October 2003 - sg16-avd - lists.packetizer.com

Rapporteur and drafting work for Q.J/16
by simao.campos＠itu.int 30 Oct '03

30 Oct '03

Dear colleagues, I am sorry if you get multiple copies of this message, as I am trying to diffuse it to the wider SG16 membership. I am pleased to inform you that Mr Vicente Travor, representing the Spanish Administration, has agreed to perform as prospective Rapporteur under the invitation of the SG 16 Chairman for Q.J/16. He will be handling the revision of the draft text for draft new Q.J/16 (E-health Multimedia Framework) aiming at the approval at the next meeting, in accordance with the decisions taken in SG 16 last meeting and to accomodate comments received from other SGs and TSAG (that starts in 2 weeks). He will also try to progress some other short-term issues detailed in the scope of the draft new question. Mr Travor works for the Polytechnic University of Valencia and has excellent understanding of E-health issues and the Multimedia work we do in SG 16. I would like to invite you all to welcome him and to contribute to the work. He will be soon addressing the mailing list for the progression of the work. A mailing list has been established for the question: tsg16ehmmf(a)ties.itu.int. Subscription to it via the TIES interface can be done using the following web page (as well as for any other elegible TIES-based mailing lists): http://www.itu.int/tiesutils/asp/login.asp?pp=/tiesutils/asp/mailinglist.asp ? Alternatively, subscription can be requested to tsbsg16(a)itu.int, however we invite all to use the web-based subscription tool above. Best regards, Simao Campos-Neto ===================================================================== Simão Ferraz de Campos Neto Counsellor, ITU-T SG 16 International Telecommunication Union Tel: +41-22-730-6805 Place des Nations Fax: +41-22-730-5853 Geneva CH1211 - Switzerland E-mail: simao.campos(a)itu.int On the web: www.itu.int/ITU-T/studygroups/com16 ===================================================================== ***** Practice random kindness and senseless acts of beauty ***** =====================================================================

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Report: H.350 Enabled Systems at Internet2
by Tyler Johnson 24 Oct '03

24 Oct '03

Report from Fall 2003 Internet2 Meeting on Directory Enabled Voice and Video Over IP At the Fall 2003 Internet2 Member Meeting the ViDe.Net team successfully demonstrated a number of systems using the H.350 standard for integrating video and voice over IP. I would like extend thanks to everyone who has helped make this a reality. It was quite impressive to see commercial and research efforts coming together to support a solution the Internet2 community has needed for some time. Special thanks to: Internet2’s Video Middleware Group ViDe ITU-T Study Group 16 We were able to show: • H.350 distributed directory searching across multiple universities to find people and their H.323 or SIP addresses. • RADVISION ECS gatekeeper that supports H.350 so that you simply point your gatekeeper at your directory and it automatically picks up all user’s H.323 addresses. No need to enter users into the gatekeeper. • A sample endpoint from RADVISION that uses H.350 to automatically configure itself using user’s single sign on credentials. No more mis-configured endpoints. This endpoint is sample code available to vendors developing their own endpoints. • A SIP proxy from HCL technologies that supports H.350 so that you simply point your proxy at your directory and it automatically picks up all user’s SIP addresses. No need to enter users into the proxy. • Directory enabled SIP video user agent from Claremont Graduate University that can self configure from LDAP and access users from the directory. This endpoint uses the DynamicSoft stack and supports directory tools right in the client. • Directory enabled presence, instant messaging and voice over IP using a SIP user agent from HCL. This user agent was not H.350-enabled and the purpose of the demo was to show how directory enabled proxies can be used to manage standard SIP functionality. • A SIP video user agent from Wave3. This user agent is not H.350 aware, but does support clickable dialing. One can simply type a name into the ViDeNet directory search and click on a result to launch a SIP videoconference. This demo showed the value of institutions implementing H.350 even if they don’t use directory enabled call servers. Details and links to these products are available at: http://www.unc.edu/video/middleware/I2FMM2003/demo/ For more information on H.350, see the Video Middleware Cookbook: http://lab.ac.uab.edu/vnet/ With sincere appreciation, Tyler Johnson University of North Carolina at Chapel Hill ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For help on this mail list, send "HELP ITU-SG16" in a message to listserv(a)lists.intel.com

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Re: H.323 Fast Connect and Versioning
by Douglas Clowes 24 Oct '03

24 Oct '03

Paul et al, Pardon my $AU 0.02 ... I thought that it was a fundamental principle that protocols were backward compatible, despite the fact that this is not always so. Making such a change breaks backward compatibility. An existing version 0 called device will respond with the mandatorily unchanged version 3. It is unsafe for the calling device to assume that the called device can handle version 3 if version 3 is not compatible with version 0. The proposed solution does not discriminate between a device that replies with offered version because it can handle it, or because it doesn't know they are incompatible. A existing version 3 calling device (if there is one) may break if it receives a modified faststart response from the called device, being unable to match the accepted faststart against the offered ones. Since this is only an issue for faststart (contained in H.225.0) it seems reasonable to base the solution on H.225.0. Option 1. ========= If you want the behaviour of changing the faststart, as indicated in the email to which this replies, then look at the protocolIdentifier, and introduce the behaviour at a particular value. There would be a magic value of protocolIdentifier which triggers the new behaviour. A called endpoint must follow earlier behaviour for values of protocolIdentifier (in Setup) less than the magic value where changed behaviour is allowed (i.e. must not change the faststart) and must follow later behaviour (set the verion) if protocolIdentifier is equal or greater. This avoids confusing an older calling endpoint. For the calling endpoint, if the protocolIdentifier (in the response e.g. Connect) is less than the magic value, it must limit the version selected to that which was available when that version of H.225.0 was decided, and if equal or greater must use the possibly modified version in the response. This requires that the value of the protocolIdentifier be modified (incremented) to achieve discrimination. Not something which should be done in a change to the IG (IMHO). Option 2. ========= Add an optional element to H.225.0 to carry the possibly modified fastStart (e.g. "modifiedFastStart SEQUENCE OF OCTET STRING OPTIONAL" wherever fastStart appears in a response) to contain the fastStart with the actual version accepted. If a called endpoint adds this to its response and the calling endpoint doesn't understand it, no harm is done because the called EP is a later vintage than the calling EP and presumably understands everything the calling EP could send. A calling EP that doesn't find this element must limit the version used as in option 1, and if it does find this element, must limit the version to that contained therein. (end of options) I feel that Option 1 is cleaner, but Option 2 is more IG-friendly. I also note that option 2 could be retrofitted to earlier versions of H.323 if the option 2 modifiedFastStart element were embedded in a NonStandardParameter of a ClearToken with a "magic" tokenOID, carried in the "tokens" element of the H.225.0 response. In this case, no change to the ASN.1 would be required, and an H.323 v2 EP (say) could indicate that it really does understand some later version of a codec that it normally wouldn't be expected to understand. However, this has a strong kludgy feel to it :). Anyway, since I'm not currently being paid for this, I guess that I should limit my time. Cheers, Douglas Clowes Consultant, Savant Solutions P/L. At 03:27 17/10/2003 -0400, Paul E. Jones wrote: >Tamura-san, > >The problem is not related to D.8-D.11. The problem is only with Fast >Connect. The scenario is this: > Calling Device Called Device > (Version 3) (Version 0) > Setup(fastStart(T38Version=3))--------------> > <------------------------------------Connect(fastStart(T38Version=3) > ^^^ > | > Responds with incorrect Version---------------------------- > >Once the Calling Device receives the fastStart message with version 3 >advertised, it will transmit UDPTL data with the wrong ASN.1 encoding for >the Called Device. The problem is really the fault of the Called Device, >because it accepted a version it did not support. However, the reason that >a called device would do this is because there is nothing in Annex D/H.323 >or Annex B/T.38 that tells the called endpoint not to accept the fastStart >proposal or to modify the version to match the actual supported version of >the endpoint. > >Probably the best solution would be to modify the T.38 and Annex D/H.323 >text to allow the following: > > Calling Device Called Device > (Version 3) (Version 0) > Setup(fastStart(T38Version=3))--------------> > <------------------------------------Connect(fastStart(T38Version=0) > ^^^ > | > Responds with actual supported Version---------------------------- > >However, I do not know which devices might break as a result of this. It >would only be devices that propose T.38 channels in the Setup message. > >Also, note that we have precisely the same problem with SIP, too. The >INVITE message and the 200 message looks almost exactly the same. Nowhere, >as far as I know, does it say how a SIP device should handle the T.38 >version field when replying to an INVITE. > >Paul > >----- Original Message ----- >From: "Hiroshi Tamura" <tamura(a)toda.ricoh.co.jp> >To: <paulej(a)packetizer.com> >Cc: <PeterP(a)vegastream.com>; <itu-sg16(a)external.cisco.com>; ><tsg16q14(a)itu.int> >Sent: Tuesday, October 14, 2003 4:41 AM >Subject: Re: H.323 Fast Connect and Versioning > > >> Paul, >> >> > Anyway, to answer your question... I don't think the procedures >documented >> > in D.8 - D.11 are a problem. In theory, the endpoint that transmits an >OLC >> > would not propose an OLC with a version number included that is not >> > supported by the other side. However, the text does not say that. As >such, >> > I think I will bring a contribution as Rapporteur to have some text >added >> > that makes it very explicit that an endpoint SHALL NOT propose in an OLC >> > version of T.38 not supported by the other endpoint. Does that sound >> > reasonable? >> >> Yes, Reasonable. >> >> But, before that, I'm very sorry for my poor understanding. >> Why does the problem happen in D.8 - D.11? >> "version" in T38FaxProfile in DataApplicationCapability in OLC is the same >> in all cases. Even in voice to fax case, for example, between the caller >with >> the version 3 and the called with the version 1, does the called possibly >> accept (CONNECT) in reponse to SETUP because it does not know our syntax >issue? >> >> Could you please explain to me? >> >> Thanks in advance. >> >> > I have also had some discussion with people about the various solutions >to >> > Fast Connect. I think one person or another thinks the various ideas >(and I >> > have about 5 now) are insufficient. What has most recently been >proposed is >> > to simply add text that says a called endpoint shall not accept a Fast >> > Connect proposal that includes a T.38 version it does not support. That >> > kind of text should have been in there, as well, but it is not. I >wonder if >> > anybody's equipment would break with such text? >> >> I hope it does not exist. If any, the version 2 implementation before the >> last meeting may do harm. >> Also, the above sentence that you suggests is ok for me. >> >> Regards, >> -- >> Hiroshi Tamura >> > >

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Re: H.323 Fast Connect and Versioning
by Paul E. Jones 23 Oct '03

23 Oct '03

Tamura-san, The problem is not related to D.8-D.11. The problem is only with Fast Connect. The scenario is this: Calling Device Called Device (Version 3) (Version 0) Setup(fastStart(T38Version=3))--------------> <------------------------------------Connect(fastStart(T38Version=3) ^^^ | Responds with incorrect Version---------------------------- Once the Calling Device receives the fastStart message with version 3 advertised, it will transmit UDPTL data with the wrong ASN.1 encoding for the Called Device. The problem is really the fault of the Called Device, because it accepted a version it did not support. However, the reason that a called device would do this is because there is nothing in Annex D/H.323 or Annex B/T.38 that tells the called endpoint not to accept the fastStart proposal or to modify the version to match the actual supported version of the endpoint. Probably the best solution would be to modify the T.38 and Annex D/H.323 text to allow the following: Calling Device Called Device (Version 3) (Version 0) Setup(fastStart(T38Version=3))--------------> <------------------------------------Connect(fastStart(T38Version=0) ^^^ | Responds with actual supported Version---------------------------- However, I do not know which devices might break as a result of this. It would only be devices that propose T.38 channels in the Setup message. Also, note that we have precisely the same problem with SIP, too. The INVITE message and the 200 message looks almost exactly the same. Nowhere, as far as I know, does it say how a SIP device should handle the T.38 version field when replying to an INVITE. Paul ----- Original Message ----- From: "Hiroshi Tamura" <tamura(a)toda.ricoh.co.jp> To: <paulej(a)packetizer.com> Cc: <PeterP(a)vegastream.com>; <itu-sg16(a)external.cisco.com>; <tsg16q14(a)itu.int> Sent: Tuesday, October 14, 2003 4:41 AM Subject: Re: H.323 Fast Connect and Versioning > Paul, > > > Anyway, to answer your question... I don't think the procedures documented > > in D.8 - D.11 are a problem. In theory, the endpoint that transmits an OLC > > would not propose an OLC with a version number included that is not > > supported by the other side. However, the text does not say that. As such, > > I think I will bring a contribution as Rapporteur to have some text added > > that makes it very explicit that an endpoint SHALL NOT propose in an OLC > > version of T.38 not supported by the other endpoint. Does that sound > > reasonable? > > Yes, Reasonable. > > But, before that, I'm very sorry for my poor understanding. > Why does the problem happen in D.8 - D.11? > "version" in T38FaxProfile in DataApplicationCapability in OLC is the same > in all cases. Even in voice to fax case, for example, between the caller with > the version 3 and the called with the version 1, does the called possibly > accept (CONNECT) in reponse to SETUP because it does not know our syntax issue? > > Could you please explain to me? > > Thanks in advance. > > > I have also had some discussion with people about the various solutions to > > Fast Connect. I think one person or another thinks the various ideas (and I > > have about 5 now) are insufficient. What has most recently been proposed is > > to simply add text that says a called endpoint shall not accept a Fast > > Connect proposal that includes a T.38 version it does not support. That > > kind of text should have been in there, as well, but it is not. I wonder if > > anybody's equipment would break with such text? > > I hope it does not exist. If any, the version 2 implementation before the > last meeting may do harm. > Also, the above sentence that you suggests is ok for me. > > Regards, > -- > Hiroshi Tamura >

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Re: H.323 Fast Connect and Versioning
by Paul E. Jones 17 Oct '03

17 Oct '03

Tamura-san, The problem is not related to D.8-D.11. The problem is only with Fast Connect. The scenario is this: Calling Device Called Device (Version 3) (Version 0) Setup(fastStart(T38Version=3))--------------> <------------------------------------Connect(fastStart(T38Version=3) ^^^ | Responds with incorrect Version---------------------------- Once the Calling Device receives the fastStart message with version 3 advertised, it will transmit UDPTL data with the wrong ASN.1 encoding for the Called Device. The problem is really the fault of the Called Device, because it accepted a version it did not support. However, the reason that a called device would do this is because there is nothing in Annex D/H.323 or Annex B/T.38 that tells the called endpoint not to accept the fastStart proposal or to modify the version to match the actual supported version of the endpoint. Probably the best solution would be to modify the T.38 and Annex D/H.323 text to allow the following: Calling Device Called Device (Version 3) (Version 0) Setup(fastStart(T38Version=3))--------------> <------------------------------------Connect(fastStart(T38Version=0) ^^^ | Responds with actual supported Version---------------------------- However, I do not know which devices might break as a result of this. It would only be devices that propose T.38 channels in the Setup message. Also, note that we have precisely the same problem with SIP, too. The INVITE message and the 200 message looks almost exactly the same. Nowhere, as far as I know, does it say how a SIP device should handle the T.38 version field when replying to an INVITE. Paul ----- Original Message ----- From: "Hiroshi Tamura" <tamura(a)toda.ricoh.co.jp> To: <paulej(a)packetizer.com> Cc: <PeterP(a)vegastream.com>; <itu-sg16(a)external.cisco.com>; <tsg16q14(a)itu.int> Sent: Tuesday, October 14, 2003 4:41 AM Subject: Re: H.323 Fast Connect and Versioning > Paul, > > > Anyway, to answer your question... I don't think the procedures documented > > in D.8 - D.11 are a problem. In theory, the endpoint that transmits an OLC > > would not propose an OLC with a version number included that is not > > supported by the other side. However, the text does not say that. As such, > > I think I will bring a contribution as Rapporteur to have some text added > > that makes it very explicit that an endpoint SHALL NOT propose in an OLC > > version of T.38 not supported by the other endpoint. Does that sound > > reasonable? > > Yes, Reasonable. > > But, before that, I'm very sorry for my poor understanding. > Why does the problem happen in D.8 - D.11? > "version" in T38FaxProfile in DataApplicationCapability in OLC is the same > in all cases. Even in voice to fax case, for example, between the caller with > the version 3 and the called with the version 1, does the called possibly > accept (CONNECT) in reponse to SETUP because it does not know our syntax issue? > > Could you please explain to me? > > Thanks in advance. > > > I have also had some discussion with people about the various solutions to > > Fast Connect. I think one person or another thinks the various ideas (and I > > have about 5 now) are insufficient. What has most recently been proposed is > > to simply add text that says a called endpoint shall not accept a Fast > > Connect proposal that includes a T.38 version it does not support. That > > kind of text should have been in there, as well, but it is not. I wonder if > > anybody's equipment would break with such text? > > I hope it does not exist. If any, the version 2 implementation before the > last meeting may do harm. > Also, the above sentence that you suggests is ok for me. > > Regards, > -- > Hiroshi Tamura >

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Re: H.323 Fast Connect and Versioning
by Paul E. Jones 16 Oct '03

16 Oct '03

Terry, Well, that's an interesting find. I didn't even know that was there. So, we have a precedent for this already. I guess we need to make some changes to the Fast Connect procedure to not restrict this text. Either that, or change this Appendix. Paul ----- Original Message ----- From: Lyons, Terry To: 'paulej(a)PACKETIZER.COM' ; itu-sg16(a)external.cisco.com Cc: Lyons, Terry Sent: Monday, October 13, 2003 2:33 PM Subject: Re: H.323 Fast Connect and Versioning As part of this discussion, Paul Jones wrote: I'm actually working on a new extension to H.323 to allowing the calling endpoint to explicitly request that the call establishment be delayed until a certain point (e.g., bi-directional media channels are opened). The calling side can control when it lets the call proceed. Likewise, the called side can control it by not acknowledging that the requested "delay point" has been reached. This might be the better way to handle T.38.... except that, as you point out, there are Fast Connect-only T.38 devices. My head hurts... I really hate to break the rules about changing the attributes of a Fast Connect proposal. 1. Sorry about your head. We appreciate your responsible stewardship of H.323. 2. There has been text since H.323 V4 that says how to CHANGE the OLCs that are sent back in a Fast Connect response and NOT just by dropping extensions that are not understood. Appendix II is admittedly non-normative and could be written more clearly, but the level of detail suggests that some vendors might implement it: II.8.2 Synchronizing RSVP with fast connect ... A calling endpoint that wishes to use RSVP in a Fast Connect procedure shall send a sequence of prioritized QoSCapability structures in the OpenLogicalChannel structures contained in the fastStart element of the Setup message. Upon receiving the Fast Connect Setup message, the called endpoint shall derive the QOSMode set using the mechanism described in Table II.1. Assuming that the derived set contains a valid (i.e. non-best effort intersection), the called endpoint shall respond to the Setup message from the calling endpoint by sending a fastStart element including only the QoSCapabilities indicated in the derived QoS set. The fastStart element shall be sent as soon as possible (e.g. in a Call Proceeding message) to expedite the resource reservation. The calling endpoint's set will be a subset of the list sent by the calling endpoint in the OpenLogicalChannel structures and will, similarly, be a sequence in decreasing order of priority by QOSMode. Each QoSCapability included in the OpenLogicalChannel in the response message indicates an acceptance of the corresponding QOS level by the called endpoint ... 3. "Synchronized RSVP" involves the idea of suspending call establishment until a requested "delay point" has been reached. Paul's new extension should address the degree to which its procedures are consistent with II.8/H.323. - tlyons(a)sonusnet.com +1 732 625-3003 x212 -----Original Message----- From: paulej(a)PACKETIZER.COM [mailto:paulej@PACKETIZER.COM] Sent: Tuesday, September 16, 2003 10:43 AM To: itu-sg16(a)external.cisco.com Subject: Re: H.323 Fast Connect and Versioning Peter, To address there V0/V2 interop problem, I agree that something like the syntax2002 would be useful. In fact, to answer your question about other H.245 fields that are unknown to the other side... that's precisely how things get quite naturally "dropped out" in the replies back. It's an indicator to the originator. Looking past v2 to the subsequent revisions, what else might change? Perhaps the syntax will remain unchanged or at least compatible, but perhaps something else in the procedures might changes. This is what I'm wondering if we should insert rules into H.323 (and Annex D would be the candidate for fax) that says that you shall not accept a proposal in Fast Connect for a version you do not support? The proper solution to this general problem, in my opinion, is to advertise termcaps in the Setup (perhaps the parallelH245Control field), along with Fast Connect, and then use either H.460.6 to re-negotiate offered channels or use H.245 logical channel signaling. There's certainly nothing wrong with not using Fast Connect at all, but it seems to be quite popular and probably something I would not want to disallow. Paul ----- Original Message ----- From: Peter Price To: 'Paul E. Jones' ; itu-sg16(a)external.cisco.com ; tsg16q14(a)itu.int Sent: Tuesday, September 16, 2003 5:00 AM Subject: RE: H.323 Fast Connect and Versioning Paul, I appreciate that Version 3, 4 etc don't exist yet but the issue we are talking about here is a specific problem caused by an editorial error when T.38 was first published that has resulted in an incompatible payload. The problem is that if a V0/V1 endpoint accepts a V2 offer it will not send a payload that is decodable by the V2 endpoint (and the V2 endpoint will send undecodable packets to the other endpoint). T.38 is broken. At this stage we have to assume that such an incompatibility would be avoided in future versions. If a future change to the standard resulted in a new incompatibility with V2 then again it is effectively a new codec and that future version would have to be protected in some way from V2 or older versions. Since (nearly) all the fields are now extensible unless someone decides we need a third error recovery mechanism it's hard to see how T.38 can be broken again. It may well be that the Fast Connect rules should be reviewed but I do not think this is the scenario that should drive the thinking. You say that the video options can't be changed but what happens when your endpoint doesn't understand them (ie can't decode them). What will the calling endpoint do when it receives a response that has probably been changed? I suspect that this changing of extended options will be the real issue in the future as this will (should) be where differences between versions will exist and any modifications to the Fast Connect rules can usefully address this type of predictable issue. I still haven't seen any response from video endpoint implementors who must have encountered this scenario and must have views on how it should be handled. Maybe they are not looking at this list and the question needs to be asked on the implementors list. The T.38 problem does not fall into this category, it is a result of an error in the standard and there is no way of of trying to anticipate future problems caused by errors (and no point or gain). The errors won't be the same (I hope) and will almost certainly require unique solutions. I am not convinced about your suggestion for changing Annex D. This is an interoperability issue between new implementations and old ones. Changing the standard in this way isn't going to stop existing endpoints accepting the channels [ unless you have some very interesting paranormal capabilities in your gateway - in which case why do you need H.323 at all! Or have you have achieved the ultimate goal - a computer that does what you want it to do, not what you tell it to do ;-) ] I still believe that the syntax2002 suggestion by itself is the best solution for this problem. 1. It allows the calling endpoint to identify which version of the ASN.1 it should use for both receive and transmit. 2. It does not require any knowledge of the problem in existing V0/V1 endpoints (a very important factor) 3. It is an isolated change that resolves the current problem and does not have any consequences for any other application area. 4. Trying to engineer a solution that can anticipate the unforeseeable future will continue to make your head hurt ;-) Incidentally, since syntax2002 would be an extended option in T38FaxProfile it would be covered by Fast Connect changes that allowed such options to be dropped. BTW I agree that not using Fast Connect at all is the best solution. H.245 tunneling or even an H.245 address in the Setup message typically allows the media to be established before any useful data can be transmitted - even a purely electronic IVR system is going to delay before transmitting a message to us poor slow humans. In fact, media can be established more quickly because it does not require any call progress messages - not many endpoints accept Fast Connect in Facility messages. Pete -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 12 September 2003 21:53 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, The danger with adding the codepoint for "syntax2002" is that it does not necessarily encompass all of the rules for version 2, 3, etc. Since those future versions do not exist, it presents us with certain problems. Perhaps the right solution is two-fold: 1.. Add a new "syntax2002" field 2.. Allow the called endpoint to modify the version number field in the Fast Connect proposal. It could *not* change it if the calling device is version 0 or not using the new "syntax2002" field, but we could add a rule that says that if the calling device included "syntax2002", it also means that the called device may change the version number in the reply to indicate the actual supported version. If we do (2), then we need to change the language in H.323 to say that parameters shall not be changed, unless explicitly allowed by the particular "controlling media profile document". For T.38, that would be Annex D/H.323. For V.150.1, that would be Annex P/H.323. The video codec issue is an interesting one... several options can be proposed with various capabilities, but they can't be changed. There is an implementation approach that could be used to solve these kinds of issues, but some folks don't like it. That is: don't use Fast Connect at all-- just do termcap exchange and only open media channels and ring the remote phone once caps are exchanged and media is opened. Regardless of whether H.245 is tunneled or on a separate connection, the exchange of all required messages can be done in about 3 TCP packets per side. As for the requirement that H.245 tunneling be used with Fast Connect--- yes, the requirement is there, but folks ignore that like they do other requirements in the standard ;-) The wording might be "must support tunneling", which does not mean it has to be used. Fast Connect certainly has certain advantages over H.245, but if we had never introduced Fast Connect in the first place, I suspect nobody would think something is missing. Most likely, folks would have engineered their products to send TCS right away, would not have alerted the user until media was established, etc. They would have optimized their code to send TCS,MSDet,OLC in the first outgoing message, replied with TCS,TCSAck,MSDet,OLCAck,OLC in the reply TCP packet, and then TCSAck,OLCAck in the sender's second TCP packet. In the rare case where the proposed OLC is not acceptable, it would require an extra exchange of messages, but certainly no worse than Fast Connect today. I'm actually working on a new extension to H.323 to allowing the calling endpoint to explicitly request that the call establishment be delayed until a certain point (e.g., bi-directional media channels are opened). The calling side can control when it lets the call proceed. Likewise, the called side can control it by not acknowledging that the requested "delay point" has been reached. This might be the better way to handle T.38.... except that, as you point out, there are Fast Connect-only T.38 devices. My head hurts... I really hate to break the rules about changing the attributes of a Fast Connect proposal. Here's another thought: What if we add text to Annex D/H.323 that says that if the proposed version is not supported, then it shall not accept the proposal. If it wants to offer a "counter proposal", it has two means: H.245 signaling or H.460.6 (Extended Fast Connect). Paul ----- Original Message ----- From: Peter Price To: 'Paul E. Jones' ; itu-sg16(a)external.cisco.com ; tsg16q14(a)itu.int Sent: Thursday, September 11, 2003 3:53 AM Subject: RE: H.323 Fast Connect and Versioning Paul, as I said before any solution is likely to be a bit dirty because of the nature of the problem. I think your "syntax2002" suggestion is perfectly valid - it is a smaller more localised change and, especially given the reluctance to add new code points, is probably a better alternative than t39faxV2. It only requires a single change to T38FaxProfile rather than changes to both DataApplicationCapability and DataApplicationMode. There is no danger that the change could affect anything other than T.38 aware endpoints. On the subject of H245 tunneling, the problem scenario we're discussing is Fast Connect and I thought that H.323 V4 says that endpoints using Fast Connect shall use H.245 tunneling! It doesn't do much for pure T.38 endpoints which don't do any H.245 though. The thread has suggested two approaches 1. resolve the issue within the Fast Connect proposal (or any subsequent requestMode/OLC etc) 2. resolve the issue by modifying some other part of the standard by introducing "special cases" As an implementor, I would prefer to see a solution within the Fast Connect proposal rather than force other changes in the standard - the danger of going that route is you don't know what the downstream consequences are going to be. Containing the solution in T38FaxProfile keeps implementation simpler - you receive a message and you know exactly what you are doing without having to go looking for other information. Logically, the tunneled H245 messages arrive after the Setup message and its easier to process the Setup completely before starting to look at the H.245. Furthermore, if H.323 endpoints are to remain interoperable with pure T.38 endpoints (are there any?) then the solution *must* be contained within the Fast Connect proposal. You suggest that "syntax002" is a bit of a kludge. It probably is but it does have the advantage of being isolated. I think that "special cases" in the standard that may have unforeseen consequences for endpoints that are not interested in T.38 are very much worse. ------------ A slight aside here (but related). Your remark about the way that all endpoints appear to decode and re-encode the Fast Connect proposals implies that the rule for not changing the proposals is effectively impossible to maintain. I only work with audio endpoints that use the basic audio codecs and T.38 so until this discussion started hadn't really thought about this issue. It's easy to say you musn't change, say, the frame count of G729 but for codecs that are defined as extensible like T.38 (and all the video codecs) there will always be a problem when new endpoints offer new features to old endpoints. Perhaps the Fast Connect rule needs some review to address the specific issue of extensible capabilities. Have video endpoints already encountered this problem? Do any video endpoint implementors have any relevent comments here? Peter -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 10 September 2003 23:35 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, I've only seen this problem with fax. To answer your last question, I've only seen T.38 use this kind of version tag. However, V.150.1 also has versioning information as part of the object identifier that identifies the capability. This will be interesting to see if we introduce the same kind of problem there. In general, it's just not good to advertise the version through an OLC... it's better to perform a full caps exchange. The trouble is that modem and (to some extent) fax timings are such that we must open channels ASAP... before a caps exchange. (Actually, we could transmit the termcap set in the Setup message, but few devices support that.) We have had non-compatible payload specifications before and we resolved that by adding new code points. However, we've been trying to avoid that. Even so, we could do it again... it's just less desirable. I had another idea. What we could do is, within the t38faxProtocol SEQUENCE, we could indicate which syntax is to be used. Older devices would not see this field and would not decode it. So, when the reply is re-encoded, it would not be present. So, even if the version was set to "2", the "Syntax2002" field, say, would not be present. This would mean that the 1998 syntax has to be used. A newer endpoint would see the field and would properly re-encode it in the reply. This is a bit of a kludge and works only because of the way the ASN.1 encoding/decoding works with every device I've seen. Another solution to the problem might be to require that endpoint use H.245 tunneling and to advertise their capabilities in the Setup message. That could allow us to avoid this problem entirely. I'm just not sure how excited people would be to be forced to use H.245 tunneling every time they use fax, modem, or text relay. Paul ----- Original Message ----- From: Peter Price To: 'Paul E. Jones' ; itu-sg16(a)external.cisco.com ; tsg16q14(a)itu.int Sent: Wednesday, September 10, 2003 12:34 PM Subject: RE: H.323 Fast Connect and Versioning Paul, I wrote the first part of this email and then reread yours - I was bogged down in the fax issue but I think you are actually raising a wider issue aren't you? See part 2 below. -------------------------- Part 1 I don't believe that 5 versions of T38 would result in 5 offered channels. The need for the different capability is due to the fact that what you are offering is a payload that is encoded in a different and incompatible way. ie its a bit like offering G.729 and the sending packets encoded according to G.723.1, they both represent speech but they are not going to be played out properly. The single extra bit introduced into the T.38 payload packet by the 2002 ASN.1 is backwards incompatible. The problem only exists for endpoints that only know about the 1998 ASN.1 and are unaware of the incompatibility - it is important that they do not think they can accept the offered channel. Once an endpoint is aware of the problem (ie it knows about the 2002 ASN.1) then it can handle versions >= V2 (as well as V0 and V1). Of course, this does assume that a similar incompatibilty does not creep into the payload ASN.1 in future versions - but that's down to careful work in the standard development and editing stage. I still think adding t38faxV2 (say) to DataApplicationCapability and DataApplicationMode is the simplest solution [ t38faxV2 would use the same definitions for t38FaxProtocol and t38FaxProfile - its only the payload that has changed ]. This protects the existing T.38 implementations and avoids the need to break the rule about modifying Fast Connect proposals. The change in the T.38 payload ASN.1 breaks the fundamental backwards compatibility that ASN.1 is supposed to guarantee and thus whatever the final solution there has to be an element of a hack involved - I think that this change would isolate the change and protect the rest of the standard. -------------------------- Part 2 The versioning issue applies to any form of payload, voice/video/fax/whatever. The problem is still going to exist in early versions of endpoints that don't understand the consequence of accepting versions that they do not understand fully. If a new version of a codec's payload is not backwards compatible then I would assert that it is a new codec and must be signalled as a different capability. The issue of multiple variations already exists anyway although not (to my knowledge) with version numbers. Endpoints already offer multiple packet sizes for exactly the reason that you are not supposed to alter the Fast Connect proposal. What happens when somebody starts to offer g729Extensions and has to offer all the combinations of Annexes because they don't know what the other end can use ( I make that 64 proposals in each direction without adding further annexes! )? I don't see that relaxing the rule about modifying the version in a Fast Connect channel will help resolve the problem of having to offer multiple proposals. You either have to allow *anything* to be modified or stick to the current rule. Exceptions allowing certain fields to be modified just makes life much more difficult and confusing. T.38 is the only codec I am aware of that actually uses a version number in this manner. Are there any others? Why was it introduced in T.38? Perhaps this is a lesson for the future about the value of introducing of such a field in other codecs. Peter -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 10 September 2003 16:01 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, I think you're on the right track. We could avoid ASN.1 changes by introducing the new capability as a generic data capability, but a new capability is required here, I think. The problem, as I see it, is that when we use Fast Connect, we can't alert the calling side as to what version the called side actually supports. This suggests that if we have 5 versions of T.38, the calling side would have to propose a channel for each version independently. That's horrible. It's only complicated further by the fact that T.38 may not be signaled by itself-- it might be part of audio proposals that also include modem, text over IP, VBD, or other media. It might even be that there are several versions of the modem (V.150.1) protocol advertised. I think the only real solution to this problem is to allow the Fast Connect proposals to be altered by the called endpoint such that they can change the version number.. and nothing else. H.323 has an explicit statement that says that the proposals can't be modified before returning them, but perhaps this simple exception might resolve these issues. I think without such, it's going to be terrible complicated. Paul ----- Original Message ----- From: Peter Price To: 'paulej(a)PACKETIZER.COM' ; itu-sg16(a)external.cisco.com Sent: Wednesday, September 10, 2003 3:23 AM Subject: RE: H.323 Fast Connect and Versioning Paul wrote "Perhaps we can require the calling device to not transmit any data until it receives at least one IFP packet from the called side and determines the ASN.1 version used to encode the message." Unfortunately this won't work - although typically the called endpoint will provide the first IFP (Probably a CED) this doesn't work when you poll for a fax - in that case the calling endpoint will probably want to send the first IFP. The only way I can see out of this is to add a new data application (say, t38faxV2) to DataApplicationCapability etc in the H.245 ASN.1. t38fax would use the 1998 ASN.1 and t38faxV2 would use the 2002 ASN.1 - and future carefully checked modifications ;-). Now there's no problem, a 2002 aware endpoint can offer both versions and a 1998 aware endpoint can only accept the ASN.1 it understands. Pete Price Vegastream Limited -----Original Message----- From: paulej(a)PACKETIZER.COM [mailto:paulej@PACKETIZER.COM] Sent: 09 September 2003 20:32 To: itu-sg16(a)external.cisco.com Subject: H.323 Fast Connect and Versioning Folks, Today, I was exchanging e-mail with somebody over the fax version number issue and the different syntax that is used (1998 vs 2002). If we open H.245 and exchange a full set of capabilities, and H.323 endpoint could determine the version supported by the other side and open a channel supporting that particular version. However, I don't think any text is explicitly clear on that. Another scenario-- and one I have more trouble with-- is Fast Connect. If a calling endpoint populates the fastStart element with "version 2" proposals, for example, the called side (say, a version 0 device) might accept the proposal and return the response. However, it is not allowed to modify the version field. The reason is that Fast Connect proposals are not ordered in a way such that replies must be ordered the same way. Rather, the calling device determines which proposals are accepted based on characteristics of the proposals returned (e.g., codec type, samples per packet, or other information). In some cases, a calling endpoint will actually not try to "match" the proposal returned, but just accept it as a proposal and run with it. The problem is that if a calling device proposes version 2 and the called device returns version 2 (but is actually a v0 device), then the wrong syntax will be transmitted on the wire. Thus, the text needs to state somewhere one of these options (or something similar): 1.. The calling device must offer a proposal for each version it wants to potentially use and the called device must accept the first proposal it can accept (in order of the proposals) and the called device must not accept any proposal for a version it does not support 2.. The calling device must wait for capability exchange to complete to determine the actual supported version of the other device Alternatively, we could make an allowance for the endpoint to change the version number in the Fast Connect proposal, but I don't think that's a good idea, as it would quite possibly break interoperability with some devices. What would a version 0 device do today if it received a Fast Connect proposal advertising version 2? Would it accept it? I suspect so and I'm afraid that we might have some interop problems regardless of the direction we go. Perhaps we can require the calling device to not transmit any data until it receives at least one IFP packet from the called side and determines the ASN.1 version used to encode the message. As much as we can push onto the shoulders of a v2 device, the better, as I don't think we have any real deployments in the field (yet)... might be wrong, but I think it would be a far less significant impact on that side. I'm open to suggestions. Perhaps this issue is even addressed and I've simply overlooked it. Thanks, Paul

1 0

Re: H.323 Fast Connect and Versioning
by Lyons, Terry 13 Oct '03

13 Oct '03

As part of this discussion, Paul Jones wrote: I'm actually working on a new extension to H.323 to allowing the calling endpoint to explicitly request that the call establishment be delayed until a certain point (e.g., bi-directional media channels are opened). The calling side can control when it lets the call proceed. Likewise, the called side can control it by not acknowledging that the requested "delay point" has been reached. This might be the better way to handle T.38.... except that, as you point out, there are Fast Connect-only T.38 devices. My head hurts... I really hate to break the rules about changing the attributes of a Fast Connect proposal. 1. Sorry about your head. We appreciate your responsible stewardship of H.323. 2. There has been text since H.323 V4 that says how to CHANGE the OLCs that are sent back in a Fast Connect response and NOT just by dropping extensions that are not understood. Appendix II is admittedly non-normative and could be written more clearly, but the level of detail suggests that some vendors might implement it: II.8.2 Synchronizing RSVP with fast connect ... A calling endpoint that wishes to use RSVP in a Fast Connect procedure shall send a sequence of prioritized QoSCapability structures in the OpenLogicalChannel structures contained in the fastStart element of the Setup message.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Upon receiving the Fast Connect Setup message, the called endpoint shall derive the QOSMode set using the mechanism described in Table II.1. Assuming that the derived set contains a valid (i.e. non-best effort intersection), the called endpoint shall respond to the Setup message from the calling endpoint by sending a fastStart element including only the QoSCapabilities indicated in the derived QoS set. The fastStart element shall be sent as soon as possible (e.g. in a Call Proceeding message) to expedite the resource reservation. The calling endpoint's set will be a subset of the list sent by the calling endpoint in the OpenLogicalChannel structures and will, similarly, be a sequence in decreasing order of priority by QOSMode. Each QoSCapability included in the OpenLogicalChannel in the response message indicates an acceptance of the corresponding QOS level by the called endpoint ... 3. "Synchronized RSVP" involves the idea of suspending call establishment until a requested "delay point" has been reached. Paul's new extension should address the degree to which its procedures are consistent with II.8/H.323. - tlyons(a)sonusnet.com +1 732 625-3003 x212 -----Original Message----- From: paulej(a)PACKETIZER.COM [mailto:paulej@PACKETIZER.COM] Sent: Tuesday, September 16, 2003 10:43 AM To: itu-sg16(a)external.cisco.com Subject: Re: H.323 Fast Connect and Versioning Peter, To address there V0/V2 interop problem, I agree that something like the syntax2002 would be useful. In fact, to answer your question about other H.245 fields that are unknown to the other side... that's precisely how things get quite naturally "dropped out" in the replies back. It's an indicator to the originator. Looking past v2 to the subsequent revisions, what else might change? Perhaps the syntax will remain unchanged or at least compatible, but perhaps something else in the procedures might changes. This is what I'm wondering if we should insert rules into H.323 (and Annex D would be the candidate for fax) that says that you shall not accept a proposal in Fast Connect for a version you do not support? The proper solution to this general problem, in my opinion, is to advertise termcaps in the Setup (perhaps the parallelH245Control field), along with Fast Connect, and then use either H.460.6 to re-negotiate offered channels or use H.245 logical channel signaling. There's certainly nothing wrong with not using Fast Connect at all, but it seems to be quite popular and probably something I would not want to disallow. Paul ----- Original Message ----- From: Peter <mailto:PeterP@vegastream.com> Price To: 'Paul E. Jones' <mailto:paulej@packetizer.com> ; itu-sg16(a)external.cisco.com <mailto:itu-sg16@external.cisco.com> ; tsg16q14(a)itu.int <mailto:tsg16q14@itu.int> Sent: Tuesday, September 16, 2003 5:00 AM Subject: RE: H.323 Fast Connect and Versioning Paul, I appreciate that Version 3, 4 etc don't exist yet but the issue we are talking about here is a specific problem caused by an editorial error when T.38 was first published that has resulted in an incompatible payload. The problem is that if a V0/V1 endpoint accepts a V2 offer it will not send a payload that is decodable by the V2 endpoint (and the V2 endpoint will send undecodable packets to the other endpoint). T.38 is broken. At this stage we have to assume that such an incompatibility would be avoided in future versions. If a future change to the standard resulted in a new incompatibility with V2 then again it is effectively a new codec and that future version would have to be protected in some way from V2 or older versions. Since (nearly) all the fields are now extensible unless someone decides we need a third error recovery mechanism it's hard to see how T.38 can be broken again. It may well be that the Fast Connect rules should be reviewed but I do not think this is the scenario that should drive the thinking. You say that the video options can't be changed but what happens when your endpoint doesn't understand them (ie can't decode them). What will the calling endpoint do when it receives a response that has probably been changed? I suspect that this changing of extended options will be the real issue in the future as this will (should) be where differences between versions will exist and any modifications to the Fast Connect rules can usefully address this type of predictable issue. I still haven't seen any response from video endpoint implementors who must have encountered this scenario and must have views on how it should be handled. Maybe they are not looking at this list and the question needs to be asked on the implementors list. The T.38 problem does not fall into this category, it is a result of an error in the standard and there is no way of of trying to anticipate future problems caused by errors (and no point or gain). The errors won't be the same (I hope) and will almost certainly require unique solutions. I am not convinced about your suggestion for changing Annex D. This is an interoperability issue between new implementations and old ones. Changing the standard in this way isn't going to stop existing endpoints accepting the channels [ unless you have some very interesting paranormal capabilities in your gateway - in which case why do you need H.323 at all! Or have you have achieved the ultimate goal - a computer that does what you want it to do, not what you tell it to do ;-) ] I still believe that the syntax2002 suggestion by itself is the best solution for this problem. 1. It allows the calling endpoint to identify which version of the ASN.1 it should use for both receive and transmit. 2. It does not require any knowledge of the problem in existing V0/V1 endpoints (a very important factor) 3. It is an isolated change that resolves the current problem and does not have any consequences for any other application area. 4. Trying to engineer a solution that can anticipate the unforeseeable future will continue to make your head hurt ;-) Incidentally, since syntax2002 would be an extended option in T38FaxProfile it would be covered by Fast Connect changes that allowed such options to be dropped. BTW I agree that not using Fast Connect at all is the best solution. H.245 tunneling or even an H.245 address in the Setup message typically allows the media to be established before any useful data can be transmitted - even a purely electronic IVR system is going to delay before transmitting a message to us poor slow humans. In fact, media can be established more quickly because it does not require any call progress messages - not many endpoints accept Fast Connect in Facility messages. Pete -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 12 September 2003 21:53 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, The danger with adding the codepoint for "syntax2002" is that it does not necessarily encompass all of the rules for version 2, 3, etc. Since those future versions do not exist, it presents us with certain problems. Perhaps the right solution is two-fold: 1. Add a new "syntax2002" field 2. Allow the called endpoint to modify the version number field in the Fast Connect proposal. It could *not* change it if the calling device is version 0 or not using the new "syntax2002" field, but we could add a rule that says that if the calling device included "syntax2002", it also means that the called device may change the version number in the reply to indicate the actual supported version. If we do (2), then we need to change the language in H.323 to say that parameters shall not be changed, unless explicitly allowed by the particular "controlling media profile document". For T.38, that would be Annex D/H.323. For V.150.1, that would be Annex P/H.323. The video codec issue is an interesting one... several options can be proposed with various capabilities, but they can't be changed. There is an implementation approach that could be used to solve these kinds of issues, but some folks don't like it. That is: don't use Fast Connect at all-- just do termcap exchange and only open media channels and ring the remote phone once caps are exchanged and media is opened. Regardless of whether H.245 is tunneled or on a separate connection, the exchange of all required messages can be done in about 3 TCP packets per side. As for the requirement that H.245 tunneling be used with Fast Connect--- yes, the requirement is there, but folks ignore that like they do other requirements in the standard ;-) The wording might be "must support tunneling", which does not mean it has to be used. Fast Connect certainly has certain advantages over H.245, but if we had never introduced Fast Connect in the first place, I suspect nobody would think something is missing. Most likely, folks would have engineered their products to send TCS right away, would not have alerted the user until media was established, etc. They would have optimized their code to send TCS,MSDet,OLC in the first outgoing message, replied with TCS,TCSAck,MSDet,OLCAck,OLC in the reply TCP packet, and then TCSAck,OLCAck in the sender's second TCP packet. In the rare case where the proposed OLC is not acceptable, it would require an extra exchange of messages, but certainly no worse than Fast Connect today. I'm actually working on a new extension to H.323 to allowing the calling endpoint to explicitly request that the call establishment be delayed until a certain point (e.g., bi-directional media channels are opened). The calling side can control when it lets the call proceed. Likewise, the called side can control it by not acknowledging that the requested "delay point" has been reached. This might be the better way to handle T.38.... except that, as you point out, there are Fast Connect-only T.38 devices. My head hurts... I really hate to break the rules about changing the attributes of a Fast Connect proposal. Here's another thought: What if we add text to Annex D/H.323 that says that if the proposed version is not supported, then it shall not accept the proposal. If it wants to offer a "counter proposal", it has two means: H.245 signaling or H.460.6 (Extended Fast Connect). Paul ----- Original Message ----- From: Peter <mailto:PeterP@vegastream.com> Price To: 'Paul E. Jones' <mailto:paulej@packetizer.com> ; itu-sg16(a)external.cisco.com <mailto:itu-sg16@external.cisco.com> ; tsg16q14(a)itu.int <mailto:tsg16q14@itu.int> Sent: Thursday, September 11, 2003 3:53 AM Subject: RE: H.323 Fast Connect and Versioning Paul, as I said before any solution is likely to be a bit dirty because of the nature of the problem. I think your "syntax2002" suggestion is perfectly valid - it is a smaller more localised change and, especially given the reluctance to add new code points, is probably a better alternative than t39faxV2. It only requires a single change to T38FaxProfile rather than changes to both DataApplicationCapability and DataApplicationMode. There is no danger that the change could affect anything other than T.38 aware endpoints. On the subject of H245 tunneling, the problem scenario we're discussing is Fast Connect and I thought that H.323 V4 says that endpoints using Fast Connect shall use H.245 tunneling! It doesn't do much for pure T.38 endpoints which don't do any H.245 though. The thread has suggested two approaches 1. resolve the issue within the Fast Connect proposal (or any subsequent requestMode/OLC etc) 2. resolve the issue by modifying some other part of the standard by introducing "special cases" As an implementor, I would prefer to see a solution within the Fast Connect proposal rather than force other changes in the standard - the danger of going that route is you don't know what the downstream consequences are going to be. Containing the solution in T38FaxProfile keeps implementation simpler - you receive a message and you know exactly what you are doing without having to go looking for other information. Logically, the tunneled H245 messages arrive after the Setup message and its easier to process the Setup completely before starting to look at the H.245. Furthermore, if H.323 endpoints are to remain interoperable with pure T.38 endpoints (are there any?) then the solution *must* be contained within the Fast Connect proposal. You suggest that "syntax002" is a bit of a kludge. It probably is but it does have the advantage of being isolated. I think that "special cases" in the standard that may have unforeseen consequences for endpoints that are not interested in T.38 are very much worse. ------------ A slight aside here (but related). Your remark about the way that all endpoints appear to decode and re-encode the Fast Connect proposals implies that the rule for not changing the proposals is effectively impossible to maintain. I only work with audio endpoints that use the basic audio codecs and T.38 so until this discussion started hadn't really thought about this issue. It's easy to say you musn't change, say, the frame count of G729 but for codecs that are defined as extensible like T.38 (and all the video codecs) there will always be a problem when new endpoints offer new features to old endpoints. Perhaps the Fast Connect rule needs some review to address the specific issue of extensible capabilities. Have video endpoints already encountered this problem? Do any video endpoint implementors have any relevent comments here? Peter -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 10 September 2003 23:35 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, I've only seen this problem with fax. To answer your last question, I've only seen T.38 use this kind of version tag. However, V.150.1 also has versioning information as part of the object identifier that identifies the capability. This will be interesting to see if we introduce the same kind of problem there. In general, it's just not good to advertise the version through an OLC... it's better to perform a full caps exchange. The trouble is that modem and (to some extent) fax timings are such that we must open channels ASAP... before a caps exchange. (Actually, we could transmit the termcap set in the Setup message, but few devices support that.) We have had non-compatible payload specifications before and we resolved that by adding new code points. However, we've been trying to avoid that. Even so, we could do it again... it's just less desirable. I had another idea. What we could do is, within the t38faxProtocol SEQUENCE, we could indicate which syntax is to be used. Older devices would not see this field and would not decode it. So, when the reply is re-encoded, it would not be present. So, even if the version was set to "2", the "Syntax2002" field, say, would not be present. This would mean that the 1998 syntax has to be used. A newer endpoint would see the field and would properly re-encode it in the reply. This is a bit of a kludge and works only because of the way the ASN.1 encoding/decoding works with every device I've seen. Another solution to the problem might be to require that endpoint use H.245 tunneling and to advertise their capabilities in the Setup message. That could allow us to avoid this problem entirely. I'm just not sure how excited people would be to be forced to use H.245 tunneling every time they use fax, modem, or text relay. Paul ----- Original Message ----- From: Peter Price <mailto:PeterP@vegastream.com> To: 'Paul <mailto:paulej@packetizer.com> E. Jones' ; itu-sg16(a)external.cisco.com <mailto:itu-sg16@external.cisco.com> ; tsg16q14(a)itu.int <mailto:tsg16q14@itu.int> Sent: Wednesday, September 10, 2003 12:34 PM Subject: RE: H.323 Fast Connect and Versioning Paul, I wrote the first part of this email and then reread yours - I was bogged down in the fax issue but I think you are actually raising a wider issue aren't you? See part 2 below. -------------------------- Part 1 I don't believe that 5 versions of T38 would result in 5 offered channels. The need for the different capability is due to the fact that what you are offering is a payload that is encoded in a different and incompatible way. ie its a bit like offering G.729 and the sending packets encoded according to G.723.1, they both represent speech but they are not going to be played out properly. The single extra bit introduced into the T.38 payload packet by the 2002 ASN.1 is backwards incompatible. The problem only exists for endpoints that only know about the 1998 ASN.1 and are unaware of the incompatibility - it is important that they do not think they can accept the offered channel. Once an endpoint is aware of the problem (ie it knows about the 2002 ASN.1) then it can handle versions >= V2 (as well as V0 and V1). Of course, this does assume that a similar incompatibilty does not creep into the payload ASN.1 in future versions - but that's down to careful work in the standard development and editing stage. I still think adding t38faxV2 (say) to DataApplicationCapability and DataApplicationMode is the simplest solution [ t38faxV2 would use the same definitions for t38FaxProtocol and t38FaxProfile - its only the payload that has changed ]. This protects the existing T.38 implementations and avoids the need to break the rule about modifying Fast Connect proposals. The change in the T.38 payload ASN.1 breaks the fundamental backwards compatibility that ASN.1 is supposed to guarantee and thus whatever the final solution there has to be an element of a hack involved - I think that this change would isolate the change and protect the rest of the standard. -------------------------- Part 2 The versioning issue applies to any form of payload, voice/video/fax/whatever. The problem is still going to exist in early versions of endpoints that don't understand the consequence of accepting versions that they do not understand fully. If a new version of a codec's payload is not backwards compatible then I would assert that it is a new codec and must be signalled as a different capability. The issue of multiple variations already exists anyway although not (to my knowledge) with version numbers. Endpoints already offer multiple packet sizes for exactly the reason that you are not supposed to alter the Fast Connect proposal. What happens when somebody starts to offer g729Extensions and has to offer all the combinations of Annexes because they don't know what the other end can use ( I make that 64 proposals in each direction without adding further annexes! )? I don't see that relaxing the rule about modifying the version in a Fast Connect channel will help resolve the problem of having to offer multiple proposals. You either have to allow *anything* to be modified or stick to the current rule. Exceptions allowing certain fields to be modified just makes life much more difficult and confusing. T.38 is the only codec I am aware of that actually uses a version number in this manner. Are there any others? Why was it introduced in T.38? Perhaps this is a lesson for the future about the value of introducing of such a field in other codecs. Peter -----Original Message----- From: Paul E. Jones [mailto:paulej@packetizer.com] Sent: 10 September 2003 16:01 To: Peter Price; itu-sg16(a)external.cisco.com; tsg16q14(a)itu.int Subject: Re: H.323 Fast Connect and Versioning Peter, I think you're on the right track. We could avoid ASN.1 changes by introducing the new capability as a generic data capability, but a new capability is required here, I think. The problem, as I see it, is that when we use Fast Connect, we can't alert the calling side as to what version the called side actually supports. This suggests that if we have 5 versions of T.38, the calling side would have to propose a channel for each version independently. That's horrible. It's only complicated further by the fact that T.38 may not be signaled by itself-- it might be part of audio proposals that also include modem, text over IP, VBD, or other media. It might even be that there are several versions of the modem (V.150.1) protocol advertised. I think the only real solution to this problem is to allow the Fast Connect proposals to be altered by the called endpoint such that they can change the version number.. and nothing else. H.323 has an explicit statement that says that the proposals can't be modified before returning them, but perhaps this simple exception might resolve these issues. I think without such, it's going to be terrible complicated. Paul ----- Original Message ----- From: Peter Price <mailto:PeterP@vegastream.com> To: 'paulej(a)PACKETIZER.COM' <mailto:'paulej(a)PACKETIZER.COM'> ; itu-sg16(a)external.cisco.com <mailto:itu-sg16@external.cisco.com> Sent: Wednesday, September 10, 2003 3:23 AM Subject: RE: H.323 Fast Connect and Versioning Paul wrote "Perhaps we can require the calling device to not transmit any data until it receives at least one IFP packet from the called side and determines the ASN.1 version used to encode the message." Unfortunately this won't work - although typically the called endpoint will provide the first IFP (Probably a CED) this doesn't work when you poll for a fax - in that case the calling endpoint will probably want to send the first IFP. The only way I can see out of this is to add a new data application (say, t38faxV2) to DataApplicationCapability etc in the H.245 ASN.1. t38fax would use the 1998 ASN.1 and t38faxV2 would use the 2002 ASN.1 - and future carefully checked modifications ;-). Now there's no problem, a 2002 aware endpoint can offer both versions and a 1998 aware endpoint can only accept the ASN.1 it understands. Pete Price Vegastream Limited -----Original Message----- From: paulej(a)PACKETIZER.COM [mailto:paulej@PACKETIZER.COM] Sent: 09 September 2003 20:32 To: itu-sg16(a)external.cisco.com Subject: H.323 Fast Connect and Versioning Folks, Today, I was exchanging e-mail with somebody over the fax version number issue and the different syntax that is used (1998 vs 2002). If we open H.245 and exchange a full set of capabilities, and H.323 endpoint could determine the version supported by the other side and open a channel supporting that particular version. However, I don't think any text is explicitly clear on that. Another scenario-- and one I have more trouble with-- is Fast Connect. If a calling endpoint populates the fastStart element with "version 2" proposals, for example, the called side (say, a version 0 device) might accept the proposal and return the response. However, it is not allowed to modify the version field. The reason is that Fast Connect proposals are not ordered in a way such that replies must be ordered the same way. Rather, the calling device determines which proposals are accepted based on characteristics of the proposals returned (e.g., codec type, samples per packet, or other information). In some cases, a calling endpoint will actually not try to "match" the proposal returned, but just accept it as a proposal and run with it. The problem is that if a calling device proposes version 2 and the called device returns version 2 (but is actually a v0 device), then the wrong syntax will be transmitted on the wire. Thus, the text needs to state somewhere one of these options (or something similar): 1. The calling device must offer a proposal for each version it wants to potentially use and the called device must accept the first proposal it can accept (in order of the proposals) and the called device must not accept any proposal for a version it does not support 2. The calling device must wait for capability exchange to complete to determine the actual supported version of the other device Alternatively, we could make an allowance for the endpoint to change the version number in the Fast Connect proposal, but I don't think that's a good idea, as it would quite possibly break interoperability with some devices. What would a version 0 device do today if it received a Fast Connect proposal advertising version 2? Would it accept it? I suspect so and I'm afraid that we might have some interop problems regardless of the direction we go. Perhaps we can require the calling device to not transmit any data until it receives at least one IFP packet from the called side and determines the ASN.1 version used to encode the message. As much as we can push onto the shoulders of a v2 device, the better, as I don't think we have any real deployments in the field (yet)... might be wrong, but I think it would be a far less significant impact on that side. I'm open to suggestions. Perhaps this issue is even addressed and I've simply overlooked it. Thanks, Paul

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Re: H.323 Fast Connect and Versioning
by Paul E. Jones 09 Oct '03

09 Oct '03

Tamura-san, Sorry for the long delay. I was out of the office last week and spending time trying to catch up this week... and fighting a horrible cold. The doctor told me I was a baby for going to see him with a fever of 100.6F, but I don't feel good :-( Anyway, to answer your question... I don't think the procedures documented in D.8 - D.11 are a problem. In theory, the endpoint that transmits an OLC would not propose an OLC with a version number included that is not supported by the other side. However, the text does not say that. As such, I think I will bring a contribution as Rapporteur to have some text added that makes it very explicit that an endpoint SHALL NOT propose in an OLC version of T.38 not supported by the other endpoint. Does that sound reasonable? I have also had some discussion with people about the various solutions to Fast Connect. I think one person or another thinks the various ideas (and I have about 5 now) are insufficient. What has most recently been proposed is to simply add text that says a called endpoint shall not accept a Fast Connect proposal that includes a T.38 version it does not support. That kind of text should have been in there, as well, but it is not. I wonder if anybody's equipment would break with such text? Paul ----- Original Message ----- From: "Hiroshi Tamura" <tamura(a)toda.ricoh.co.jp> To: <paulej(a)packetizer.com> Cc: <PeterP(a)vegastream.com>; <itu-sg16(a)external.cisco.com>; <tsg16q14(a)itu.int> Sent: Wednesday, October 01, 2003 10:01 PM Subject: Re: H.323 Fast Connect and Versioning > Paul, > > Thanks for your comment. > > One confirmation. > > > > Why are there issues in Fast Connect only? > > > > With regular H.245 capability exchange and the use of OLCs, both sides will > > know the actual capabilities. Version 2 devices should then only send an > > OLC with a version that it knows the remote side can accept. > > > The problem has to do with sending a Fast Connect proposal (channel > > proposal) for T.38v2 (2002 syntax) to a version 0 device (1998) syntax and > > that device accepting the proposal and, subsequently, sending 2002-encoded > > IFP packets. The version 0 device cannot decode the IFP packets. > > I understand it. > > My question is, > In Figure D.8 - D.11 in H.323 Annex D, does the same issue happen? > > I think so. > > > In short, there is a potential for sending the wrong ASN.1 PER encoded > > messages. > > Yes. > > Regards, > -- > Hiroshi Tamura >

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Re: FW: Outcome of the Paris meeting
by OKUBO Sakae 07 Oct '03

07 Oct '03

Dear Mr. Wilmot, At 18:03 +0100 03/10/06, <chris.d.wilmot(a)bt.com> wrote: >I have tried to look at the meeting report, but for some reason it >will not open correctly. Thank you for your advice. I have confirmed that somehow AVD-2410.zip seems to have contained AVD-2410.doc in Mac format. Windows Word says some converter is required. Now I have zipped all the four files on a Windows machine. http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/AVD-2410.zip should be OK also for Windows. Could you please report back if it is true? -- Best regards, OKUBO Sakae e-mail: sokubo(a)waseda.jp Visiting Professor Graduate School of Science and Engineering Waseda University ******************************************************************* <YRP> Waseda University, YRP Ichibankan 312 Tel: +81 46 847 5406 3-4 Hikarinooka, Yokosuka-shi, Kanagawa-ken Fax: +81 46 847 5413 239-0847 Japan <Nishi-Waseda> 29-7 Waseda University Bldg. Tel: +81 3 5286 9841 1-3-10 Nishi-Waseda, Shinjuku-ku, Tokyo Fax: +81 3 5286 3832 169-0051 Japan *******************************************************************

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Outcome of the Paris meeting
by OKUBO Sakae 03 Oct '03

03 Oct '03

Dear SG16 experts, The following documents have been placed at the 0309_Par/ directory: http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/AVD-2410.zip http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/WP2_Question_formulat… http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/WP2_comments_on_NGN20… http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/SG16_comments_to_JRG-… The first document AVD-2410 is the integrated report of the Paris meeting of Questions D,F,G,2-5 including 3 dispatched liaison statements. The second document is a compilation of revised and new draft Questions for reporting to Chairman of SG16. The third document is also a compilation of comments on SG13's NGN2004 project description for reporting to Chairman of SG16 The fourth document is an input document from SG16 management to the JRG-NGN meeting held this week in Munich. This is reflecting the action from the Paris meeting as recorded in the third document. -- Best regards, OKUBO Sakae e-mail: sokubo(a)waseda.jp Visiting Professor Graduate School of Science and Engineering Waseda University ******************************************************************* <Yokosuka Research Park> Waseda University, YRP Ichibankan 312 Tel: +81 46 847 5406 3-4 Hikarinooka, Yokosuka-shi, Kanagawa-ken Fax: +81 46 847 5413 239-0847 Japan <Nishi-Waseda> 29-7 Waseda University Bldg. Tel: +81 3 5286 9841 1-3-10 Nishi-Waseda, Shinjuku-ku, Tokyo Fax: +81 3 5286 3832 169-0051 Japan *******************************************************************

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