Proper understanding of
2007-01-01 17:54:00 GMT
I’m looking at the changes in MPA from draft 02 (against which the conformance suite was written) to draft 08. I would like to understand how to take the following text from page 25 (clause 6).
“To 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
Question: Is an implementation allowed to use the marker, as described below, to “unambiguously” 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 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 have to validate the FPDU in which the marker is received (perform CRC check) before it can use it. However, since a portion of the FPDU is missing this would not be possible to do. Therefore a conformant device MUST NOT use this marker to detect the start of the FPDU.
Is this the correct understanding of this requirement?
_______________________________________________ rddp mailing list rddp <at> ietf.org https://www1.ietf.org/mailman/listinfo/rddp