FW: Some H.225 Annex G questions (LONG)

Paul E. Jones paul.jones at TIES.ITU.INT
Sat Jan 1 19:17:21 EST 2000

Michael and Ellen,

> > 2. Receiving Response to Specific Queries describe a BE coupled
> > with the firewall. When an AccessRequest arrives, it shall respond two
> > templates: one with a short lifetime owning Setup type, others with
> > AccessRequest type for other AliasAddress. Could you give me a bit more
> > detailed explanation about that?
> >
> This is a good question - maybe somebody (Glen?) can enlighten us?

The idea here is that the firewall may have a port open for a short period
of time to allow the Setup message to pass through, but may then close.  In
the future, another AccessRequest would need to be sent in order to get a
new call signaling address.  By returning both a "Send Setup" and "Send
AccessRequest" type of response, one could use the setup address for the
immediate call (or until the firewall closes the port) and then can use the
information in the "Send AccessRequest" for subsequent queries.

> > 6. Why need Annex G? RAS is good, why introduce Annex G?
> RAS was not designed with interdomain communications in mind. For example,
> there is no discussion of how dialing
> plans or billing-related information can be transferred between domains.
> Annex G fills in many of these holes
> (for example, via AddressTemplates and UsageIndications).

As Michael and Boaz point out, Annex G provides the necessary messages and
fields to support billing and exchange of dial plans (or at least the means
of accessing a domain).  In addition, these messages may be exchanged
periodically-- outside the scope of a call-- to keep ADs up-to-date.  This
can yield a significant improvement in call setup time when the GK can
perform a local query and know right away where to direct a call.  LRQs for
each call can be costly.  Granted, AccessRequests for every call can also be
costly, but at least with Annex G one can perform a more directed query.
With RAS alone, one may not know which entity handles a particular
destination address.  With Annex G, at least, one can learn that to "reach
numbers starting with 330449, send a query to device Y", for example.  With
RAS, to do the same thing would require provisioning of every GK and is
certainly not very dynamic.  Annex G is much more dynamic.


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