IP FAQ: How can I avoid drop-outs over IP connections?
Most PCs contain software that is scheduled to run at regular intervals. For example, virus scanners download new definitions every day or so, email programs usually check for mail every five minutes - and let's not forget those regular Windows updates. In addition, the time clock in a PC is synchronized, so activities from many PCs transferring small amounts of information can accumulate at points in time - causing more traffic and increasing the potential for drop-outs in audio.
It is very hard to determine which PCs will be using what data at any point in time. As a result, we highly recommend installing a dedicated internet connection for your broadcast codec, or engage the services of an IT company to configure your network for Quality of Service (QoS). This will ensure your codec data traffic has priority over PC data traffic.
If your codecs have a dedicated connection and you are still experiencing drop-outs, see if you can link them to a certain time of the day. On some cheap residential unlimited data plans, the availability of data is limited by the number of users connected at a point in time. Peak times like when children get home from school can bring reduced bandwidth.
If your service provider is providing a residential plan with contended bandwidth then ask for a business plan where bandwidth is not contended. A contended plan will usually limit bandwidth to users as demand increases. It is also a good idea to ensure both ends of a codec connection are with the same service provider.
Link Quality (LQ)
Use the LQ (Link Quality) numbers on your codec to determine the magnitude of any data problem. Return (Local or "L" on a G3 codec) and Send (Remote or "R" on a G3 codec) LQ numbers can also help you to determine if the problem is occurring at both ends of the connection or only one.
For example, on an IP connection the Return (or "L" on a G3
codec) reading represents the audio being downloaded from the
network locally (i.e. audio data is being sent by the remote
codec). Conversely, the Send (or "R" on a G3 codec) link quality
reading represents the audio data being sent by the local codec
(i.e. being downloaded by the remote codec).
- The Return link quality reading is exactly the same as the Local (L) setting displayed on a G3 codec.
- The Send link quality reading is exactly the same as the Remote (R) setting displayed on a G3 codec.
If you are connecting over wireless IP, start with a conservative bit-rate setting of 24Kbps, and then see how the network performs at this bit-rate. We do not recommend connecting immediately at higher bit-rates of say 64-128Kbps over 3G networks until you are sure your network will support these data rates. It is a case of trial and error and the data rates supported will often vary greatly from region-to-region, and even from day-to-day. In addition, the "Ss" wireless signal strength reading on the codec screen should be between 4 and 9 to connect reliably.
Forward Error Correction
Tieline IP audio codecs are designed to provide error concealment and can also implement Forward Error Correction (FEC), which is designed to increase the stability of UDP/IP connections in the event that data packets are lost.
FEC works by sending a secondary stream of audio packets over a connection so that if your primary IP audio stream packets are lost or corrupted, then packets from the secondary stream can be substituted to replace them. The amount of FEC required depends on the number of data packets lost over the IP connection. Both the local and remote codec FEC settings can be configured in Tieline IP codecs before dialing. These settings can also be changed ‘on the run’ while the codecs are connected. FEC should only be used if link quality displayed on the codec is below L:99 R:99, as it is of no benefit otherwise. Click here to read more about FEC and how to program it in Tieline IP codecs.