Revised H.323 URL document

Orit Levin orit at
Mon Sep 11 15:01:19 EDT 2000

Below is my take on the current situation.  
The three of us have the following different views on the possible use of the H.323 URL.
If I try to map them into the H.323 "classic" picture of EP1---GK1-------GK2---EP2 . The GKs are optional. If exist, they may contain BE as well.
I understand the following:

Bob:: indirect: EP1---GK1; direct: EP1 --------Zone2
Paul:: indirect: Zone1-------GK2; direct: Zone1------EP2
Orit:: Zone1-------Zone2 (with H.225.0 Q.931, LRQ or Annex G) possible between them for a specific call.

We "agree" that all of the scenarios should be allowed. 
"It seems like" we disagree about the priority/emergency of each of the applications above.
Saying that, I don't like very much to define a solution based on the "perceived priority" of the applications.
My proposed approach is, above all, guided by the fact, that the DESTINATION is the one to design its URL scheme, implement and, eventually, publish its URL(s).
The URL 
-    has a key (I.e. the DNS domain) for IP resolution only
-    says what is the first H.323 protocol to contact this IP address, all the scenarios above are addressed.

If the DNS portion (I.e. "host") is not present, it automatically means, that the local (pre-configured or RAS discovered) gatekeeper will resolve the "user" name (using RAS, Annex G, another DNS lookup, other means). It is an exception, but it is still consistent with the approach above (The local zone is responsible for the URL scheme, it published.)

The bottom line: I agree with the last proposal for H.323v4:
No parameters at all. The default: H.225.0/Q.931/Setup with its default TCP port. 

Best Regards,
Orit Levin
RADVision Inc.
575 Corporate Drive Suite 420
Mahwah, NJ 07430
Tel: 1 201 529 4300  (230)
Fax: 1 201 529 3516
orit at
  -----Original Message-----
  From: Callaghan, Robert <Robert.Callaghan at>
  To: 'Orit Levin' <orit at>
  Cc: ITU-SG16 at <ITU-SG16 at>
  Date: Monday, September 11, 2000 1:53 PM
  Subject: RE: Revised H.323 URL document



  Let us try to focus on a few points first:  (These are snippets from the thread.)


  OL: Are you interested in efficiently running H.323 over the Internet?

  RC: Yes!  For clarification, this is the H.323 as defined in H.323v4 and H.225.0v4.  For the November decision, there should not be any extensions, implicit or explicit.


  OL: The picture, in my mind, is different from yours and fits the "traditional" H.323. For every H.323 call, logically there are (at least) two GKs: source and destination. (Physically, both of them are optional, based on the "mode" policy inside the corresponding H.323 zones.)

  RC:  I agree with your model of two endpoint each with an optional GKs based on zone policies.  The source and destination policies are independent from each other.  I don’t know how this is different, as you state.


  OL: By specifying in H323-URL the "mode" of operation between the source EP and a GK, you propose to use the URL for "publishing" the relations between the EP and "ITS" GK PER DESTINATION! It is, indeed, very different from the H.323 today. Moreover, you implicitly introduce a concept of a "source" GK, being re-defined each time BY THE DESTINATION. (This case may be considered as an additional application for the H.323 URL)

  RC: I make so such assumption.  In the “Direct” model, I assume that the given address is directly callable.  The routing model is not specified nor assumed.  If the term “Direct” is a problem in that the term overlaps with the routing model then the use of “Callable” would be fine.  The use of the DNS service to convert the DNS domain to an IP address is assumed.  This is also the only use of the DNS server.  No DNS records beyond the “A” record will be used.  If the initial use of the H.323 URL could be limited to this service.

  RC:  The use of the “Indirect” or “non callable” form has bothered me in that its use is not clearly defined.  My view is that this was a means to access an H.323 repository to obtain the true address.  Apparently there are other views.  Therefore I suggest that a solution would be to drop this form for now.


  OL: The natural use of URLs is between the zones/domain. For H.323, it is an OPTION, what kind of address resolution to propose and use. The beauty of the URL approach is that the DESTINATION provides an option to be reached using the DNS lookup, if it chooses so and populates properly the DNS.

  RC: The may be beautify for some; but it is definitely new.  I know of nothing in H.323v4 that describes the procedures and rules for this type of address resolution.  This can be discussed as part of Annex O, after the decision on H.323v4.


  OL: We don't have to agree on the mailing list. We can spend more then one meeting in order to reach "the consensus". In that case, I would support the inclusion of the minimal H323-URL only (without any parameters and without the PORT number) towards the H.323v4.

  RC: I agree that it is not possible to agree to a complex solution on the mailing list.  However, I hope that we can agree to a simple URL without any parameters or port (ouch! J) where this URL is the actual address to be used in a SETUP message.  This should not change anything in H.323 including the use of the GK.


  I hope that this helps.





  Robert Callaghan

  Siemens Enterprise Networks

  Tel: +1.561.923.1756              Fax: +1.561.923.1403

  Email:      Robert.Callaghan at



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