Subject: RE: last call on control and ethernet drafts

From: Keith Knightson <[email-masked]>
Date: Mon, 10 Nov 2003 14:40:34 -0500

At 2:17 PM -0500 10/11/03, Prayson Pate wrote:
>I would also like to add my support for having an option to preserve
>Ethernet FCS.
>
>Prayson
>
I have a few quick questions..

How would a user know or test whether the FCS has or has not been 
carried across the PW?

Is this service verifiable?  By sending a deliberately corrupted FCS 
and seeing what happens?

Is this simply a question of trust?

It would seem to imply that in the case where it is carried it is not 
looked at, at the ingress.  I can't imagine seeing a false FCS and 
continuing as if it were correct.

Does current hardware preserve the FCS for re-use?

Regards

Keith

---

From: "Andrew G. Malis" <[email-masked]>
Date: Mon, 10 Nov 2003 15:51:34 -0500

Keith,

>How would a user know or test whether the FCS has or has not been carried 
>across the PW?

It's part of the SLA with their service provider.

>Is this service verifiable?  By sending a deliberately corrupted FCS and 
>seeing what happens?

That's one way ... or by putting a monitoring box between the service 
provider and the CE (many vendors sell these, BTW) that can report this and 
other perceived problems with the service.

>Is this simply a question of trust?

See above.

>continuing as if it were correct.

That's a good point to mention explicitly - I'll add to the draft that the 
FCS SHOULD (or MUST?) be examined at the ingress to prevent errored frames 
that would be discarded at the receiving CE anyway from wasting bandwidth.

>Does current hardware preserve the FCS for re-use?

Depends on the framer.  But yes, there exists framers that can retain the FCS.

Cheers,
Andy

---

From: Ali Sajassi <[email-masked]>
Date: Mon, 10 Nov 2003 22:29:01 -0800

>that would be discarded at the receiving CE anyway from wasting bandwidth.

Same error detection logic applies to within a P/PE nodes such that while 
forwarding packets from ingress to egress ports of a PE/P node and error is 
detected, then the packet should be discarded. If the platform cannot do 
that and the error can only be detected by the CE (via FCS retention), then 
isolating the location of the error would be an interesting task !!
If the P/PE nodes have such capability and FCS retention is still needed, 
then I would question the value added of it ?
Have we run any test to see the probability of an undetected error via 
platforms capable of CRC-protection ? If the probability of it is 
negligible (e.g., 10**-12), does it still make sense to do it ?

-Ali