question on proxy server:
what is PAC (proxy auto config) file?
question for protocol stacking?
how different are transport layers of TCP and UDP?
submitted by CC16
darshan thappa
priya m.s.
satchidanand das
karthik k.
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HTTP PROXY SERVER:
A proxy auto-config (PAC) file defines how web browsers and other user agents can automatically choose the appropriate proxy server (access method) for fetching a given URL.
A PAC file contains a JavaScript function "FindProxyForURL(url, host)". This function returns a string with one or more access method specifications. These specifications cause the user agent to use a particular proxy server or to connect directly.
Multiple specifications provide a fallback when a proxy fails to respond. The browser fetches this PAC file before retrieving other pages. The URL of the PAC file is either configured manually or determined automatically by the Web Proxy Autodiscovery Protocol.
More advanced PAC files can reduce load on proxies, do load balancing, fail over, or even black/white listing before the request hit the proxies.
how different are transport layers of TCP and UDP?
UDP :userdatagram protocol is a connectionless,unreliable transport protocol.It doesn't add anything to the services of IP except to provide process to process communication instead of host to host communication.And it performs very limited error checking
TCP:transmission control protocol,like udp,is a process to process protocol.TCP is a connection oriented ,reliable transport protocol,i.e it creates a virtual connection between two tcp's to send data.it uses flow and error control mechanisms at the transport level.it adds connection oriented ,reliablility to the services of IP
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