Principles of Application Layer Protocols (HTTP_2)

Principles of Application Layer Protocols (HTTP_2)

HTTP Performance

What effects?

Different kinds of requests:

– Lots of small requests (loading a web page)

– Big request (fetching a download)

Requires different solutions!

Small requests

Latency matters:

Governed by RTT between hosts.

Two major causes of delay:

– Opening a TCP connection

– Data response-request

Solutions:

– Persistent connections (Why?)

– Pre-fetching !

– Others?

Big requests

Eg: When doing a big request (big file to download).

Problem is throughput on bottleneck links (usually edge links)

A solution:

Use an HTTP proxy cache or mirror

– Can also improve latency!

big requests in HTTP

Old Cached Data

Cache needs a way to conditionally ask for a document as Items in the cache

can get staled ( eg: We don’t want to read stored of weeks ago)

- Cache can issue a conditional GET (with an “If-modified-since”

header)

- Server can reply with a “304 Not Modified”

Web caching

Cache acts as both client and server.

- Typically cache is installed by ISP (university, company,

residential ISP)

- Reduce response time for client request

- Reduce traffic on an institution’s access link

HTTP Transaction

HTTP Transaction