Subject: [mpls-tp] R: Is MS-PW a Transport Service layer Transport Path?

From: "BUSI, ITALO (ITALO)" <[email-masked]>
Date: Fri, 15 Oct 2010 20:00:05 +0200

Maarten,

Please refer to the following quotes from RFC 5659:

"
   o PW Switching Point.  The reference point in an S-PE where the
     switching takes place, e.g., where PW label swap is executed.
"

"
The receiving S-PE swaps the existing PW
   demultiplexer for the demultiplexer of the next segment and then
   sends the PDU over transport tunnel in PSN2.  Where the ingress and
   egress PSN domains of the S-PE are of the same type, e.g., they are
   both MPLS PSNs, a simple label swap operation is performed, as
   described in Section 3.13 of RFC 3031 [3].
"

I therefore think that the MS-PW is a Transport Service layer network per RFC 5654 terminology.

The case you mentioned of having multiple SS-PWs interconnected via the client layer is mentioned in RFC 5659 section 4.1.1 and 4.1.2:

"
4.2.1.  Inter-Provider Switching Using ACs

   In this model, the PW reverts to the native service at the provider
   boundary PE.  This AC is then connected to a separate PW at the peer
   provider boundary PE.  In this case, the reference models of RFC 3985
   apply to each segment and to the PEs.  This is similar to the case in
   Section 4.1.1, except that additional security and policy enforcement
   measures will be required.  The remaining PE architectural
   considerations in this document do not apply to this case.
"

Italo

-----Messaggio originale-----
Da: [email-masked] [mailto:[email-masked]] Per conto di Maarten Vissers
Inviato: lunedì 26 luglio 2010 16.41
A: 'venkatesan mahalingam'; [email-masked]
Oggetto: Re: [mpls-tp] Is MS-PW a Transport Service layer Transport Path?

Venkat,

The text you quote does not state explicit that the client signal is not
decapsulated and then again encapsulated; it only refers that it would not
do client demultiplexing and remultiplexing. Missing (but perhaps in another
paragraph/section) is text that states that PW labels are swapped and no
other operation on the packets with client information is performed.

Regards,
Maarten

________________________________

From: venkatesan mahalingam [mailto:[email-masked]] 
Sent: maandag 26 juli 2010 14:14
To: [email-masked]; [email-masked]
Subject: Re: [mpls-tp] Is MS-PW a Transport Service layer Transport Path?

Maarten,
As per RFC-5659, Section 8.1.  Multiplexing

   The purpose of the PW Demultiplexer Layer at the S-PE is to
   demultiplex PWs from ingress PSN tunnels and to multiplex them into
   egress PSN tunnels.  Although each PW may contain multiple native
   service circuits, e.g., multiple ATM virtual circuits (VCs), the
   S-PEs do not have visibility of, and hence do not change, this level
   of multiplexing because they contain no Native Service Processor
   (NSP).

<VM> IMO, client signals will not be decapsulated in the S-PE. 
S-PE does only the asociation of one segment PW with the another PW segment.
In which case, the client signals of one PW segment need to be decapsulated
and encapsulated in the next segment PW in S-PE?
 
Thanks,
Venkat.

*	From: Maarten Vissers <maarten.vissers at huawei.com
<mailto:[email-masked]> > 
*	To: mpls-tp at ietf.org <mailto:[email-masked]>  
*	Date: Mon, 26 Jul 2010 10:55:45 +0200 

________________________________

Based on a discussion I was involved in last week I have a question if a
MS-PW is a Transport Service layer Transport Path?

Up to last week I assumed that the answer to this question was 'yes'. My
assumption was based on the expectation that a MS-PW in MPLS-TP would
perform a simple label swap in a S-PE node. Now I am not sure that my
understanding is correct... It could be that a MS-PW in a MPLS-TP node
decapsulates its client signal on its S-PE ingress line card, transport this
client signal over the backplane to the egress line card and then
encapsulate the client signal again in a next PW...

If this latter is the case, then a MS-PW is not a Transport Service layer
Transport Path, but instead a set of SS-PWs interconnected via the client
layer (e.g. Ethernet, TDM). A MS-PW would in this case have to be replaced
by a SS-PE transported in a multi-segment service-LSP. The multi-segment
service-LSP would in this case be monitored (e.g. CC/CV, packet loss,
loopback).

Regards,
Maarten

-- 
Best Regards,
Venkatesan Mahalingam.

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