Subject: Some comments on draft-ietf-pwe3-segmented-pw-11

From: Sherry Xue <[email-masked]>
Date: Wed, 20 May 2009 17:02:15 +0800

Hi,
I have reviewed the draft-ietf-pwe3-segmented-pw-11, and have some comments,
please find below.

1)	Section 4, some confused about figure 2, there are two "emulated
service" identifiers, between the egress of CE1 and ingress of CE2, also
between the ingress of PE1 and the egress of PE4.Does some amendment should
be done to avoid the reduplicate emulated service?

2)	Section 4, in the penultimate paragraph, "this document describes
procedures for building multi-segment pseudo wires using manual
configuration of the switching point PE2", the Switching point" PE2" should
be "S-PE "which will be coincident with figure 3. And the identifier of the
Switch point in the sentence should be consistent with figure 3. 

3)	Section 4, in the last paragraph, " no control messages are
exchanged yet as the S-PE PE dose not have.", there are a redundant "PE",
please delete it.

4)	Section 4, in the last paragraph, sentence as "first the S-PE is
configured to switch a SS-PW from a specific peer to another SS-PW destined
for a different peer".
 I have some confusion about SS-PW definition used in the MS-PW as PW
segment role. SS-PW is defined as "a PW setup directly between two T-PE
devices. Each PW in one direction of a SS-PW traverses one PSN tunnel that
connects the two T-PEs." in the terminology section of [segmented-pw]. But
SS-PW is defined "a PW setup directly between two PE devices. Each direction
of an SS-PW traverses one PSN tunnel that connects the two PEs" in RFC5254.
They are different, because SS-PW is terminated on different PE roles, T-PE
in former case, T-PE or S-PE in latter case. 
IMO, SS-PW should be setup between TWO T-PE devices, there are some
differences between SS-PW and PW segment. If it is right, the SS-PW could
not be used the same as PW segment. So the sentence should be restructured
as "first the S-PE is configured to switch a PW segment from a specific peer
to another PW segment destined for a different peer...".  And concerted
action should be taken in the draft.

5)	Section 7, in the first paragraph, the nomenclature should be
identical with figure 3, such as PE2, PE3 should be amended as S-PE and
T-PE, etc.

6)	Section 7.4, in the second sentence, Should the"PW switching point
TLV" in line 3 be "S-PE TLV"? In the fourth and fifth paragraphs, should the
"PW switching point TLV" in line 1 be "S-PE TLV"?

7)	Section 7.4.1, The title of section 7.4.1 should be accordant with
the title of section 7.4, so "S-PE sub-TLV" may be better?

8)	Section 8, the title, "MPLS-PW to PW-L2TPv3 control plane switching"
may be amended as "MPLS-PW to L2TPv3-PW control plane switching"

9)	Section 8.4.1, I have some confused about the session establishment.
In the two example exchanges of message, I understand that the MS-PW is
setup in one direction totally, and then the other direction. Dose I make a
mistake? Now I have a question, take L2TPv2 PW- MPLS PW for example, whether
the L2tpv3 ICRP must be send after the LDP label mapping receiving from the
PE3? Should the PW switching node, map to LDP Label mapping forward and send
L2TPv3 ICRP backwards simultaneity? 

And I have a question, which is why VCCV CC type 2 is not supported for
MS-PW? I think the reason is that the P device, which is neither S-PE nor
T-PE, is not responsible to inspect the VCCV message? That is right?

Regards 

Sherry