Multiple aliases in ARQ destinationInfo

Santo Wiryaman swiryaman at VIDEOSERVER.COM
Fri Jan 22 18:40:18 EST 1999

As a GK developer, I share Paul Long's desire to arrive at some concensus on
how a GK (or a collection of GK's) should treat multiple aliases in an ARQ.
Several suggestions had been offered such as interpretation 1,
interpretation 4, interpretation 4 plus Chris' refinements, and so on.

Before we define how the GK should interpret multiple aliases, I think we
need to find out what the endpoints (or users of those endpoints) mean when
they send multiple aliases in a call.  In this short email discussion of 4
people, there seemed to be multiple opinions on what this means:

1. Paul Long envisions an endpoint that would send a call request,
specifying MULTIPLE aliases to the GK. These aliases match to different
systems (e.g. #@work, #@home, cellphone#, fax#, etc.).  The GK would find a
match to one of these devices and the call would get routed to one of them.

2. Jim Toga envisions an endpoint that would send a call request, specifying
MULTIPLE aliases to the GK.  These aliases all match to a single device.
The GK would find the device and the call would get connected.  The two
devices would then negotiate what kind of call it is (audio only vs.
multimedia) by way of evaluating the aliases in the order they were

3. Chris Purvis suggested an endpoint that would send a call request,
specifying MULTIPLE aliases to the GK. The first alias would be the GW of
choice. Subsequent alias(es) would contain the address of the "ultimate"

4. Chris Purvis described an endpoint that would send a call request,
specifying ONE alias to the GK.  This alias is assigned to a person who may
be in different places (i.e different endpoints) at different times. S/he
somehow notifies the system where to route the call.  At the time of the
call, the GK would consult a dBase and route the call to the endpoint where
the person is.  This scenario is not really relevant to the issue at hand
because the endpoint sends ONE alias in the ARQ.  It is mentioned here to
show as an example for how the objectives of scenario 1 can be accomplished
without sending multiple aliases.

5. Santo knows of systems out there (MCU's) that register multiple aliases,
each corresponding to a conference.  Say, MCU1 registers "CONF_A", "CONF_B",
"CONF_C" as its aliases.  When EP1 calls "CONF_A", the GK would return the
address of MCU1.  The SETUP from EP1 would later arrive at MCU1 and the
destination is "CONF_A".  Becuase of this, MCU1 knows that the endpoint
wants to joint "CONF_A" and the call is accepted.  However, if MCU1 receives
a SETUP with multiple destinations such as "CONF_A", "CONF_B", "CONF_C" it
might get confused and drop the call (or use interpretation 1 and therefore
use the first alias only).  This is an example of a potential problems that
can result from multiple aliases, not at the GK but at the destination
endpoint (e.g. an MCU).

I am sure the list above is not comprehensive.  If 3 or more people join in
the discussion they may have half a dozen more uses for multiple aliases.
Some of the multiple alias interpretations (such as #1 - #3 described above)
may all have valid and good reasons behind them.   Since there can be many
interpretations for multiple aliases from the users' point of view (some
perhaps conflicting, e.g. #1 conflicts with #3) , it would be hard to
specify a rule on the GK which can satisfy all the users' requirement.

Some comments to Jim Toga's posting are within the enclosed text.


> -----Original Message-----
> From: Jim Toga [SMTP:jim.toga at INTEL.COM]
> Sent: Friday, January 22, 1999 12:46 PM
> To:   ITU-SG16 at
> Subject:      Re: Multiple aliases in ARQ destinationInfo
> At 10:50 AM 1/22/99 -0500, Santo wrote:
> [SNIP]
> >Of course I am not saying that if it hasn't been done it is a bad thing.
> I
> >am merely suggesting that there may be a better way of doing it (such as
> the
> >system in the UK described by Chris).  It was not a rethoric question
> >either; I truly wanted to know if Paul knows of any system out there
> where
> >you can "blast" dial with multiple numbers and hope to get connected to
> one
> >of them.
> I would offer as a model both DNS (which allows multiple 'aliases' to
> point
> to a single host) and 'hunt groups' as mentioned by ChrisP which are very
> useful in situations other than call centers.  To Chris's point, I also
> believe that this functionality should be partially (if not completely)
> implemented by a Gatekeeper - the multiple aliases simply gives the GK an
> effiecient start.
        [Santo Wiryaman]  The DNS analogy is done today by e.g. an MCU
        registering multiple aliases for the same CallSignalAddress.  Even
if a machine
        has multiple DNS names (aliases) such as in:  pj , PaulJ, pJones, Paul_Jones

        when user applications would "connect" to that system, they would
        use one of them, e.g. :

          ping pj
          ftp PaulJ

        What we are dealing here is specifying multiple destinations all at
once.    It is
        like saying:

           ftp m1,m2,m3,m4

        Which machine should the system connect to?  Perhaps m3 because m1
        m2 are on a different domain?

        I fully agree with Jim and Chris that routing and hunt-group
functionality should
        be implemented partly if no completely in the GK. I am still having
problem seeing
        how multiple aliases helps the process.  Unless, of course the GK is
setup to use
        the same interpretation rules as specified by the site.  Then this
becomes a site
        configuration issue doesn't it?

        Another facet to this is if the aliases have some implied (agreement
> between calling and called parties) functionality to them.  For example I
> might have both and rfc822 alias and an E.164 alias.  The implications
> might be that they are associated with a multimedia recipient and an
> audio-only client respectively.  Depending on what the caller wants to do
> they might put one 'higher' in the alias array.  Note that these are (or
> might be) _service_ level capabilities, not the same thing as offered by
> H.245....
> With respect to 'errror' conditions or inconsistencies on the GK database
> when doing look-ups, it seems as though that would really be a policy
> issue.  The usual behaviour of 'least astonishment' should be the default.
> Comments?
> jimt.
> >
> >I share Chris' concern about such a "blast" dial system which is
> >non-determinism.
> >
> >
> >Regards,
> >
> >-santo
> >
> >> -----Original Message-----
> >> From: Chris Purvis [SMTP:CPurvis at MADGE.COM]
> >> Sent: Friday, January 22, 1999 5:33 AM
> >> To:   ITU-SG16 at
> >> Subject:      Re: Multiple aliases in ARQ destinationInfo
> >>
> >> Time for me to wade in on a couple of points here too, I'm afraid...
> >>
> >> First let me say what we've implemented so far:
> >> 4.      Respond with ACF if at least one alias is registered, starting
> >> with
> >> the first one.
> >>
> >> Having said that, I'm not certain that's how things should be.  I
> believe
> >> the "right" answer is none of those Paul suggests.  My starting point,
> >> though, is that at this stage of placing a call, line-hunting is the
> job
> >> of
> >> the gatekeeper, not the endpoint.  If one wants to do line-hunting at
> the
> >> endpoint, one should be sending a number of ARQs - note that there's no
> >> reason an endpoint can't have multiple ARQs outstanding at the same
> time,
> >> so
> >> this should not add significantly to call setup latency.
> >> Hence what I believe SHOULD happen is that the gatekeeper
> >> 1. If it can match anything within its zone, should ensure that
> different
> >> aliases in the ARQ do not point to different destinations within the
> zone.
> >> If there is such disagreement, the GK should return ARJ.
> >> Either:
> >> 2a. Repeat the same policy at any other levels of search that it
> engages
> >> in
> >> (LRQs etc).
> >> or (probably "better" from the point of view of call setup times,
> although
> >> less deterministic):
> >> 2b. If a search procedure needs to be done outside of the zone, use the
> >> first positive reply you get
> >>
> >> One use I see for these multiple aliases, is to avoid the abomination
> of
> >> dial-prefixes for dialing out through gateways.  The first alias should
> >> point to a gateway (probably by name rather than number), subsequent
> >> aliases
> >> in a setup message should tell the gateway what to do.  Clever
> gatekeepers
> >> may want to have policy on what outside lines are permitted to certain
> >> users, and therefore need to see this information at this stage.
> >> Unfortunately nobody seems to use multiple aliases like this...
> >>
> >> In answer to a couple of other specific points:
> >>
> >> [Santo]
> >> >In practice, could you tell us an example of a widely deployed
> >> communication
> >> >system where you can "dial" multiple destinations (e.g. home phone,
> work
> >> >phone, cell phone, fax number, emailID) at once and "it" will get you
> the
> >> >most suitable destination?  I can imagine a smart phonebook/dialer
> which
> >> >would take the addresses and "dial" one number at a time until it gets
> >> >connected.  But the smarts is in the application, not in the "switch"
> (in
> >> >our case the GK).
> >> Are you suggesting that if such a thing hasn't been done before it is
> not
> >> a
> >> "good" thing to do?
> >> Incidentally the start of such a thing does exist, at least in the UK.
> I
> >> have friends for whom I can dial a single number.  They tell the server
> >> for
> >> this number where they are at any given time, and when I dial their
> >> "personal numebr" I talk to the person, whether they happen to be at
> home
> >> (on their home number), at work (on their work number) or elsewhere (on
> >> their mobile phone).  We have a huge opportunity to improve users'
> >> experience.
> >>
> >> [Paul]
> >> >Is an EP required to use the exact same alias list in the Setup that
> it
> >> used
> >> >in the ARQ? I don't think so. Sounds like it should use the alias list
> >> sent
> >> >back in the ACF's destinationInfo field, which would presumably
> contain
> >> only
> >> >the alias(es) that resolved into the provided transport address. Good
> >> point,
> >> >though. Needs more thought. What if more than one alias resolved into
> the
> >> same
> >> >address and the GK returned all of the resolved aliases? But then,
> maybe
> >> we're
> >> >trying to over-engineer the problem. Maybe it just makes good sense to
> >> the
> >> >users in these situations to provide a single alias, and everything
> just
> >> >works... :-)
> >> The ACF's destinationInfo field only appears in version 2, but yes this
> is
> >> certainly what you should use where present (if it's absent, you can't
> do
> >> anything other than use what you used in the setup message).  Do any
> >> endpoints complain when they see extra, superfluous aliases in setup
> >> messages addressed to them?  I doubt it.  Even gateways should surely
> use
> >> what they can make sense of  and ignore anything else.  The question
> mark
> >> is
> >> how the destinationInfo, destExtraCallInfo and remoteExtensionAddress
> >> fields
> >> in ACF should be mapped to the various fields in the setup message
> >> (CalledPartyNumber, CalledPartySubAddress, destinationAddress,
> >> DestExtraCallInfo, remoteExtensionAddress).  I seem to remember hearing
> at
> >> some point that they should be mapped into the fields of the same name,
> >> except that the first destinationInfo that is a phone number is moved
> into
> >> CalledPartyNumber, and CalledPartySubAddress.  I believe if implemented
> >> this
> >> is a potential source of incompatibility with TIPHON however, because
> >> (again
> >> from memory - no doubt I'll be corrected if I'm wrong!) TIPHON
> equipment
> >> is
> >> instructed to ignore CalledPartyNumber.  Whatever "correct" procedure
> is,
> >> though, it should be agreed and documented.
> >>
> >> [Paul]
> >> >Simple, return the transport address of the first resolved alias.
> What's
> >> wrong
> >> >with that?
> >> Possible non-determinism (see 2b above).
> >>
> >> Regards,
> >> Chris
> >> --
> >> Dr Chris Purvis - Senior Development Engineer, WAVE CC Software
> >> Madge Networks Ltd, Wexham Springs, Framewood Road, Wexham, Berks.
> >> Phone: +44 1753 661 359  email: cpurvis at
> >
> +1-503-264-8816(voice)              Intel - Hillsboro, OR
>  mailto:jim.toga at         mailto:james.toga at
>  PGP keyID 36 07 86 49 7D 74 DF 57  50 CB BA 32 08 9C 7C 41

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