Subject: [Sigtran] [M3UA] ASP UP in IPSP DE mode

From: Santhana <[email-masked]>
Date: Thu, 06 Jan 2011 10:26:34 +0530

Dear Brian

            In IPSP DE mode, is the double exchange of ASP UP messages
mandatory? As per the M3UA RFC 4666, in section 4.3.4.1.2 para2 says double
exchange of ASPSM is MUST.

Whereas in section 5.6.2 in the sequence diagrams it says second exchange is
optional.

If it is mandated, then what purpose it solves?

Regards

Santhanakrishnan

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Thu, 6 Jan 2011 02:45:50 -0700

Santhana,

Please see comments below...

Santhana wrote:                               (Thu, 06 Jan 2011 10:26:34)
>    mandatory? As per the M3UA RFC 4666, in section 4.3.4.1.2 para2 says
>    double exchange of ASPSM is MUST.
> 
>    Whereas in section 5.6.2 in the sequence diagrams it says second
>    exchange is optional.
> 
> 

I don't know what purpose it solves.  There was a change from RFC3332 to
RFC4666 in 4.3.4.1.2 para2, but the example in 5.6.2 did not change.  But
then the editor of RFC4666 did a poor job of keeping examples up to date
with the text.

 RFC 4666

   Alternatively, when using the IPSP DE model, an interchange of ASP Up
   messages from each end MUST be performed.  Four messages are needed
   for completion.

 RFC 3332

   Alternatively, an interchange of ASP Up messages from each end can be
   performed. This option follows the ASP state transition diagram. It
   would need four messages for completion.

The only reason I can remember for requiring double exchange of ASP-UP
for DE was so that a misconfiguration between SE and DE would be detected.
The original intent from RFC 3332 is described at the end of example
RFC4666/5.6.2 or RFC3332/5.5.2 (which are identical).

   In this approach, only one single exchange of ASP Up message can be
   considered as enough since the response by the other peer can be
   considered as a notice that it is in ASP_UP state.

But, in general, DE mode is always a situation of performing two message
exchanges where one will do.  Use SE mode wherever possible.

--brian

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/

---

From: Chris Benson <[email-masked]>
Date: Thu, 6 Jan 2011 11:02:16 -0800 (PST)

Brian and Santhana,

Noting first that "Brian was there", and "I was not",
I had considered that the DE mode was to cater to
different ASP states at each end of the IPSP pairing.

I think this means that in DE mode, sending an ASP-UP-Ack
meant that you were permitting the other side to enter
ASP UP state, but weren't implying that you were requesting
the same for your own state.

The usefulness of one side being UP and the other side
not UP in a single peer-to-peer relationship is beyond
my imaginings, though.  I think Brian's implication
is that if you are allowing the other side to move to
ASP-UP then you are admitting that you are happy to go
ASP-UP too, and I agree that SE is always the preferred
IPSP mode.

With thanks, from Chris Benson.

On Thu, 6 Jan 2011, Brian F. G. Bidulock wrote:

>>  Date: Thu, 6 Jan 2011 02:45:50 -0700
>>  From: Brian F. G. Bidulock <[email-masked]>
>>  To: Santhana <[email-masked]>
>>  Cc:  <[email-masked]>
>>  Subject: Re: [Sigtran] [M3UA] ASP UP in IPSP DE mode
>>  
>>  Santhana,
>>  
>>  _______________________________________________
>>  Sigtran mailing list
>>  [email-masked]
>>  https://www.ietf.org/mailman/listinfo/sigtran
>>

---

From: "Jaddu, Suresh (NSN - IN/Bangalore)" <[email-masked]>
Date: Fri, 7 Jan 2011 13:29:10 +0800

Hi,

Since SE/DE is under discussion I have one relevant question. RFC talks
about the two modes one is SGASP and another one IPSP (point to point)
but it is possible to have point to multi point network as well as shown
below (model-2).

model 1)
--------

Node 1  |  ------->   Node 2  [IPSP-SE]

model 2)
--------

	 |    ------>   Node2
Node 1 |    		      [IPSP-DE]
	 |    ------->  Node3

RFC talks about the IPSP is for point to point (which I understood as
model 1) but it does not talk much (atleast I could not find mentioning
of this) about the model-2 and possible configuration options. I know
the model-2) is also can be achieved using the IPSP but this is not
exactly the point to point some additional considerations are required,
I am not sure any one has encountered this before?? Question is what is
the recommended configuration for model-2? I do not think SE model will
straight way work for model-2?? From what I understand DE is more
suitable here?? Any one has similar views??

Suresh.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of ext Chris Benson
Sent: Friday, January 07, 2011 12:32 AM
To: Brian F. G. Bidulock
Cc: [email-masked]
Subject: Re: [Sigtran] [M3UA] ASP UP in IPSP DE mode

Brian and Santhana,

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Fri, 7 Jan 2011 03:44:47 -0700

Suresh,

If by Model 2 you mean that Node2 can communicate with Node3 via Node1
then it is explicitly not supported by IPSP in M3UA.  Only point-to-point.
If you want Node2 to communication with Node3 via Node1, then Node1 must
be an SG and Node2 and Node3 must be ASPs.  That is, the recommended mode
is an ASP-SG mode.

--brian

Jaddu, Suresh (NSN - IN/Bangalore) wrote:     (Fri, 07 Jan 2011 13:29:10)

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/