Traffic measurements Video

Voice and video analysis

Schematic sketch of the situation:

In the screenshot below, the following events were measured:

• @4 sec: Video was turned on
• @14 sec: Video was set to black (connection lost with DVdriver)
• @20 sec: Video showed moving pictures again.

Legenda:

• Black: traffic from and to Trixbox #1
• Red: traffic between the 2 Windows machines running X-lite
• Green: traffic between laptop #1 and its Asterisk
• Blue: traffic between the two Asterisk PBX's
• Pink: traffic between Windows machine #1 and its Asterisk

The following graph shows the traffic is almost constant. Till 35sec the conversation included audio and video. The rest is audio-only.

This measurement shows there is no traffic between both SIP-phones, only via (both) Asterisk PBX.

Differences between voice and video

For this test (captured Ethereal data), we connected 2 SIP phones to the same Asterisk PBX. We measured the bandwitdh used between the following 3 points:

1. SIP-phone #1 with camera
2. SIP-phone #2 without camera
3. Asterisk PBX

Legenda:

• Black shows audio & video from SIP-phone #1 to the PBX (video starting at the 10^th second)
• Blue shows audio-only from SIP-phone #2 to the PBX
• Pink shows all traffic between SIP-phone #1 and the PBX (both directions)

The debug-screen

of X-lite (Ctrl + F9) told us the SIP-phone assumed a total available bandwith of 256/256 kbps.

This was filled with 64 kbps for speech (protocol g711u) and 131 kbps for video (protocol H263-1998)

When looking at the speech traffic:

• 50 packets/sec (measured with Ethereal)
• 214 Bytes/packet (measured with Ethereal)
• +/- 10,7 kByte/s
• 160 bytes audio-data per packet (64 kbps = 8000 Bytes/sec, 50 packets/sec)
• UDP-packet-header: 28 Bytes.

Measured IAX-overhead: (the g711u codec uses a CBR of 64kbps) 214 - 28 - 160 = 26 Bytes/packet. Thus 1300 Bytes/sec IAX overhead. (10k4 bps)