Guntram,

I raised this issue over a year ago. In addition, H.225.0 does not address this issue regarding RAS (it does regarding call signaling), so I suppose one could pack multiple RAS messages per unreliable-transport PDU. As you say, it doesn't make sense to pack messages, and I don't think anyone does it. We should probably add something like the following to section 6.1 of the next revision of H.225.0.

"When messages are sent on the H.225.0 RAS channel, only one whole message shall be sent within the boundaries defined by the transport; there shall be no fragmentation of H.225.0 RAS messages across transport PDUs."

We should also insert the indicated text, below, into existing text in the same section.

"When messages are sent on the reliable H.245 control channel, >>>exactly one message should be sent but<<< more than one message may be sent within the boundaries defined by the reliable transport PDU as long as whole messages are sent;"

Paul Long Smith Micro Software, Inc.

-----Original Message----- From: Guntram Diehl [SMTP:gdiehl@innovaphone.com] Sent: Wednesday, June 30, 1999 4:14 AM To: 'Bancroft Scott'; 'Srikanth Nayani' Cc: 'h323implementors@imtc.org' Subject: RE: PDU & ASN parser

Yes this can be done, but does any implementation actually do it? Why would anyone want to do this, it just saves 4 bytes tpkt header per additional H.245 message and it does not change the fragmentation of the whole thing by IP.

Or is there another reason why this was specified in the standard this way?

Guntram

-----Original Message----- From: Bancroft Scott [mailto:baos@OSS.COM] Sent: Wednesday, June 30, 1999 3:54 AM To: Srikanth Nayani Cc: h323implementors@imtc.org Subject: Re: PDU & ASN parser

On Tue, 29 Jun 1999, Srikanth Nayani wrote:

> In the H.225 document chapter 6 mentions that multiple messages can be > sent over the reliable H.245 control channel within the boundaries of the > reliable transport channel . Does that mean that two H.245 PDUs encoded > using PER and whose total encoded length is within the boundary of the > H.245 TCP channel can be merely concatenated and sent as a single payload > of the H.245 TCP channel. > If so how does a ASN.1 decoder know that there are two messages in the > payload and the offset at which the second message starts.

An PER decoder does not know that there are two messages in the payload. It does know where the first message ends, so the location of the next message can be derived from this knowledge.

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