Regarding Switching capability and GPID in OSPF-TE and GMPLS-RSVP

[Sameer K <sameerdw@yahoo.com>]

Hello All,

I have some questions regarding switching capability
descriptor, encoding type and GPID parameters, and the
correlation between the values signaled in signaling
request and the values advertised in OSPF TE LSAs.

From the previous discussions, it appears that if a
data capable device has to establish LSP through a
network of OXCs, the switching type requested would be
FSC, the encoding type would be SDH/SONET with GPID
being PPP (assuming that the data device that is LSP
ingress wants to send IP data over the LSP).  Now, the
LSP will be established without any problem as long as
the destination node is advertising a switching
capability FSC and the encoding type SONET/SDH for all
its interfaces.

However, for the LSP to be of any use to ingress node,
the destination must be capable of terminating PPP
(which in turn requires data capability on the
incoming interface of egress node).  The way to ensure
this would be to read GPID and then egress can reject
the LSP if it cannot support the GPID.

However, what if destination is a multi-service switch
and bears certain interfaces that are FSC capable and
can terminate PPP as well (that is, support data over
FSC -if you will), other than the FSC only interfaces.
 CSPF running at ingress can never tell the difference
between these (data over FSC type) interfaces and
other (FSC only) interfaces and the LSP might end up
on an interface that cannot support PPP termination. 
In such a case, even though the node supports PPP at
certain interfaces, the LSP will have to be rejected.


Now, if some "higher layer" information (PPP
termination capability for this example), is
advertised as a part of OSPF TE LSAs, the CSPF running
on the ingress node can pick up the correct incoming
interface on egress node based on the GPID desired,
thus reducing the probability of LSP failures.

Would like to hear opinions.
TIA
- Sameer.

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