Information Technology Reference
In-Depth Information
With cRTP
Bandwidth = ( [1 + 6] + 2 + 160) = 169 bytes * 8 = 1352 bits * 50 pps = 67,600 bps = 67.6 Kbps
Bandwidth savings
82,800 - 67,600 = 15,200 bps
(15,200 / 82,800) * 100 = 18.36 percent savings
Note that when calculating voice bandwidth, it is important to take into account these factors:
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Layer 2 headers/overhead
PPP/MLP = 7 bytes
HDLC = 7 bytes
Frame Relay/FRF.12 = 7 bytes
ATM = 5 bytes
MLP over Frame Relay = 14 bytes
Ethernet = 18 bytes, including CRC
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Layer 3 and 4 headers
IP header = 20 bytes
UDP header = 8 bytes
RTP header = 12 bytes
cRTP (IP/UDP/RTP) header = 2 (or 4) bytes
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Sample sizes
G.711 uses a sample size of 80 bytes/10 ms and has a default voice payload size of 160 bytes/20 ms (default payload includes
2 samples). If the payload is 240 bytes, this equates to 30 ms.
