WAN issues usually result from high latency, packet loss, jitter, or temporary loss of the Internet connection and can result in everything from delayed voice to dropped calls.  These are the problems that you face with your connection from the modem out to the internet.  They can be the result of poor signal levels with your ISP's connection or unusual high delay and jitter occurring from routers and/or network congestion.  This brief introduction and troubleshooting guide is meant to help look for some of the more identifiable possibilities.

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Cable modems and Signal Levels:

Your cable modem is designed to operate with signal levels that are within certain ranges (dB).  If these signal levels are not within that range, the modem can temporarily loose sync, or struggle to maintain a connection with the CMTS.  In either case, this can cause your connection to the Internet to be briefly interrupted.  In more extreme cases you will probably notice your loss of connection. Your modem will have to reconnect, and in doing so you should notice the indicator lights of the modem flashing.  It is the less obvious problem that can be more vexing, where a brief loss of connectivity can result in dropped calls or loss of dial tone.  In this case, you should look at the actual signal power levels.  This can be done by either calling your ISP and have a technician look at them, or you can connect directly to your modem through a web browser and read the power levels that will be displayed on the internal pages of the modem.  The signal levels should be:

• Downstream power: Between -15db to +15db is within most modems tolerances, but generally -9db to +10. 
• Upstream power:  This should be less than 55, but would be better to be less than 52.
• SNR signal to noise ratio:  Definitely greater than 25, but above 28 would be best.

• Motorola Surfboards: The online light should be solid green if the modem is acquired.  Important: Motorola Surfboard cable modems have a Standby button.  The Standby button shuts down the front panel's LEDs and disconnects communication between the cable modem and the devices connected through the cable modem, while remaining active on the cable operators RF network.  Make sure that you do not have Standby set, as you will not have an active Internet connection.
• Toshiba:  The cable light should solid green if it's registered and ready.
• Ambit:  The sync light should be solid green if it has established two- way communication with the cable operator.
• Terayon:  The cable light should be solid green when the modem is registered and ready.
• RCA:  The cable light should be solid green when it is synced.
• 3Com (Tailfin):  The link status light should be solid green when the connection is established.

More information about two cable modems, the Ambit and the Motorola Surfboard.

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Bandwidth, Latency and other Issues:

Bandwidth, or the available bandwidth that your VoIP connection can access, can have a direct effect on voice quality.  In many cases the first evidence of a bandwidth problem would be a choppiness quality to the voice or "dead spots".  This can be experienced on the incoming voice, the outgoing voice or both.  You may also find that your outgoing voice disappears for periods of time.  Sometimes it will appear to be a complete loss, but usually if you maintain the connection, you will find that the audio returns, even if for just brief periods.  If you experience "choppy calls" then the first step would be to do a bandwidth test, where both the upload and download are measured. 

• You should have 80 to 90kbps on both the upload and download for a single two-way conversation using the G711 codec.  The G711 codec nominal data rate is 64kbps, but added to this will be headers and other information, adding up to an approximate total of 80 to 90kbps.   (There are some codecs that use higher compression ratios and can be used with lower bandwidth, like G729 and others.)  And if you use a VPN tunnel for connectivity back to an office that carries your VoIP connection, then the VPN protocols will add additional headers adding more bandwidth overhead.  (VPN and VoIP)
• And your computers will need to share the Internet access.  For total VoIP bandwidth consumption over a period of time read this information that shows approximate usage.  Some applications on your computer may even try to grab the available bandwidth, effectively stepping on the voice transmission causing dead spots or creating choppy calls.  check your bandwidth
• If when making three-way calls you notice choppiness or a degraded voice quality, then chances are that you have exceeded your bandwidth.  If you can't make three-way calls at all, then you may want to check your available bandwidth.
• File sharing programs and Spyware can cause computers to use the available bandwidth, stepping all over the voice transmission.  This can usually be determined by testing calls with and without the computer or computers on.  You may want to check your computers for these malicious files as a good practice.  Ad aware and Spybot are two good utilities that will help in locating many of them.

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Packet Loss, High Latency & Jitter

Packet loss is a condition where data packets appear to be transmitted correctly from one end of a connection, but due to bad network conditions or internet congestion will fail to make it to their intended destination.   Unfortunately, VoIP connections are very susceptible to this type of condition and even a small amount of packet loss will result in poor voice communication.  Latency is the time that it takes for data packets to make it to their destination.  Every networking device on the traveled route introduces some delay.  Routers, in particular, can increase the delay depending on the amount of traffic and congestion on that particular hop (router).  Jitter is the variation in time between the arriving packets caused by network congestion, timing drift, or route changes.

• For packet loss try to ping out to a web site using a continues ping for an test (i.e. ping 68.142.226.33 -t). 
• For a test that could indicate problems with Internet congestion, latency and problem routers try to use the tracert tool.

High Latency can result in numerous voice or quality issues.  These issues can be temporary, resulting in an evening of terrible quality or can last longer, sometimes up to days or even weeks.  Some of the descriptions of the problematic voice symptoms that can be a result of high latency or network problems are:

• Talk-over or starting to speak before the other party is finished.
• Unusual delays in voice transmission.
• Missing parts of sentences or periods of dead silence where that portion of the audio drops, then comes back.
• Garbled audio, distorted audio and unusual sounds.

If you are experiencing occasional or frequent slow-downs, disconnects, or believe you might have general connectivity issues, including some of the above mentioned issues, then PingPlotter can help in diagnosing and troubleshooting many of these types of problems.  You can find an excellent description of the issues and problems that can occur and ways to diagnose them at PingPlotter's Tutorial.  The quality of your VoIP service is dependant on a stable broadband connection with enough bandwidth to carry your voice connections and computer needs.  If your ISP is telling you that the problem is on your side, not theirs, and you have checked out your LAN side, then this utility can help show problems out on the WAN side.