Някой го е сметнал като е взел предвид и ATM само че не ми се превежда:

When we estimate VoIP bandwidth efficiency we have to take into account not only codec compression and silence suppression rates, but also data protocol overheads. Otherwise, our bandwidth estimate will be overly optimistic. If we use G.729 codec (8 Kbps) with 50 percent silence suppression and ignore protocol overheads, we need only 4 Kbps bandwidth in this case.

Suppose, however, that we send voice over IP over ATM (AAL2). For every 20 byte payload (2 voice frames) we have 40 bytes RTP/UDP/IP overhead + ATM overhead (5 byte ATM header + 1 byte AAL2 header per every 53 byte ATM cell + 3 bytes AAL2 header per every payload packet). Overall, we need about 14.2 Kbps bandwidth, which is 3.5 higher than 4 Kbps.