Bandwidth estimates

Packet overhead

Communication over an IP-network has some overhead for each data-packet.

TCP over Ethernet:

• Assuming no header compression (e.g. not PPP)
• Add 20 Bytes IPv4 header or 40 Bytes IPv6 header (no options)
• Add 20 Bytes TCP header
• Add 12 Bytes optional TCP timestamps
• Max TCP Payload data rates over ethernet are thus:
  • (1500-40)/(38+1500) = 94.9285 % IPv4, minimal headers
  • (1500-52)/(38+1500) = 94.1482 % IPv4, TCP timestamps
  • (1500-52)/(42+1500) = 93.9040 % 802.1q, IPv4, TCP timestamps
  • (1500-60)/(38+1500) = 93.6281 % IPv6, minimal headers
  • (1500-72)/(38+1500) = 92.8479 % IPv6, TCP timestamps
  • (1500-72)/(42+1500) = 92.6070 % 802.1q, IPv6, ICP timestamps

UDP over Ethernet:

• Add 20 Bytes IPv4 header or 40 Bytes IPv6 header (no options)
• Add 8 Bytes UDP header
• Max UDP Payload data rates over ethernet are thus:
  • (1500-28)/(38+1500) = 95.7087 % IPv4
  • (1500-28)/(42+1500) = 95.4604 % 802.1q, IPv4
  • (1500-48)/(38+1500) = 94.4083 % IPv6
  • (1500-48)/(42+1500) = 94.1634 % 802.1q, IPv6

(Source)

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)