I am running VoIP services on 1.2Mb realtime link (anything above the bandwidth will be dropped). The voip protocol is proprietary (by Etrali telecom), not anywhere close to other industry standards. These are not the typical VoIP phones either; specialized broker 'turrets', that can handle 2 handsets and 6 so-called open broadcasts (OBs), which are audio channels 'assigned' directly to the device. Should trader hit the button on the other end, voice will be heard on the OB channel. Otherwise, it's quiet. To make things more complicated, there is bandwidth used, no matter if there is audio present on the OBs. It's like they transmit 'empty' data. Etrali does not use any voice compression (why?), which results 80Kbps per channel with overhead. I have done some dumps with Ethereal to analyze the UDP packets (that's how the voice is being sent). The size of a typical packet is 302 bytes total (260 data) 75% of the time, the remaining 25% is 542 bytes (500 data). I believe, the difference in size depends on how many OBs has been placed on the client's turret; important to say is, that the packets sizes should not exceed 600 bytes. A typical small-size packet looks like this: (i have marked the start of the data part by ***), there were concurrent 2/3 conversations active at the time of the probe.
0000 00 11 93 bc 28 43 00 06 47 30 03 39 08 00 45 b8 ....(C.. G0.9..E. 0010 01 20 f1 bf 00 00 40 11 28 4d c0 a8 04 84 42 09 . ....@. (M....B. 0020 57 d3 10 00 10 e0 01 0c 00 00***90 17 3c 8f 3f ec W....... ....- posted
17 years ago