Subject: isup maintenance msgs (was RE: [Sipping] RE: [Sip] Sip support fo r TCAP queries)

From: "Peterson, Jon" <[email-masked]>
Date: Wed, 19 Nov 2003 16:23:59 -0600

Just to be even more explicit about this point - there are no CICs between
gateways that reside on the Internet. Separate calls between these gateways
are differentiated by the transport-layer (i.e. UDP) port over which RTP is
sent. ISUP maintenance messages (like BLO, say) refer to a particular CIC or
set of CICs. Those indications are necessarily hop-by-hop - they are only
meaningful between the origination and destination point codes for which
they are sent, since the bindings between these CICs and their corresponding
circuits is a matter of arbitrary hop-by-hop convention established by the
switches.

The necessary guidance for translating applicable maintenance conditions
into SIP messages is already given in RFC3398, Section 11, so this was not
overlooked by that document entirely. But what could possibly be the meaning
of sending (via encapsulation) the BLO received by a gateway to some other
gateway on the Internet? Transposing this question to the PSTN, what would
be the meaning of, say, a tandem forwarding a BLO that it received to
another switch? Even if we proceed on the (misguided but least implausble)
assumption that a remote gateway would use these sorts of maintenance
messages as rough indicators of the capacity of its peers, this would still
entail that every gateway has a rough idea of the total number of CICs
supported by every other gateway to which it might connect, which in turn
entails a nightmare of n^2 provision and bilateral associations between
gateways that is, ultimately, redundant with capacity management
capabilities that SIP already possesses.

I would be very interested to hear how a requirement for encapsulating ISUP
maintenance messages in SIP is motivated. The omission of these messages
from our encapsulation strategy was not an oversight, or a "to do" flag.

Jon Peterson
NeuStar, Inc.

> -----Original Message-----
> From: Tolga Asveren [mailto:[email-masked]]
> Sent: Wednesday, November 19, 2003 12:16 PM
> To: Frank W. Miller; 'Drage, Keith (Keith)'
> Cc: [email-masked]
> Subject: RE: [Sipping] RE: [Sip] Sip support for TCAP queries
[snip]
> >
> > Let me be very plain, RFC 3398 is not sufficient.  It lacks support for
ISUP
> > maintenance commands and access to SCPs via TCAP.  These are functions
that
> > are required by vendors and carriers integrating SIP with the existing
PSTN.
> [TOLGA]Why do you need those maintanence messages? Your voice trunks
> terminate at the gateway and it is the gateway, which is interested in
them,
> and which receives them via ISUP. Why do you need to propogate them to a
> pure SIP entity in the network? Why should they care about management of
> circuits, which are physically terminated at the gateway?
> And again for SCP access, if one wants to speak TCAP to them, one needs
> TCAP(over SCCP or over a SIGTRAN protocol like M3UA/SUA etc...). If SCP
> understands it -or if one introduces a TCAP gateway for it-, one also
might
> use something (HTML, SOAP, XML-RPC etc...) over HTTP. I believe, the point
> is, SIP is not a transport protocol.
> 

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