Http Response ExampLe(review) Http/1.1200 ok Date Tue, 27 Mar 2001 03 49: 38 GMT Server: Apache/1.3.14(Unix)(Red-Hat/Linux)mod ssl/2.7. Open SSL/0.9.5a DAV/1.0.2 PHP/4.0. 1pl2 mod_perl/1.24 Last-Modified: mon 29 Jan 2001 17: 54: 18 GMT ETag: 7al1f-10ed-3a75ae4a Accept-Ranges: bytes Content-Length: 4333 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html Lecture19:2006-11-02
Lecture 19: 2006-11-02 11 HTTP Response Example (review) HTTP/1.1 200 OK Date: Tue, 27 Mar 2001 03:49:38 GMT Server: Apache/1.3.14 (Unix) (Red-Hat/Linux) mod_ssl/2.7.1 OpenSSL/0.9.5a DAV/1.0.2 PHP/4.0.1pl2 mod_perl/1.24 Last-Modified: Mon, 29 Jan 2001 17:54:18 GMT ETag: "7a11f-10ed-3a75ae4a" Accept-Ranges: bytes Content-Length: 4333 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html …
Outline Http intro and details Persistent Http Http caching Content distribution networks Lecture19:2006-11-02
Lecture 19: 2006-11-02 12 Outline • HTTP intro and details • Persistent HTTP • HTTP caching • Content distribution networks
Typical Workload (Web Pages) Multiple(typically small)objects per page File sizes Heavy-tailed Pareto distribution for tail Lognormal for body of distribution For reference/interest only · Embedded references Number of embedded objects pareto-p(x)=aka(at1 Lecture19:2006-11-02
Lecture 19: 2006-11-02 13 Typical Workload (Web Pages) • Multiple (typically small) objects per page • File sizes • Heavy-tailed • Pareto distribution for tail • Lognormal for body of distribution -- For reference/interest only -- • Embedded references • Number of embedded objects = pareto – p(x) = akax -(a+1)
Http0.9/1.0(mOstly review One request/response per TCP connection Simple to implement Disadvantages Multiple connection setups three-way handshake each time Several extra round trips added to transfer Multiple slow starts Lecture19:2006-11-02
Lecture 19: 2006-11-02 14 HTTP 0.9/1.0 (mostly review) • One request/response per TCP connection • Simple to implement • Disadvantages • Multiple connection setups → three-way handshake each time • Several extra round trips added to transfer • Multiple slow starts
Single Transfer EXample Client Server O RTT SYN Client opens TO尸 SYN connection 1 RTT Client sends Http request DAT for html ACK server reads from DAT disk 2RTT ACK Client parses HTML FIN Client opens TCP connection ACK SYN SYN rTT ACK Client sends Http request DAT for image Server reads from ACK disk 4 RTT DAT Image begins to arrive Lecture19:2006-11-02 15
Lecture 19: 2006-11-02 15 Single Transfer Example Client Server SYN SYN SYN SYN ACK ACK ACK ACK ACK DAT DAT DAT DAT FIN ACK 0 RTT 1 RTT 2 RTT 3 RTT 4 RTT Server reads from disk FIN Server reads from disk Client opens TCP connection Client sends HTTP request for HTML Client parses HTML Client opens TCP connection Client sends HTTP request for image Image begins to arrive