RE: Fw: [RPRWG] CRC check in each node?
Bob,
what happens when this bit (outside the CRC coverage) is corrupted, i.e. the
CRC is good but the bit indicates it's bad?
Igor
-----Original Message-----
From: RDLove [mailto:rdlove@xxxxxxxxx]
Sent: Monday, July 02, 2001 2:00 PM
To: igorz
Cc: ieee 802.17 list
Subject: Re: Fw: [RPRWG] CRC check in each node?
Igor, referring to the 802.5 MAC, there are a number of bits which are
outside of the CRC. Those bits include reservation bits which can get
changed by stations as the frame circulates around the ring, the Frame copy
bit, and the CRC check bit which gets flipped from a 0 to a one if the CRC
is bad. In addition, there is never any attempt to create a valid CRC for
bad data. Therefore, once the CRC is bad, it does nothing to tell about
further errors.
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
----- Original Message -----
From: "igorz" <igorz@xxxxxxxxxx>
To: "Pankaj K Jha" <pkj@xxxxxxxxxxx>; <afaber@xxxxxxxxxxxxx>
Cc: "ieee 802.17 list" <stds-802-17@xxxxxxxx>
Sent: Monday, July 02, 2001 1:18 PM
Subject: RE: Fw: [RPRWG] CRC check in each node?
>
> Pankaj/Angela/Bob,
>
> I have a question: where is this bit located - in the header, protected by
> the header's CRC or in the payload, protected by payload's CRC?
>
> Igor
>
> -----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 12:40 PM
> 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
>