Hi Dimitri,
Please see inline.
On Sun, 01 Feb 2004 15:39:33 +0100,
Dimitri.Papadimitriou@alcatel.be wrote:
hi, see in-line
Yoshihiko SUEMURA wrote:
P&R Design Team,
In the 1:1/Shared Mesh Restoration described in
draft-lang-ccamp-gmpls-recovery-e2e-signaling-02, activation of a
secondary LSP is done only by a Path message. The Protection object is
carried only in a Path message.
However, I think a Resv message should also carry the Protection object.
Consider the following case.
A-----------B
\ /
C-------D
/ \
E F
A-B: Primary LSP
A-C-D-B: Secondary LSP
E-C-D-F: Extra (preemptable) LSP
Activating the Secondary LSP using only a Path message may cause
unintended connection (A-C-D-F) between the Secondary LSP and the Extra
LSP.
here i would agree that there is a condition on the next_hop
to delete the extra_lsp state before activating the xc for
the secondary lsp and in order to guarantee this commit of
the resources activation may be done upon resv reception
also the use of hard preemption before committing this
operation decreases (if not completely elevates if used
to commit action when received from D in this example)
the time occurrence of this transient state:
- PathErr with PAth_State_Removed flag towards E and a PathTear
to the destination F
- or a PathErr with Path_State_Removed flag towards F and a
PathTear towards E
therefore there are other faster triggers for this purpose
the issue being at the end to either perform this operation
as fast as possible when reaching the last common node,
or simply delete in downstream direction and commit along
the upstream direction as said above (there are more complex
cases where this might be at the end more easy to process)
This can be prevented by applying a two-way activation scheme using
both Path and Resv messages.
nothing prevent this from the above (the paragraph that
describes this doesn't say commit at the data plane this
is left out to the implementation) some clarification in
the document are certainly needed here
You can delete the Extra LSP by the Path
message, and activate the Secondary LSP by the Resv message.
you may want to apply this activation scheme, in such a case
all the nodes would have their extra-traffic lsp deleted
through the downstream path message
Yes. This is what I want to apply. I want to delete all the
extra-traffic LSPs through the downstream Path message, and then,
activate the secondary LSP through the upstream Resv message.
However, if the Resv message for activation does not carry the
Protection object, it cannot be distinguished from a refresh Resv
message. This still causes unintended connection in the following case.
(1) At node C, a crossconnect for the Extra LSP is deleted when
receiving a Path message.
(2) Then, if node C receives a refresh Resv message from D, it sets up a
crossconnect for the Secondary LSP because it cannot distinguish the
refresh Resv message from a Resv message for activation.
referring to 2961 p12/13 don't see how see this could happen,
would you clarify, in order to address this point in case, also
the resv is considered implicitly here as trigger message
After (1), node C waits for the upstream Resv message for activating the
secondary LSP. However, it may receive a refresh Resv message (refresh
for a Resv message for PROVISIONING the secondary LSP) from D before
receiving the Resv for activation. Currently, C cannot distinguish it
from the Resv for activation because there is no difference between
their formats. This may trigger C to activate the secondary LSP
unintentionally before the downstream nodes delete their extra-traffic
LSPs.