Article http over transport protocols

Modeling the Performance of HTTPOver Several Transport Protocols

Modeling the Performance of HTTPOver Several Transport Protocols

● Persistent-Connection HTTP● Transaction TCP● UDP-Based Request–Response Protocols

Modeling the Performance of HTTPOver Several Transport Protocols

● Persistent-Connection HTTP● HTTP requests and responses can be pipelined on

a connection.

● Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.

Modeling the Performance of HTTPOver Several Transport Protocols

● Persistent-Connection HTTP

Modeling the Performance of HTTPOver Several Transport Protocols

● T-TCP (RFC 1644)

● The goal of T/TCP is to allow each transaction, i.e., each request/response sequence, to be efficiently performed as a single incarnation of a TCP connection.

● Bypass the 3-way handshake

Modeling the Performance of HTTPOver Several Transport Protocols

● ARDP

● ARDP’s main design goal is to provide a reliable yet light-weight communication mechanism to transport requests and responses between clients and servers.

● TCP-style flow-control

● Congestion-avoidance

● Retransmission algorithms●

● Avoids TCP’s three-way handshake, instead randomly selecting connection identifiers

Modeling the Performance of HTTPOver Several Transport Protocols

Network Model

Modeling the Performance of HTTPOver Several Transport Protocols

Modeling the Performance of HTTPOver Several Transport Protocols

● Traffic Model

● Small page: Single 5 kB web page.

● Medium page: Single 25 kB web page.

● Large page: Single 100 kB web page.

● Small cluster: Single 6651 B page with embedded 3883 B and 1866 B images.

● Medium cluster: Single 3220 B page with three embedded images, sizes 57613 B, 2344 B, and 14190 B.8

● Large cluster: Single 100 kB page with 10 embedded 25 kB images.

Modeling the Performance of HTTPOver Several Transport Protocols

● Protocol Analysis

● TCP: HTTP currently runs over TCP, opening a new connection for each transaction.

● Connection caching protocols: To avoid connection setup overheads, P-HTTP and T/TCP cache connections or connection information across multiple requests.

● UDP-based request–response protocols: ARDP employs UDP to avoid TCP setup costs.

Modeling the Performance of HTTPOver Several Transport Protocols

● Minimum Transit Times

Modeling the Performance of HTTPOver Several Transport Protocols

● Minimum Transit Times

A series of independent requests will incur only one roundtrip latency because they are pipelined. The total required time will, therefore, be:

Modeling the Performance of HTTPOver Several Transport Protocols

Simple Model

Modeling the Performance of HTTPOver Several Transport Protocols

● HTTP over TCP

● TCP slow start

● Performance and Discussion

Modeling the Performance of HTTPOver Several Transport Protocols

TCP slow start

Modeling the Performance of HTTPOver Several Transport Protocols

http://user.it.uu.se/~carle/Notes/43_TCP.html

Modeling the Performance of HTTPOver Several Transport Protocols

● Performance & Discussion

Cost of accessing an object via HTTP over TCP

Modeling the Performance of HTTPOver Several Transport Protocols

● HTTP Over TCP with Connection Caching

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Modeling the Performance of HTTPOver Several Transport Protocols

● HTTP Over Multiple, Concurrent TCP Connections

Many web browsers open multiple concurrent connections to mitigate TCP start-up costs (HTTP over parallel connec- tions). We can bound their performance by HTTP over TCP with and without connection caching. Our HTTP-over-TCP model overestimates transmission time by not considering parallelism in the concurrent slow-start of each connection. HTTP over connection caching underestimates transmission time by assuming that there is no penalty for slow-starts of later requests in a cluster. A better approximation might be obtained by treating as if it were , for concurrent connections. Completely specifying behavior with multiple parallel connections is an area of continuing work.

Modeling the Performance of HTTPOver Several Transport Protocols

● HTTP Over UDP-Based Protocols

Time to complete a HTTP transaction over ARDP

Modeling the Performance of HTTPOver Several Transport Protocols

● HTTP Over UDP-Based Protocols

Total time to complete a series of independent HTTP requests

Overhead

Modeling the Performance of HTTPOver Several Transport Protocols

● Validation

● Methodology

● Slow Start Validation

● Model Adjustments● Server processing time● Request independence● Inexact Bandwidth

Modeling the Performance of HTTPOver Several Transport Protocols

● Protocol Discussion

● HTTP over TCP overhead is fairly low under net- working characteristics today.

●

● TCP overhead becomes significant when the band- width–delay product rises.

●

● A recent technical note by W3C has suggested that pipelining substantially reduces packet counts for persistent- connection HTTP

TCP Overhead

Connection-caching protocols

End

Modeling the Performance of HTTPOver Several Transport Protocols