RE: Fw: [RPRWG] CRC check in each node?
The alternative to setting the bit is (as suggested by Robin, I think), is
to use inverted (but corrected) CRC. But the bit seems to be simpler one.
Regards,
Devendra Tripathi
CoVisible Solutions Inc.
(formerly VidyaWeb, Inc)
Pune, India
Tel: +91-20-433-1362
> -----Original Message-----
> From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On Behalf Of Pankaj K Jha
> Sent: Monday, July 02, 2001 9:40 AM
> To: afaber@xxxxxxxxxxxxx
> Cc: ieee 802.17 list
> Subject: Re: Fw: [RPRWG] CRC check in each node?
>
>
>
> Angela/Bob:
>
> Yes it does. I'm ok with the following summary:
>
> - If there is an error in RPR header, the node discards the
> packet (since it
> doesn't know for sure who the destination node is), and updates
> its statistics.
>
> - Same is true if both RPR header and payload CRC are bad
> - If RPR header is ok but the payload CRC is bad, the node
> optionally (under
> program control) sets a bit, and updates its own statistics, and sends the
> packet downstream. This is done so the end node can tell the link is not
> functioning properly rather than assume the link is fine but no one is
> transmitting packets to it.
>
> Any thoughts?
>
> -Pankaj
>
>
> afaber@xxxxxxxxxxxxx wrote:
>
> > hello Pankaj
> >
> > Since CRC can be used for identifying if there is a problem in the link
> > (i.e., signal degradation causing the CRC error), it is
> desirable to only
> > record this data in the first node that sees this CRC error (so that one
> > can see that there may be a fault in the link). If every node
> that sees the
> > same CRC error accumulate such data, how are you going to identify which
> > one is the link that generated the error? The bit set is used
> (as I heard
> > from the 802.5 folks) to say that the CRC error was already detected
> > upstream and there is no need to use that information on performance
> > monitoring of downstream nodes...
> >
> > Does it make sense?
> >
> > Angela
> >
> > Pankaj K Jha <pkj@xxxxxxxxxxx> on 07/02/2001 11:42:04 AM
> >
> > To: RDLove <rdlove@xxxxxxxxx>
> > cc: "Angela T. Faber" <afaber@xxxxxxxxxxxxx>, "ieee 802.17 list"
> > <stds-802-17@xxxxxxxx> (bcc: Angela T. Faber/Telcordia)
> > Subject: Re: Fw: [RPRWG] CRC check in each node?
> >
> > I've one doubt I'd like to clarify. If it is only for the local
> station to
> > record statistics, why would it have to set a bit in the packet
> to do so?
> > It
> > already knows there is a CRC error and it can update its statistics
> > locally. As
> > far as other other downstream nodes are concerned, they too
> will find the
> > CRC
> > errors during reception because they'll be checking for CRC
> errors anyway.
> > What
> > exactly does the bit setting help in? It doesn't help in node
> > identification in
> > a series of nodes. Please advise.
> > Regards,.
> > Pankaj
> >
> > RDLove wrote:
> >
> > > Pankaj, the reason to set a bit when a station sees a CRC error, is so
> > that
> > > the station that first sees the error can record the "error created"
> > event.
> > > It is that station, and not the destination station with the
> information
> > > available for transmitting to a station that gathers statistics.
> > >
> > > Best regards,
> > >
> > > Robert D. Love
> > > Chair, Resilient Packet Ring Alliance
> > > President, LAN Connect Consultants
> > > 7105 Leveret Circle Raleigh, NC 27615
> > > Phone: 919 848-6773 Mobile: 919 810-7816
> > > email: rdlove@xxxxxxxx Fax: 208 978-1187
>
>