Subject: [Pce] Question about PCEP Keepalive

From: "Adrian Farrel" <[email-masked]>
Date: Sat, 25 Aug 2007 01:56:47 +0100

Hi,

I'm looking at r08 sections 6.3 and 7.2.

Section 6.3 has

   Note that sending Keepalive messages to maintain the session alive is
   optional and PCEP peers may decide to not send Keepalive messages
   once the PCEP session is established.

Section 7.2 has

   Keepalive (8 bits): maximum period of time (in seconds) between the
   sending of PCEP messages.  The minimum value for the Keepalive is 1
   second.  When set to 0, once the session is established, no further
   Keepalive messages need to be sent to the remote peer.

And also

   A sends an Open message to B with Keepalive=10 seconds and
   Deadtimer=30 seconds.  This means that A sends Keepalive messages (or
   ay other PCEP message) to B every 30 seconds and B can declare the
   PCEP session with A down if no PCEP has been received from A.

I find this peculiar. Sending a keepalive message does not verify for the
sender that the session is open. It verifies for the receiver. So, surely
the parameter in the Open object says how frequently the sender of the Open
message wants to receive a Keepalive message. That is, how often the
receiver of the Open message must send a Keepalive message.

For example, if a PCC is worried that the session may fail, it will want to
operate the keepalive process. But as currently specified, the PCC can only
tell the PCE how often the PCC will send Keepalive messages, and after what
period the PCE may declare the session dead. This is no help to the PCC! If
the PCE decides that it will not send Keepalive messages then the PCC cannot
determine the health of the session and cannot switch to a new PCE.

In other words, the keepalive process is back-to-front.

Further, I don't see why you need the keepalive timer value and the dead
timer value. One value can be derived from the other, probably through a
recommended ratio of 3.5.

Lastly, when describing that the use of keepalive is optional, there are a
couple of points:

1. Optional should be an RFC 2119 word
2. You need to make it clear that it is not the "PCEP peers"
    that decide to not send keepalives, but "each PCEP peer"
    that decides "whether it wants to receive keepalives"
3. You should indicate the circumstances surrounding
    the choice for this option. I think that, you might suggest
    that if PCE discovery is in use, the failure of a PCE can
    be speedily detected by the failure of the IGP, and can
    be flooded by timing out the LSA containing the discovery
    information. In this case, keepalive would not be needed.

Yes?

Adrian

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