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Networking & Wireless forum


Collision in Aloha protocol

by angeloangeloangelo / January 5, 2016 1:54 PM PST

I'm sorry but the following situation is not described in any of my network-book .Considering a communication between HostA and HostB in pure Aloha protocol: HostB transmits a message to HostA .When the message is trasmitted but still not propagated, HostA trasmits a message to hostB .if the trasmission time is loger than the propagation time , is there a collision ?

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Clarification Request
What's the underlying system?
by R. Proffitt Forum moderator / January 5, 2016 2:38 PM PST

IP? If so, and if on modern gear, no collision. Since I'm not in a classroom with a whiteboard my answers will be short.

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by angeloangeloangelo / January 6, 2016 1:03 AM PST

Thank you for the answer .
The underlying system isn't described in my book , the only thing that i know is that HostA and HostB communicate through a broadcast channel.
Anyway as You said there is no collision , and this means that HostA sends successfully the ACK to HostB .
Now , HostB have to wait , first , for the message from HostA and then for the ACK , Why HostB doesnt't timeout?

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Then you can't tell what will happen.
by R. Proffitt Forum moderator / January 6, 2016 8:35 AM PST
In reply to: Clarification

Here, the office and lab we have switched hubs and the packets are doing what they do on switched hubs. So no collision. This is basic stuff so I must keep it short.

Repeat. Switched Hubs = almost never a collision. That is, in 2+ decades, yet to see a collision.

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