Fred Baker

PIE: A lightweight control scheme to address the bufferbloat problem

Bufferbloat is a phenomenon where excess buffers in the network cause high latency and jitter. As more and more interactive applications (e.g. voice over IP, real time video conferencing and financial transactions) run in the Internet, high latency and jitter degrade application performance. There is a pressing need to design intelligent queue management schemes that can control latency and jitter; and hence provide desirable quality of service to users. We present here a lightweight design, PIE (Proportional Integral controller Enhanced), that can effectively control the average queueing latency to a reference value. The design does not require per-packet extra processing, so it incurs very small overhead and is simple to implement in both hardware and software. In addition, the design parameters are self-tuning, and hence PIE is robust and optimized for various network scenarios. Simulation results, theoretical analysis and Linux testbed results show that PIE can ensure low latency and achieve high link utilization under various congestion situations.

Hop-by-Hop Routing in Wireless Mesh Networks with Bandwidth Guarantees

Wireless Mesh Network (WMN) has become an important edge network to provide Internet access to remote areas and wireless connections in a metropolitan scale. In this paper, we study the problem of identifying the maximum available bandwidth path, a fundamental issue in supporting quality-of-service in WMNs. Due to interference among links, bandwidth, a well-known bottleneck metric in wired networks, is neither concave nor additive in wireless networks. We propose a new path weight which captures the available path bandwidth information. We formally prove that our hop-by-hop routing protocol based on the new path weight satisfies the consistency and loop-freeness requirements. The consistency property guarantees that each node makes a proper packet forwarding decision, so that a data packet does traverse over the intended path. Our extensive simulation experiments also show that our proposed path weight outperforms existing path metrics in identifying high-throughput paths.

A strategy for fair coexistence of loss and delay-based congestion control algorithms

Delay-based TCP variants have attracted a large amount of attention in the networking community because of their ability to efficiently use network resources, control queuing delays, exhibit virtually zero packet loss, etc. One major issue that discourages the wider deployment of delay-based TCP variants is their inability to co-exist fairly with standard loss-based TCP. In this note we propose a simple mechanism that allows delay- and loss-based (AIMD) TCP flows to compete fairly with each other. Further, our approach ensures that delay-based flows automatically (and swiftly) switch to a low-delay regime if no loss-based flows are present. We provide analytical and simulation results to validate presented algorithm.

Routing in multi-hop wireless mesh networks with bandwidth guarantees

This paper presents a distributed polynomial algorithm for finding the maximum bandwidth path in Wireless Mesh Networks (WMNs). Our proposed algorithm can be applied for designing the proactive hop-by-hop routing protocol with bandwidth guarantee. To the best of our knowledge, our work is the first distributed path calculation algorithm in WMNs.

Reservations about Reservations

The panel discussed the current state and likely future development of how to provide differentiated quality of service in an Internet context, primarily through reservations. The panel agreed that it appears unlikely that a single approach will fit all applications, with different trade-offs between complexity, level of guarantee and scaling

Approximation Algorithm for QoS Routing with Multiple Additive Constraints

In this paper, we study the problem of computing the supported QoS from a source to a destination with multiple additive constraints. The problem has been shown to be NP-complete and many approximation algorithms have been developed. We propose a new approximation algorithm called multi-dimensional relaxation algorithm. We formally prove that our algorithm produces smaller approximation error than the existing algorithms. We further verify the performance by extensive simulations.

An approximation algorithm for QoS routing with two additive constraints

The problem of finding a path that satisfies two additive constraints, such as delay and cost, has been proved to be NP-complete. Many heuristic and approximation algorithms have been developed to identify a path given a certain QoS request. Unfortunately, these algorithms cannot be applied directly in the Internet because routing in the Internet is based on table lookups and routing tables are computed before a request arrives. In this paper, we develop an approximation algorithm for computing the supported QoS going across a domain. We analyze the approximation error of our algorithm and formally prove that the approximation error of our proposed algorithm is smaller than those of the existing approaches. We further verify our performance using extensive simulations.

Comprehensive understanding of TCP Incast problem

Since TCP Incast has been identified as a catastrophic problem in many typical data center applications, a lot of efforts have been made to analyze or solve it. The analysis work intends to model Incast problem from certain perspective, and the solutions try to solve the problem through designing enhanced mechanisms or algorithms. However, the proposed models are either closely coupled with particular protocol version or dependent on empirical observations, and the solutions cannot eliminate Incast problem entirely because the underlying issues are not identified completely. There is little work which attempts to close the gap between “analyzing” and “solving”, and present a comprehensive understanding. In this paper, we provide an in-depth understanding of how TCP Incast problem happens. We build up an interpretive model which emphasizes particularly on describing qualitatively how various factors, including system parameters and mechanism variables, affect network performances in Incast traffic pattern, but not on calculating the accurate throughput. With this model, we give plausible explanations why the various solutions for TCP Incast problem can help, but do not solve it entirely.

Routing with QoS information aggregation in hierarchical networks

In this paper, we consider the problem of routing with two additive constraints in the hierarchical networks, such as the Internet. In order for scalability, the supported QoS information in the hierarchical networks has to be aggregated. We propose a novel method for aggregating the QoS information. To the best of our knowledge, our approach is the first study to use the area-minimization optimization, the de facto optimization problem of the QoS information aggregation. We use a set of real numbers to approximate the supported QoS between different domains. The size of the set is predefined so that advertisement overhead and the space requirement will not grow exponentially as the network size grows. The simulation results show that the proposed method outperforms the existing methods.

CTE: cost-effective intra-domain traffic engineering

1. PROBLEM STATEMENT Internet Traffic Engineering (TE) is a very important research topic for production networks, where TE is typically formulated into minimizing the maximum link utilization (MLU). For example, with increasing IPv6 traffic, the backbone network of CERNET2[1] is suffering big traffic pressure on some critical longhaul links under the traditional shortest-path routing. Taking CERNET2 as an example, we develop a practical and costeffective intra-domain TE method in this paper. Existing intradomain TE proposals, such as MPLS-based proposal [2], OpenFlow-based proposal [3] and reactive-TE proposal [4], need to make great modifications to routers, and even have to replace existing routers with brand new routers, which makes the deployment be very high-cost. Other TE proposals, such as the work [5], optimize OSPF weights for the goal of TE. Although these methods have low deployment cost, they need to frequently change OSPF weights based on dynamically changed traffic matrices. Each change to OSPF weights may lead to transient routing loops or traffic disruption. Frequent routing loops or traffic disruption is intolerable for network operators. Therefore, in this paper, we propose a new intra-domain TE method named CTE. CTE works in an OSPF/IS-IS network, where shortest-path routing is run. The core idea of CTE is to use loop-free next hops [7] to route some traffic, which is realized by configuring some static routes and some access control list (ACL) rules. CTE does not make any modifications to existing routers. We only need to develop a remote control program that can configure static routes and ACL rules on routers. In addition, CTE can be incrementally deployed. We now use an example to illustrate how CTE works. Figure 1 is a network topology composed a set of nodes and a set of links. The lowercase letters beside a node denote the prefixes associated with the node. We suppose that the capacity of each link is 100 units and the weight of each link is 1. We give the shortest-path tree towards the destination F as shown in Figure 2. In Figure 2, the solid arrows direct the next hops towards the destination F and the dash lines will not be used by the traditional shortest-path routing towards the destination F. Table 1 shows a prefixgranularity traffic matrix. Table 2 shows the corresponding nodegranularity traffic matrix. Under this traffic matrix, the MLU A F