Subject: Re: [Sigtran] Sigtran Plugtest SUA/M3UA/M2UA/IUA - Day 2

From: [email-masked]
Date: Wed, 4 Dec 2002 15:16:46 +0530

bidulock,

>
> Sandeep  >> No, That's not always the case. GT is performed in response
messages
> also. Please see the following text from section 2.7.3 of Q.714.
>
> "When the called party address in an XUDT or LUDT or UDT message has the
routing
> indicator  set  on  "Route  on  GT",  the routing indicator in the calling
party
> address  shall  also  be  set to "Route on GT", unless the destination is in
the
> same MTP network and that its MTP routing tables allows the message to be
routed
> back."

I think you need to understand how SCCP is used in real networks.  GTT is never
performed on the response.  Repsonses are routed DPC only and must be relayed at
MTP Level 3.
Sandeep >> In case of SCCP CL message transport responses (UDTS/XUDTS/LUDTS) are
sent only when request message  (UDT/XUDT/LUDT) could not be delivered to peer
side and the originator has set the "return on error" option. This is an error
condition and should not happen too frequently in case of correctly configured
and managed real network.
I also disagree with you about how these responses are sent (when they are
sent). Using MTP3 relaying you can't sent back responses across SS7 networks and
some times within the same SS7 network. SS7 is used in variety of ways across
the world, You need to produce some real evidence to say that what is clearly
recommended in specifications (and which is logical also) is not used any where.

This is especially true of SMS messages, which was the case in point.
Sandeep >> SCCP behaviour is independent on type of User data and hence it can't
behave differently for SMS traffic. SCCP never knows if it is transporting SMS
traffic.

>
> Successful SCCP relay communications relies on STP function at MTP for CL and
> typically also requires it for CO (non-coupling of connection sections).  Such
> an IPSP would not be very useful for relay.
>
> Sandeep >> Non Coupled connection sections may not be possible as there is no
> relay at M3UA level. But there are many scenarios in SS7 network also where
> non-coupled connection sections will not be possible. Following is what
section
> 2.7.3 of Q.714 recommends about usage of Routing Indicator of Calling Address
of
> CR message.
>
> "For  a  CR message, the calling party address may be of the form "Route on
SSN"
> because the subsequent messages will be routed section by section."

Do you know of an SCCP user that couples connection sections through STPs?
Sandeep >> SCCP Users are never aware if the SCCP connection they are using in
Coupled or Non-Coupled.

I know of no real world example.  All current connection oriented applications
(RANAP, BSSAP) do not couple through STPs (BSSAP doesn't even pass through an
STP).

Rather than quoting what is possible in the spec, but never used in real
networks, can you cite a real world example where relaying at SCCP only
without the capability to transfer at MTP would be sufficient?

Sandeep >> Point I want to make is that nodes in the IP network (and using
SIGTRAN) should be able to talk to each other without a SG in between. SG should
only be needed in case a connectivity to SS7 network is needed . You raise a
concern that in some cases MTP3 level relaying is used in reverse direction and
the absence of M3UA level relaying will cause problem in those case and SG-SG
communication is the only option.
This is certainly not the case. I agree that in some cases MTP3 level relaying
is used in responses, but I see no disadvantage in case M3UA level relaying is
absent and SCCP level relaying being used in reverse direction. Which happens in
SCCP also in many cases.

-Sandeep

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---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 4 Dec 2002 03:06:09 -0700

samahajan,

[email-masked] wrote:                                                     (Wed, 04 Dec 2002 15:16:46)
> recommended in specifications (and which is logical also) is not used any where.

I'm not talking about UDTS.  UDTS has nothing to do with it.  I'm talking about
TCAP response messages, which are routed on DPC only.

> behave differently for SMS traffic. SCCP never knows if it is transporting SMS

But TCAP knows its sending SMS responses and routes them on DPC only.

> SIGTRAN) should be able to talk to each other without a SG in between.

The can: point-to-point and without relay which is provided for in the RFC.

> SG should only be needed in case a connectivity to SS7 network is needed.

It is also needed for relay, because IPSPs cannot handle relay.

> You raise a concern that in some cases MTP3 level relaying is used in
> reverse direction and the absence of M3UA level relaying will cause problem
> in those case and SG-SG communication is the only option.

The other option is not to relay.  IPSPs work fine in point-to-point
configuration.

> absent and SCCP level relaying being used in reverse direction. Which happens in

What cases?  SCCP level relaying is never used in the reverse direction.  Can
you provide an SCCP application example where MTP relaying is not used in the
reverse direction?

--brian

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