I have a remark and some concerns regarding the ASN.1 coding. There is already a H.450.1 field behind the three dots in the H.225 V2. Here is a copy of the current V2 definition:
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, empty NULL -- used when a FACILITY message is sent, -- but the Facility-UUIE is not to be invoked -- (possible when transporting supplementary -- services messages) }, nonStandardData NonStandardParameter OPTIONAL, ..., h4501SupplementaryService SEQUENCE OF OCTET STRING OPTIONAL -- each sequence of octet string is defined as one -- H4501SupplementaryService APDU as defined in -- Table 3/H.450.1
Of cource it would be possible to add the new field of nonStandardSequence either before or after the h4501SupplementaryService, but the question is whether it is necessary.
The H.450.1 provides namely (in addition to the standardized H.450.x supplementary service signalling) for a coordinated method of vendor specific signalling. With H.450.1 header the sender can not only identify itself, but the sender can, for example, tell what the receiver has to do if it does not understand the contents of the message. For this purpose the header contains the type and address of source (sender) and destination entity (intended receiver) and Interpreter. H.450.1 may sound a little bit more complicated than just the nonStandardParameter, but it allows the SENDER to have some control what the receiver does. Since h4501SupplementaryService is already a SEQUENCE, different entities (i.e. enpoint stack, application, gatekeeper, gateway ...) can use the H.450.1 for their own purposes indepently from each other. If everybody would use the H.450.1 for their vendor specific functionality, we have a better change to cope with the installed base in the future as we continue increasing the H.323 capabilities.
So the question remains: Do we still need yet another method of sending non-standard information in H.225 ? Perhaps somebody has an argument that I did not see, yet.
Markku
-----Original Message----- From: Toby Nixon [SMTP:tnixon@MICROSOFT.COM] Sent: Monday, January 19, 1998 1:36 PM To: ITU-SG16@mailbag.jf.intel.com Subject: Re: H.323 delta doc
That would certainly make me happier than overwriting existing nonStandardData.
-- Toby-----Original Message----- From: Scott Petrack [SMTP:Scott_Petrack@vocaltec.com] Sent: Sunday, January 18, 1998 12:08 AM To: ITU-SG16@mailbag.jf.intel.com Cc: Toby Nixon Subject: Re: H.323 delta doc
Thinking about Toby's concern, the only way I can think of to mandate preservation and to be totally backward compatible is to add to the H323-UU-PDU structure a new field after the dots:
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, ... }, nonStandardData NonStandardParameter OPTIONAL, ... nonStandardSequence SEQUENCE of NonStandardParameter OPTIONAL }
v2 implementations should be told not to write into the old nonStandardParameter and to use the new one. Such a change is pretty tiny, and if I'm not mistaken would guarantee complete backward compatible and give the required new function.
If it is really too late it could be done in the implementor's guide, I suppose.
Scott
tnixon@MICROSOFT.COM on 01/16/98 09:57:39 PM
Please respond to ITU-SG16@mailbag.jf.intel.com
To: ITU-SG16@mailbag.jf.intel.com cc: (bcc: Scott Petrack) Subject: Re: H.323 delta doc
While we don't necessarily oppose migrating to a sequence of nonStandardParameter in the nonStandardData element of H323-UU-PDU in H.225.0 messages, everyone should be aware that NetMeeting does make use of this element in the "old" unstructured form. I think you'd find NetMeeting users disturbed by the loss of functionality that occurred if intermediate devices overwrote nonStandardData, as provided for in the last paragraph of the proposed text. We would be much more comfortable if the text did not permit overwriting -- or mandated preservation -- when the message is being conveyed between H.323v1 endpoints. -- Toby ___________________________________________________________ Toby Nixon, Program Manager - NetMeeting http://www.microsoft.com/netmeeting Microsoft Corporation, Applications and Internet Client Group, Redmond WA USA +1 (425) 936-2792 Fax: +1 (425) 936-7329 mailto:tnixon@microsoft.com
-----Original Message----- From: Pete Cordell [SMTP:pete.cordell@BT-SYS.BT.CO.UK] Sent: Friday, January 16, 1998 4:59 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: H.323 delta doc
Gary,
Two things....
- I included the wrong text in the mail I originally sent you... The
text should have been:-
"To include multiple elements of nonStandardData in an H.225 message the nonStandardParameter is used in the following way. This special use of the nonStandardParameter is identified by setting the nonStandardIdentifier to be an OBJECT IDENTIFIER of type {itu-t (0) recommendation (0) h (8) 2250}. In this case the information contained in the data part of the nonStandardParameter consists of a fragment of ASN.1 encoded into an OCTET STRING (The ASN.1 encoding rules are the same as those for all H.225 messages). The ASN.1 fragment has the following syntax:
ExtendNonStandard ::= SEQUENCE OF NonStandardParameter
It is recommended that entities use this method for including nonStandardData in messages even if they only insert one piece of information as it allows other entities in the signalling path to either add or delete their own nonStandardData without overwriting information inserted by the originating entity.
If intermediate entities on the signalling path need to insert nonStandardData when there is already nonStandardData present that is not of the extended form described above they are encouraged to take measures to ensure that the original nonStandardData can be recovered by entities further down the signalling path once those entities have removed any nonStandardData specific to them. This can be achieved by nesting the original nonStandardData field inside the nonStandardParameter created by the intermediate entity.
However, endpoints should be aware that if they do not insert nonStandardData in the extended form it may be overwritten by intermediate signalling entities."
This is less enforcing than the text you received before, which seems more in line with backwards compatibility.
- If you're imply that it should be in H.225.0 I think that makes
sense (even though I had originally assumed it would go in H.323). In the discussion on nonStandardParameter in Section 7.6 H.225.0 seems a good place.
Regards,
Pete
Pete Cordell BT Labs E-Mail: pete.cordell@bt-sys.bt.co.uk Tel: +44 1473 646436 Fax: +44 1473 645499 =================================
From: Gary A. Thom[SMTP:gthom@DELTA-INFO.COM] Sent: 16 January 1998 00:40 To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: H.323 delta doc
Pete,
Is this text for a new section in H.323 or for the non-standard semantics in H.225.0???
Gary
From: Pete Cordell pete.cordell@BT-SYS.BT.CO.UK Subject: Re: H.323 delta doc Date: Wed, 14 Jan 1998 14:01:48 -0000 To: ITU-SG16@MAILBAG.INTEL.COM
Gary,
I think we got consensus on the nonStandard issue to the point that
no
one objected (!) and most people seemed to be positive. The
suggested
wording (including wording to cover off Joerg's comments) was:
"To include multiple elements of nonStandardData in an H.225 message
the
nonStandardParameter SHALL BE in the following way. This special use
of
the nonStandardParameter is identified by setting the nonStandardIdentifier to be an OBJECT IDENTIFIER of type {itu-t (0) recommendation (0) h (8) 2250}. In this case the information
contained
in the data part of the nonStandardParameter SHALL CONSIST of a
fragment
of ASN.1 encoded into an OCTET STRING (The ASN.1 encoding rules are
the
same as those for all H.225 messages). The ASN.1 fragment has the following syntax:
ExtendNonStandard ::= SEQUENCE OF NonStandardParameter
Entities SHOULD use this method for including nonStandardData in messages even if they only insert one piece of information as it
allows
other entities in the signalling path to either add or delete their
own
nonStandardData without overwriting information inserted by the originating entity.
If intermediate entities on the signalling path need to insert nonStandardData when there is already nonStandardData present that is not of the extended form described above (i.e. this sentence goes
below
what I originally presented, just avoid any confusion!) they are encouraged to take measures to ensure that the original
nonStandardData
can be recovered by entities further down the signalling path once
those
entities have removed any nonStandardData specific to them. This can
be
achieved by nesting the original nonStandardData field inside the nonStandardParameter created by the intermediate entity.
However, endpoints should be aware that if they do not insert nonStandardData in the extended form it may be overwritten by intermediate signalling entities."
Regards,
Pete
================================= Pete Cordell BT Labs E-Mail: pete.cordell@bt-sys.bt.co.uk Tel: +44 1473 646436 Fax: +44 1473 645499 =================================
From: Gary A. Thom[SMTP:gthom@DELTA-INFO.COM] Sent: 09 January 1998 23:00 To: ITU-SG16@MAILBAG.INTEL.COM Subject: H.323 delta doc
<<File: H323DL.DOC>> Hi all,
Attached is the Delta document for H.323.
I did not include any changes for nonStandard or Fast Start as I did not hear a widely accepted proposal.
If I missed anyones comments, please let me know.
Gary
Name : Gary A. Thom Company: Delta Information Systems, Inc. Address: 300 Welsh Rd., Bldg 3 Horsham, PA 19044 USA Phone : +1-215-657-5270 Fax : +1-215-657-5273 E-mail : gthom@delta-info.com
---------------End of Original Message-----------------
Name : Gary A. Thom Company: Delta Information Systems, Inc. Address: 300 Welsh Rd., Bldg 3 Horsham, PA 19044 USA Phone : +1-215-657-5270 Fax : +1-215-657-5273 E-mail : gthom@delta-info.com