1. Packet Pseudowire Encapsulation over an MPLS PSN draft-bryant-pwe3-packet-pw-02.txt
{Stewart Bryant, Sami Boutros, Luca Martini,
Siva Sivabalan, George Swallow,
David Cisco Systems
Andy Verizon Communications

2. Candidate Mechanisms
During the Pkt-PW design investigation we considered four candidate mechanisms:
A protocol identifier (PID) in the PW Control Word (CW)
A PID label
Parallel PWs - one per protocol
Virtual Ethernet

3. PID In CW Proposed in draft 0 of this document
PID appended to the generic CW
CW effectively 6 bytes or 2 bytes
Virtual PPP interface
Not as simple as the PID label or multiple PW approaches
Not deployable on many existing h/w platforms

4. PID Label Described in Version 2 of this doc.
PID label is extra label after PW label.
New LDP FEC signaled protocol type to PID label binding.

5. PID Label 2
Complies with strict defn. of MPLS, but not with how some h/w designer's interpreted MPLS
Assumption in many designs that forwarding decision made on the basis of a single label
Not supported by commodity chips sets
New h/w would inc. cost of deployment and delay the introduction of packet PW service.

6. Parallel PWs One PW per protocol type
A packet-PW consists of a bundle of PWs
Simple and efficient from a forwarding point of view
# of parallel PWs normally relatively small - IPv4, IPv6, MPLS and CLNS

7. Problems with Parallel PW
Lack of fate sharing protocol types can lead to complex faults difficult to diagnose
Either
Run an OAM on each PW and bind results, or
Single OAM session on one PWs as a proxy for the others - mitigated through the use of BFD.
The need to configure manage and synchronize the behavior of a group of PWs as if they were a single PW

8. Virtual Ethernet
Use virtual Ethernet and Ethernet PW [RFC4448] to carry the user traffic
Simple and can be implemented today without any further standards action
Some deployed equipments can already do this
Larger MTU than the other approaches, but – not an issue on jumbo-gram n/w

9. Analysis
Parallel PW rejected because of operational complexity and the breaking of fate sharing
The PIDL may break implicit behavioral and label stack size assumptions – may need new h/w
The PID in CW new h/w
Virtual Ethernet –
Well known protocol stack
Well known (internal) client interface.
Widely implemented

10. Recommendation
Having considered a number of initially promising alternatives simplicity and existing hardware make the virtual Ethernet packet PW the most attractive solution Draft includes a number of applicability considerations