User's Manual

268 BreezeMAX Modular Base Station System Manual
Appendix B - Defining Service Profiles for Generic VoIP Gateways
B.2 1 POTS Basic VoIP G.729 Service Profile
B.2.1 Service Characteristics
 G.729 codec, 20msec sample interval
 1 POTS
 No Fax
 Priority marking behind the SU is not used: All VoIP related traffic is classified
onto a single Continuous Grant (CG) connection.
 Multiple media streams to support Call-Waiting: If the traffic exceeds the BW
allocated to the CG connection, the SU may request to double the allocated
BW.
B.2.2 RTP BW Calculation
The required bandwidth for a G.729 call (8 Kbps codec bit rate) with RTP and 20
bytes of voice payload is:
Total packet size (bytes) = (Ethernet of 18 bytes) + (IP/UDP/RTP header of 40
bytes) + (voice payload of 20 bytes) = 78 bytes
Total packet size (bits) = (78 bytes) * 8 bits per byte = 624 bits
PPS (Packets Per Second) = (8 Kbps codec bit rate) / (160 bits) = 50 pps
Note: 160 bits = 20 bytes (voice payload) * 8 bits per byte
Bandwidth per call = Total packet size (624 bits) * 50 pps = 31.2 Kbps
B.2.3 RTCP BW Calculation
RTCP BW is 10% of RTP: 10% of 31.2 Kbps is 3.12 Kbps.
B.2.4 QoS Profile
The calculated bandwidth required for RTP traffic is 31.2 Kbps. To accommodate
for other traffic types, such as RTCP (up to 3.1 Kbps), Voice Signaling (up to 2
Kbps) and Data (Device Management), we allocate to it a total bandwidth of 31.2 x
1.5=46.8 Kbps (equivalent to a Packet Size of 936 bits, or 117 bytes). The SU may