Subject: AII differences between PW routing and l2vpn signalling draft provisionong methods.

From: Luca Martini <[email-masked]>
Date: Fri, 02 Dec 2005 11:09:00 -0700

WG,

After a good discussion with Bruce Davie,  we came up with the following 
explanation on why we need to have different AII type int he PW setup 
and maintenance protocol.
This note explains why draft-ietf-l2vpn-signaling-06.txt (the L2VPN 
Signaling draft) and draft-balus-bocci-martini-dyn-ms-pwe3-00.txt (the 
MS PW draft) make use of different AII types, as defined in 
draft-metz-aii-aggregate-01.txt.
 In a nutshell, the two drafts use different AII types because they are 
tackling different problems. Specifically, L2VPN Signaling draft is 
concerned with setting up all the PWs for a given L2VPN, while the MS PW 
draft is concerned with setting up individual PWs.
 Because it is concerned with building L2VPNs, the L2VPN Signaling draft 
makes use of the AGI (the contents of which effectively identify the 
VPN) plus the AII to identify a particular PW. Hence, the AII only needs 
to identify a "pool" or a VSI relative to a particular AGI. Hence a 
simple 32 bit AII is sufficient.
By contrast, because the MS PW draft is concerned with setting up 
individual PWs, not L2VPNs, it has no use for the AGI - there is no 
"group" concept. Hence it fully identifies the PW in the AII. Because 
there may be many PWs connected to a given U-PE device, it is necessary 
to identify the PWs relative to a given U-PE. And it is necessary to 
identify the U-PE within the AII so that the signaling message can be 
routed toward the correct U-PE. Hence the requirements for the AII are 
quite different, and it makes sense to use an AII type that is designed 
to meet these requirements.
It is obvious that the simple AII type could be encoded in the more 
complex AII type by leaving various fields set to zero, but this does 
not seem to serve any useful purpose.

Luca

---

From: "Mustapha Aissaoui" <[email-masked]>
Date: Fri, 2 Dec 2005 13:57:41 -0500

Luca,
I do not believe there is any substantial difference that warrants to
standardize two different AII types. A MS-PW can also terminate on a VSI,
e.g., VPLS.

The issue is to be able to encode the target termination interface: an
endpoint for a p2p PW or a VSI for a VPLS in a way such that it will work
for both single hop PWs and MS-PWs. Both types can be used for the various
L2VPN applications.

Pragmatically, the way to go is to deprecate the FEC 129 as defined in
draft-ietf-l2vpn-signaling-06.txt (Type 1) and extend the Type 2 to cover
the various applications. One other reason to deprecate Type 1 is that we do
not want an implementation to use different FEC 129 types for single-hop PW
and MS-PW. FEC 128 will be restricted to singe hop PW and will be fine as
long as we specify a way to reach U-PEs which are on a FEC 129 Type 2
network.

Mustapha.
-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Luca Martini
Sent: Friday, December 02, 2005 1:09 PM
To: L2VPN
Cc: David McDysan; [email-masked]
Subject: AII differences between PW routing and l2vpn signalling draft
provisionong methods.

WG,

After a good discussion with Bruce Davie,  we came up with the following
explanation on why we need to have different AII type int he PW setup and
maintenance protocol.
This note explains why draft-ietf-l2vpn-signaling-06.txt (the L2VPN
Signaling draft) and draft-balus-bocci-martini-dyn-ms-pwe3-00.txt (the MS PW
draft) make use of different AII types, as defined in
draft-metz-aii-aggregate-01.txt.
 In a nutshell, the two drafts use different AII types because they are
tackling different problems. Specifically, L2VPN Signaling draft is
concerned with setting up all the PWs for a given L2VPN, while the MS PW
draft is concerned with setting up individual PWs.
 Because it is concerned with building L2VPNs, the L2VPN Signaling draft
makes use of the AGI (the contents of which effectively identify the
VPN) plus the AII to identify a particular PW. Hence, the AII only needs to
identify a "pool" or a VSI relative to a particular AGI. Hence a simple 32
bit AII is sufficient.
By contrast, because the MS PW draft is concerned with setting up individual
PWs, not L2VPNs, it has no use for the AGI - there is no "group" concept.
Hence it fully identifies the PW in the AII. Because there may be many PWs
connected to a given U-PE device, it is necessary to identify the PWs
relative to a given U-PE. And it is necessary to identify the U-PE within
the AII so that the signaling message can be routed toward the correct U-PE.
Hence the requirements for the AII are quite different, and it makes sense
to use an AII type that is designed to meet these requirements.
It is obvious that the simple AII type could be encoded in the more complex
AII type by leaving various fields set to zero, but this does not seem to
serve any useful purpose.

Luca