Subject: [PWE3] more comments on draft-jin-pwe3-cbit-negotiation-03

From: Luca Martini <[email-masked]>
Date: Mon, 28 Feb 2011 15:57:05 -0700

Authors,

In section 3 on page 4 is the following text :

"The procedure of PE1 and PE2 for the case in figure 1 should be as
   follows:

       1. PE2 changes locally configured control word to PREFERRED.

       2. PE2 will then send label withdraw message to PE1.

       3. PE2 MUST send label request messages to PE1 although it
          already received the label mapping with C-bit=0.

       4. PE1 will send label release in reply to label withdraw message
          from PE2.

       5. PE1 will send label mapping message with C-bit=1 again to PE2
          (Note: PE1 MUST send label mapping with locally configured CW
           parameter).

       6. PE2 receives the label mapping from PE1 and updates the remote
          label binding information.  PE2 MUST wait for PE1 label
          binding before sending its label binding with C-bit set, only
          if it previously had a label binding with C-bit = 0 from PE1.

       7. PE2 will send label mapping to PE1 with C-bit=1.
"

First of all the steps above are asynchronous, so it seems that step 4
should appear before step 3 or the old label mapping might be sent.
Step 5 is in response to step 3 , but that is not clear from the above list.

Also what happens if PE1 cannot support the CW ?  The above description
assumes PE1 can support the CW.

Also this label withdraw + label request procedure is fully backward 
compatible with previous implementations. The document should explain
this point.
 
The label withdraw should really wait for the label release, as in the
case of MS-PWs , sending an immediate label request can cause a race
condition , and result in the wrong state.

Thanks.
Luca