P1394 Mail Archive: Re: P1394> 1394PWG Thick Transport Stack Requirements

P1394 Mail Archive: Re: P1394> 1394PWG Thick Transport Stack Requirements

Re: P1394> 1394PWG Thick Transport Stack Requirements

Brian Batchelder (brianb@vcd.hp.com)
Fri, 24 Oct 1997 12:48:52 -0700

At 09:54 PM 10/24/97 +0900, Toru Ueda wrote:
>
>Brian,
>
>Thank you for forwarding your client requirements for thick
>transport stack document.
>
>I have one question about thick "MUST".
>
>I don't understand how to use buffer service.
>Why must thick transport have buffer service ?

The buffer service is used by clients who need to have data delivered with
well-defined starting and ending points. For example, this data might be a
message that needs to be delivered whole. If a byte stream service is
used, the message might be broken into multiple buffers, or if might have
other data appended to it. This might make the message impossible to
interpret by the receiving service.

>My understanding is the transport will handle the
>differences of physical buffer sizes of sending and
>receiving endpoints.

Yes, the transport must handle varying buffer sizes in each direction. For
the byte stream service it must be able to break up a large request buffer
into multiple send buffers. For the buffer service it must either be able
to somehow ommunicate to the client the largest buffer that can be sent or
provide buffer segmentation and reassembly services. Maybe this should be
added to the requirements?

>I assume that the indication of receiving the 30bytes packet
>to upper layer will issue when 30bytes data receives whether
>this packet is divided into 2-15 bytes or 3-10 bytes data if
>the transport packet size is 30 bytes.

I think the requirement is that the 30 bytes be delivered as a buffer if
the transmitted buffer is 30 bytes and there is some indication that it
should be delivered as a single, whole buffer. I don't think it is a
requirement that the smaller packets be reassembled into one larger buffer
(in other words, that a reassembly service be provided).

>But buffer service allows to send only fixed(30bytes in this
>case) data.

The buffer service would allow UP TO 30 bytes of data to be delivered as a
single, whole buffer. A buffer of less than 30 bytes could also be
transmitted.

>Does this help to write application ?

It does help some applications that want to send messages without those
messages inherently providing some way to be extracted from a byte stream.

>I misunderstand buffer service ?

I think that the requirements document is not complete. For now, we
probably have many interpretations of the requirements. Our challenge is
to refine the requirements list until we all agree on them.

Brian
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