Subject: Draft PWE3 Charter

From: Stewart Bryant <[email-masked]>
Date: Fri, 30 Jul 2004 15:22:32 +0100

Here is the proposed updated PWE3 Charter that Danny and I sent
to Thomas a little while ago.

We will be working on this at the meeting next week, but comments
ahead of time would be appreciated.

- Stewart

Description of Working Group:

Network operators and their subscribers are seeking to rationalize
their networks by migrating to a single, IP or MPLS based packet
switched network. This migration requires communications
services that can emulate the essential properties of traditional
communications links over a packet switched network (PSN).

Pseudowire Emulation Edge to Edge (PWE3) will specify the encapsulation,
transport, control, management, interworking and security of
services emulated over IETF specified packet switched networks.

A pseudowire emulates a point-to-point link, and provides a
service which is perceived by its user as an unshared link
or circuit of the chosen service.

It is not intended that an emulated service will be
indistinguishable from the service that is being emulated.
The emulation need only be sufficient for the satisfactory
operation of the service. Emulation necessarily involves
a degree cost-performance trade-off. In some cases it may
necessary to design more than one emulation mechanism in
order to resolve these design conflicts. All emulated
service definitions will provide an applicability statement
describing the faithfulness of the emulation.

Switching, multiplexing, modification or other operation on
the traditional service, unless needed as part of the emulation
is out of the scope of the PWE3 WG.

PWE3 will make use of existing IETF specified mechanisms
unless there are technical reasons why the existing mechanisms
are insufficient or unnecessary.

PWE3 will not exert control on the underlying PSN, other than
to use any existing QoS or path control mechanism to provide
the required connectivity between the two ends of the PW.

PWE3 will use RTP where necessary to perform clock recovery and
other real-time signaling functions.  This work will be
coordinated with the AVT WG and payloads will follow RFC 2736.

WG Objectives (in order of priority):

Specify the following PW types:
Ethernet, Frame Relay, PPP, HDLC, ATM, TDM and SONET

Specify the control and management of the PW types
identified above.

Specify OAM mechanisms for all PW types, suitable for
operation over both IP and MPLS PSNs, and capable of
providing the necessary interworking with the OAM mechanisms
of the emulated service.

Enhance packet-based PW specifications as necessary to
allow the emulated service to be carried transparently
over the PSN, for example by the retention of the FCS
across the PW.

Define mechanisms to permit the operation of a PW over
a PSN that deploys equal cost multiple path packet (ECMP)
switching.

Specify the encapsulation, control and management of an
IP PW type.

A PW operating over a shared PSN does not have the same
intrinsic security as a dedicated purpose built network.
In some cases this is perfectly satisfactory. In other
cases it will be necessary to enhance the security of
the PW to emulate the intrinsic security of the
emulated service.

Whilst a service provider may traffic engineer their network
is such a way that PW traffic will not cause significant
congestion, a PW deployed by an end-user may cause
congestion of the underlying PSN. Suitable congestion
mechanisms are therefore needed to protect the Internet
from the unconstrained deployment of PWs.

Define mechanisms to allow the interconnection of PWs.

Define mechanisms to allow the inter-domain operation of PWs.

Define the mechanisms needed to allow the operation of switched
virtual circuits over a PSN.

---

From: "Busschbach, Peter B (Peter)" <[email-masked]>
Date: Fri, 30 Jul 2004 14:46:47 -0400

Hi Stewant,

Two comments:

1) "Define mechanisms to allow the interconnection of PWs"

I propose that we formulate this as "define mechanisms to create multi-hop PWs". A PW that consists of multiple segments is from a user's perspective still a single emulated point-to-point link, i.e. a single PW. A PW segment by itself is nothing. So, the issue is not interconnecting PWs, but interconnecting PW segments to create a PW.   

2) "Define the mechanisms needed to allow the operation of switched virtual circuits over a PSN."

Could this be clarified? To me this seems to be primarily as issue related to the control plane protocol of the emulated service (e.g. PNNI). Why would the IETF work on that? PWE3 provides the tools for PW setup. How they are used is outside the scope of the WG.

Peter

> -----Original Message-----
> From: Stewart Bryant [mailto:[email-masked]]
> Sent: Friday, July 30, 2004 10:23 AM
> To: [email-masked]
> Cc: Thomas Narten; Danny McPherson
> Subject: [PWE3] Draft PWE3 Charter
> 
> 
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