Debanjan Saha

A self-configuring RED gateway

The congestion control mechanisms used in TCP have been the focus of numerous studies and have undergone a number of enhancements. However, even with these enhancements, TCP connections still experience alarmingly high loss rates, especially during times of congestion. To alleviate this problem, the IETF is considering active queue management mechanisms, such as random early detection (RED), for deployment in the network. In this paper, we first show that the effectiveness of RED depends, to a large extent, on the appropriate parameterization of the RED queue. We then show that there is no single set of RED parameters that work well under different congestion scenarios. In light of this observation, we propose and experiment with more adaptive RED gateways which self-parameterize themselves based on the traffic mix. The results show that traffic cognizant parameterization of RED gateways can effectively reduce packet loss, while maintaining high link utilizations under a range of network loads.

The BLUE active queue management algorithms

In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the ietf has been considering the deployment of active queue management techniques such as Red [14]. While active queue management can potentially reduce packet loss rates in the Internet, we show that current techniques are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they use queue lengths as the indicator of the severity of congestion. In light of this observation, a fundamentally different active queue management algorithm, called Blue, is proposed, implemented, and evaluated. Blue uses packet loss and link idle events to manage congestion. Using both simulation and controlled experiments, Blue is shown to perform significantly better than Red, both in terms of packet loss rates and buffer size requirements in the network. As an extension to Blue, a novel technique based on Bloom filters [2] is described for enforcing fairness among a large number of flows. In particular, we propose and evaluate Stochastic Fair Blue (SFB), a queue management algorithm which can identify and rate-limit nonresponsive flows using a very small amount of state information.

Stochastic fair blue: a queue management algorithm for enforcing fairness

This paper describes and evaluates stochastic fair blue (SFB), a novel technique for enforcing fairness among a large number of rows. SFB scalably detects and rate-limits non-responsive flows through the use of a marking probability derived from the blue queue management algorithm and a Bloom (1970) filter. Using analysis and simulation, SFB is shown to effectively handle non-responsive flows using an extremely small amount of state information.

Key management for secure lnternet multicast using Boolean function minimization techniques

The Internet provides no support for privacy or authentication of multicast packets. However, an increasing number of applications require secure multicast services in order to restrict group membership and enforce accountability of group members. A major problem associated with the deployment of secure multicast delivery services is the scalability of the key distribution protocol. This is particularly true with regard to the handling of group membership changes, such as member departures and/or expulsions, which necessitate the distribution of a new session key to all the remaining group members. As the frequency of group membership changes increases, it becomes necessary to reduce the cost of key distribution operations. This paper explores the use of batching of group membership changes to reduce the frequency, and hence the cost, of key re-distribution operations. It focuses explicitly on the problem of cumulative member removal and presents an algorithm that minimizes the number of messages required to distribute new keys to the remaining group members. The algorithm is used in conjunction with a new multicast key management scheme which uses a set of auxiliary keys in order to improve scalability. In contrast to previous schemes which generate a fixed hierarchy of keys, the proposed scheme dynamically generates the most suitable key hierarchy by composing different keys. Our cumulative member removal algorithm uses Boolean function minimization techniques, and outperforms all other schemes known to us in terms of message complexity.

IP over optical networks: architectural aspects

The Internet transport infrastructure is moving toward a model of high-speed routers interconnected by intelligent optical core networks. A consensus is emerging in the industry on utilizing an IP-centric control plane within optical networks to support dynamic provisioning and restoration of lightpaths. At the same time, there are divergent views on how IP routers must interact with optical core networks to achieve end-to-end connectivity. This article describes the architectural alternatives for interconnecting IP routers over optical networks, considering the routing and signaling issues. Also, the application of IP-based protocols for dynamic provisioning and restoration of lightpaths, as well as the interworking of multivendor optical networks is described.

Transport layer security: how much does it really cost?

The last couple of years has seen a growing momentum towards using the Internet for conducting business. One of the key enablers for business applications is the ability to setup secure channels across the Internet. The Secure Sockets Layer (SSL) protocol provides this capability and it is the most widely used transport layer security protocol. In this paper we investigate the performance of SSL both from a latency as well as a throughput point of view. Since SSL is primarily used to secure Web transactions, we use the SPECWeb96 benchmark suitably modified for use with the SSL protocol. We benchmark two of the more popular Web servers that are in use today and find that they are a couple of orders of magnitude slower when it comes to serving secure Web pages. We investigate the reason for this deficiency by instrumenting the SSL protocol stack with a detailed profiling of the protocol processing components. Based on our findings we suggest two modifications to the protocol that reduce the latency as well as increase the throughput at the server.

Design, implementation and performance of a content-based switch

In this paper, we share our experience in designing and building a content-based switch which we call L5. In addition to the layer 2-3-4 information available in the packet, a content-based switch uses application level information to route traffic in the network. Making routing decisions based on information contained in the payload is not a new idea. In fact application level proxies which are functionally equivalent to a content-based switch, have been around for years. Our contribution is in combining the functionalities of an application level proxy with the data handling capabilities of a switch into a single system. In this paper, we describe the architecture of the L5 system along with the details of how application level information can be efficiently processed in the switch hardware. We cover two specific application examples that we believe are ideal candidates for content-based switching: one is routing HTTP sessions based on uniform resource locators (URL) and the other is session-aware dispatching of secure socket layer (SSL) connections.

Adaptive packet marking for maintaining end-to-end throughput in a differentiated-services internet

This paper examines the use of adaptive priority marking for providing soft bandwidth guarantees in a differentiated-services Internet. In contrast to other proposals for achieving the same objective, the proposed scheme does not require resource reservation for individual connections and can be supported with minimal changes to the network infrastructure. It uses modest support from the network in the form of priority handling for appropriately marked packets, and relies on intelligent transmission control mechanisms at the edges of the network to achieve the desired throughput levels. This paper describes the control mechanisms and evaluates their behavior in various network environments. These mechanisms are show in to have several salient features which make them suitable for deployment in an evolving Internet.

Static and Dynamic Processor Scheduling Disciplines in Heterogeneous Parallel Architectures

Most parallel jobs cannot be fully parallelized. In a homogeneous parallel machine-one in which all processors are identical-the serial fraction of the computation has to be executed at the speed of any of the identical processors, limiting the speedup that can be obtained due to parallelism. In a heterogeneous architecture, the sequential bottleneck can be greatly reduced by running the sequential part of the job or even the critical tasks in a faster processor. This paper uses Markov chain based models to analyze the performance of static and dynamic processor assignment policies for heterogeneous architectures. Parallel jobs are assumed to be described by acyclic directed task graphs. A new static processor assignment policy, called Largest Task First Minimum Finish Time (LTFMFT), is introduced. The analysis shows that this policy is very sensitive to the degree of heterogeneity of the architecture, and that it outperforms all other policies analyzed. Three dynamic assignment disciplines are compared and it is shown that, in heterogeneous environments, the disciplines that perform better are those that consider the structure of the task graph, and not only the service demands of the individual tasks. The performance of heterogeneous architectures is compared with cost-equivalent homogeneous ones taking into account different scheduling policies. Finally, static and dynamic processor assignment disciplines are compared in terms of performance.

Capacity performance of dynamic provisioning in optical networks

This paper describes an architecture and analyzes the performance of dynamic provisioning of lightpaths in an optical network. In dynamic provisioning, a lightpath is set up in real-time without rearranging the working and protection routes of existing lightpaths, and without the knowledge of future lightpath provisioning events. This paper develops a general model of the physical topology of the optical network, and outlines routing approaches for dynamic provisioning of lightpaths. It analyzes via simulations the performance of dynamically provisioned unprotected, 1+1 protected and mesh-restored lightpaths. The analysis of the efficiency of network utilization of dynamic provisioning focuses on the spare capacity needed for protection, and in particular focuses on the impact of sharing of wavelength channels for mesh-restored lightpaths. The main conclusion from the performance studies is that significant capacity gains are achieved with sharing of wavelength-channels for mesh-restored lightpaths with dynamic provisioning even for sparse topologies, and even at moderate loads.