Paul,
Yes, it definitely breaks backward compatibility: that was clearly stated. However, it was also an editorial error. If we can determine whether or not anybody has shipped a V3 product to date-- and there are several companies with V3 at the moment-- we can make an informed decision. I have contacted every company that I know that has a V3 product.
As a general rule, it is bad to change the ASN.1 in such a manner. However, these changes were proposed by me as Editor of the Implementers Guide because the ASN.1 truly was in error. We could resolve this by changing the H.225.0 text, rather than the ASN.1. The main reason for having the fields defined as OPTIONAL was to provide a means of allowing an H.323v3 or higher endpoint to use Annex E when talking with an H.323v2 device that also supports Annex E. However, it has since been pointed out that: 1) There are no Annex E implementations to worry about 2) Even if there were, TCP would still work, so they're not broken
However, now that we've started down this path, I believe that folks agree that there is benefit in this approach: 1) It allows us to provide a call signaling address for Annex E, rather than necessitating the use of the registered port number 2517 2) It allows us to add additional transport support in the future in a backward compatible way and without adding new fields to these messages.
So, I would like every company to carefully consider this issue. We must have closure on this within one week, since we must finish the Implementers Guide and H.225.0v4 documents soon-- and we do not need issues like this to become a problem. Also, those people building H.323v3 devices need to have a high comfort level that we will not be changing the ASN.1 further-- I do not want any company to have to wait until November (when the next Implementers Guide is approved) to feel comfortable that their equipment is not going to be broken.
Paul
----- Original Message ----- From: "Paul Long" Plong@SMITHMICRO.COM To: ITU-SG16@mailbag.cps.intel.com Sent: Friday, June 02, 2000 3:44 PM Subject: Re: ASN.1 Changes in H.225.0v3
Paul,
Yes, I have a problem with this. I thought you said that the three fields would be made OPTIONAL and new fields would be added after them. However, you syntax shows that you would _replace_ these fields. That would cause a decode error in our and I assume other H.323v3 vendor's products. Making them OPTIONAL and then adding other extension additions after them is
risky
enough, but replacing them is not just risky but deadly.
Paul Long Smith Micro Software, Inc.
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