I wanted to try and find out exactly how Skype handles audio conference calls, and what the bandwidth requirements were, especially for the person who hosts the call and becomes the conference bridge.
The recommended upload/download bandwidth requirements for a single Skype audio call are 100Kbps/100Kbps, i.e. your audio to the recipient of the call requires 100Kbps in the transmit/upload direction, and the audio stream from the person you call requires 100Kbps in the receive/download direction.
This bandwidth requirement is pretty low, with most DSL bases broadband services ranging from at least 2Mbps to 16Mbps download speeds, and between 512Kbps and 1Mbps upload which is why Skype calling works pretty well most of the time. (The minimum requirement is 30Kbps – but speech quality at this bit rate will be poor.)
The problem comes with audio conferencing and the way Skype creates the audio conference bridge.
The person hosting the conference call mixes ALL the audio streams together.
Whatever computer is running Skype for the person who initiates the conference call becomes the “conference bridge”. It receives all incoming audio streams, mixes them together, and then sends the resulting combined stream back out to all participants.
For example if you create a Skype audio conference to 4 other people, your computer will become the audio bridge for the conference call traffic. Based on the figures above you will be receiving 4x100Kbps=400Kbps, mixing the audio together and streaming it back to the recipients also at 4X100Kbps.
An upstream rate of 400Kbps for some copper based DSL broadband connections may be more that it can handle, and this will result in poor audio conferencing quality for all the recipients in the call.
The bandwidth requirements for video conferencing are much, much greater e.g. a group video call for 5 people has a recommended bandwidth requirement of 4Mbps/512Kbps.
To try and ensure the best quality Skype audio conferencing:
1. Make sure the person with the fastest upload/download Internet connection initiates the conference call and becomes the audio bridge for the conference streams.
2. Make sure other users of your broadband connection are not uploading/downloading large files at the same time as the conference!
3. Use a wired connection for your computer to avoid any added complications of streaming the audio bridge data over a wireless lan connection.
4. Get a faster internet connection – 100Mbps fibre, thankyou please.