Srinivasan Keshav

Bio: Srinivasan Keshav is an academic researcher from University of Cambridge. The author has contributed to research in topics: The Internet & Network packet. The author has an hindex of 51, co-authored 219 publications receiving 12620 citations. Previous affiliations of Srinivasan Keshav include Cornell University & Wilmington University.

Analysis and simulation of a fair queueing algorithm

Abstract: We discuss gateway queueing algorithms and their role in controlling congestion in datagram networks. A fair queueing algorithm, based on an earlier suggestion by Nagle, is proposed. Analysis and simulations are used to compare this algorithm to other congestion control schemes. We find that fair queueing provides several important advantages over the usual first-come-first-serve queueing algorithm: fair allocation of bandwidth, lower delay for sources using less than their full share of bandwidth, and protection from ill-behaved sources.

A control-theoretic approach to flow control

Abstract: This paper presents a control-theoretic approach to reactive flow control in networks that do not reserve bandwidth. We assume a round-robin-like queue service discipline in the output queues of the network's switches, and propose deterministic and stochastic models for a single conversation in a network of such switches. These models motivate the Packet-Pair rate probing technique, and a provably stable rate-based flow control scheme. A Kalman state estimator is derived from discrete-time state space analysis, but there are difficulties in using the estimator in practice. These difficulties are overcome by a novel estimation scheme based on fuzzy logic. We then present a technique to extract and use additional information from the system to develop a continuous-time system model. This is used to design a variant of the control law that is also provably stable, and, in addition, takes control action as rapidly as possible. Finally, practical issues such as correcting parameter drift and coordination with window flow control are described.

An Engineering Approach to Computer Networking: ATM Networks, the Internet, and the Telephone Network

Abstract: (Most chapters contain a Summary.) Preface xiii. SECTION II. INTRODUCTION. 1. Atoms, Bits, and Networks. Introduction. Common Network Technologies. Networking Concepts and Techniques. Engineering Computer Networks. In Closing. 2. The Telephone Network: Concepts, History, and Challenges. Concepts. End-Systems. Transmission. Switching. Signaling. Cellular Communications. Historical Sketch. Challenges. Summary. 3. The Internet: Concepts, History, and Challenges. Concepts. Basic Internet Technology. Addressing. Routing. Endpoint Control. History. Challenges. Summary. 4. Atm Networks: Concepts, History, and Challenges. Virtual Circuits. Fixed-Size Packets. Small Packet Size. Statistical Multiplexing. Integrated Service. History. Challenges. Summary. SECTION II. TOOLS AND TECHNIQUES. 5. Protocol Layering. Protocols and Protocol Layering. Importance of Layering. Problems With Layering. Iso-Osi Reference Model. The Seven Layers. Summary. 6. System Design. Introduction. Resource Constraints and Their Metrics. Common Design Techniques. Performance Analysis and Tuning. Summary. 7. Multiple Access. Introduction. Choices and Constraints. Base Technologies. Centralized Access Schemes. Distributed Schemes. Summary. 8. Switching. Introduction. Circuit Switching. Packet Switching. Switch Fabrics. Buffering. Multicasting. Summary. 9. Scheduling. Introduction. Requirements. Fundamental Choices. Scheduling Best-Effort Connections. Scheduling Guaranteed-Service Connections. Comparison. Packet Dropping. Summary. 10. Naming and Addressing. Introduction. Naming and Addressing. Hierarchical Naming. Addressing. Addressing in the Telephone Network. Addressing in the Internet. Nsaps: Addressing in ATM Networks. Name Resolution. Datalink Layer Addressing. Finding Datalink Layer Addresses. Summary. 11. Routing. Introduction. Routing Protocol Requirements. Choices. Routing in the Telephone Network. Distance-Vector Routing. Link-State Routing. Choosing Link Costs. Hierarchical Routing. Internet Routing Protocols. Routing Within a Broadcast Lan. Multicast Routing. Routing With Policy Constraints. Routing for Mobile Hosts. Summary. 12. Error Control. Causes of Bit Errors. Bit-Error Detection and Correction. Causes of Packet Errors. Packet-Error Detection and Correction. Summary. 13. Flow Control. Model. Classification. Open-Loop Flow Control. Closed-Loop Flow Control. Hybrid Flow Control. Summary. 14. Traffic Management. Introduction. An Economic Framework for Traffic Management. Traffic Models. Traffic Classes. Time Scales of Traffic Management. Scheduling. Renegotiation. Signaling. Admission Control. Peak-Load Pricing. Capacity Planning. Summary. SECTION III. PRACTICE. 15. Common Protocols. Introduction. Telephone Network Protocols. Internet Protocols. Atm Network Protocols. Ip Over Atm. Summary. 16. Protocol Implementation. Introduction. Factors Affecting Protocol Stack Performance. Common Protocol Stack Procedures. Partitioning Strategies. Interface Among Protocol Layers. Protocol Implementation. Some Rules of Thumb. Summary. References. Glossary. Answers to Review Questions and Selected Exercises. Index. 0201634422T04062001

It's not easy being green

Abstract: Large-scale Internet applications, such as content distribution networks, are deployed across multiple datacenters and consume massive amounts of electricity. To provide uniformly low access latencies, these datacenters are geographically distributed and the deployment size at each location reflects the regional demand for the application. Consequently, an application's environmental impact can vary significantly depending on the geographical distribution of end-users, as electricity cost and carbon footprint per watt is location specific. In this paper, we describe FORTE: Flow Optimization based framework for request-Routing and Traffic Engineering. FORTE dynamically controls the fraction of user traffic directed to each datacenter in response to changes in both request workload and carbon footprint. It allows an operator to navigate the three-way tradeoff between access latency, carbon footprint, and electricity costs and to determine an optimal datacenter upgrade plan in response to increases in traffic load. We use FORTE to show that carbon taxes or credits are impractical in incentivizing carbon output reduction by providers of large-scale Internet applications. However, they can reduce carbon emissions by 10% without increasing the mean latency nor the electricity bill.

Rate controlled servers for very high-speed networks

Abstract: Future high-speed networks are expected to carry traffic with a wide range of performance requirements. Two queue service disciplines, rate-based scheduling and hierarchical round robin scheduling, are described. These disciplines allow some connections to receive guaranteed rate and jitter performance, while others receive best-effort service. Rate based scheduling is designed for fast packet networks, while hierarchical round robin is an extension of round robin scheduling suitable for use in networks based on the asynchronous transfer mode (ATM) being defined in CCITT. Both schemes are feasible at rates of 1 Gb/s. The schemes allow strict bounds on the buffer space required for rate controlled connections and can provide efficient utilization of transmission bandwidth. >

Planetary boundaries: Guiding human development on a changing planet

Abstract: The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

Random early detection gateways for congestion avoidance

Abstract: The authors present random early detection (RED) gateways for congestion avoidance in packet-switched networks. The gateway detects incipient congestion by computing the average queue size. The gateway could notify connections of congestion either by dropping packets arriving at the gateway or by setting a bit in packet headers. When the average queue size exceeds a present threshold, the gateway drops or marks each arriving packet with a certain probability, where the exact probability is a function of the average queue size. RED gateways keep the average queue size low while allowing occasional bursts of packets in the queue. During congestion, the probability that the gateway notifies a particular connection to reduce its window is roughly proportional to that connection's share of the bandwidth through the gateway. RED gateways are designed to accompany a transport-layer congestion control protocol such as TCP. The RED gateway has no bias against bursty traffic and avoids the global synchronization of many connections decreasing their window at the same time. Simulations of a TCP/IP network are used to illustrate the performance of RED gateways. >

A survey of spectrum sensing algorithms for cognitive radio applications

Abstract: The spectrum sensing problem has gained new aspects with cognitive radio and opportunistic spectrum access concepts. It is one of the most challenging issues in cognitive radio systems. In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented. Various aspects of spectrum sensing problem are studied from a cognitive radio perspective and multi-dimensional spectrum sensing concept is introduced. Challenges associated with spectrum sensing are given and enabling spectrum sensing methods are reviewed. The paper explains the cooperative sensing concept and its various forms. External sensing algorithms and other alternative sensing methods are discussed. Furthermore, statistical modeling of network traffic and utilization of these models for prediction of primary user behavior is studied. Finally, sensing features of some current wireless standards are given.

A generalized processor sharing approach to flow control in integrated services networks: the multiple node case

Abstract: Worst-case bounds on delay and backlog are derived for leaky bucket constrained sessions in arbitrary topology networks of generalized processor sharing (GPS) servers. The inherent flexibility of the service discipline is exploited to analyze broad classes of networks. When only a subset of the sessions are leaky bucket constrained, we give succinct per-session bounds that are independent of the behavior of the other sessions and also of the network topology. However, these bounds are only shown to hold for each session that is guaranteed a backlog clearing rate that exceeds the token arrival rate of its leaky bucket. A much broader class of networks, called consistent relative session treatment (CRST) networks is analyzed for the case in which all of the sessions are leaky bucket constrained. First, an algorithm is presented that characterizes the internal traffic in terms of average rate and burstiness, and it is shown that all CRST networks are stable. Next, a method is presented that yields bounds on session delay and backlog given this internal traffic characterization. The links of a route are treated collectively, yielding tighter bounds than those that result from adding the worst-case delays (backlogs) at each of the links in the route. The bounds on delay and backlog for each session are efficiently computed from a universal service curve, and it is shown that these bounds are achieved by "staggered" greedy regimes when an independent sessions relaxation holds. Propagation delay is also incorporated into the model. Finally, the analysis of arbitrary topology GPS networks is related to Packet GPS networks (PGPS). The PGPS scheme was first proposed by Demers, Shenker and Keshav (1991) under the name of weighted fair queueing. For small packet sizes, the behavior of the two schemes is seen to be virtually identical, and the effectiveness of PGPS in guaranteeing worst-case session delay is demonstrated under certain assignments. >