Subj : Packet Vs Circuit Switch
To   : Andy Ball
From : Bo Simonsen
Date : Fri Oct 22 2004 12:25 am

Hello Andy!

Monday October 18 2004 08:54, you wrote to me:

 AB>> Out-of-order packet reception springs to mind.

 BS>> Hm. Please explain, not familear with that expression.

 AB> On a circuit-switched link (such as a dial-up call between my modem
 AB> and yours) all the data sent from my end to your end take the same
 AB> route and arrive in the same order that they were sent.

Yes,

 AB> On a
 AB> packet-switched network (such as the Internet), it is possible for
 AB> packets to take different routes to reach you, and for a packet to
 AB> arrive ahead of one that was sent before it was (arriving out of
 AB> order).

 AB> Thinking about it though, Telnet works over TCP which almost certainly
 AB> re-orders packets that it receives in the wrong order before passing
 AB> them up to Telnet, so although it's a valid difference between
 AB> circuit-switched and packet- switched networks, it's sort of
 AB> irrelevent from Telnet's point of view.  :-)

But if we see in the OSI model, it's not really the application layers job to 
make scure the data is valid. Which we actually do anyhow, with fx. CRC check 
in Zmodem and brothers.

Bo
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