Improving the Performance of Internet Data Transport

With the explosion of the World Wide Web, the Internet infrastructure faces new challenges in providing high performance for data traffic. First, it must be able to pro-vide a fair-share of congested link bandwidth to every flow. Second, since web traffic is inherently interactive, it must minimize the delay for data transfer. Recent studies have shown that queue management algorithms such as Tail Drop, RED and Blue are deficient in providing high throughput, low delay paths for a data flow. Two major shortcomings of the current algorithms are: they allow TCP flows to get synchronized and thus require large buffers during congestion to enable high throughput; and they allow unfair bandwidth usage for shorter round-trip time TCP flows. We propose algorithms using multiple queues and discard policies with hysteresis at bottleneck routers to address both these issues. Us-ing ns-2 simulations, we show that these algorithms can significantly outperform RED and Blue, especially at smaller buffer sizes. Using multiple queues raises two new concerns: scalability and excess memory bandwidth usage caused by dropping packets which have been queued. We propose and evaluate an architecture using Bloom filters to evenly distribute flows among queues to improve scalability. We have also developed new intelligent packet discard algorithms that discard packets on arrival and are able to achieve performance close to that of policies that may discard packets that have already been queued. Finally, we propose better methods for evaluating the performance of fair-queueing methods. In the current literature, fair-queueing methods are evaluated based on their worst-case performance. This can exaggerate the differences among algorithms, since the worst-case behavior is dependent on the the precise timing of packet arrivals. This work seeks to understand what happens under more typical circumstances

Intelligent Packet Discard Policies for Improved TCP Queue Management

Recent studies have shown that suitably-designed packet discard policies can dramatically improve the performance of fair queueing mechanisms in internet routers. The Queue State Deficit Round Robin algorithm (QSDRR) preferentially discards from long queues, but in-troduces hysteresis into the discard policy to minimize synchronization among TCP flows. QSDRR provides higher throughput and much better fairness than simpler queueing mech-anisms, such as Tail-Drop, RED and Blue. However, because QSDRR discards packets that have previously been queued, it can signficantly increase the memory bandwidth require-ments of high performance routers. In this paper, we explore alternatives to QSDRR that provide comparable performance, while allowing packets to be discarded on arrival, saving memory bandwidth. Using ns-2 simulations, we show that the revised algorithms can come close to matching the performance of QSDRR and substantially outperform RED and Blue. Given a traffic mix of TCP flows with different round-trip times, longer round-trip time flows achieve 80% of their fair-share using the revised algorithms, compared to 40% under RED and Blue. We observe a similar improvement in fairness for long multi-hop paths competing against short cross-traffic paths. We also show that these algorithms can provide good performance, when each queue is shared among multiple flows

Link Buffer Sizing: a New Look at the Old Problem

In this paper, we revisit the question of how much buffer an IP router should allocate for its output link. For a long time, the intuitive answer of setting the buffer size to the bitrate-delay product has been widely regarded as reasonable. Recent studies of interaction between queueing at IP routers and TCP congestion control proposed alternative answers. First, we expose and explain contradictions between existing guidelines for link buffer sizing. Then, we argue that the problem of link buffer sizing needs a different formulation. In particular, the chosen buffer size should accommodate not only common versions of TCP but also UDP traffic. Besides, our new formulation of the problem contains an explicit constraint of not engaging IP routers in any additional signaling. We conclude the paper by outlining a promising direction for solving the reformulated problem

Selecting the Buffer Size for an IP Network Link

In this paper, we revisit the problem of selecting the buffer size for an IP network link. After a comprehensive overview of issues relevant to the link buffer sizing, we examine usefulness of existing guidelines for choosing the buffer size. Our analysis shows that the existing recommendations not only are difficult to implement in the context of IP networks but also can severely hurt interactive distributed applications. Then, we argue that the networking research community should change its way of thinking about the link buffer sizing problem: the focus should shift from optimizing performance for applications of a particular type to maximizing diversity of application types that IP networks can support effectively. To achieve this new objective, we propose using small buffers for IP network links

Hardware Based Error and Flow Control in the Axon Gigabit Host-Network Interface

We have proposed a new architecture called Axon that meets the challenges of delivering high performance network bandwidth directly to applications. Its pipelines network interface must perform critical per packet processing in hardware a packets flow through the pipeline, without imposing any store-and-forward buffering of packets. This requires the design of error and flow control mechanisms to be simple enough for implementation in the network interface hardware, while providing functionality required by applications. This paper describes the implementation of the Axon host-network interface, and in particular the hardware design of the critical per packet processing with emphasis on error and flow control. An extensive simulation model of the network interface hardware has been used to determine the feasibility and performance of hardware implementation of these functions

Intelligent Packet Discard Policies for Improved TCP Queue Management

Recent studies have shown that suitably-designed packet discard policies can dramatically improve the performance of fair queueing mechanisms in internet routers. The Queue State Deficit Round Robin algorithm (QSDRR) preferentially discards from long queues, but introduces hysteresis into the discard policy to minimize synchronization among TCP flows. QSDRR provides higher throughput and much better fairness than simpler queueing mechanisms, such as Tail-Drop, RED and Blue. However, because QSDRR discards packets that have previously been queued, it can significantly increase the memory bandwidth requirements of high performance routers. In this paper, we explore alternatives to QSDRR that provide comparable performance, while allowing packets to be discarded on arrival, saving memory bandwidth. Using ns-2 simulations, we show that the revised algorithms can come close to matching the performance of QSDRR and substantially outperform RED and Blue. Given a traffic mix of TCP flows with different round-trip times, longer round-trip time flows achieve ¡£¢¥¤ of their fair-share using the revised algorithms, compared to ¦ under RED and Blue. We observe a similar im-provement in fairness for long multi-hop paths competing against short cross-traffic paths. We also show that these algorithms can provide good performance, when each queue is shared among multiple flows

per-flow Queue

Recent studies have shown that suitably-designed packet discard policies can dramatically improve the performance of fair queueing mechanisms in internet routers. The Queue State Deficit Round Robin algorithm (QSDRR) preferentially discards from long queues, but introduces hysteresis into the discard policy to minimize synchronization among TCP flows. QSDRR provides higher throughput and much better fairness than simpler queueing mechanisms, such as Tail-Drop, RED and Blue. However, since QSDRR needs to maintain a separate queue for each active flow, there is a legitimate concern that it may be too costly for the highest speed links. In previous studies, we have shown that QSDRR can deliver almost the same performance with one-tenth the number queues as flows, if the flows are evenly distributed across the queues. In this paper, we develop and evaluate a flow distribution algorithm using a Bloom filter architecture with dynamic rebalancing. We show that our algorithm significantly reduces the memory requirement compared to maintaining per-flow state and can achieve near optimal flow distribution. Thus, using this algorithm in conjunction with QSDRR, we can achieve the performance of per-flow queueing at a significantly reduced cost

Selecting the Buffer Size for an IP Network Link

In this paper, we revisit the problem of selecting the buffer size for an IP network link. After a comprehensive overview of issues relevant to the link buffer sizing, we examine usefulness of existing guidelines for choosing the buffer size. Our analysis shows that the existing recommendations not only are difficult to implement in the context of IP networks but also can severely hurt interactive distributed applications. Then, we argue that the networking research community should change its way of thinking about the link buffer sizing problem: the focus should shift from optimizing performance for applications of a particular type to maximizing diversity of application types that IP networks can support effectively. To achieve this new objective, we propose using small buffers for IP network links

Efficient Queue Management for TCP Flows

Packets in the Internet can experience large queueing delays during busy periods. Backbone routers are generally engineered to have large buffers, in which packets may wait as long as half a second (assuming FIFO service, longer otherwise) . During congestion periods, these buffers may stay close to full, subjecting packets to long delays, even when the intrinsic latency of the path is relatively small. This paper studies the performance improvements that can be obtained by using more sophisticated packet schedulers, than are typical of Internet routers. The results show that the large buffers found in WAN routers contribute only marginally to improving router throughput, and the higher delays that come with large buffers makes them a dubious investment. The results also show that better packet scheduling algorithms can produce dramatic improvements in fairness. Using ns-2 simulations, we show that algorithms using multiple queues can significantly outperform RED and Blue, especially at smaller buffer sizes. Over a single-bottleneck link, the variance in TCP goodput using the proposed multiqueue packet schedulers is one-tenth that obtained with RED and one-fifth that obtained with Blue. Given a traffic mix of TCP flows with different round-trip times, longer round-trip time flows achieve of their fair-share using multiqueue schedulers, compared under RED and Blue. We observe a similar performance improvement for multi-hop paths