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Total packet size (bytes) = (Ethernet of 18 bytes) + (IP/UDP/RTP header of 40
bytes) + (voice payload of 36 bytes) = 94 bytes
Total packet size (bits) = (94 bytes) * 8 bits per byte = 752 bits
PPS = (14.4 Kbps bit rate) / (288 bits) = 50 pps
Note: 288 bits = 36 bytes (voice payload) * 8 bits per byte
Bandwidth per call = total packet size (752 bits) * 50 pps = 37.6 Kbps
As Fax BW is lower than Voice BW, the Voice BW requirement mandates the CG
connection's attributes. This is true for all G.711 codecs.
B.5.5
FAX RTCP BW Calculation
RTCP BW is 10% of RTP: 10 % of 37.6 Kbps is 3.76 Kbps.
B.5.6
QoS Profiles
B.5.6.1
CG QoS for RTP traffic
The calculated bandwidth required for RTP traffic is 87.2 Kbps (equivalent to a
Packet Size of 1744 bits, or 218 bytes). Thus, the CG 88 QoS Profile parameters
are:
Packet Size: 218 bytes
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Sample Interval: 20 msec
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B.5.6.2
RT QoS for RTCP and VoIP Signaling
The required bandwidth is 10.72 Kbps (8.72 Kbps for Voice RTCP plus 2 Kbps for
VoIP Signaling). We round it up to 611 Kbps. Thus, the required RT 11 QoS Profile
parameters are:
CIR: 11 Kbps
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CT: Short
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WiLink-I Modular Base Station System Manual
1 POTS Advanced VoIP G.711 Service Profile
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