Comment # 12
on bug 10611
from Stephen Donnelly
(In reply to Guy Harris from comment #11)
> I don't know what the "messageLength" field in the PTP header means - I'll
> buy a copy of the damn paywalled standard if I need to - but if it's an
> actual message length, *that* should be used to determine whether there are
> TLVs or not.
>
> As Stephen noted, it's not the job of *any* protocol running atop Ethernet
> to dissect the FCS, so I've approved and merged his change.
>From Draft 2.2 (pre-standard):
13.3.2.4 messageLength (UInteger16)
The value of the messageLength shall be the total number of octets that form
the PTP message. The counted octets start with the first octet of the header
and include and terminate with the last octet of any suffix or, if there are no
suffix members with the last octet of the message as defined in Clause 13.
NOTE—The message length does not include any padding bits specified in Annex D.
So I believe the point is that to determine how many (if any) suffixes (TLV
entries) are present you have to know the 'base length' for each messageType
(64 bytes for Announce messages) as well as the messageLength value.
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