Sorry, I don't really like this approach because it conflicts with
what I said in the first sentence. Here's how I would like to revise
the paragraph:
Since the ability to suppress silence is one of the primary
motivations for using packets to transmit voice, the RTP header
carries both a sequence number and a timestamp to allow a receiver
to distinguish between lost packets and periods of time when no data
was transmitted. Discontiguous transmission (silence suppression)
MAY be used with any audio payload format. Receivers MUST assume
that senders may suppress silence unless its use is restricted by
signaling specified elsewhere. (Even if the transmitter does not
suppress silence, the receiver must be prepared to handle periods
when no data is present since packets may be lost.)