Subject: [mpls-tp] draft-ietf-mpls-tp-gach-dcn

From: "Elisa Bellagamba" <[email-masked]>
Date: Thu, 14 May 2009 13:45:20 +0200

Hello,

I've been reading draft-ietf-mpls-tp-gach-dcn and I have a question.

The point which is not clear for me is how the signaling of a new LSP
can be done at the very beginning, when a G-Ach is not present yet. If
I'm not wrong, the G-Ach itself is carried in an LSP (being the
signaling done in-band).

In the introduction it has been stated that:

"  Label Switching Routers (LSRs) in MPLS networks may be operated using
   management protocols or control plane protocols. Messaging in these
   protocols is normally achieved using IP packets exchanged over IP-
   capable interfaces. However, some LSRs in MPLS-TP networks may be
   constructed without support for direct IP encapsulation on their
   line-side interfaces and without access to an out-of-fiber data
   communication network. In order that such LSRs can communicate using
   management plane or control plane protocols channels must be provided
   and the only available mechanism is to use an MPLS label.
   The G-ACh provides a suitable mechanism for this purpose, and this
   document defines processes and procedures to allow the G-ACh to be
   used to build a management communication network (MCN) and a
   signaling communication network (SCN) together known as the data
   communication network (DCN) "

Does the following part mean that a manual LSP setup should be performed
in the initial phase? I don't see any other alternatives.

   "Provider Edge nodes may wish to set up PWs using a singaling
protocol
   that uses remote adjacencies (such as LDP [RFC5036]). In the absence
   of an IP-based control plane network, these PEs MUST first set up an
   LSP tunnel across the MPLS-TP network. This tunnel can be used both
   to carry the PW once it has been set up and to provide a G-ACh based
   DCN for control plane communications between t`he PEs."

Thank you!

Regards,
Elisa

---

From: "Adrian Farrel" <[email-masked]>
Date: Thu, 14 May 2009 13:19:52 +0100

Hi,

All of this debate only applies both if the control plane is used and if the 
management plane is used, but may be more interesting with the "horizontal" 
communications used in the control plane.

It is possible to perform point-to-point signaling between physically 
adjacent nodes by using the G-ACh on the MPLS section between the nodes. 
I.e. using the GAL as the top label.

This is just like the ATM reserved VCI.

For physically non-adjacent nodes, it is necessary to create an LSP first so 
that a G-ACh associated with that LSP can be used. That LSP itself can be 
created using the MPLS section approach as described above.

Of course, die-hard IETFers may consider that an IP-capable control plane 
includes certain benefits including the ability to reach and control nodes 
where the physical adjacency may be broken.

Cheers,
Adrian

----- Original Message ----- 
From: "Elisa Bellagamba" <[email-masked]>
To: <[email-masked]>
Sent: Thursday, May 14, 2009 12:45 PM
Subject: [mpls-tp] draft-ietf-mpls-tp-gach-dcn

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---

From: <[email-masked]>
Date: Thu, 14 May 2009 13:42:55 +0100

Totally agree with Adrian on this.  regards, Neil 

> -----Original Message-----
> From: [email-masked] 
> [mailto:[email-masked]] On Behalf Of Adrian Farrel
> Sent: 14 May 2009 13:20
> To: Elisa Bellagamba; [email-masked]
> Subject: Re: [mpls-tp] draft-ietf-mpls-tp-gach-dcn
> 
> Hi,
>