Re: [RPRWG] CRC check in each node?

["Angela T. Faber" <afaber@xxxxxxxxxxxxx>]

Hello Raj

 

When you say "ultimate destination entity connected to an RPR MAC" are you talking about the client connected to the RPR network (and therefore connected to the egress RPR node)? If so, if the headers are corrupted, why wouldn't we prevent the misrouting as soon as we detect it (instead of allowing the destination to do it)? That would avoid BW to be wasted with packets that will be dropped at the destination (since I believe they make no use of that...). In addition it would be better to localize a possible fault (i.e., the segment where it went bad), and would help to correlate with other packets that also had some sort of error in that segment...

Am I missing something in here?

 

Angela

 

 

----- Original Message -----

From: Raj Sharma

To: 'Angela T. Faber' ; ieee 802.17 list

Sent: Thursday, June 21, 2001 6:40 PM

Subject: RE: [RPRWG] CRC check in each node?

Angela,

 

This is an intesting question and is sort of the tip of an iceberg

(pardon the cliché - I feel the answer to this question is loaded)

 

There are fundamentally 2 issues here. Misrouting of packets due

to errors and corruption of the payload.

 

IMHO, packets whose headers are corrupted must be discarded

in order to prevent misrouting. The question is whether the misrouting

prevention is limited between RPR MACs or to the ultimate destination

entity connected to a RPR MAC. I am assuming that a RPR MAC has

multiple clients.

 

Certain services require persistent delivery of frames. Such services

will make their won decision on what to do with corrupted frames.

For these services it may require that corrupted frames be still delivered

to the specific MAC client.

 

Now, it maybe of significant value in debugging networks and from

an operational perspective to know over which span on the ring the

frame got corrupted. Hence CRC recomputation at every node may

have some value from an operational perspective. Also, since the TTL

field is part of the frame CRC recomputation cannot be avoided at least for

the header.

 

raj

 

 

-----Original Message-----
From: Angela T. Faber [mailto:afaber@xxxxxxxxxxxxx]
Sent: Thursday, June 21, 2001 12:44 PM
To: ieee 802.17 list
Subject: [RPRWG] CRC check in each node?

Folks

 

One question regarding CRC check: are we assuming CRC will be checked at every node (as the frame is forwarded) or it will be checked only at the destination/source node?

My initial thought on this is that, if we don't do it at every node, than how do we remove the frame from ring if the source and destination addresses are corrupted? On the other hand I assume that if every node checks it, more time is spent with forwarding it....

 

Any insights are welcomed.

Thanks!

 

Angela