Re: M3UA: ASP Route Availability to SG/STP

Hi Lincoln,

Comments below. 

This does not address my main concern though which is a perceived
ambiguity in the M3UA specification. Do you feel the specification is
clear about whether the SG/STP (actually SG/STP/SEP) should be presumed
available?

Regards

> -----Original Message-----
> From: Haresign Lincoln [mailto:[email protected]]
> Sent: 03 September 2008 14:07
> To: Howard May; [email protected]
> Cc: [email protected]
> Subject: RE: [Sigtran] M3UA: ASP Route Availability to SG/STP
> 
> Howard,
> 
> If it is providing GTT service, this is at a layer higher than
M3UA/MTP.
> If the GTT service (SCCP layer) is not avialable, the SG should
respond
> with a DUPU upon receipt of a message.

Agreed

> 
> The MTP restart procedure in the SS7 world does not assure us that the
> SCCP layer (GTT functionality) at the STP is available.   I'm not sure
> why you are looking for this in the M3UA world.

I'm not. My comments on MTP Restart were in response to comments made by
Brian. I don't believe that the M3UA protocol is able to emulate the
MTP3 restart behaviour. This is not what I'm concerned about right now
though.

> 
> Regards,
> Lincoln
> 
> -----Original Message-----
> From: Howard May [mailto:[email protected]]
> Sent: Wednesday, September 03, 2008 8:50 AM
> To: Haresign Lincoln; [email protected]
> Cc: [email protected]
> Subject: RE: [Sigtran] M3UA: ASP Route Availability to SG/STP
> 
> Hi Lincoln,
> 
> I would agree that it is not unlikely that when the SG/STP sends ASP
> Active that any user part at the SG/STP is available to receive
traffic.
> 
> 
> My chief concern is that it is unclear to me whether the M3UA protocol
> mandates this.
> 
> In the scenario I am concerned with the SG/STP is also acting as an
SEP
> (perhaps it is providing a GTT service). As such it is offering an SG
> service and a distinct SEP service. I could imagine the SG service
being
> available and not the SEP service.
> 
> Best Regards
> 
> 
> > -----Original Message-----
> > From: Haresign Lincoln [mailto:[email protected]]
> > Sent: 03 September 2008 13:35
> > To: Howard May; [email protected]
> > Cc: [email protected]
> > Subject: RE: [Sigtran] M3UA: ASP Route Availability to SG/STP
> >
> > Howard,
> >
> > It would seem to me that if the SG acknowledgs the ASP Active
message
> > from the ASP, it implies that the SG is configure and ready to start
> > receiving traffic from the ASP.  In other words, the M3UA
> functionality
> > in the SG can begin to process messages.  This has also been our
> > experience in networks when interfacing to switches that are acting
as
> 
> > SGs.
> >
> > Sometimes we see that the SG does not acknowledge our ASP Active.
> This
> > is usually the case when either the SG is not completely configured
> and
> > ready to receive our ASP Active, or the connection is not
configured.
> >
> > I can't imagine why the SG would respond to an ASP Active if it is
not
> 
> > ready to receive traffic.
> >
> > Regards,
> > Lincoln
> >
> > -----Original Message-----
> > From: Howard May [mailto:[email protected]]
> > Sent: Wednesday, September 03, 2008 8:29 AM
> > To: Haresign Lincoln; [email protected]
> > Cc: [email protected]
> > Subject: RE: [Sigtran] M3UA: ASP Route Availability to SG/STP
> >
> > Hi Lincoln,
> >
> > I'm concerned about the availability of the Route to the STP not
> routes
> > via the STP. If the STP has point code 'Alpha' then the ASP may have
a
> 
> > route to point code 'Alpha'. It is the availability of this route at
> the
> > ASP I am concerned with.
> >
> > It is clear that routes via the SG/STP will only become active after
> > receiving DAVA.
> >
> > Best Regards
> >
> > > -----Original Message-----
> > > From: Haresign Lincoln [mailto:[email protected]]
> > > Sent: 03 September 2008 13:20
> > > To: Howard May; [email protected]
> > > Cc: [email protected]
> > > Subject: RE: [Sigtran] M3UA: ASP Route Availability to SG/STP
> > >
> > > Howard,
> > >
> > > It would seem to me that if the SG responds to an ASP Active
> message,
> > > that in effect tells the ASP that the SG is available to begin
> > receiving
> > > traffic.
> > >
> > > It's not clear to me.  Are you concerned about the ability of the
SG
> > to
> > > begin processing traffic.  Or are you concerned about the
> > > availability/status of all the point codes on the other side of
the
> > SG?
> > >
> > >
> > > Regards,
> > > Lincoln
> > >
> > > -----Original Message-----
> > > From: [email protected] [mailto:[email protected]]
On
> > > Behalf Of Howard May
> > > Sent: Wednesday, September 03, 2008 6:01 AM
> > > To: [email protected]
> > > Cc: [email protected]
> > > Subject: Re: [Sigtran] M3UA: ASP Route Availability to SG/STP
> > >
> > > Hi,
> > >
> > > I want to ask Sigtran list members / authors opinions about an
area
> of
> >
> > > perceived ambiguity in the M3UA spec.
> > >
> > > Brian, at present the reasoning behind your expected ASP behaviour
> is
> > > based on the MTP3 specs rather than the M3UA specs and an
assertion
> > that
> > > M3UA should behave the same. The MTP3 specs clearly identify
routes
> to
> >
> > > adjacent signalling points become available when the direct link
set
> 
> > > comes into service at layer 3 (or after restart completes) and the
> > Route
> > > Set Test procedures are not used across the direct link set for
the
> > > adjacent signalling point. But the M3UA spec does not define
similar
> 
> > > behaviour. M3UA does not seem to discuss any mechanism for route
> > > availability other than reception of DAVA messages.
> > >
> > > While I recognise there may be ambiguity, I feel that at present
the
> 
> > > specification suggests the adjacent signalling point at the SG/STP
> > > should generate DAVA/DUNA messages and respond to DAUD messages
and
> > > should not be presumed to be available following AS Activation.
> > >
> > > I am concerned about this perceived ambiguity on account of the
> > > interoperability impact and would value a clear consensus and
> > > clarification as to the expected behaviour.
> > >
> > > Best Regards
> > >
> > > Howard
> > >
> > > **********
> > >
> > > Concerning M3UA acting in the role of a restarting MTP. MTP
Restart
> > > procedures aim to allow sufficient bandwidth and route
> synchronisation
> >
> > > prior to the commencement of traffic. They also aim to reduce the
> time
> >
> > > for restart procedures to complete to allow traffic restart as
> quickly
> >
> > > as possible. They do this by prohibiting the transfer of traffic
in
> > > either direction prior to exchange of TRA messages and by
presuming
> > > route availability and exchanging only TFP messages.
> > >
> > > M3UA does not support such mechanisms and so will have to handle
> > traffic
> > > prior to having a fully synchronised routing table risking
possible
> > > message loss.
> > >
> > > **********
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Brian F. G. Bidulock [mailto:[email protected]]
> > > > Sent: 02 September 2008 17:03
> > > > To: Howard May
> > > > Cc: [email protected]
> > > > Subject: Re: [Sigtran] M3UA: ASP Route Availability to SG/STP
> > > >
> > > > Howard,
> > > >
> > > > There are three scenarios:  ASP/SG, multiple SG as STP and IPSP.
> > > > I think that you are talking of the multiple SG as STP case.
> > > >
> > > > For the multiple SG as STP scenario, the ASP can be viewed as a
> > > > separate SEP with its own signalling point code distinct from
that
> > of
> > > > the STP point codes.  The associations to the SG/STP can be
viewed
> > as
> > > > a linkset.  The STP signalling point codes can be viewed as
> adjacent
> >
> > > > STP.  In the normal SS7 case where the SEP is connected by
> A-links,
> > > > the STP signalling point codes are treated as available whenever
a
> 
> > > > signalling link in the directly connecting link set is available
> at
> > > > level 3, or whenever a routeset to the STP via the alternate STP
> is
> > > > available.
> > > >
> > > > When the first association to an SG/STP pair becomes available
to
> > > > carry traffic (AS-ACTIVE), the ASP is acting in the role of a
> > > > restarting MTP at an SEP.  Instead of traffic restart messages,
> the
> > > > M3UA at the ASP can use the DAUD procedure to effect MTP
restart.
> > > > When an association to an SG/STP becomes available and there is
an
> 
> > > > existing association, or the ASP has sufficient recent knowledge
> of
> > > > routing, the ASP is not a restarting MTP however the DAUD
> procedure
> > > > may still be used to establish the availability of destinations
> via
> > > > the SG/STP before starting or restarting traffic to the SG/STP.
> > > > Nevertheless, the ASP may simply restart traffic to the SG/STP
and
> 
> > > > handle whatever DUNA messages it receives as a result of
> restarting
> > > > traffic instead of using the DAUD procedures.
> > > >
> > > > As regards the point code of the STP itself: the ASP is acting
as
> a
> > > > directly connected SEP (as though it was connecting using
> > > > A-links) and therefore, as soon as a link in the linkset (in
> M3UA's
> > > > case, an association) is available at level 3 directly connected
> to
> > > > the STP, the STP's point code is available.  In SS7, no TFA or
TFP
> > is
> > > > sent to the SEP on a directly connected A-linkset for the STP's
> own
> > > > point code, only for point codes available via the STP.
> > > >
> > > > So, yes, the ASP acting as an SEP in a multiple SG as STP case
can
> 
> > > > assume that once it has an association to the SG/STP and is
> > AS-ACTIVE
> > > > for traffic via that SG/STP, it can assume that the SG/STP's
point
> 
> > > > code is available.  However, the point I was trying to make is
> that
> > > > the ASP can simply assume that any point code is available via
an
> > > > association and route traffic to it, dealing, of course, with
any
> > DUNA
> > >
> > > > that it receives regarding the traffic it sends.
> > > >
> > > > --brian
> > > >
> > > >
> > > > Howard May wrote:                            (Tue, 02 Sep 2008
> > > 10:59:07)
> > > > > Hi Brian,
> > > > >
> > > > > Thanks for your response but I'm still unclear whether when
the
> AS
> >
> > > > > becomes active M3UA should immediately consider the route to
the
> > > SG/STP
> > > > > as available or whether it should wait for a DAVA. I'm also
> > unclear
> > > > > whether the SG should respond to DAUD concerning the SG/STPs
> Point
> > > Code
> > > > > or not.
> > > > >
> > > > > Best Regards
> > > > >
> > > > > Howard
> > > >
> > > > --
> > > > Brian F. G. Bidulock
> > > > [email protected]
> > > > http://www.openss7.org/
> > > _______________________________________________
> > > Sigtran mailing list
> > > [email protected]
> > > https://www.ietf.org/mailman/listinfo/sigtran