Skype Journal: Sorry, could you repeat that?
September 13, 2006 10:04 AMI was being interviewed for a podcast last night. As always, the purpose of the "stupid network" is to enable crazy new things, not connectivity arbitrage. The setup was that I'm in my hotel room using the woefully over-contended in-room Internet access. The caller could only record calls made using his landline phone, so he called me on my SkypeIn number.
The audio experience was OK, but about that of a typical cellular call. Not ideal for a podcast.
This does, however, provide great fodder for a "Voice 2.0"-ish story. Normally, VoIP uses the UDP protocol for media transmission. If the packet doesn't get there within 300ms, or whatever, forget it. No point in asking for reliability and re-transmission of lost data. The TCP protocol is used for signalling and other purposes where a reliable, in-sequence connection is required.
Now in this case, when a call is being recorded, the need is rather more subtle. In the real-time portion of the conversation, it just needs to be good enough for us to understand each other to hold a conversation. What we then want is to "fill in the gaps" and allow the person recording to request re-transmission of packets corresponding to gaps and dropouts, but in a way that doesn't impinge on the bandwidth allocated to the ongoing conversation. So we might send the media over UDP still, but there's a TCP-like component at the side.
Another alternative is for my VoIP client to record the conversation in wideband audio, and then upload that (possibly after the conversation has finished). It would embed suitable synchronisation data so that the audio from both ends of the conversation can easily be mixed into one stream.
This highlights a case of user needs often being subtle and unexpected. As always, the purpose of the "stupid network" is to enable crazy new things, not connectivity arbitrage. Sometimes, a phone conversation is more than a phone call.
Catch Martin's streams at Telepocalypse.
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Thought provoking. Could also be useful in computer speech recognition; I put some ideas in the VOIPSA blog.
Posted by: Martyn Davies at September 21, 2006 3:14 AM