help3002

It's UWAweek 48

help3002

This forum is provided to promote discussion amongst students enrolled in CITS3002 Computer Networks.

Please consider offering answers and suggestions to help other students! And if you fix a problem by following a suggestion here, it would be great if other interested students could see a short "Great, fixed it!" followup message. How do I ask a good question?

Displaying the 4 articles in this topic

Showing 4 of 503 articles.
Currently 1 other person reading this forum.

UWA week 11 (1st semester, week 3) ↓

labs Lab 2 Topology query (all 4)

3:21pm Thu 14th Mar, Cameron L.

Good Afternoon, For Lab 2, STOPANDWAIT2 has a variable called ber, set to 0.00005, is this the probability of frame corruption? If not, how is frame corruption handled in this topology? I've managed to get the Negative Acknowledgement working (or at least, when a corrupt frame is identified, it sends one, and the message is resent), but every time a message that has a corrupted frame is noted, the resent message will also be corrupt, and I'm not sure if that's on my end yet. Cheers

labs Lab 2 Topology query (all 4)

3:28pm Thu 14th Mar, Christopher M.

"Cameron Locke" <21*3*2*2@s*u*e*t*u*a*e*u*a*> wrote:

> For Lab 2, STOPANDWAIT2 has a variable called ber, set to 0.00005, is this the probability of frame corruption? If not, how is frame corruption handled in this topology?

It stands for 'bit error rate' - the probability that one-or-more bits in a frame will be corrupted.

> I've managed to get the Negative Acknowledgement working (or at least, when a corrupt frame is identified, it sends one, and the message is resent), but every time a message that has a corrupted frame is noted, the resent message will also be corrupt, and I'm not sure if that's on my end yet.

Yes, there's an additional problem that needs to be solved. It's easy to detect a damaged frame, and send back a negative-acknowledgement, but what needs to happen if that negative-acknowledgement frame is damaged?

labs Lab 2 Topology query (all 4)

3:28pm Thu 14th Mar, Cameron L.

On looking further, I assume ber is Bit Error Rate. That doesn't explain why one failed checksum will always resend into another failed checksum, so I'll keep looking.

labs Lab 2 Topology query (all 4)

3:56pm Thu 14th Mar, Cameron L.

I would assume that to avoid the two generals problem, corrupt acknowledgment frames are ignored after a point (for simplicity, if not efficiency, I've been ignoring them entirely and allowing them to timeout). But I'm still not sure why a resent corrupt message is always corrupt. Thanks for the quick reply!