sender
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... receiver with the value of the ROC the
sender is currently using. For instance, it can be transferred in
the Common Header Payload ...
... receiver will not be able to synchronize his ROC with the
one used by the sender, even if it is signaled to him out of band.
Examples of where synchronization failure will appear are:
...
... join the service until after a few hours, at which point
the sender's sequence number (SEQ) has wrapped around, and so the
...
... sequence number (SEQ) has wrapped around, and so the
sender, meanwhile, has increased the value of ROC. When the user
joins the service ...
... receiver
will not have its ROC synchronized with the sender, and it is not
possible to recover without out-of-band signaling.
...
... SEQ has recently wrapped
around (say, SEQ = 0x0001). The sender generates a MIKEY message
and includes the current value of ROC ...
... 4. Similarly to (3), since the initial SEQ is selected at random by
the sender, it may happen to be selected as a value very close to
0xffff. In this case, should the first few packets be lost, the
receiver ...
... RCC for short), works as follows.
The sender processes the RTP packet according to RFC 3711prop. When
...
... 3711prop. When
applying the message integrity transform, the sender checks if the
SEQ is equal to 0 modulo some non-zero ...
... non-zero integer constant R. If that
is the case, the sender computes the MAC in the same way as is done
when using the default integrity transform ...
...
If the SEQ is not equal to 0 mod R, the sender just proceeds to
process the packet according to RFC 3711prop without performing the
...
... ROC_local is replaced by ROC_sender (retrieved from the packet).
This works as follows. In the step where integrity protection is to
...
... RFC3711]), but
concatenated with ROC_sender instead of concatenated with the
local_ROC. The receiver ...
... MAC_tr for the MAC verification in
the same way the sender did. Note that the session key used in the
MAC calculation ...
... application layer can indicate to it
that the local ROC is synchronized with the sender (hence, the packet
would be processed using the local ROC). Note that the received ROC ...
... integrity
protected in mode 1, so unless R = 1, the mechanism should be seen
for what it is: a way to improve sender-receiver synchronization, and
not a replacement for integrity protection ...