Fax Rtcp Bw Calculation; Qos Profiles - Nera WiLink-I Series System Manual

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) = (94bytes) * 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 (752bits) * 50 pps = 37.6 Kbps
Since Fax BW is higher than Voice BW, the Fax BW requirement mandates the CG
connection's attributes. This is true for all G.729 and G.723 codecs.
B.3.5

FAX RTCP BW Calculation

RTCP BW is 10% of RTP: 10 % of 37.6 Kbps is 3.76 Kbps.
B.3.6

QoS Profiles

B.3.6.1 CG QoS for RTP traffic
The calculated bandwidth required for RTP traffic is 37.6 Kbps (equivalent to a
Packet Size of 752 bits, or 94 bytes). Thus, the CG 38 QoS Profile parameters are:
Packet Size: 117 bytes
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Sample Interval: 20 msec
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B.3.6.2 RT QoS for RTCP and VoIP Signaling
The required bandwidth is 5.76 Kbps (3.76 Kbps for Fax RTCP plus 2 Kbps for
VoIP Signaling). We round it up to 6 Kbps. Thus, the required RT 6 QoS Profile
parameters are:
CIR: 6 Kbps
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CT: Short
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B.3.6.3 BE QoS for Data
As stated, the recommended QoS Profile for Data is BE 64, with the following
parameters:
MIR: 64 Kbps
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CT: Medium
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WiLink-I Modular Base Station System Manual
1 POTS Advanced VoIP G.729 Service Profile
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