Improving World-wide Web Latency

The HTTP protocol, as currently used in the World-wide Web, causes excessive latency and overhead. Each client request uses a separate TCP connection, which adds unnecessary overheads for connection set-up, TCP slow-start, and connection tear-down. Use of separate requests for each document and its inlined images means that each retrieval requires at least one network round-trip.

We modified the NCSA HTTP server and the Mosaic client to maintain TCP connections for multiple requests. The server can close inactive connections, if necessary, to manage its resources. We also added two new HTTP primitives, to avoid unnecessary round-trips: GETALL, which retrieves a document and all of its inlined images, and GETLIST, which retrieves a client-specified set of documents. Our implementations interoperate with unmodified HTTP implementations.

With a geographically remote server (round-trip time = 80 ms), our measurements show that the latency seen by the client declines by 15-50%, depending on the number and size of inlined images. Even with a local server, latency improves by 10-40%.

We also modified Mosaic to retain FTP control connections for multiple requests; this also significantly improves response time, typically cutting it down to less than half.

We are currently investigating the performance of a server that prefetches files, using past access patterns to predict future requests. This could mask disk latencies, by performing disk I/O in parallel with network activity, thereby improving response time.

Venkata Padmanabhan's Vita

Present

• Research Intern at Digital Equipment Corporation Western Research Laboratory (May - Aug 1994).

Education

• Undergraduate: B.Tech. in Computer Science, Indian Institute of Technology, Delhi (1993)
• Graduate: Ph.D. program in Computer Science, University of California at Berkeley (Aug 1993 onwards)

Research Interests

• Computer Networks, Operating Systems

Contact Address

Jeffrey Mogul's Vita

7/86 to present

• Consultant Engineer, Digital Equipment Corporation Western Research Laboratory.
• Research on computer systems design and implementation.

Education

• Ph.D., March 1986, Stanford University
• Dissertation title: Representing Information About Files

Selected publications

• David R. Boggs, Jeffrey C. Mogul, Christopher A. Kent. Measured Capacity of an Ethernet: Myths and Reality. SIGCOMM '88, pages 222-234. Stanford, CA, August, 1988.
• Deborah Estrin, Jeffrey C. Mogul, and Gene Tsudik. Visa Protocols for Controlling Inter-Organization Datagram Flow. IEEE Journal on Selected Areas in Communication 7(4):486-498, May, 1989.
• Christopher A. Kent and Jeffrey C. Mogul. Fragmentation Considered Harmful. SIGCOMM '87, pages 390-401. Stowe, VT, August, 1987.
• Jeffrey C. Mogul. Simple and Flexible Datagram Access Controls for Unix-based Gateways. Summer 1989 USENIX, pages 203-221. Baltimore, MD, June, 1989.
• Jeffrey C. Mogul. Efficient Use Of Workstations for Passive Monitoring of Local Area Networks. SIGCOMM '90, pages 253-263. Philadelphia, PA, September, 1990.
• Jeffrey C. Mogul. Network Locality at the Scale of Processes. TOCS 10(2):81-109, May, 1992.
• Jeffrey C. Mogul. Observing TCP Dynamics in Real Networks. SIGCOMM '92, pages 305-317. Baltimore, MD, August, 1992.
• Jeffrey C. Mogul. A Recovery Protocol for Spritely NFS. USENIX Workshop on File Systems, pages 93-109. Ann Arbor, MI, May, 1992.
• Jeffrey C. Mogul. IP Network Performance. In Dan Lynch and Marshall Rose, Internet Systems Handbook. Addison-Wesley, Reading MA, 1992, pages 575-675, Chapter 15.
• Jeffrey C. Mogul and Stephen Deering. Path MTU Discovery. RFC 1191, November, 1990.
• Jeffrey C. Mogul, Christopher A. Kent, Craig Partridge, and Keith McCloghrie. IP MTU Discovery Options. RFC 1063, July, 1988.
• Jeffrey Mogul and Jon Postel. Internet Standard Subnetting Procedure. RFC 950, August, 1985.
• Jeffrey C. Mogul, Richard F. Rashid, Michael J. Accetta. The Packet Filter: An Efficient Mechanism for User-Level Network Code. SOSP-11, pages 39-51. Austin, Texas, November, 1987.
• Jeffrey C. Mogul and Anita Borg. The Effect of Context Switches on Cache Performance. ASPLOS-IV, pages 75-84. Santa Clara, CA, April, 1991.
• V. Srinivasan and Jeffrey C. Mogul. Spritely NFS: Experiments with Cache-Consistency Protocols. SOSP-12, pages 45-57. Litchfield Park, AZ, December, 1989.

Other

• Program Committee chair, USENIX Winter '94 Technical Conference
• Program Committee member, ACM SIGCOMM '88, '92; USENIX Summer '93; USENIX High-Speed Networking Symposium '94.
• Associate Editor, Internetworking: Research and Experience