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

From: [email-masked]
Date: Wed, 4 Dec 2002 13:20:54 +0530

bidulock,

> Sandeep >> RFC does not allow M3UA to relay messages, but in case both SCCP
and
> M3UA layers at node acting as IPSP, SCCP layer can relay messages and this is
> very much allowed in RFC. For example in case IPSP1, IPSP2 and IPSP3 are three
> nodes and IPSP1 is connected to IPS2 and IPSP2 is connected to both IPSP1 and
> IPSP3. In this case message from SCCP application at IPSP1 can be sent to SCCP
> application at IPSP3 via IPSP2. SCCP at IPSP2 will relay message in this case.

I'm suprised by your oversimplification of SCCP.  Although such an arrangement
could relay at SCCP performing GTT on forward SCCP messages, it takes MTP
relaying (STP function) to transfer messages in the backwards direction.  GTT
is not normally performed on responses (CL), nor is it normally performing on
DT1 or DT1 (CO).

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."

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."

>
>
> > [Herve] The example given above is being developped now on the basis of what
> > is described in the RFC text which fits the need.
>
> As relay is not supported in IPSP, I suggest that you contribute to
> work on an extension draft for SG-SG behavior.
>
> Sandeep >> M3UA level relay is not really required as SCCP level relay is
> present. In the scenario of SMS off-load, IPSP communication with SCCP level
> relay can be used and there is no requirement for SG-SG communication. SG
should
> be required in the network in case Nodes in IP network needs to talk to SS7
> network. For nodes within IP network to talk to each other SG should not be
> required.

Again, forward UDT can relay on GTT, however, the response requires STP
transfer at MTP.

--brian

--
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/
_______________________________________________
Sigtran mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/sigtran

DISCLAIMER: This message is proprietary to Hughes Software Systems
Limited (HSS) and is intended solely for the use of the individual
to whom it is addressed. It may contain  privileged or confidential
information  and should not be circulated or used for any purpose other
than for what it is intended. If you have received this message in error,
please notify the originator immediately. If you are not the intended
recipient, you are notified that you are strictly prohibited from using,
copying, altering, or disclosing the contents of this message. HSS accepts
no responsibility for loss or damage arising from the use of the information
transmitted by this email including damage from virus.

_______________________________________________
Sigtran mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/sigtran

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 4 Dec 2002 01:21:25 -0700

samahajan,

[email-masked] wrote:                                                     (Wed, 04 Dec 2002 13:20:54)
> same MTP network and that its MTP routing tables allows the message to be routed

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.  This is especially true of SMS messages, which was
the case in point.

> because the subsequent messages will be routed section by section."

Do you know of an SCCP user that couples connection sections through STPs?
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?

--brian