Re: IPsec & Markers

Culley, Paul wrote:

>>>The Markers are to enable the receiving side to locate the start of 
>>>MPA Frames even when TCP Segments are received out-of-order.
>>
>>Out of order or "unaligned"?  When the entire FPDU fits in 
>>the TCP segment (e.g. aligned), I have no problem locating 
>>the start of MPA Frames, in (TCP sequence) order or not.
>>
> 
> Unfortunately, just because an FPDU might fit in a TCP segment, does not
> mean that it MUST always be aligned.  It is legal (but unwise) for a
> sender to segment the TCP stream at other than FPDU boundaries.

Agreed.  In fact, this happens all the time with an MTU change (e.g. 
jumbo to 1500).  An unacked TCP segment that once fit in an entire FPDU 
now needs to be retransmitted in many TCP segments.

On the receive side, until I have the entire FPDU, so as to calculate 
the CRC, regardless of what order these TCP segments arrive in I can't 
do much with the data.

In general, (to simplify) a receiver can take any given TCP segment, use 
the "length" to find the CRC.  If the CRC doesn't match, I don't have an 
FPDU.

Regards,
MikeC

-- 
Michael C. Cambria

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