Traffic measurements Video

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Voice and video analysis

Schematic sketch of the situation:

Schematic overview of the test-setup. The colors in the sketch match the colors in the following Ethereal-screenshots

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.

Ethereal graph voice and one-way-video.png

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.

Ethereal graph voice and one-way-video2.png

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

Ethereal graph showing the differences in traffic between audio and video (resp. g711u and H263-1998 codec). Black: from SIP-phone #1 to PBX. Blue: from SIP-phone #2 to PBX Pink: all traffic between SIP-phone #1 and the PBX

Legenda:

  • Black shows audio & video from SIP-phone #1 to the PBX (video starting at the 10th 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

X-lite 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)