Subject: Re: [PWE3] Pseudo-wires: uni-directional o bi-directional?

From: Javi <[email-masked]>
Date: Thu, 15 Jul 2010 12:50:00 +0200

Hi everyone,

I would like to achieve an agreement on this topic. I sum some comments:

===
<Javi>
A pseudo-wire is: uni-directional o bi-directional?. I found confusing 
references:

RFC 3985 (PWE3 Architecture)
7.3.1.  Pseudo Wire Up/Down Notification
    If a native service requires bi-directional connectivity, the
    corresponding emulated service can only be signaled as being up when
    the *PW* and PSN tunnels (if used), are *functional in both directions*.

RFC 5087 (TDMoIP PWs), clause 6
Since TDM *PWs are inherently bidirectional

*RFC 5087 (TDMoIP PWs), clause 3
Since TDM is inherently bidirectional, the *association of two PWs in 
opposite directions is required*

<Ignacio Goyret> => Bidirectional for L2TPv3
I'm not an MPLS expert, but I can tell you that all L2TP sessions
are always capable of bidirectional traffic, regardless of the type
of data they may carry. This is an intrinsic feature of L2TP.

<Javi>
I understand a "L2TPv3 PW" is a PW which "PW Demultiplexer layer"
(or PW label) is based on a L2TPv3 Session ID, using the L2TPv3 control 
plane.

<Yaakov> => Unidirectional or bidirectional, depending on the native service
If the native service being emulated is bidirectional, then the PW will 
be bidirectional.
MPLS LSPs are unidirectional. So when supporting a bidirectional 
service, two LSPs in opposite directions will need to be associated.

<Sasha> => Bidirectional for MPLS
I think the problem is actually a typo in 5087. If you read "association 
of LSPs in two opposite directions" (which I believe was the intention), 
this text would be OK.

<Javi>
We must take into account that RFC 5087 does not only consider MPLS PW. 
Otherwise, according with clause 4, it also considers UDP/IP, L2TPv3 and 
Ethernet PWs. So, when it asserts (clause 4):

Since TDM is inherently bidirectional, the association of two PWs in 
opposite directions is required

We can not change it for:

Since TDM is inherently bidirectional, the association of LSPs in two 
opposite directions is required

because it woult only cover the MPLS PWs.

<Stewart> => Bidirectional
PWs are co-routed bi-directional since it is required that they go 
through the same xPEs in each direction, and the xPEs knows about the 
association of the two directional components.

<Sasha> => Bidirectional for MPLS
I agree with "co-routed" means "co-routed in the immediate lower layer", 
and hence PWs (both single-segment and multi-segment) are co-routed 
bi-directional LSPs.

===

Then, may we conclude?:

"Any PW is always bidirectional, regardless of its kind (MPLS, L2TPv3, 
UDP/IP, Ethernet, ...)"

Javi

---

From: Mach Chen <[email-masked]>
Date: Thu, 15 Jul 2010 19:44:45 +0800

Hi Javi,

IMHO, P2P PWs are almost bidirectional, P2MP PWs are unidirectional to 
date(there may be bidirectional P2MP PW in the future, seems some guys are 
working on bidirectional P2MP PW). I tend to agree Yaakov's statement: it 
depends on the native service.

Best regards,
Mach

--------------------------------------------------
From: "Javi" <[email-masked]>
Sent: Thursday, July 15, 2010 6:50 PM
To: "Alexander Vainshtein" <[email-masked]>; "Yaakov 
Stein" <[email-masked]>; "'Stewart Bryant'" <[email-masked]>; 
<[email-masked]>; <[email-masked]>
Subject: Re: [PWE3] Pseudo-wires: uni-directional o bi-directional?

> _______________________________________________
> pwe3 mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pwe3
>

---

From: Javi <[email-masked]>
Date: Fri, 16 Jul 2010 13:38:49 +0200

Hi Mach,

> date(there may be bidirectional P2MP PW in the future, seems some guys 
> are working on bidirectional P2MP PW). I tend to agree Yaakov's 
> statement: it depends on the native service.

A L2TPv3 session is always bidirectional. So, a L2TPv3 PW would always 
be bidirectional, regardless if it is used to emulate an uni-directional 
o bi-directional native service.

Regards,

Javi

---

From: Javi Muñoz <[email-masked]>
Date: Mon, 19 Jul 2010 17:18:36 +0200

Hi Sasha, Yaakov, Stewart and Mach,

According with your proposals, which is the conclusion about this topic?

1 - PWs are always (co-routed) bi-directional. So, any PW is always 
bidirectional, regardless of its kind (MPLS, L2TPv3, UDP/IP, Ethernet, ...).
As support for this proposal, we have that a L2TPv3 session is always 
bidirectional. So, a L2TPv3 PW would always be bidirectional, regardless 
if it is used to emulate an uni-directional o bi-directional native service.

or

2 - It depend on the native service. If the native service being 
emulated is bidirectional, then the PW will be bidirectional. In other 
case, it would be uni-directional.
     But this would imply that a L2TPv3 may be uni-directional while a 
L2TPv3 session is always bi-directional.

I think this is a relevant feature of the PWs, so it would be clearer in 
the RFCs.

Regards,

Javi

El 16/07/2010 13:38, Javi escribió:
> Hi Mach,
>
>> Hi Javi,
>>
>> IMHO, P2P PWs are almost bidirectional, P2MP PWs are unidirectional 
>> to date(there may be bidirectional P2MP PW in the future, seems some 
>> guys are working on bidirectional P2MP PW). I tend to agree Yaakov's 
> be bidirectional, regardless if it is used to emulate an 
> uni-directional o bi-directional native service.
>
> Regards,
>
> Javi
>
>>
>> Best regards,
>> Mach
>>
>> To: "Alexander Vainshtein" <[email-masked]>; 
>> "Yaakov Stein" <[email-masked]>; "'Stewart Bryant'" 
>> <[email-masked]>; <[email-masked]>; <[email-masked]>

---

From: Javi Muñoz <[email-masked]>
Date: Fri, 23 Jul 2010 10:37:06 +0200

Hi Yaakov and Ignacio,

According with your answers to my question "A pseudo-wire is 
uni-directional o bi-directional?":

<Yaakov>
It depends on the native service. If the native service being emulated
is bidirectional, then the PW will be bidirectional.

<Ignacio>
An L2TP session is always 100% bidirectional. L2TP does not have
the capability to create unidirectional sessions.

How a L2TP PW (or a L2TP session) may emulate an uni-directional native 
service?

Regards,

Javi