04-02-2013, 12:50 PM
Protocols
Protocols.ppt (Size: 625.5 KB / Downloads: 25)
Communication protocols are agreed sets of rules and procedures for computers to exchange information.
Like humans agreeing to speak the same language during a conversation.
For two computers to exchange data, they must be using the same protocols.
Human Protocols
during a phone call, saying “Uh huh”, “Mmmm” or “Yeah” while the other person speaks
nodding to show understanding
waiting for the other person to stop talking before you start
raising pitch of voice after a question
airline pilots speak English, refer to heights in feet, agree on which direction to turn to avoid collision, pronounce 9 as “niner”, spell out letters with words (Alpha, Bravo, Charlie etc.)
Choosing Protocols
Sometimes there is more than one choice of protocol for a task, such as how messages pass across a network (IPX/SPX vs TCP/IP, POP vs IMAP).
As long as all the connected computers use the same protocol, it really does not matter which protocol is used (like diplomats agreeing on a language for negotiations)
The internet only works because TCP/IP, POP, FTP and HTTP are universal standards, used by all shapes and sizes of computers.
Protocols – TCP/IP
IP (Internet Protocol)…
Once a file has been chopped into packets, the IP protocol delivers each packet to its destination.
each packet can take a different route from A to B, bouncing from router to router getting more precise with each hop.
the route is dynamically chosen for each packet, based on internet conditions at that time.
Packet Switching
Why use packet switching?
A single bad bit in a file can ruin an entire file.
It’s quicker to re-send a portion of the file rather than the whole file.
Important with ‘noisy’ and unreliable communication paths, such as dial-up modem.
Many computers get to transmit some data, rather than 1 PC tying up a channel for ages with a huge transfer.
Imagine mailing a house from Melbourne to Sydney one brick at a time.