Efficient Support for Pipelined Requests in Content-Based Switches Using Asymmetric TCP Splicing

Masayoshi KOBAYASHI  Tutomu MURASE  

IEICE TRANSACTIONS on Communications   Vol.E86-B   No.6   pp.1812-1820
Publication Date: 2003/06/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Content Delivery Networks)
Category: Content Routing and Server Selection
content-based switch,  layer 7 switch,  TCP splicing,  World Wide Web,  

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A content-based switch makes forwarding decisions (server selections) based on an application layer information and forwards data in the application layer. After making forwarding decisions, existing content-based switches improve their forwarding performance by TCP splicing, which releases them from maintaining TCP endpoints and allows them to forward data by packet forwarding. However, once content-based switches invoke TCP splicing, they are unable to use the application layer information for forwarding decisions. Thus the existing content-based switches cannot perform a handoff of pipelined HTTP transactions, which can greatly reduce client perceived latencies. This paper proposes an asymmetric TCP splicing and a method to perform the handoff of HTTP transactions between servers. Asymmetric TCP splicing allows the content-based switches to use all the application layer information in the TCP data stream from clients to servers, although it allows the switches to forward the TCP data stream from servers to clients by packet forwarding. The proposed handoff method content-based switches support pipelined HTTP transactions in combination with asymmetric TCP splicing. In the proposed method, the content-based switch utilizes the common function of TCP (TCP half-close) to detect the end of the series of responses from the currently selected server, and it changes the forwarding destination after the client finishes receiving a series of responses from the server. Our evaluation validates that the content-based switch which supports pipelined HTTP transactions by our method can reduce client-perceived latencies when there is a large correlation between destinations of any two consecutive requests.