Revised H.323 URL document
Paul E. Jones
paulej at ACM.ORG
Wed Sep 6 23:20:19 EDT 2000
To prevent the HTML mail headaches, I will comment by item number.
0) Yes, I believe that DNS may be used to locate the "host" and an LRQ then sent to port "port" of "host". "host" will resolve the address and return an LCF. The user is not necessarily registered with the GK. Actually, the LRQ might even be forwarded (available in v4) and the GK to which the user is actually registered may reply. Now, that does not mean that the endpoint has to perform the DNS query and resolve the address-- it may pass it to the GK for resolution. The Gatekeeper might also pass it to a border element for resolution, since Annex G can send templates around with domain names in them indicating the domains it can resolve. So, I think there are two possible resolution mechanisms available to a Gatekeeper. I believe what I meant to say I was going to remove is the statement in parentheses about the LRQ message being used. Essentially, we're left with just saying that the default protocol is "ras", which means that a GK should resolve the address. However, mentioned separately.. somewhere.. that I think it might be reasonable to specify the resolution "mode" rather than the protocol: "direct" (i.e., one sends a setup to the address) or "indirect" (i.e., RAS must be used by the endpoint and the GK may use RAS or Annex G, a database, a carrier pigeon, etc.)
1) I did not make my point very clear at all-- I apologize. What I was trying to say is that users enter aliases, not IP addresses. Today, most H.323 users enter telephone numbers or some type of alias and not the IP address of the called endpoint. I unsuccessfully tried to draw a parallel between alias vs IP and user vs host. In my opinion, the most common forms of the URL will be either "h323:user at host" or "h323:user". The former will be the most popular, by far. The latter will be more widely used inside corporate networks. We see this today with popular e-mail programs, etc. Some companies are so large that multiple domains are necessary, so it doesn't work well. However, most companies keep all e-mail address for the company under one domain. So, "h323:user" would be very likely in many corporate environments. I prefer to allow these two syntaxes as I believe they are most common. I do not want "h323:paulej@"-- that I just don't like.
----- Original Message -----
From: Callaghan, Robert
To: 'Paul E. Jones' ; Orit Levin
Cc: Mailing list for parties associated with ITU-T Study Group 16 (E-mail)
Sent: Tuesday, September 05, 2000 10:54 AM
Subject: RE: Re: H.323 URL Specification (second try)
Siemens Enterprise Networks
Tel: +1.561.923.1756 Fax: +1.561.923.1403
Email: Robert.Callaghan at ICN.Siemens.com
(0) The use of url means the "address resolution" is done (by the local GK) using the DNS, not RAS! This is why the "user only" url of H.323, is really an exceptional case. It is a question, if we want to keep it within the url. It lets the local (source) GK know, that the "address resolution" procedure should performed by other, then DNS, means. The "protocol" means: the signaling H.323 protocol to contact the (next hop towards the) destination, after the IP address had been resolved.
(0) I will remove the reference to RAS and expect to see an explicit description of the procedure in Annex O. What I would expect is that the hostport part will resolve to a GK to which LRQ messages are directed.
[RWC] Now I am confused. I thought that DNS was used to locate the resolution server. Then LRQ(RAS) was used to communicate with that server to resolve the address of the user. The server doing the address resolution may not be involved in the final connections.
(1) I disagree that it is the exception. I would contend that calling a specific machine would be the exception. Sure, one can call and endpoint directly, but that's not typical. It is in testing and development environments, but in production environments, users enter telephone numbers. Also, I can imagine intranets where the h323 URL might be used. At work, I might post a page with "h323:paulej", but I would never post "h323:@cisco.com". However, the latter is allowed, of course. What I do not want is "h323:paulej@" on a web page. That's ugly, in my opinion. I realize that the SIP folks chose that, but it seems illogical to me.
[RWC] I do not see any relationship between an URL and a telephone number. If a user enters a telephone number the connection should be established using either the dialedDigits alias or the partyNumber alias not the URL-id alias. For me, the URL user should be a name type structure like in email users. This allows for a number as a name but not as a telephone number. I do not accept the SIP and ENUM concept where telephone numbers are funny names with a default domain for DNS. In fact, I think that this will not work due to difficulties with administration ownership of telephone numbers.
[RWC] I do agree that user only will be an exception because it forces the use of a default domain for DNS. It is not likely that there will be universal default domain.
(2) If I provided "h323:@192.168.1.1;proto=q931", a device should assume that it can reach it on the default 1720 port or the default Annex E port (as described in Annex E). If, however, I use a different port like "h323:@192.168.1.1:2500;proto=q931", I would say that Annex E is out of the picture. That is another reason why I believe the first step to resolution should be through a Gatekeeper. The gatekeeper can not only resolve the address, but also indicate any non-standard ports, including both the TCP and Annex E transport information.
[RWC] In this case the endpoint that wished to use Annex E must support the requirement of Annex E that requires the ability to fall back to TCP.
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