Hi again Carsten:
I mixed your latest comments in:
3.2.2. Compressing UDP checksum
The UDP checksum operation is mandatory with IPv6 [RFC2460] for all
packets. For that reason [RFC4944] disallows the compression of the
UDP checksum.
With this specification, a compressor in the source transport
endpoint MAY elide the UDP checksum in certain cases for instance:
Upper Layer Message Integrity Check: In this case, there is some
other form of integrity check in the UDP payload that covers at
least the same information as the UDP checksum (pseudo-header,
data) and has at least the same strength.
Tunneling: In this case, 6LowPAN is deployed as a wireless pseudo-
fieldbus by tunneling existing field protocols over UDP. If the
tunneled PDU possesses its own addressing, security and integrity
check, the tunneling mechanism MAY authorize to elide the UDP
checksum in order to save on the encapsulation overhead.
This elision is indicated by setting the 'C' bit in the LOWPAN_NHC
header.
A 6LoWPAN endpoint that compresses the LOWPAN_NHC header MUST NOT
elide the UDP checksum (set the C bit) unless it has been authorized
to do so by the source of the packet. In the source transport
endpoint, this authorization can come from upper layer transport or
application protocol instance that originated the packet. In a
forwarding node, this authorization is implied when the incoming
packet had the optimization applied (add the C bit set).
A 6LoWPAN endpoint that expands the LOWPAN_NHC header MUST
reconstitute the UDP checksum by computing the valid value for the
datagram as specified in [RFC0768] and [RFC2460], and place the
result of that computation in the restored UDP header, unless it has
been authorized to ignore the checksum operation. In the destination
transport endpoint this authorization can come from upper layer
transport that will receive the packet and would ignore the UDP
checksum should it be restored.
What do you think?
Pascal
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