http://prweb.com/releases/2011/2/prweb8132754.htm

Deployment problems manifest themselves with quality of voice issues.    Technical articles which offer advice on solving VoIP voice quality problems discuss jitter, latency and MOS scores.  You do not have to become a VoIP nerd to make a phone call.  This article shares the most common deployment issues that cause jitter, latency and poor MOS scores without ever discussing them.

Symptoms of mild voice quality problems consist of robotic, distorted or slightly choppy voice.  In most cases, all the words can still be understood.  Moderate problems are occasional broken words which have to be repeated.  Severe problems include frequently distorted and choppy voice, lost sentences and dropped phone calls.  If you are experiencing any of the problems, here is a short list of common causes:

1. Voice Prioritization.  Most Internet connections are though DSL or Cable.  These connections typically offer more bandwidth from the Internet (download) than to it (upload).  Because the upload speed is smaller, voice packets usually need to be prioritized going out to the Internet.  If you can hear the outside caller just fine but they have trouble hearing you, than this may be the problem.

Voice prioritization MUST be enforced between the cable or DSL modem and your LAN.  More and more routers include this ability and it is becoming easier for the average user to set-up, however, a VoIP professional may still be needed.

Any use of a DSL or cable modem integrated WiFi access point is likely bypassing your voice prioritization.  Further, you may experience Internet problems just by having your WiFi radio active in your modem when using your microwave or cordless telephone.  It is strongly recommended that you disable this feature in modems and use a separate WiFi access point whose traffic must pass through voice prioritization to get to the Internet.

2.  Poor Service from Internet Service Provider (ISP).  VoIP is very sensitive to problems in the Internet and many ISPs do not take care that they provide a reliable circuit.  ISP networks are comprised of many routers frequently called hops.  Each hop has a potential for network congestion which may be fine for normal data traffic but will cause problems for VoIP.

Other causes of poor ISP service are faulty DSL or cable modem, old outside cabling that has become susceptible to weather and router problems within ISP network.  Further, DSL service may be degraded by frequency interference in the providers cable bundle, load coils and bridge taps.

3.  Hubs and Ethernet Switches. Ethernet switches and hubs are the boxes that all of your data cabling connects to tie your computer devices together.  Your LAN cannot contain any hubs.  Instead Ethernet switches must be used, 100BaseT minimum.

4.  Multiple Chained Ethernet Switches.  Homes and offices with older wiring may use multiple Ethernet switches at desks, rooms and blocks of cubes to share single wiring drops back to the main LAN Ethernet switch.  Passing VoIP through multiple Ethernet switches to reach the Internet can cause problems.  Find ways to eliminate these extra devices through wireless access points and additional cabling.

5.  Insufficient Bandwidth for Number of VoIP Calls.  Without going into the dirty details of voice compression and codecs, you should in general have about 60kbps of upload bandwidth for every simultaneous voice call.  Insufficient bandwidth will choke your voice packets.

6.  Poor Wiring Inside Building before Cable or DSL Modem.  For DSL, each building or home has a DMARC (characterized by a wire block with orange cover) or Network Interface Box (homes).  The line carrying the DSL circuit should go straight from the DMARC to DSL filter and then DSL modem.  No other devices or connections should be in between.  Cable modems must work off of the primary splitter (not go through multiple splitters) and should be the leg with the highest decibel level.  When your cable repairman visits, he can verify.

7.  Other Applications May Prioritize Their Packets.  Any application can choose to use prioritization flags in their packets.  These applications may be in use with or without the network administrator’s knowledge including video and the myriad of consumer voice services such as Skype, Vonage, IMs, etc.  Assuming the use of these services is approved, your voice prioritization programming and Internet bandwidth needs to account for the extra bandwidth consumption.

These are 7 of the most common problems that may cause jitter, latency, poor MOS scores or just bad voice quality.  In some instances, you will need professionals to help with proper programming and problem detection.  Many tools exist as well.  If you believe all inside your house or building is in good shape, determining whether the problem is caused by your ISP can be difficult.