A Little Bit of History
Many VoIP installations are designed with an initial architecture that assumes inter-office phone calls will reside within the confines of the company LAN. Internal LANs are almost always 100 megabit and consist of multiple paths between end points. The basic corporate LAN design usually provides more than enough bandwidth to route all inter-office VoIP calls without congestion.
As enterprises become more dispersed geographically, care must be taken when extending VoIP calls beyond the main office. Once a VoIP call leaves the confines of your local network and traverses over the public Internet link, it will have to compete for space with any data traffic that might also be destined for the Internet. Without careful planning, your Enterprise will most likely start dropping VoIP calls during busy traffic times.
The most common way of dealing with priority or VoIP is to set what is called the TOS bit. The TOS bit acts like a little flag inside each Internet packet of the VoIP stream. An Internet router can rearrange the packets destined for the Internet, and give priority to the outgoing VoIP packets by looking at the TOS bit. The downside of this method is that it does not help with VoIP calls originating from the outside coming into your network. For example, somebody receiving a VoIP call in the main office from a VPN user working at home, may experience some distortion on the incoming VoIP call. This is usually caused when somebody else in the office is doing a large download during the VoIP call. Routers typically cannot set priority on incoming data, hence the inbound data download can dominate all the bandwidth, rendering the VoIP call inaudible.
How NetEqualizer Solves VoIP Congestion Issues
The NetEqualizer solves the problem of VoIP traffic competing with regular data traffic by using a simple method. A NetEqualizer provides priority for both incoming and outgoing VoIP traffic . It does not use TOS bits. It is VoIP and Network agnostic. Sounds like the old Saturday Night Live commercial where Chevy Chase hawks a floor cleaner that is also an ice cream topping.
Here is how it works…
It turns out that VoIP streams require no more than 100kbs per call, usually quite a bit less. Large downloads, on the other hand, will grab the entire Internet Trunk if they can get it. The NetEqualizer has been designed to favor streams of less than 100kbs over larger data streams. When a large download is competing with a VoIP call for precious resources, the NetEqualizer will create some artificial latency on the download stream causing it to back off and slow down. No need to rely on TOS bits in this scenario, problem solved.
Conceptually, that is all there is to it. Obviously, the NetEqualizer engineering team has refined and tuned this technique over the years. In general, the NetEqualizer Default Rules need very little set-up, and a unit can be inline in a matter of minutes.
The scenarios where NetEqualizer is appropriate for ensuring that your VoIP system runs smoothly are:
- You are running an Enterprise VoIP service with remote offices that connect to your main PBX over VPN links
- You are an ISP and your customers use a VoIP service over limited bandwidth connectivity
Other vendor White Papers on the subject: River Bed
Other suggested reading: http://www.bandwidth.com/wiki/article/QoS_(Quality_of_Service)