ASN.1 vs Text

Tom-PT Taylor taylor at NORTELNETWORKS.COM
Wed Mar 31 22:16:57 EST 1999


Since the other responses seem to have gone off into a discussion of
firewalls, let me respond to this more directly by recalling a bit of past
discussion.

1) On the Megaco list, we finally agreed that the text vs. binary question
is something to be resolved by experiment.

2) In Turin (I think), the general opinion was that the protocol would have
to be binary to achieve the required performance.  Interestingly enough,
however, no one that I recall felt that it should be PER ASN.1 (or even, I
think, BER ASN.1).  Good reasons were given at the time.  It would be good
if someone can remember them, but I think it has something to do with
processing performance and less risk of fragmentation than call signalling.

3) We have had an occasionally recurring suggestion on the Megaco list that
the Media Gateway control protocol should conform to the format of other
messaging out of the MGC, for the reason you give (i.e. to minimize
transcoding).  Interestingly, the person advocating this was talking about
billing data, not signalling.  The counter-argument on the list is that the
Media Gateway control protocol must work with different signalling protocols
(for example in H.GCP's case, with any of the H-series systems), so there is
no point in optimizing it for just one.

The real sticking point of debate is going to be whether the media
description structures will be those defined for H.245 OLC etc., or SDP.
Text vs. binary is a closely related but broader debate.

I'd suggest we start thinking about experimental design.

> -----Original Message-----
> From: Ami Amir [SMTP:amir at RADVISION.RAD.CO.IL]
> Sent: Wednesday, March 31, 1999 4:15 AM
> To:   ITU-SG16 at MAILBAG.INTEL.COM
> Subject:      H.320 gateways a MEGACO / ITU
>
> Hi
>
> During the last MEGACO conference call - Tom Taylor asked what could
> hinder
> ITU acceptance of the MEGACO work. It is obviously to everybody's interest
> that IETF and ITU standards merge. As an example - it would be great if
> the
> MEGACO work could become an ITU SG 16 contribution.
>
> An obvious item is efficient multimedia support (as reflected also in
> John's
> mail).
>
> However, I think that one of the even more major difficulties facing us
> will
> be the encoding scheme (ASN.1 vs Text).
>
> There are many who feel that ASN.1 is too heavy and complex for simple
> devices, and should be avoided. This was one of the major reasons for the
> emergence of SIP.
>
> On the other hand, experience in the ITU H.323 work has shown that since
> ASN.1 is the encoding scheme on the PSTN side, the use of ASN cleared the
> way for PSTN to IP interoperability. This feature will be extremely
> important in hybrid networks that need to provide Intelligent Network (IN)
> services (e.g. "800"), while retaining the investment in existing IN,
> billing and directory services (411).
>
> Another problem is that if ASN.1 is not chosen, every device that will
> have
> to connect between a MEGACO component and H.323 will need to dis-assemble
> and re-assemble (transcode) messages, and hence network performance will
> suffer, and those devices will be more complex. A prime example - MGC to
> GK
> communications.
>
> I am not promoting a specific approach. I just think that this complex
> issue
> needs to be addressed if we want to be able to be able accept a universal
> protocol.
>
> Do you think this is really a problem?
> If so - any ideas on how to bridge the gap?
>
> Ami
>
>         -----Original Message-----
>         From:   John Segers [SMTP:jsegers at lucent.com]
>         Sent:   Tuesday, March 30, 1999 6:27 PM
>         To:     ITU-SG16 at mailbag.cps.intel.com
>         Subject:        H.320 gateways
>
>         People,
>
>         In yesterday's conference call, the subject of H.320 GWs was
> raised
>         briefly. In my opinion, the connection model and protocol should
> be
> able
>         to deal with H.320.  I would like to continue discussion on it on
> the
>         mailing list.
>
>         H.320 allows a user to have a session with both audio and video on
> a
>         single 64 kbit/s channel such as an ISDN B-channel.  The same
> channel
>         carries some signalling information (frame alignment, bitrate
>         allocation).  To a MG supporting H.320, this means that on a
> single
>         endpoint, three streams can come in, carrying different types of
> media.
>         The current connection model of megaco/H.gcp does not cater to
> this.
> I
>         see two possible solutions:
>
>         The first is to allow multiple media in one context and to
> describe
> for
>         terminations the logical streams they carry.  In a picture:
>
>                               +----------+
>                               |          |
>                               |          +--------- signalling (FAS, BAS)
>                               |          |
>         B-channel   ==========+          +--------- audio (16 kbit/s)
>                               |          |
>                               |          +--------- video (46.4 kbit/s)
>                               |          |
>                               +----------+
>
>         The second solution is to have separate terminations for the
> different
>         streams.  They would all "connect to" the same physical endpoint.
> In
>         order to properly identify the terminations, it is necessary to
> have
>         logical names for them.  The physical endpoint they connect may
> have
> the
>         hierarchical name proposed in the megaco document.
>
>         Another example of a H.320 session is the case of two B-channels
> being
>         used for an audiovisual call.  The following frame structure is
> then
>         possible.
>
>            +--------------------------++-----------------------+
>            | Channel 1                || Channel 2             |
>            +-----+--+--+--+--+--+--+--++--+--+--+--+--+--+--+--+
>            |Bit 1|B2|B3|B4|B5|B6|B7|B8||B1|B2|B3|B4|B5|B6|B7|B8|
>            +-----+--+--+--+--+--+--+--++--+--+--+--+--+--+--+--+
>         1  | a1  |a2|a3|a4|a5|a6|v1|F ||v2|v3|v4|v5|v6|v7|v8|F |
>         2  | a7  |a8|a9|a |a |a |v9|F ||v |v |v |v |v |v |v |F |
>         3  | a   |a |a |a |a |a |v |F ||v |v |v |v |v |v |v |F |
>         4  | a   |  |  |  |  |a |v |F ||v |              |v |F |
>         5  | a   |  |  |  |  |a |v |F ||v |              |v |F |
>         6  | a   |  |  |  |  |a |v |F ||v |              |v |F |
>         7  | a   |  |  |  |  |a |v |F ||v |              |v |F |
>         8  | a   |  |  |  |  |a |v |F ||v |              |v |F |
>            +---------------------------------------------------+
>         9  | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         10 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         11 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         12 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         13 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         14 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         15 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>         16 | a   |  |  |  |  |a |v |B ||v |              |v |B |
>            +---------------------------------------------------+
>         17 | a   |  |  |  |  |a |v |v ||v |              |v |v |
>          .
>          .
>          .
>         80 | a   |  |  |  |  |a |v |v ||v |              |v |v |
>            +---------------------------------------------------+
>
>         (a=audio, v=video, F=FAS, B=BAS).
>
>         We see that the video stream is split up over two channels.  In
> order to
>         cater to this, it seems we have to allow terminations to receive
> media
>         from and send it to multiple physical endpoints.  The two
> approaches
>         outlined above can both be extended to allow this. Both extensions
> will
>         lead to the introduction of logical names for terminations.  In
> the
>         first approach there will be one termination "containing" two
> B-channels
>         on one side and three logical streams on the other.  In the second
>         approach there will be three terminations, the one for the video
> stream
>         referencing both B-channels, the ones for signalling and audio
>         referencing only channel 1.
>
>         The second approach allows us to keep separate contexts for
> different
>         media types.  It is then easy to delete, for instance, the video
> part of
>         a session (session used loosely to desribe the contexts for the
> audio
>         and video).
>
>         The first approach groups the streams coming from/going to one
> user,
>         making it possible to remove a user from a context more easily.
>
>
>         Personally, I can't decide which approach I would prefer.  How do
> others
>         feel about these ideas?
>
>         Regards,
>
>         John Segers
>         --
>         John Segers                                  email:
> jsegers at lucent.com
>         Lucent Technologies                                        Room HE
> 344
>         Dept. Forward Looking Work                      phone: +31 35 687
> 4724
>         P.O. Box 18, 1270 AA  Huizen                      fax: +31 35 687
> 5954



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