The implementation of such a change is likely to enable radical new applications that cannot be foreseen today. Large-scale deployment, however, involves significant challenges in interoperability and security. Less clear, perhaps, are the "immediate" benefits of such a paradigm shift, and how they might be used to justify migration towards active networking. In this paper, we focus on the benefits of active networking with respect to a problem that is unlikely to disappear in the near future: network congestion. In particular, we consider application-specific processing of user data within the network at congested nodes. Given an architecture in which applications can specify intra-network processing, the bandwidth allocated to each application's packets can be reduced in a manner that is tailored to the application, rather than being applied generically....

This paper analyzes two popular heuristics for ensuring packet integrity in ATM switching systems. In particular, we analyze the behavior of packet tail discarding, in order to understand how the packet level link efficiency is dependent on the rates of individual virtual circuits and the degree of the imposed overload. In addition, we study early packet discard and show that the queue capacity needed to achieve high efficiency under worst-case conditions grows with the number of virtual circuits and we determine the efficiency obtainable with more limited queue capacities. Using the insights from these analyses, extensions to early packet discard are proposed which achieve high efficiency with dramatically smaller queue capacities (independent of the number of virtual circuits). 1 Introduction ATM networks are intended to carry a mix of information streams with widely different bandwidth characteristics. At one extreme, we have continuous applications that transmit at a steady, fixe...

We propose a new transport protocol, TCP Boston, that turns ATM's 53-byte cell-oriented switching architecture into an advantage for TCP/IP. At the core of TCP Boston is the Adaptive Information Dispersal Algorithm (AIDA), an efficient encoding technique that allows for dynamic redundancy control. AIDA makes TCP/IP's performance less sensitive to cell losses, thus ensuring a graceful degradation of TCP/IP's performance when faced with congested resources. In this paper, we introduce AIDA and overview the main features of TCP Boston. We present detailed simulation results that show the superiority of our protocol when compared to other adaptations of TCP/IP over ATMs. 1.

Networked applications generate messages that are segmented into smaller, fixed or variable size packets, before they are sent through the network. In high speed networks, acknowledging individual packets is impractical, so when congestion builds up and packets have to be dropped entire messages are lost. For a message to be useful, all packets comprising it must arrive successfully at the destination. The problem is therefore which packets to discard so that as many complete messages are delivered, and that congestion is alleviated or avoided altogether.

This paper reports on a simulation study of the relative performances of the ATM ABR and UBR service categories in transporting TCP#IP #ows through an ATM Network. The objectiveistwo-fold: #i# to understand the interaction between the window - based end-to-end #owcontrol TCP and the rate based #owcontrol ABR which is restricted to the ATM part of the network, and #ii# to decide whether the greater complexity of ABR #than UBR# pays o# in better performance of ABR #than UBR#. The most important conclusion is that there does not seem to be strong evidence that for TCP#IP workloads the greater complexity of ABR pays o# in better performance. 1 Introduction The ATM Forum has #nalized a draft standard #1# for a number of service categories for transporting the cells of VCs #Virtual Circuits# through an ATM network. Among these service categories are ABR #Available Bit Rate# and UBR #Unspeci#ed Bit Rate#. Section 2 in this paper contains a quicksketchofhow these service categories work. De...

We investigate the performance of the Early Packet Discard#EPD# and the Early Selective Packet Discard#ESPD# scheme that we have previously proposed#12#. In an e#ort to reduce the complexity while maintaining goodperformance, we pick out two special cases of ESPD and compare their performance with that of EPD. For performance evaluation purposes, the e#ective throughput and fairness index was determined through a simulation study. We observed that ESPD scheme improves e#ective throughput over EPD by up to 16# with our network model. We also found that ESPD is more e#ective in alleviating TCP's unfairness among connections which have di#erent roundtrip times. A major factor causing throughput degradation of EPD was determined to be the synchronization of TCP windows. 1

We investigate packet discarding schemes for TCP over ATM with UBR service. In doing so, we tested the effective throughput of two existing schemes, Partial Packet Discard (PPD) and Early Packet Discard (EPD), as compared to the Random Cell Discard (RCD) scheme which discards any incoming cells after buffer overflow. We observed that PPD alleviates the effect of packet fragmentation so that it gets effective throughput enhancement over RCD, and EPD provides further enhancement over PPD. After closer investigation, we found that there is a sustained congestion problem other than packet fragmentation that causes the effective throughput to be degraded. We noted that sustained congestion resulted in the synchronization of TCP window expansion and shrinkage. Toprovide a solution for this problem, we propose the Early Selective Packet Discard (ESPD) policy, a strategy which makes sessions take turns in accessing network capacity by discarding packets from selected sessions rather than randomly. Our results shows that ESPD achieves throughput and fairness enhancement over EPD with only a modest increase in implementation complexity.

We address interactive voice services over Best E ort packet networks where tra c is subject to unpredictable congestions. The quality ofvoice services can be signi cantly a ected by network delay and jitter due to the rejection of late packets. LIFO has proven to be an interesting overload strategy in delay constrained systems. We propose the use of the LIFO discipline in the context of congested packet networks where voice packets are subject to delay bounds. We analyze how delay accumulates in congested queues and show that serving voice packets in LIFO improves user-level quality. An extensive simulation study shows that LIFO scheduling in congested nodes signi cantly reduces the fraction of late packets compared to the FIFO discipline. The enhancement of user-level quality is emphasized by using the ITU-T P.861 standard for perceptual evaluations of reconstructed voice. Finally, weshowhow the proposed mechanism can be easily used in the Internet.

Previous papers have described and evaluated the performance of packet discard techniques for maintaining packet integrity during overload in ATM switches but without taking into account di erent classes of service. In this paper a packet discard scheme is proposed with the goal to provide incoming ows of cells with output link bandwidth depending on the class of service they belong to. Also good performance in terms of throughput and fairness in bandwidth sharing among equal priority ows are considered as the requirements to meet. In the scenarios here considered, the proposed discard scheme is shown to provide very good results and to represent a possible solution for dealing with the most demanding data ows during congestion intervals. Numerical results are reported and discussed for di erent operating conditions and tra c patterns. 1