Subject: Re: [PWE3] Re: Bridge or

From: Danny McPherson <[email-masked]>
Date: Wed, 04 Dec 2002 00:04:19 -0700

> LAN products support MAC frame forwarding as well as Bridge protocols
> such as STP/RSTP/MSTP and GARP/GMRP/GVRP and MAC control protocols
> such as PAUSE and LCAP. Handling rules for these protocols in a Bridge
> or LAN are completely different. Therefore, to verify conformity with
> existing LAN products, semantics must be clarified first.

Semantics was probably a bad choice of words, though I do believe
a large part of the issue here is a misalignment in *terminology*.  
 
> Otherwise, why can we claim that the PW conforms with existing LAN
> standards?

It's important to remember that it's not necessarily a goal for PWE3 
to provide exact faithfulness to that of the native protocol (the FW 
document suggests PWE3 emulates "essential attributes" of a service).  
As such, with keeping the above in mind, Juergen is correct in stating
that "PWE3 defines the transport of L1/L2 client signals over a PSN
(paraphrased)".

I believe the latter of your concern here was regarding the term used 
to define the "native protocol" (or "service") itself and do agree 
aligning terminology certainly makes sense.  You folks were OK with 
"(Ethernet) LAN Emulation" or "Bridged (Ethernet) LAN Emulation", just 
not "Bridge Emulation", correct?  I think we can work with this...?

That being said, as Eric stated, while a PW does include NSP functionality
for the service that's being emulated, the NSP is NOT part of the PW.
 
Now, back to the first issue:

I believe the initial concerns were triggered by Section 3.1.6
of the Ethernet encapsulation draft, where it states that the PAUSE 
frames MUST NOT be transmitted across a PW (paraphrased).  If I'm
not mistaken, that text was added quite a while ago in order to 
suggest [to naive implementers] that it doesn't make sense to forward 
IEEE802 flow-control frames across a PW/PSN.  

Being that the "MAC Entity", which resides within the NSP function, 
provides PAUSE frame termination, perhaps removing the current text 
and clarifying by employing additional NSP-specific terms will ease 
your concerns?  If so, perhaps you could provide some text here?

We should also clarify other NSP functions such as handling CRC errors, 
framing errors, runt conditions, etc.., and equally, PW functions that 
result in PW "generalized bit errors" (e.g., out-of-order packets, packet 
loss, etc..), as Akiva suggests.

And we're certainly not providing the "medium connection", between 
"Medium Dependent Interfaces"!

-danny

---

From: Muneyoshi Suzuki <[email-masked]>
Date: Fri, 06 Dec 2002 17:21:24 +0900

Danny,

> document suggests PWE3 emulates "essential attributes" of a service).  

Yes, but limitation must be addressed in the applicability statement,
so semantics must be clarified.

> that "PWE3 defines the transport of L1/L2 client signals over a PSN

Agreed.

> aligning terminology certainly makes sense.  

Exactly.

> You folks were OK with 

I think the PW Ethernet reference configuration defined in section 2
can be termed Bridged (Ethernet) LAN Emulation, from viewpoint service
customers.

> for the service that's being emulated, the NSP is NOT part of the PW.

As Cheng-Yin pointed out, the scope of draft-ietf-pwe3-ethernet-encap-01.txt
is one of issues. 

According to the abstract, this draft discuss encapsulation of 
Ethernet/802.3 PDUs within a pseudo-wire.

>Abstract
>   existing PSN to offer ethernet services. This document addresses the
>   encapsulation of Ethernet/802.3 PDUs within a pseudowire, and issues
>   associated with the point-to-point emulation of ethernet within a PW.

But, the draft mainly consists of section 3 that is titled "Requirements
for Ethernet Pseudo-Wire Emulation". It seems to me, this section does
not discuss requirements, but if it is really requirements, this section 
should be entirely moved to the PWE3 requirements document.

I think requirements mean description of conditions that should be 
satisfied by a solution. However, it seems to me section 3 addresses 
implementation model and technical specification. So, if the draft
specifies PW protocol, it should focus PW protocol only, NSP and
CE-to-CE service are out scope of the draft.

If the draft specifies PW protocol and CE-to-CE service scenario using the
PW, these must be described separately. And it seems to me, NSP does not
emulate anything; for me it consists of MAC entity that terminates CE-PE link
and MAC relay entity, but if it emulates something, emulated entity that
is specified in existing standard or recommendation must be clarified.

> IEEE802 flow-control frames across a PW/PSN.  

I don't think "forwarding PAUSE frame across PW does not make sense",
because, a PW is not Ethernet, so PAUSE frame is undefined in that section.

> your concerns?  If so, perhaps you could provide some text here?

I think it depends on the scope of the draft. But if needed a small note
is sufficient, e.g.,

Note that PAUSE frame is undefined on the PW, because it is not Ethernet.

> loss, etc..), as Akiva suggests.

I'm very confused now. The above functions are indispensable for Ethernet 
frame transport over GRE/LSP tunnel. Nevertheless, you claim that the NSP 
is not the part of the PW.......

I would like to suggest to carefully sort our functionalities of PW model
from viewpoint of protocol architecture.

> "Medium Dependent Interfaces"!

I fully agree with this. Therefore, the PW Ethernet reference configuration,
defined in section 2, does NOT provide LAN emulation or emulated LAN 
service to customers.

Thanks,

Muneyoshi Suzuki
Nippon Telegraph and Telephone Corp.

---

From: "Cheng-Yin Lee" <[email-masked]>
Date: 6 Dec 2002 16:48:59 -0500

Danny,

>   from viewpoint of protocol architecture.

I am puzzled too. Where will the above so-called NSPs functions be specified?

BTW,  if you agree with Juergen, it's option (a),  not (b).  In Option (a), which
I believe is the technically correct thing to do in PWE3, we can use IEEE specs
in some of the emulation blocks as well, it doesn't mean PWE3 need to specify
them.

thanks
cheng-yin

Muneyoshi Suzuki wrote:

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