Re: Proper understanding of

Barry,

In the situation you described, the receiver could not use the marker=20
information in the 3rd segment until the 2nd segment had also arrived.
This means the receiver must be prepared to do some amount of=20
(per-session) buffering. Fortunately the amount of this buffering is=20
small since the marker period is only 512B.

Mike Seufert
www.neterion.com

bbr wrote:
>
> Folks,
>
> I=92m looking at the changes in MPA from draft 02 (against which the=20
> conformance suite was written) to draft 08. I would like to understand=20
> how to take the following text from page 25 (clause 6).
>
> =93To detect the start of the FPDU unambiguously one of the following
>
> MUST be used:
>
> 1: In an ordered TCP stream, the ULPDU Length field in the current
>
> FPDU when FPDU has a valid CRC, can be used to identify the
>
> beginning of the next FPDU.
>
> 2: For optimized MPA/TCP receivers that support out of order
>
> reception of FPDUs (see section 4.3 MPA Markers on page 15) a
>
> Marker can always be used to locate the beginning of an FPDU (in
>
> FPDUs with valid CRCs). Since the location of the Marker is
>
> known in the octet stream (sequence number space), the Marker can
>
> always be found.
>
> 3: Having found an FPDU by means of a Marker, an optimized MPA/TCP
>
> receiver can find following contiguous FPDUs by using the ULPDU
>
> Length fields (from FPDUs with valid CRCs) to establish the next
>
> FPDU boundary.=94
>
> Question: Is an implementation allowed to use the marker, as described=20
> below, to =93unambiguously=94 detect the start of a FPDU?
>
> Condition under which marker was received:
>
> 1. Markers being used (negotiated on)
>
> 2. Large FPDU being sent which consumes three TCP segments (not=20
> desired but allowed)
>
> 3. Second TCP segment lost
>
> 4. Marker located in third TCP segment
>
> Issue: In item two above it would appear that the implementation would=20
> have to validate the FPDU in which the marker is received (perform CRC=20
> check) before it can use it. However, since a portion of the FPDU is=20
> missing this would not be possible to do. Therefore a conformant=20
> device MUST NOT use this marker to detect the start of the FPDU.
>
> Is this the correct understanding of this requirement?
>
> Barry Reinhold
>
> (603) 868-8411
>
> [email protected] <mailto:[email protected]>
>
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