Cable Modems

This document addresses common performance-related questions and issues that new owners of uBR900 series cable modems may encounter. For information about other aspects of configuring and using uBR900 series cable modems, consult the following documents:

A. When your uBR900 cable modem connects to your service provider's network, a special set of parameters governing the download and upload speeds is sent to the cable modem.

A. Assuming that your cable modem is connected to your service provider's network and is online, you can log into your uBR900 cable modem and issue the following commands to view the maximum upload and download rates.

Note: These commands are case-sensitive.

Router# show controller cable-modem 0 Mac state | incl Downstream_Rate 
Max Downstream Rate: 2000000 
Router# show controller cable-modem 0 Mac state | incl Upstream_Rate 
Max Upstream Rate: 512000 
Min Upstream Rate: 0 
Router#

In this case, the uBR900 cable modem has a maximum download rate of 2,000,000 bits per second and a maximum upload rate of 512,000 bits per second.

A. There are no configuration commands that can be used to increase the service provider-assigned upload or download rate on a uBR900 cable modem. The Cisco Technical Assistance Center (TAC) and other Cisco personnel do not have the ability to change these parameters either.

Note: Most cable service providers would view an attempt to alter the provisioned upload and download limits on a cable modem as a theft of service. In addition, most major cable service providers have measures in place to instantly detect this sort of activity.

A. Bring this issue up with your service provider. There may be a source of cable system noise that is affecting your service, or your local cable segment may be overutilized and it might be time for your cable service provider to add more bandwidth capacity to your area.

A. All models of the uBR900 cable modem are capable of downloading data from the Internet at speeds of over 10 Megabits per second, which is the maximum capacity of the Ethernet port. This means that it is highly unlikely that your download speeds would be affected by a performance bottleneck in the uBR900 cable modem.

If you are experiencing slow download rates the most likely reason is that the particular Internet site you are trying to access is busy, or because the cable service provider's network is experiencing congestion.

A. If the uBR900 cable modem can be configured for routing mode, then any number of workstations may connect to the Internet through the cable modem; however, you need to make special arrangement with the service provider or run Network Address Translation (NAT) in order to use routing mode.

If your uBR900 cable modem is in default bridging mode, then there are no configuration commands that can be used to increase the number of PCs or workstations allowed to connect to the service provider's network. The Cisco Technical Assistance Center (TAC) and other Cisco personnel do not have the ability to change these parameters either.

Note: Most cable service providers view an attempt to alter the provisioned maximum allowed number of PCs allowed to connect through a cable modem as theft of service. In addition, most major cable service providers have measures in place to instantly detect this sort of activity.

A. Try the following procedure:

1. Disconnect the old PC from the uBR900 cable modem.

2. Power cycle your uBR900 cable modem (in other words, remove the power connector for ten seconds and then plug it back in).

3. With the second PC turned off, connect the second PC to the uBR900 cable modem.

4. Turn on the second PC.

The reason that you may have to perform this procedure is that the uBR900 cable modem always remembers the identity of the first PC plugged into it after the modem is powered on. If the cable service provider has provisioned the uBR900 cable modem to only allow one PC access to the Internet, then it only allows this first PC through. The only way to make the uBR900 cable modem forget about the first PC is to power cycle it or to reset it using the reload command.

If this procedure does not work and your new PC still cannot get Internet access, then it may be that the cable service provider's equipment has remembered your old PC's identity and only allows the old PC access to the Internet. If this is the case, call your service provider and ask them to clear their equipment's record of your old PC. Alternatively, you can disconnect all PCs from your cable modem and wait about four hours and the service provider's equipment automatically forgets about your old PC. At this stage, connect your new PC to your cable modem and proceed online.

If you plan to regularly swap PCs, then you may need to speak with your service provider about changing the service parameters for your cable modem to allow multiple PCs Internet access.

One other factor to consider when swapping PCs is that some service providers maintain records of the MAC address and name of PCs that you are allowed to connect to your cable modem. If your service provider is in this category, then you may always need to call your cable service provider before being able to swap an old PC for a new one.