VoIP – Per Gesprek bandbreedte

Bron: http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml
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 2or 4bytes (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, including 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, including 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.
Note:

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		60 Bytes	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	67.6Kbps	87.2 Kbps
ilbc_mode_20(15.2Kbps)	38 Bytes	20 ms	NA	38 Bytes	20 ms	50	34.0Kbps	18.8 Kbps	38.4Kbps
ilbc_mode_30(13.33Kbps)	50 Bytes	30 ms	NA	50 Bytes	30 ms	33.3	25.867 Kbps	15.73Kbps	28.8 Kbps

Per Call Bandwidth requirements for various codecs

Codec & Bit Rate (Kbps)	Codec Sample Size (Bytes)	Codec Sample Interval (ms)	Voice Payload Size (Bytes)	Voice Payload Size (ms)	Bandwidth Ethernet (Kbps)
G.711 (64 Kbps)	80 Bytes	10ms	160 bytes	20ms	87.2Kbps
G.729 (8 Kbps)	10 Bytes	10ms	20 bytes	20ms	31.2Kbps
G.723.1 (6.3 Kbps)	24 Bytes	30ms	24 bytes	30ms	21.9Kbps
G.723.1 (5.3 Kbps)	20 Bytes	30ms	20 bytes	30ms	20.8Kbps
G.726 (32 Kbps)	20 Bytes	5ms	80 bytes	20ms	55.2Kbps
G.726 (24 Kbps)	15 Bytes	5ms	60 bytes	20ms	47.2Kbps
G.728 (16 Kbps)	10 Bytes	5ms	60 bytes	30ms	31.5Kbps
G722_64k(64 Kbps)	80 Bytes	10ms	160 bytes	20ms	87.2Kbps
ilbc_mode_20(15.2Kbps)	38 Bytes	20ms	38 bytes	20ms	38.4Kbps
ilbc_mode_30(13.33Kbps)	50 Bytes	30ms	50 bytes	30ms	28.8Kbps
speex(24.6 Kbps)	66 Bytes	20ms	56 bytes	25ms	42.4 Kbps
speex(18.2 Kbps)	46 Bytes	20ms	56 bytes	20ms	42.4 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 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, corresponding 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, corresponding to 10 bytes (80 bits) per sample at a bit rate of 8 Kbps. (codec bit rate = codec sample size / codec sample interval).
MOS	MOS is a system of grading 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 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) ]

Bandwidth Calculation Formulas

These calculations are used:

• Total packet size = (L2 header: MP or FRF.12 or Ethernet) + (IP/UDP/RTP header) + (voice payload size)
• PPS = (codec bit rate) / (voice payload size)
• Bandwidth = total packet size * PPS

Sample Calculation

For example, the required bandwidth for a G.729 call (8 Kbps codec bit rate) with cRTP, MP and the default 20 bytes of voice payload is:

• Total packet size (bytes) = (MP header of 6 bytes) + ( compressed IP/UDP/RTP header of 2 bytes) + (voice payload of 20 bytes) = 28 bytes
• Total packet size (bits) = (28 bytes) * 8 bits per byte = 224 bits
• PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps
  Note: 160 bits = 20 bytes (default voice payload) * 8 bits per byte
• Bandwidth per call = voice packet size (224 bits) * 50 pps = 11.2 Kbps