The MPLS WG Archive

["Qureshi, Muhammad A (Akber)" <mqureshi@lucent.com>]

Hi Defeng,

See my comments inline:

Regards,
Akber.

-----Original Message-----
From: lidefeng [mailto:lidefeng@huawei.com]
Sent: Tuesday, August 26, 2003 5:16 AM
To: mqureshi@lucent.com
Cc: mpls@UU.NET
Subject: About "extra traffic" and "seperate LSP" in Y.1720


In section 7.1.4("Switch initiation criteria") of TD25R1(plen) at the ITU-T
SG13 meeting of Geneva,21 July - 1 August 2003(Draft Revised Recommendation
Y.1720 (Protection
switching for MPLS networks)), it notes that "NOTE 1 - A forced switch for
working LSP should not be overridden by a Signal Fail on the protection LSP.
Since unidirectional protection switching is being performed and no APS
protocol is supported over the protection LSP, Signal Fail on the protection
LSP does not interfere with the ability to perform a forced switch for
working LSP."
[Akber] This means that when a forced switch is in place (either at the
egress side for 1+1 or ingress side for 1:1) the signal fail condition
on the protection LSP cannot make a switch from the protection to the
working LSP. Further, the note is ellaborating that since there is really no
APS supported on the protection LSP, Signal Fail on the protection
LSP will not any way interfere with forced switch from working to 
protection LSP.

But if there is a Signal Fail on the protection LSP,how can the protection
LSP work normally,after the traffic on the working LSP is "Forced Switched"
to the protection LSP,then the traffic may be in outage,is there any
detection action or any alarm signal sent before the forced switch?
[Akber] When there is a failure on the protection LSP it will be detected
at the sink of the protection LSP (note that the protection LSP is
being monitored independent of the working LSP). Forced switch is a manual
operation and can be avoided when the protection LSP is in fail state.

What is your consideration?


Defeng Li
Huawei Technologies