RE: AS concepts and Relay in SUA and M3UA

  Hello SIGTRAN community,
   
  I have had a discussion with Tolga Asveren about fundamental concepts around SUA Relay. I have noticed that most of my communication with him was held outside the SIGTRAN community mailing list (I addressed him directly) therefore I correct this now. You can look for the first part of the discussion at http://www1.ietf.org/mail-archive/web/sigtran/current/msg05525.html and the rest is below.
   
  My point is that SUA Relay hardly fits into the AS/RC concept which is originally designed for SGP-ASP and IPSP-IPSP (direct) communication. The point is that if the applications are in IP network there is no relay between them on the level of SUA protocol.
   
  However Tolga convinced me that actually SUA Relay means:
   
  ASP1-SGP-ASP2
   
  I do not have conceptual problems with this and I accept this! Note also that this means that one can build SUA relay between two IP resident applications only in one relay stage, since SGP-SGP is not part of SUA specification!
   
  However I have tremendous problems with something like this:
   
  IPSP1-IPSP_R1-IPSP_R2-IPSP_R3-........-IPSP2
   
  where IPSP_Rx stands for IPSP process equipped with relay capability.
   
  The problems get even bigger if one wants to build the whole (fully or partly) meshed network of IPSP_Rx processes. This is impossible to incorporate into the AS/RC concept which is normally used on the IPSP-IPSP interface.
   
  I would like to hear what other members of the SIGTRAN community think about this since by looking into the SIGTRAN mail archive I see that many people think that SUA might relay with many IPSP processes interconnected what seems to me hardly compatible with fundamental AS/RC concepts.
   
  Please look into the mail below for discussion.
   
   
  I would also like to draw attention to the unofficial draft being written by Tolga for SG-SG communication for M3UA (see mail below for address where you can fetch it).
   
  I think that this concept is especially usefully for SUA and should be extended to SUA as well. For example if one wants to have GT translation distributed in space (i.e. to build network of relay nodes that are to perform GT translation) then we need SGP-SGP communication.
   
  I also think that we should have AS/RC concepts kept away from the SGP-SGP interface.
   
  Currently (according to Tolga's view, and my also) only ASP1-SGP-AS2 relay is possible in SUA with just one relay stage.
   
  I kindly ask SIGTRAN comunity to give us its opinion.
   
  best regards/ Stanislav Ivanovich
   


Tolga Asveren <[email protected]> wrote:    Stanislav,

SG-SG work is going on, initially for M3UA but it hopefully will be extended
for SUA as well. Currently it is not an official WG-item, if you think it is
some useful concept, you can express yur opinion in the SIGTRAN WG mailing
list. For a draft to become WG-item, there should be enough interested
parties in it and right now we probably are short of it.

The link for M3UA SG-SG draft is:
http://www.ietf.org/internet-drafts/draft-asveren-sigtran-m3uasgsg-00.txt

Tolga
-----Original Message-----
From: Stanislav Ivanovich [mailto:[email protected]]
Sent: Thursday, December 15, 2005 1:43 PM
To: Tolga Asveren
Subject: RE: [Sigtran] AS concepts and Relay in SUA and M3UA


Tolga,

Now I see Your point and I must admit that I fully agree with You!

I have a proposal how to define SUA relay and at the same time be fully
compatible with the AS/RC concepts which are originally tailored for SGP-ASP
and IPSP-IPSP communication without any relay (except in SGP between SS7 and
IP).

My essential point here is that if one wants to incorporate a relay process
in between SGP and ASP or two IPSP'es he/she will finish in tremendous
conceptual problems especially in the environment of multiple processes and
multiple AS'es per signalling process environments.

I am not saying that it is impossible to define SRP1 (SUA Relay Process in
between SGP-ASP) and SRP2 (SUA Relay Process in between IPSP-IPSP) which are
both to use AS concepts. For example SRP1 would mimic an SGP (or maybe even
several SGP's) when communicating with an ASP and ASP (or maybe even several
APS'es) when communicating with an SGP.

But this seems to be feasible only for very simple configurations without
many AS'es and processes involved.

Even more if we allow a relay process which will send SSNM messages to an
IPSP this could be considered as a violation of fundamanetal AS principles
since exchange of this calss of messages (expcet of course SCON) is not
allowed there.

One might then say: "OK if a relay proces is supposed to send SSNM messages
then instaed of IPSP we have ASP".

We need just one additional step to find the soltuinon -> the SCCP alike
relay (GT or maybe even SPC based) is essentialy possible as you once said
between SGP processes.

Thus we finish in this configuration:

ASP1---SGP1--------SGP2---ASP2

In this case we equip (define) the SGP'es with procedures to relay from IP
to IP network (i.e. access to SS7 network is not always necessary) and
that's it!

However it is essentially important to note that in this case AS concpet
finishes/terminates on the SGP'es. In another words we have AS1 served by
ASP1 and "terminated" at SGP1 and AS2 served by ASP2 and "terminated" by
SGP2. But SGP'es do not use AS concept for SGP-SGP communication but instead
use SCTP associations like SCCP uses MTP links (or Route Sets.... whatever).

In this way the construction is closed and the relay perfectly fits into SUA
network and is comaptible with AS concepts which are kept away from the
SGP-SGP interfaces. And the original prinicples of AS are kept intact and
consistent!

What do You think?

best regards/ Stanislav


Tolga Asveren wrote:
Stanislav,

a)Both for SUA or M3UA, IPSPs can't relay.
b) Relaying in SUA is *NOT* IPSP communication and its details are not well
defined, but I don't see why it should effect ones understanding of IPSP,
because they are not related.
c) Whether relaying entity is called SGP or ASP is not very important,
important is that it follows the procedures defined in the specification.

I know relaying in SUA is kind of fuzzy right now, but I am with you on the
same boat on that issue.

Thanks,
Tolga

-----Original Message-----
From: Stanislav Ivanovich [mailto:[email protected]]
Sent: Wednesday, December 14, 2005 5:42 PM
To: Tolga Asveren
Subject: RE: [Sigtran] AS concepts and Relay in SUA and M3UA


Tolga,

Please allow me to say that now I am totally confused!

You say that IPSP cannot relay SUA traffic. At the same time SGP can "host
local applications" and is the only process that relays according to your
opinion.

What is the difference then between IPSP1-IPSP_with relay-IPSP2 from
SGP1-SGP_with_relay-SGP2 ???

In the latter case SGP1 and SGP2 host local applications in the IP domain
and do not have any access to the calssical SS7 netowork (therefore do
actually behave as an IPSP processes)!

But then we finish at the starting point -> AS/RC concept is originally
desinged for direct-to-direct communications and relay seems not to be
elaborated in the SUA RFC at all (e.g. how should relay behave in the
environment of multiple AS'es/RC'es per signalliong processes etc...)! All
of your answers to my previous questions are based on the assumption that
IPSP cannot relay SUA traffic!

Take your time and please help me to understand SUA Relay! Looking into the
SIGTRAN mail archieve this seems to bother many people.

This relay thing in SUA seems to be totally incompatible with AS/RC concept
which is copy/pasted from the M3UA specification which on the other hand
forbids relay!

kind regards/ Stanislav



Tolga Asveren wrote:
Stanislav,


-----Original Message-----
From: Stanislav Ivanovich [mailto:[email protected]]
Sent: Wednesday, December 14, 2005 4:50 PM
To: Tolga Asveren
Subject: RE: [Sigtran] AS concepts and Relay in SUA and M3UA


Tolga,

Thank You very much! Now it is clear!

Could You please explicilty confirm or denay with TRUE or FALSE the
following statement:

Once a message comes from SS7 to SUA network it can be relayed only at two
places, namely SGW and ASP but not at IPSP place.
[TOLGA]Actually, if an ASP is capable of relaying messages I would call it
SGP, so I would say only a SGP is capable of relaying messages -please note
that a SGP can host local applications-. It is true that IPSP can't realy
messages.

with very best regards/ Stanislav



Tolga Asveren wrote:
Stanislav,

If the whole SPMC is down (ISUP, SCCP etc..) then you send TFC. Otherwise,
you don't send anything, just mark the user part, which is down as
"unavailable". If a message from SS7 network arrives to that user part, you
reply with UPU, no different than with regular SS7 case.

Thanks,
Tolga
-----Original Message-----
From: Stanislav Ivanovich [mailto:[email protected]]
Sent: Wednesday, December 14, 2005 4:33 PM
To: Tolga Asveren
Subject: RE: [Sigtran] AS concepts and Relay in SUA and M3UA


Tolga,

You didn't understood my TFP point below -> actually I asked what if SUA
gateway looses connection to SPC in the SUA network, should it send TFP in
the MTP network?

Then you have my objection on how to indicate inaccessiblity of particular
application only (SCCP application in this case at SPC but not ISUP or BICC
at the same SPC)!

Thank You!

kind regards/ stanislav



Tolga Asveren wrote:
Stanislav,


-----Original Message-----
From: Stanislav Ivanovich [mailto:[email protected]]
Sent: Wednesday, December 14, 2005 4:09 PM
To: Tolga Asveren
Subject: RE: [Sigtran] AS concepts and Relay in SUA and M3UA


Tolga,

SUA RFC:

1.3.1.2. Signalling Gateway as relay-point


"A Global Title translation is executed at the signalling gateway, before
the destination of the message can be determined. The actual location of the
SCCP-user is irrelevant to the SS7 network. GT Translation yields an "SCCP
entity set", from which an Application Server can be derived. Selection of
the Application Server is based on the SCCP called party address (and
possibly other SS7 parameters
depending on the implementation)."
[TOLGA]Check 1.4.6 as well. 1.3.1.2 is nothing else than the good old GTT.
1.4.6 talsk about the SUA specific relay functionality.

There is no word about SPC based relay in SUA gateway. If you think that SPC
relay in SUA gateway (!) is supposed to relay based on SPC is it supposed to
send TFP when the SPC is inaccessible (i.e. to behave as MTP STP)?
[TOLGA]You should use SUA defined SSNM messages.

If so how you can inidcate inaccessiblity of only SCCP applications by means
of TFP? MTP message TFP indicates inaccessiblity to all user parts not just
particular one!

You are saying that IPSP does not contain relay. Are you saying that only
ASP can relay to the final IPSP which cannot relay further?
[TOLGA]An IPSP communicated only with another IPSP. Any other type of
communication requires interworking on application level.

thank You!

/stanislav


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