Toru Hasegawa

Locating congested segments over the Internet by clustering the delay performance of multiple paths

Abstract Delay variation-based detection and location of congestion in a large network is considered. Since the Internet is still highly prone to performance deterioration due to transient large delays, locating a part of the network (segments) responsible is vital to ensure that Internet Service Providers can mitigate or prevent such performance deterioration. In the proposed method, the end-to-end packet delays from multiple origins to multiple destinations are actively and continuously measured. By analyzing those data on delay variation along each monitored path, congestion is detected by finding a delay performance deterioration worse than a predefined criteria and a congested segment responsible could be inferred by finding a set of paths among which delay variations are strongly correlated. This is a network tomographic approach based on a clustering technique that effectively tackles the correlation among packet delay variation along individual paths. The proposed method was evaluated through a real-world long-term experiment on the Japan’s commercial Internet, and was shown to have considerable potential to promptly locate congested segments through various analyses on the experimental results.

Experimental TCP Performance Evaluation on Diffserv Assured Forwarding over ATM SBR Service

In these days, the deployment of Diffserv (Differentiated Services) that enables the QoS guarantee is urgently required by the IP network customers. However, AF (Assured Forwarding) PHB (Per Hop Behavior) in Diffserv still has not been provided by conventional routers. It is a realistic solution that SBR3 (Statistical Bit Rate 3) of ATM emulates AF PHB, but it is not clear whether TCP traffic over AF PHB emulated by ATM is differentiated from the best effort TCP traffic over DF (Default Forwarding) PHB. To confirm the differentiation, we have experimentally studied TCP performance through the link into which TCP connections over AF PHB and DF PHB is aggregated. This paper describes the experimental results and discusses the possibility of the TCP performance differentiation between AF PHB and DF PHB over ATM.

High speed TCP/IP experiment over international ATM test bed

AT&T, KDD and NTT conducted a joint ATM trial called Multimedia Application Project (MAP) for the purpose of testing and validating network-based broadband multimedia applications and services between US and Japan. Although the Internet based network is promising for broadband multimedia communications, there is a performance problem that TCP is the throughput bottleneck in an international ATM network with large propagation delay. In MAP, the high speed TCP/IP experiment was jointly performed by the three companies with the leadership of KDD, for the purpose of validating the high speed TCP/IP infrastructure using TCP gateway proposed by KDD. In this infrastructure, a pair of TCP gateways are introduced in international ATM networks, and they improve the TCP throughput by introducing a link-by-link flow control and a sufficient window size between gateways, without any modifications to end terminals.

OSI protocol testing system based on user friendly test scenario specification functions

As the OSI protocols come to be widely adopted in various communication systems, the testing of OSI protocol implementations becomes important. In this paper, we propose the OSI protocol testing system with user friendly test scenario specification functions aiming to support both the state transition oriented testing and the parameter oriented testing for the Transport through Application layer protocols. Our system introduces the separate tools with friendly human interface for specifying the test scenarios, for the test execution and for analyzing the test results. This paper describes the function and implementation of our system and shows its usefulness compared with the conventional testing system based on formal specification language.

A TCP Test System Specifying only Exceptional Packet Sequences

Although TCP is widely used in Internet, new specifications are still proposed and implemented. In the circumstance above, it is highly possible that some errors are detected on the communication between new and old implementations. Several test tools were developed so far. However, they do not have enough function to customize test sequence or need significant effort to specify the sequence. We developed a TCP test system which specifies only exceptional packet sequence in the test scenario. The system performs exceptional packet sequence only when the condition specified in the test scenario is satisfied. Otherwise, it performs ordinary TCP behavior. The system is implemented by modifying TCP module of NetBSD with SACK code developed by Pittsburgh Supercomputing Center. We also evaluated SACK implementation as an example of recent specification using the test system.