Re: H.323 (8.1) Phase A - Call Setup
Paul,
I don't understand why the intent was Alerting.
"If an endpoint can respond to a Setup message with a Connect, Call Proceeding, or Release Complete within 4 seconds, it is not required to send the Alerting message."
Why, if an endpoint can respond to a Setup with a Call Proceeding within 4 seconds, should it not have to send the Alerting? How will the user get a ringing sound in his ear then?
I know that Alerting (and Connect) also stops T303. However, in Table 9-1/Q.931 (refernced by H.225 (7.5)), receipt of an Alerting starts T301, while receipt of Call Proceeding starts T310. I realise that T310 is not explicitly required by H.323 but the second para of (8.1.8.2) implies that the mechanism it represents IS required (I know its says should and not shall - perhaps this is a second error)
"A Gateway should send a Call Proceeding message after it receives the Setup message (or after it receives ACF) if it expects more than 4 seconds to elapse before it can respond with Alerting, Connect, or Release Complete."
The specific reason for sending Call Proceeding here is to stop T303 timing out and the call failing.
The point is that for H.323 endpoints Call Proceeding is superfluous, if a terminal device cannot respond with an Alerting or Release Complete within 4 seconds it has problems [ or it's running windows (-; ] and the call probably should fail. However, gateways are different. If they interface to a large network then the Alerting must not be sent to the caller until an appropriate message has been received [ also in (8.1) "In the case of interworking through a Gateway, the Gateway ***shall send Alerting when*** it receives a ring indication from the SCN." ie WHEN it receives the ring indication and not before ] and this might take longer than 4 seconds - hence the need for gateways to send Call Proceeding and the relevance of 4 seconds in the sentence in question.
My original assertion that the text in (8.1) is incorrect stands.
"If an endpoint can respond to a Setup message with a Connect, Alerting, or Release Complete within 4 seconds, it is not required to send the Call Proceeding message."
Alternatively, if an endpoint *cannot* respond to a Setup message with a Connect, Alerting, or Release Complete within 4 seconds, it *should* (shall?) send a Call Proceeding message.
The only other interpretation I can come up with is that the intent was "If an endpoint can respond to a Setup message with a Connect within 4 seconds, it is not required to send the Alerting message." If it responds with a Release Complete within 4 seconds it's not going to send an Alerting!
I've just seen Chris's reply as well - I think my observations still stand. I think in fact that the whole paragraph is poorly structured, mixing a number of different ideas. I was juts trying to suggest the simplest change.
Peter
-----Original Message----- From: Paul E. Jones [mailto:paulej@PACKETIZER.COM] Sent: 20 July 2001 12:48 To: ITU-SG16@mailbag.cps.INTEL.COM Subject: Re: H.323 (8.1) Phase A - Call Setup
Peter,
Alerting was the intent. Call Proceeding not produce a ringing sound in the caller's ear. H.323 devices have to be able to send an Alerting, though they're not required to do so if they can send a Connect within 4 second. The 4 seconds is the T303 timeout and the T303 timer is disabled when receiving Alerting, too... not just Call Proceeding.
The ideas are related, but independent. What we have seen some folks do is send a Call Proceeding to the caller and then nothing else until the connect. The result is that the calling party hears silence for a very long time: that's not good.
Paul
----- Original Message ----- From: "Peter Price" PeterP@VEGASTREAM.COM To: ITU-SG16@mailbag.cps.INTEL.COM Sent: Friday, July 20, 2001 6:54 AM Subject: H.323 (8.1) Phase A - Call Setup
Hi folks,
I think I may have found some incorrect text in H.323 8.1
The same text appears in both V3 and V4 so I suspect nobody
has commented
before.
In the paragraph beginning: "An endpoint shall be capable of sending the Alerting message. ..."
it goes on to say: "If an endpoint can respond to a Setup message with a Connect, Call Proceeding, or Release Complete within 4 seconds, it is not
required to send
the Alerting message. An endpoint sending the Setup message
can expect to
receive either an Alerting, Connect, Call Proceeding, or
Release Complete
message within 4 seconds after successful transmission."
I believe the first sentence here should really be discussing the requirement to send a Call Proceeding (not Alerting) message. The period of 4 seconds in the last sentence is related to
T303 which is
specifically terminated by a Call Proceeding message in
order to extend the
timeout for the sending endpoint.
I think the sentence should read: "If an endpoint can respond to a Setup message with a
Connect, Alerting, or
Release Complete within 4 seconds, it is not required to
send the Call
Proceeding message."
This is then consistent with the use of Call Proceeding described in
8.1.8.2
(second para).
Peter Price
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Peter Price