Abstract. The transport protocol for SIP can be chosen based on the requirements of services and network conditions. How does the choice of TCP affect the scalability and performance compared to UDP? We experimentally analyze the impact of using TCP as a transport protocol for a SIP server. We first investigate scalability of a TCP echo server, then compare performance of a SIP registrar server for two TCP connection lifetimes: transaction and persistent. Our results show that a Linux machine can establish 400,000+ TCP connections and maintaining connections does not affect the transaction response time. This is applicable to other servers with very large TCP connection counts. Additionally, the transaction response times using the two TCP connection lifetimes and UDP show no significant difference at 2,500 registration requests/second in our SIP server implementation. However, sustainable request rate is lower for TCP than for UDP, since using TCP requires more message processing, which causes longer delays at the thread queue for the server implementing a thread-pool model. Finally, we suggest how to reduce the impact of TCP for a scalable SIP server especially under overload control.

Abstract-The Stream Control Transmission Protocol (SCTP) is a relatively recent transport protocol, offering features beyond TCP.Although SCTP is an alternative transport protocol for the Session Initiation Protocol (SIP), we do not know how SCTP features influence SIP server scalability and performance. To estimate this, we measured the scalability and performance of two servers, an echo server and a simplified SIP server on Linux, for both SCTP and TCP. Our measurements found that using SCTP does not significantly affect data transfer latency. However, the number of sustainable associations drops to 17-21% or to 50% of the TCP value if we adjust the acceptable gap size of packet reordering.

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No abstract

The information retrieval systems on a wide area distributed network, such as the World-Wide W e b ( W ) , become popular among the extremely large number of users. The caching proxy has an important role on these systems for improving their accessibility and serviceability.The caching proxy mechanism is discussed in this paper as follows: First, the role and structure of the caching proxy are explained, and two major problems of existing systems are pointed out. Our solution to overcome these problems is proposed next. Changing afile size, by controlling a quality level of cached multimedia data, is proposed as a measure to overcome one problem. As a solution to the other problem, making a cluster among neighboring caching proxies, using hyperlink information, is proposed. Finally, an improved caching proxy mechanism based upon these ideas is shown.