Subject: Re: [mpls-tp] Interworking

From: Maarten Vissers <[email-masked]>
Date: Mon, 04 May 2009 13:27:25 +0200

Hi Jing,

Please see line marked [mv].. 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: donderdag 30 april 2009 8:37
To: [email-masked]; [email-masked]
Subject: RE: [mpls-tp] Interworking

Hi Maarten,

Please see inline. 

-----Original Message-----
From: Maarten Vissers [mailto:[email-masked]]
Sent: Thursday, April 30, 2009 12:55 PM
To: [email-masked]; [email-masked]
Subject: RE: [mpls-tp] Interworking

Hi Jing,

The difference between (3) and (4) is the following:

(3) all services are supported via the EVC layer; i.e. the EVC layer is the
service/channel layer and starts/ends at the UNI-N ports. The PW is a SS-PW
layer and monitors p2p EVC link connections.

PE nodes switch/bridge only EVC signals (as all customer service signals are
supported via EVCs).

------

(4) the p2p and p2mp services are supported via the PW layer (MS-PW) and the
rmp and mp2mp services are supported via the EVC layer; i.e. the PW layer is
the service/channel layer for p2p/p2mp services and for those services
start/end at the UNI-N ports, while the EVC layer is the service/channel
layer for rmp/mp2mp services and for those services start/end at the UNI-N
ports.

Jingrq->So you mean for  the rmp and mp2mp services, we don't need PW
layers. 

[MV] rmp and mp2mp services do not need a "PW layer". 
These services use the "PW label stack entry header" to identify each EVC
within an LSP.
These services don't need the "PW OAM" that comes with the "PW Layer", while
the EVCs have their own ETH OAM. 

Jingrq->I think there are two problems with this approach. 
Firstly, this is different from the practice of VPLS in MPLS network. 

[MV] What I have seen from the practice of VPLS in MPLS network is that the
VPLS instances are identified by a PW label and that the VPLS priority/drop
eligible information is carried by the PW TC bits. As VPLS is just another
name for a VLAN and thus another name for an EVC, I have always understood
that my approach is the common practice of VPLS in MPLS network.

Jingrq->Secondly, I think there are scalability problem in core network
without
PW layers.

[MV] I have been studying the scalability of packet transport networks in
some detail over the past years and have not found any scalability problem
in either metro of core network domains when I would run EVC (VPLS/VLAN/ETH)
directly over an MPLS(-TP) LSP layer. Each EVC within an LSP is identified
by a PW label. As EVC and PW have a 1-to-1 relationship, there is nothing to
win when an EVC is first mapped into a PW and then the PW is mapped into an
LSP. However, when I studied the impact of an additional PW trail between
EVC link connection and LSP, then I found that the complexity of the NNI
port cards and the network management where increased compared to the case
without PW trail between EVC link connection and LSP. Perhaps this is best
illustrated with a comparison of functional models of NNI interface ports. I
will create some later this week.

Rmp/mp2mp customer services (Ethernet) are either clients of the EVC layer,
or peer with the EVC layer.

P2p/p2mp customer services (PDH, SDH, ATM, Ethernet, ..) are clients fo the
PW layer (and may in future also peer with the PW layer).

PE nodes will be able to switch/bridge both PW and EVC signals. Switch
fabrics must support as such PW switching and Ethernet bridging/switching.

PW connections terminate on the UNI-N ports for the case of p2p/p2mp
services. 
PW connections terminate on the NNI ports for the case of rmp/mp2mp
services. 

------

Interconnecting a MPLS-TP domain according to layer stack (4) with an
Ethernet domain with layer stack (5) via an 802.3 interface results in the
following for rmp/mp2mp services (Ethernet E-Tree, E-LAN):

    (5)                         (4)
-----------------------------------
|   EVC           EVC       EVC   |
----------------------------------------
|   EVP    |   | 802.3 |    |    PW    |
------------   ---------    ------------
| T.Media  |                |   LSP    |
------------                ------------
                            |  T.Media |
                            ------------

Jingrq-> I think above layer stack should be the common one for all the
services, not only for EVC, but for all the services  (PDH CES, ATM, SDH
CES, ..)

[MV] I am getting the feeling that I have not made the relationship with the
customer/client services and this layer stack clear enough. Let me retry by
adding some of the client signals (ETH, PDH, SDH, FR, ATM) to the figure
(see below).

  p2p
  p2mp
  rmp                                p2p
 mp2mp      client services          p2mp
  ETH                                ETH
  PDH                                PDH
  SDH                        rmp     SDH
  FR                        mp2mp    FR
  ATM                        ETH     ATM
   |                          |       |
-----------------------------------   |
|   EVC           EVC     EVC/VPLS|   |
----------------------------------------
|   EVP    |   | 802.3 |    |    PW    |
------------   ---------    ------------
| T.Media  |                |   LSP    |
------------                ------------
                            |  T.Media |
                            ------------

[MV] In MPLS-TP, the rmp and mp2mp ETH signals from the customer are client
signals of the EVC/VPLS. The p2p/p2mp ETH, PDH, SDH, FR and ATM signals from
the customer are client signals of the PW.

[MV] In an Ethernet transport network, all signals from the customer are
client signals of the EVC.

[mv] The EVC layer is as such a layer that is owned by the transport
network, and not by the customer networks.

[MV] Like it is possible in SDH, ATM and OTN that the customer owns the
endpoint of a VC-n, VC or ODUk, it is possible in Ethernet that a customer
owns an endpoint of an EVC. Similarly, it is possible that in future a
customer owns an endpoint of a PW. For those cases the customer signals are
not longer clients of the PW and clients of the EVC. Those signals are now
peers of the PW and peers of the EVC. 

-----------------------------------  
|   EVC           EVC     EVC/VPLS|---------- ETH (peering service)
----------------------------------------
|   EVP    |   | 802.3 |    |    PW    |----- PW (peering service)
------------   ---------    ------------
| T.Media  |                |   LSP    |
------------                ------------
                            |  T.Media |
                            ------------

Best Regards,
Maarten

Best Regards
 
Jing Ruiquan