Re: 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