The common sense guide to video conferencing on ADSL circuits

5 Aug 2015 | Cloud Services, Networks

In a perfect world all video conferencing systems would need guaranteed symmetric upload and download bandwidth in order to provide the best video quality possible, for both incoming and outgoing video. The reality of broadband internet in the UK is a different matter entirely. ADSL is still the most prominent form of broadband. In rural areas, it is the only type of broadband.

With video conferencing on ADSL the clue to the problems it can cause is in the acronym, as ADSL stand for Asymmetric Digital Subscriber Line. ADSL provides much faster download speeds than upload speeds, which is fine for surfing the internet, watching YouTube videos or streaming films and TV shows from Netflix as these activities only require good and reasonably steady download speeds. With ADSL, upload speeds are the usually no more than a tiny fraction of download speeds That, after all, is what the asymmetric in ADSL means. Added to this, the available bandwidth of the circuit can fluctuate. As a result, if thedefault upload bandwidth speeds on a typical video conferencing system are used on an ADSL connection there is only one possible outcome: packet loss. Packet loss is like kryptonite to the Superman of video conferencing usage and adoption. Due to the asymmetric nature of ADSL it’s normally the far end video system in a call that experiences the messy end of the stick due to poor upload speeds on the near end system.

Packet loss affects different VC systems in different ways. It can manifest as latency with video, cause lip sync issues, blurring of the picture and in a worse case scenario make participants in a conference look like green tinged alien mutants made of Lego. This is simply because most video conferencing system come out of the box with symmetric settings for upload and download speeds. For example Cisco Jabber (a popular software based video conferencing client) will optimistically try to upload 512k  of video and audio data a second by default. If the circuit can only support 256k of uploads, half of the video and audio packets from the Jabber client will be lost and the consequences in terms of video quality will be devastating and show stopping.

The trouble is, as download speeds on ADSL are generally very good, the received video image on the system with the packet loss problem will typically look excellent (assuming the far end system is not also suffering from packet loss) . This can often cause confusion as it makes it difficult for the average video conferencing user to figure out where the problem is. There is an alarming tendency for people to carry on regardless with a video call plagued with packet loss.

This is where the ability to configure independent bandwidth settings for upload and download becomes critical. If you reduce the upload speed in Jabber to 20% lower than the maximum upload speed that the circuit supports, then you can largely eliminate packet loss in calls. Jabber works surprisingly well at lower bandwidths. While you won’t be able to transmit a HD video stream you can transmit a “Full SD” video stream with the upload bandwidth set to as little as 256k. Jabber can even produce reasonable CIF video with as little as 64k of upload bandwidth. Asymmetric bandwidth settings are also available on most current generation hardware VC systems, so the same principle applies.

On older legacy systems that do not have separate settings for upload and download bandwidth, the only viable option is the set the overall maximum bandwidth the system will use to 20% lower than the maximum upload speed that the circuit supports. This will result in lower quality incoming video, but it is the only way to eliminate ADSL related packet loss on older systems.

So how can you find out what sort of speeds you are getting on an ADSL broadband circuit? Fortunately, this is very simple. There are a number of speed test websites available that will allow you to check the upload and download speeds of the ADSL connection you are using. Currently, speedtest.net is one of the most popular and has become something of a de-facto standard for testing:

http://www.speedtest.net/ (Click to open in a new browser window)

Simply run a speed test on a computer on the same ADSL circuit as the VC system and use the figures it returns as a guide for configuring the upload and download settings on the VC system.

Dos and Don’ts for ADSL Video Conferencing

  • Set upload and download speeds to 20% less than the figures returned by the speed test for both upload and download. This will give the system some “wiggle room” as the upper speed limits on the circuit can fluctuate.
  • Don’t connect other devices to the same ADSL circuit as the VC unless you can’t avoid it. If at all possible use a dedicated ADSL circuit for video conferencing.
  • If you have a laptop or desktop computer connected to the same ADSL circuit as a hardware VC system turn it off during a conference or disconnect it from the LAN. Most operating systems have automatic update functionality for security patches and these will inevitably occur when you need every last scrap of bandwidth for your VC.
  • If possible, disable WiFi on the ADSL router to prevent nearby iOS or Android devices from eating your bandwidth with automatic app updates or simply turn them off.
  • Don’t blame the VC system for poor quality if you are using ADSL. ADSL can be subject to contention. While this is unlikely to be an issue with rural broadband it can be a real problem in built up areas.
  • Invest in fibre optic broadband or SDSL for VC as soon as it becomes available in your area.

Some cutting edge software VC clients can now dynamically adjust to adverse network conditions by using H264 SVC to produce good quality video on “lossy” networks. Please contact us for more information.