Packet loss will cause VoIP calls to have choppy, broken, robotic and distorted voice quality and may disconnect calls in progress. Streaming video may frequently pause, experience pixilation or take too long to download. Online gamers may suffer lag, stuttering and disconnects from gaming servers.

Packet loss may be caused by the computer, the Internet Service Provider (ISP) and anything in between. To solve the problem, the source of packet loss must first be found. This article is written to help the typical user locate the source.

Basic Troubleshooting Concepts

Expert troubleshooters systematically eliminate potential areas of trouble until the source is identified. For the performance problems discussed above, divide the Internet logically into three areas: 1) the ISP including the broadband modem/router; 2) the Local Area Network (LAN) which includes routers, switches and cabling inside the house or office; and 3) the computer. Now the goal is to determine which area produces the packet loss. Sometimes to learn the area producing the packet loss, areas that are not producing packet loss must be eliminated until only one area is left.

There is no correct order to eliminating each area. Usually, the areas that are the most suspicious or the easiest to eliminate are tested first. For purposes of a different IP endpoint other than a computer such as a VoIP telephone or an Internet TV, the IP endpoint is the 3rd logical area.

Testing the ISP and Internet Modem

This Packet Loss Test will determine whether the ISP and Internet modem may be the source of the problem. If it finds significant packet loss or latency at the IP address of the Internet modem, then the problem is between the last node of the ISP and the Internet modem. Before calling the ISP, check to make sure the modem is properly vented and any integrated wireless access point is turned off. Also, inspect all cables and connectors. Rebooting the modem is always a good idea. For cable modems, check the Signal Noise Ratio or SNR. For DSL modems, check the SNR and attenuation.

Is the Problem in the LAN?

To eliminate the LAN as the potential source, connect the PC directly into the Internet modem and test the application. If that solves the problem, then the LAN is the source. Start putting switches and routers back into service while testing the application each step of the way. When the problem returns, the source of the issue will be what just went back into service. It is important to remember that the source can be cables, jacks and/or connectors.

If the problem was not solved by plugging directly into the Internet modem, then the LAN has been eliminated as the source of trouble.

Is the Computer the Problem?

Eliminating the computer as the source of lost packets can be as simple as finding another PC on the same network and connected to the Internet in a similar fashion. Does it experience the same problem? If so, then the problem is something in common to both. If it does not experience the same problem, then the issue is with the computer or something unique to its connection to the Internet such as cable, connector or Ethernet switch port. Tech Support Forums offers the ability to describe problems in detail and get knowledgeable help for free on PC related matters.

If another computer is not available for this test, then the computer could be taken to another network to test the application. If neither of these actions are feasible, then eliminate the other areas first.

Drawing a Conclusion

Once 2 of the 3 areas have been eliminated, the problem is likely in the 3rd. If it is possible, test that assumption before hours are spent focused in the wrong area. Internet trouble can be particularly frustrating because of the many pieces required for proper operation, gaps in knowledge and faceless ISPs. However, most Internet problems can be solved with patience and perseverance.

If you are having trouble with your cable provided Internet circuit, your first step is to determine whether the problem is in the Internet Service Provider’s (ISP) network or specific to your location. The best tool for determining the location of Internet trouble is an IP Packet Loss and Delay Test Tool.

Let’s assume that you have used an IP Packet Loss Tool and found either significant latency or packet loss happening at your site. In other words, the problem is specific to your location. What should you do next? Check the signal-to-noise ratio (SNR or S/N) on the cable modem.

Signal-to-Noise Ratio

According to Wikipedia.org, “signal-to-noise ratio (SNR) is a measure used in science and engineering to quantify how much a signal has been corrupted by noise. It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise.”

An everyday example of SNR is listening to music in your car over road noise or other people talking. The louder the radio compared to the other noise in the car, the more clearly you hear the music. The same is true for your cable modem “hearing” the signal transporting your Internet traffic on your cable system. When the signal is loud compared to the noise, Internet communication happens at a faster speed with less packet loss. When the signal is not loud enough compared to the noise, speeds slow down causing latency. Packets may be lost, creating retransmissions of data packets and trouble with realtime applications such as Voice over Internet Protocol (VoIP) used by Vonage, Skype and Hosted PBX providers. In fact, any realtime application will suffer including video streaming from Netflix, Blockbust and others or any type of online gaming.

Good SNR Values for Cable Modems

SNR values for cable modems are measured separately for downstream and upstream signals. Downstream is the signal transmitting from the cable provider or ISP to the cable modem. Upstream is the signal from the cable modem back to the provider.

Each cable modem is a little different but typical good values are:

Downstream SNR – 30:1 or more
Downstream Power – -8 to 8db (decibels)
Upstream SNR – 29:1 or more
Upstream Power – less than 55db

Determining the Values for Your Cable Modem

Many cable modem configuration pages can be viewed at the internal address of 192.168.100.1. Refer to http://broadband.modemhelp.net/cable_modem_info/index.shtml and look up the specific make and model of your cable modem. This website will give the modem configuration page address of the cable modem and the SNR values for optimal performance. Just plug the address in your web browser and the page should come up. As you check your cable modem’s SNR values, remember that these values can fluctuate. If you are experiencing intermittent problems, check the values when experiencing trouble and compare to the values when all is well.

Improving the Cable Modem’s SNR Values

Cabling and connectors are the most common cause of poor SNR values. Inspect all cabling and connectors in line with the cable modem. There should not be any cable splices and the modem should be connected to the primary splitter entering your facility. In addition, the coax cable should not have any sharp bends. Repair any obvious problems and check the SNR values again.

If no obvious problems exist or repairs have not improved the SNR values, try moving the cable modem to the most immediate entry point in the facility. Attach it to the main feed, if possible. If the SNR values are good, then the problem is cabling in the facility. If the SNR values are still unacceptable, the problem is in the cable modem, outside cabling or equipment of the cable provider. You can try changing the cable modem, if you feel comfortable with that task. Otherwise, it is time to get the ISP/cable provider involved. You can report your findings of the SNR values.

Finding the Source of Internet Problems

Remember, to solve your Internet problems, you must systematically eliminate sources until you find the trouble. Randomly changing settings and replacing hardware will usually take more time and cause lots of frustration. The most logical first step is to determine whether the problem is inside or outside your facility. In other words, cable modem out versus cable modem inward. Before examining SNR values, use an IP Packet Loss and Delay Test Tool to quickly determine whether the problem is happening at your location or within the ISP. If it finds packet loss and/or latency at your site, it is now time to check the SNR.

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.