protocole GO BACK N

[Hamdi Jmii]

Hello guys. I want to implement GO BACK N protocol in ns3. But, I don't know how does sender stop to wait ACK from receiver. It's like time out. How does sender set its time out? And then, when sender receives ACK, how to continue sending next packet? If any one know it, please give me some guides? Thank you very much!

[Tommaso Pecorella]

Hi,

I hate t repeat myself.

Go Back N is NOT a protocol.
It is an ARQ mechanism, see http://en.wikipedia.org/wiki/Go-Back-N_ARQ

In order to have a "protocol" you need also other stuff, e.g., a packet format.

About your other questions:

"how does sender stop to wait ACK from receiver. It's like time out." - well, that's the problem of how to find out if a data packet has been lost, assuming that ACKs too can be lost.

This problem (the data segment loss calculation) alone has generated a shitload of publications, algorithms and techniques. Heck, the whole TCP congestion control system is based on HOW you detect a loss... best suggestion: grab a book. Any book.

How to continue when you receive an ACK ? Check this: http://en.wikipedia.org/wiki/Sliding_window_protocol

In ns-3, it's "just" a matter of: receive an ACK, trash the acknowledged data, move the sliding window, check if you have pending data to send, send them.

Anyway, as I said (already), GBN isn't a protocol. You have to define the missing parts before implementing it.

T.

[Hamdi Jmii]

thank you well, I already simulated the behavior of this protocol (form of packet, alghorithm, phenomenon of sliding window
but my real poblème is in the coding of the protocol in ns3. I like someone guide me so that I do not run head down in the jungle

[Tommaso Pecorella]

Study the tutorial and the manual, thats the best advice.

If you have specific questions feel free to ask them.

T.