VoIP - Per Call Bandwidth
These protocol header assumptions are used for the calculations:
- 40 bytes for IP (20 bytes) / User Datagram Protocol (UDP) (8 bytes) / Real-Time Transport Protocol (RTP) (12 bytes) headers.
- Compressed Real-Time Protocol (cRTP) reduces the IP/UDP/RTP headers to 2 or 4 bytes (cRTP is not available over Ethernet).
- 6 bytes for Multilink Point-to-Point Protocol (MP) or Frame Relay Forum (FRF).12 Layer 2 (L2) header.
- 1 byte for the end-of-frame flag on MP and Frame Relay frames.
- 18 bytes for Ethernet L2 headers, which include 4 bytes of Frame Check Sequence (FCS) or Cyclic Redundancy Check (CRC).
Note : This table only contains calculations for the default voice payload sizes in Cisco CallManager or Cisco IOS® Software H.323 gateways. For additional calculations, which includes different voice payload sizes and other protocols, such as Voice over Frame Relay (VoFR) and Voice over ATM (VoATM), use the TAC Voice Bandwidth Codec Calculator (registered customers only) tool.
Codec Information Bandwidth Calculations
Codec & Bit Rate (Kbps) Codec Sample Size (Bytes) Codec Sample Interval (ms) Mean Opinion Score (MOS) Voice Payload Size (Bytes) Voice Payload Size (ms) Packets Per Second (PPS) Bandwidth MP or FRF.12 (Kbps) Bandwidth w/cRTP MP or FRF.12 (Kbps) Bandwidth Ethernet (Kbps)
G.711 (64 Kbps) 80 Bytes 10 ms 4.1 160 Bytes 20 ms 50 82.8 Kbps 67.6 Kbps 87.2 Kbps
G.729 (8 Kbps) 10 Bytes 10 ms 3.92 20 Bytes 20 ms 50 26.8 Kbps 11.6 Kbps 31.2 Kbps
G.723.1 (6.3 Kbps) 24 Bytes 30 ms 3.9 24 Bytes 30 ms 33.3 18.9 Kbps 8.8 Kbps 21.9 Kbps
G.723.1 (5.3 Kbps) 20 Bytes 30 ms 3.8 20 Bytes 30 ms 33.3 17.9 Kbps 7.7 Kbps 20.8 Kbps
G.726 (32 Kbps) 20 Bytes 5 ms 3.85 80 Bytes 20 ms 50 50.8 Kbps 35.6 Kbps 55.2 Kbps
G.726 (24 Kbps) 15 Bytes 5 ms 20 ms 50 42.8 Kbps 27.6 Kbps 47.2 Kbps
G.728 (16 Kbps) 10 Bytes 5 ms 3.61 60 Bytes 30 ms 33.3 28.5 Kbps 18.4 Kbps 31.5 Kbps
G722_64k (64 Kbps) 80 Bytes 10 ms 4.13 160 Bytes 20 ms 50 82.8 Kbps 67.6 Kbps 87.2 Kbps
ilbc_mode_20 (15.2Kbps) 38 Bytes 20 ms NA 38 Bytes 20 ms 50 34.0 Kbps 18.8 Kbps 38.4 Kbps
ilbc_mode_30 (13.33Kbps) 50 Bytes 30 ms NA 50 Bytes 30 ms 33.3 25.867 Kbps 15.73 Kbps 28.8 Kbps
Explanation of Terms
|Codec Bit Rate (Kbps)||Based on the codec, this is the number of bits per second that need to be transmitted in order to deliver a voice call. (codec bit rate = codec sample size / codec sample interval).|
|Codec Sample Size (Bytes)||Based on the codec, this is the number of bytes captured by the Digital Signal Processor (DSP) at each codec sample interval. For example, the G.729 coder operates on sample intervals of 10 ms, which corresponds to 10 bytes (80 bits) per sample at a bit rate of 8 Kbps. (codec bit rate = codec sample size / codec sample interval).|
|Codec Sample Interval (ms)||This is the sample interval at which the codec operates. For example, the G.729 coder operates on sample intervals of 10 ms, which corresponds to 10 bytes (80 bits) per sample at a bit rate of 8 Kbps. (codec bit rate = codec sample size / codec sample interval).|
|Mean Opinion Score (MOS)||MOS is a system used to grade the voice quality of telephone connections. With MOS, a wide range of listeners judge the quality of a voice sample on a scale of one (bad) to five (excellent). The scores are averaged in order to provide the MOS for the codec.|
|Voice Payload Size (Bytes)||The voice payload size represents the number of bytes (or bits) that are filled into a packet. The voice payload size must be a multiple of the codec sample size. For example, G.729 packets can use 10, 20, 30, 40, 50, or 60 bytes of voice payload size.|
|Voice Payload Size (ms)||The voice payload size can also be represented in terms of the codec samples. For example, a G.729 voice payload size of 20 ms (two 10 ms codec samples) represents a voice payload of 20 bytes [ (20 bytes * 8) / (20 ms) = 8 Kbps ]|
|PPS||PPS represents the number of packets that need to be transmitted every second in order to deliver the codec bit rate. For example, for a G.729 call with voice payload size per packet of 20 bytes (160 bits), 50 packets need to be transmitted every second [50 pps = (8 Kbps) / (160 bits per packet) ]|
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