Is the Signal to Noise Ratio (SNR) of Your Cable Modem Slowing Down Your Internet Speed?
By James Waldrop
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. I’ve included some information on how to find and use one of these tools at the end of this article.
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.
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).
Good SNR Values
SNR values 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 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. 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 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
Before examining SNR values, the first step in troubleshooting Internet problems is always determining the location of the trouble. Use an IP Packet Loss and Delay Test Tool to quickly determine whether the problem is happening at your location or within the ISP. The packet loss tool at the link above is free as it is 100% sponsored by HostMyCalls. HostMyCalls uses this tool to help its customers with their Internet connections. It is one of the top reasons why HostMyCalls delivers the best Hosted PBX voice quality of all VoIP Providers on the Internet.
Signal To Noise Ratios
Wikipedia Article – http://en.wikipedia.org/wiki/Signal-to-noise_ratio
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