The congestion control mechanisms of TCP make it vulnerable in an environment where flows with different congestionsensitivity compete for scarce resources. With the increasing amount of unresponsive UDP traffic in today's Internet, new mechanisms are needed to enforce fairness in the core of the network. We propose a scalable Diffserv-like architecture, where flows with different characteristics are classified into separate service queues at the routers. Such class-based isolation provides protection so that flows with different characteristics do not negatively impact one another. In this study, we examine different aspects of UDP and TCP interaction and possible gains from segregating UDP and TCP into different classes. We also investigate the utility of further segregating TCP flows into two classes, which are class of short and class of long flows. Results are obtained analytically for both Tail-drop and Random Early Drop (RED) routers. Class-based isolation have the following salient features: (1) better fairness, (2) improved predictability for all kinds of flows, (3) lower transmission delay for delay-sensitive flows, and (4) better control over Quality of Service (QoS) of a particular traffic type.

This paper introduces a new packet marking algorithm that can be used in the context of Assured Forwarding (AF) in the Differentiated Services (DiffServ) framework [1], [2]. The new marking algorithm is called Equation-Based Marking (EBM) and is based on the TCP model in [3]. EBM is to handle the problems found in other marking schemes regarding fairness among heterogeneous TCP flows through a tight feedback-loop operation and adaptation of the packet marking probability to network conditions. We design a packet marker that uses EBM as the marking algorithm, and evaluate its performance using in-depth simulation. We also prove analytically the correctness of the marking algorithm and compare it with other marking schemes for different network scenarios. Our evaluation results demonstrate the effectiveness of EBM in providing the required fairness among heterogeneous flows and ensuring protection against non-assured traffic. I.

TCP connection throughput is inversely proportional to the connection Round Trip Time (RTT). To mitigate TCP bias to short RTT connections, a differentiated services traffic conditioner can ensure connections with long RTTs do not starve when connections with short RTTs get all extra resources after achieving the target rates. Current proposals for RTT-aware conditioners work well for a small number of connections when most TCP connections are in the congestion avoidance phase. If there is a large number of TCP connections, however, connections time-out and go to slow start. We show that current RTT-aware conditioners over-protect long RTT flows and starve short RTT flows in this case. We design and evaluate a conditioner based on RTT as well as the Retransmission Time-out (RTO). The proposed RTT-RTO aware traffic conditioner works well for realistic situations with a large number of connections. Simulation results in a variety of situations confirm that the conditioner mitigates RTT bias.

INTRODUCTION The Differentiated Services (Diffserv) architecture [2] has recently become the preferred method for addressing QoS issues in IP networks. An end-to-end differentiated service is obtained through the concatenation of per-domain services and Service Level Agreements (SLAs) between adjoining domains along the traffic path, from source to destination. Per-domain services are realized by traffic conditioning at the edge and simple differentiated forwarding mechanisms at the core of the network. One of the forwarding mechanisms recently standardized by the IETF is the Assured Forwarding (AF) [4] Per Hop Behaviors (PHB). The basis of the AF PHB is differentiated dropping of packets during congestion at a router. To build an end-toend service with AF, subscribed traffic profiles for customers are maintained at the traffic conditioning nodes at the edge of the network. The aggregated traffic is monitored; and packets are marked at the traffic conditioner. When an

Recent demands for real time applications have given rise to a need for Quality of Service (QoS) in the Internet. Differentiated Services (DiffServ) is one of such efforts currently pursued by IETF. Previous researchers found unfairness in the DiffServ network. To solve the unfairness problem, we propose a new TSW based three-color marker (ItswTCM ), which achieves proportional fair share of excess bandwidth among aggregates in a DiffServ network. We have compared the fairness of our proposed ItswTCM marker with srTCM, trTCM, and tswTCM. Results show that our proposed marker performs better than the other three schemes for low to medium network provision level (20 -- 70%); we believe that all well provisioned network will operate in this region. Results also show that our proposed marker is not as sensitive to the number of flows in an aggregate as the previous marking schemes. We point out that yellow packets play a significant role in achieving proportional fair share of excess bandwidth among aggregates. We conclude that in order to achieve proportional fair sharing of excess bandwidth, it is important to inject right amount of yellow packets into the network.

The current best effort approach to quality of service in the Internet can no longer satisfy a diverse variety of customer service requirements, and that is why there is a need for alternative strategies. In order to solve this problem a number of service differentiation models have been proposed. Unfortunately, these schemes often fail to provide proper service differentiation during periods of congestion. To deal with the issue of congestion, we introduce a new load control mechanism that eliminates congestion based on the feedback from the network core by dynamically adjusting traffic load at the network boundary. We introduce four methods for calculating load distribution among the ingress routers and among different flows in each ingress router, and we evaluate these proposed methods through simulation.

Abstract—We design and evaluate an adaptive traffic conditioner to improve application performance over the differentiated services assured forwarding behavior. The conditioner is adaptive because the marking algorithm changes based upon the current number of flows traversing through an edge router. If there are a small number of flows, the conditioner maintains and uses state information to intelligently protect critical TCP packets. On the other hand, if there are many flows going through the edge router, the conditioner only uses flow characteristics as indicated in the TCP packet headers to mark without requiring per flow state. Simulation results indicate that this adaptive conditioner improves throughput of data extensive applications like large FTP transfers, and achieves low packet delays and response times for Telnet and WWW traffic. I.

The current best effort approach to Quality of Service in the Internet can no longer satisfy a diverse variety of customer service requirements, because of which there is a need for alternative strategies. A promising approach for dealing with this problem is a method called Load Distribution Scheme (LDS) which dynamically adjusts traffic load at the network boundary based on feedback from the network. In order to fairly share available resources among individual flows, the load distribution scheme relies on a message exchange protocol which in certain cases may cause significant overhead in the system. In this paper, we examine the issues related to the problem of the message overhead in the LDS, propose solutions to the problem, and evaluate these solutions through simulation in OPNET.

This study addresses the end-to-end congestion control support over the DiffServ Assured Forwarding (AF) class. The resulting Assured Service (AS) provides a minimum level of throughput guarantee. In this context, this paper describes a new end-to-end mechanism for continuous transfer based on TCP-Friendly Rate Control (TFRC) originally proposed in [11]. The proposed approach modifies TFRC to take into account the QoS negotiated. This mechanism, named gTFRC, is able to reach the minimum throughput guarantee whatever the flow’s RTT and target rate. Simulation measurements show the efficiency of this mechanism either in over-provisioned or exactly-provisioned network. In addition, we show that the gTFRC mechanism can be used in the same DiffServ/AF class with TCP or TFRC flows. 1

Abstract. This study addresses the end-to-end congestion control support over the DiffServ Assured Forwarding (AF) class. The resulting Assured Service (AS) provides a minimum level of throughput guarantee. In this context, this article describes a new end-to-end mechanism for continuous transfer based on TCP-Friendly Rate Control (TFRC). The proposed approach modifies TFRC to take into account the QoS negotiated. This mechanism, named gTFRC, is able to reach the minimum throughput guarantee whatever the flow’s RTT and target rate. Simulation measurements and implementation over a real QoS testbed demonstrate the efficiency of this mechanism either in over-provisioned or exactly-provisioned network. In addition, we show that the gTFRC mechanism can be used in the same DiffServ/AF class with TCP or TFRC flows.