Bandwidth estimates
Packet overhead
Communication over an IP-network has some overhead for each data-packet. This overhead can be seen as a constant value in calculations, although it is dependant on a few parameters like the networkstructure and wether it is an TCP or UDP packet.
For TCP, an overhead of 52 Bytes is average and for UDP it is 28 Bytes.
See for more detailed information ethernet payload datarates.
Trunking
Because of this packet-overhead, several protocols (like IAX2) support some kind of multiplexing. This means in each datapacket which is sent over the network, several packets of multiple conversations are put together in order to minimize the amount of packets on the network, thus maximizing the payload and minimizing the overhead.
Audio codecs
Bandwidth Requirements for Several Common VoIP Compression Algorithms
| Codec | Bit rate | NEB |
|---|---|---|
| G.711 | 64 Kbps | 87.2 Kbps |
| G.729 | 8 Kbps | 31.2 Kbps |
| G.723.1 | 6.4 Kbps | 21.9 Kbps |
| G.723.1 | 5.3 Kbps | 20.8 Kbps |
| G.726 | 32 Kbps | 55.2 Kbps |
| G.726 | 24 Kbps | 47.2 Kbps |
| G.728 | 16 Kbps | 31.5 Kbps |
| iLBC | 15 Kbps | 27.7 Kbps |
NEB = Nominal Ethernet Bandwidth (one direction)
- G711u/a - Requires 64+Kbps (inbound and outbound) continuous data stream for a quality call, plus the SIP signal. A 128Kbps connection has shown to be the minimal connection needed in our testing.
- G723 - Requires 6.4+Kbps (I and O) continuous data stream and also needs room for the SIP signal, 28.8Kbps connection has shown to be the minimal connection.
(Source)
