TD-27 text for h.323
gthom at DELTA-INFO.COM
Fri Sep 19 14:47:19 EDT 1997
I was working on a TD in Sunriver to suggest that Notify should be used,
but I was advised that this was not the right message. It may be that
Notify is the closest message to what is required and so I have no
objections to it being used.
Glen has also suggested that additional fields such as reRouteReason,
endpointAlias, originalDestination, and reRouteCounter should be added.
The first two I agree with. The second one I'm not sure of what it
means so don't know whether I agree with it or not. On reRouteCounter,
I'm not sure what it would be counting. For the Facility-UUIE based
re-route this is used so that the endpoint can check for infinite loops.
As this would be used as a notify that a re-route had already been
done, then the usefulness of this information is limited.
As to whether we include an indication of this sort, I am very wary of
feature creep also. However, to me this seems such a fundamental call
control feature that it shouldn't require supplementary service support.
It should also be emphasized that this is not a replacement for
anything in H.450.2, and ctComplete should be used when H.450.2 is in
use. It is also light weight to implement; endpoints would not have to
process it on reception, and re-routers should generate it, but it
shouldn't be mandatory for them to generate it (for reasons such a
anonymity in security and things like that).
Given these suggestions, a revised PDU might be:
H323-UU-PDU ::= SEQUENCE
nonStandardData NonStandardParameter OPTIONAL,
h4501SupplementaryService SEQUENCE OF H4501SupplementaryService OPTIONAL
ReRouteIndication ::= SEQUENCE
-- display no longer needed as this is in Notify message
endpointAlias SEQUENCE OF AliasAddress,
E-Mail: pete.cordell at bt-sys.bt.co.uk
Tel: +44 1473 646436
Fax: +44 1473 645499
>From: Ernst Horvath[SMTP:Ernst.Horvath at SIEMENS.AT]
>Sent: 19 September 1997 10:40
>To: ITU-SG16 at mailbag.jf.intel.com
>Subject: Re: reRouteIndication
>some observations on your mail:
>> It has been mentioned that when a gatekeeper performs a re-route it
>> would be good for the client to know about it. After much
>> investigation, there seems to be no message in Q.931 that handles this
>The Notify message could be used for that purpose (as an alternative to
>Facility), but again, its use is supplementary-service specific (and
>removed from H.450.1). In QSIG we use Facility whenever the information
>is to be processed by the endpoint, which is nearly always the case.
>Notify is restricted to situations where (less important) information
>passed to the user without acting on it, and loss of the information
>would not be of great concern for the overall working of a feature.
>> In the text that I proposed in Sunriver I suggested that a
>> Facility message with a H.450 ctComplete should be sent.
>> However, this is not much use to an entity that does
>> not support supplementary services.
>The same situation can arise in the ISDN and QSIG case. But that does
>not prevent the re-routing from taking place, it only means that this
>terminal cannot display the information.
>> Therefore it might be useful to add can extra case to the
>> H323-UU-PDU to cover this, e.g.:
>> H323-UU-PDU ::= SEQUENCE
>> h323-message-body CHOICE
>> setup Setup-UUIE,
>> callProceeding CallProceeding-UUIE,
>> connect Connect-UUIE,
>> alerting Alerting-UUIE,
>> userInformation UI-UUIE,
>> releaseComplete ReleaseComplete-UUIE,
>> facility Facility-UUIE,
>> progress Progress-UUIE,
>> dummy NULL,
>> reRouteIndication ReRouteIndication
>> nonStandardData NonStandardParameter OPTIONAL,
>> h4501SupplementaryService SEQUENCE OF H4501SupplementaryService
>> ReRouteIndication ::= SEQUENCE
>> display IA5String (SIZE( 0..255) ),
>> endpointInfo EndpointType,
>> This could then be sent by a gatekeeper when a re-route has been done.
>Your proposal does not say which message you would use. If it is
>Facility, then the Facility-UUIE could be enhanced instead.
>However, I have a more general concern with this new proposal:
>An endpoint would still have to be upgraded to understand this coding.
>The only advantage compared to your original proposal (i.e. using an
>operation) might be slightly less complex coding. However, it goes
>against the intention of H.450.x. The idea behind the approach in H.450
>is *not* to add new coding in H.225.0 whenever new functionality is
>created, but to use the *generic* container 'H4501 Supplementary
>APDU' and confine all new functionality plus coding to the
>service recommendation. This allows a neat modular approach where you
>tailor your system by choosing the right building blocks.
>Therefore I prefer using operations wherever possible.
>Tel: +43 1 1707 45897
>Fax: +43 1 1707 56992
>Email: ernst.horvath at siemens.at
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