Posted by Randy Kremlacek on Sep 19, 2012 12:38:00 PM
The 4 Horseman
In this multiple part series, I’ll cover the four evils that are the curse of high quality Virtual PBX: Bandwidth, jitter, packet loss, and latency.
Today, we’ll discuss latency.
What is Latency?
VoIP latency is the delay between when the data packets of your voice conversation are sent and when they are received.
For most regular data like your email or when you're downloading a webpage, a few microseconds of latency won't impact your user experience. It doesn't really matter that an email arrives a quarter of a second later or a website takes a moment longer to load.
Voice is Different
But voice is different. Voice is real time, for real.
When you speak, you expect to be heard immediately. A delay of as little as two tenths of a second, makes a voice conversation extremely challenging. The industry standard for acceptable latency for a Business VoIP conversation is only 120 milliseconds. This is less time than the blink of an eye at around 140 milliseconds!
As a way of comparison, an old fashioned analog line has a latency of about 60 milliseconds and phone calls between cell phones can be up to 150 milliseconds. Cell phones have “trained” users that noticeable voice latency is a fact of modern life.
What are the Factors That Effect Latency?
There are really 5 primary factors that affect latency in any business VoIP connection:
1. Lack of bandwidth
If your data network is over capacity, latency will increase substantially. It’s simply a matter of overcrowding. You see the same thing every day on the freeway. The solution is pretty obvious- you need more bandwidth, either by increasing the speed of your existing circuit, or moving to a faster circuit.
If you're making a call across town, latency is very low, as little as 25-40 milliseconds. Make that same call across the continent and the latency increases to 60-90 milliseconds. Now make that same call to India and it might be at 250 milliseconds– far from acceptable. What does help is to have the highest quality data network possible, and the carrier should be the same company on both ends.
Check out this latency table from Verizon to learn more about how latency varies. You’ll see quite a variation based on region.
3. Router Delay
Every router involved in a data transmission injects a bit of delay. On a private circuit, the path between the locations is very direct with a minimal number of routers. But voice transmissions across public internet circuits take a more circuitous path, thus slowing transmission. This is where Hosted Business Voice can run into issues.
The solution is to have a high quality provider with robust bandwidth in their network, allowing calls to take the shortest path possible.
4. Firewall Delay
Firewalls stop the bad guys by “inspecting” the data packets that are coming in. That inspection takes time, again adding latency to the phone call. An undersized or older firewall will induce greater delays than a current firewall sized correctly to the amount of bandwidth being processed.
5. Codec Delay
Codecs are the technology used to compress voice bandwidth. An uncompressed voice call takes approximately 80 Kbps of bandwidth. Using compression, that number can drop to 20 Kbps of bandwidth.
If bandwidth is precious (think remote locations and international connections), a compressed call conserves valuable bandwidth. But the trade-off is that the act of compressing and decompressing the data takes time.
The best approach is to make the best engineering compromise between bandwidth consumption and latency. Fortunately, there are many codecs available to use for this purpose.
While excess latency is a frequent problem, most times it can be resolved with the application of the correct technology, proper carrier and experienced engineering. A quality Virtual PBX provider should have the skills and tools available to defeat this horseman.
About the Author
President | Head Chef
Randy Kremlacek is president and Head Chef of TeleDynamic Communications, and is a Digium Select Partner and 2013 Pinnacle Award winner. TeleDynamic Communications provides turnkey premises-based PBX and hosted PBX, SIP trunking and Unified Communications. Randy Kremlacek prides himself on knowing the telecommunications industry as well as he knows his way around his own kitchen. READ MORE
Topics: Virtual PBX