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Bandwidth Usage FAQ

What is bandwidth?

Bandwidth is the maximum amount of data that can travel a communications path in a given time. Bandwidth is typically measured in bits per second. If you think of the communications path as a pipe, then bandwidth represents the width of the pipe that determines how much data can flow through it all at once.

What is inbound and outbound traffic?

Inbound traffic is data that is received by your computer from another computer. Outbound traffic is data that is sent from your computer to another computer.

Why has Carnegie Mellon Computing Services established bandwidth usage guidelines?

Previous to establishing guidelines, the performance of our network link had slowed to where normal traffic, dataflow, and usability had been degraded, often to the point of being an outage. We discovered that a significant amount of the traffic from Carnegie Mellon to the commodity Internet was caused by a relatively small number of computers. In an effort to free our clogged commodity Internet connection, Computing Services implemented the Network Bandwidth Usage Guideline in February 2003. The purpose of the guideline is to define reasonable use of network resources.

Why were the bandwidth usage guidelines changed?

When the guidelines were initially implemented, only outbound traffic was a problem. Because of this, the initial guideline set limits on outbound usage. The result was a welcome decrease in outbound traffic. However, a recent increase in inbound traffic resulted in a need to establish limits there as well. With the latest iteration of the guideline, outbound bandwidth limits were increased and limits for inbound traffic were established.

Exactly what are the limits for bandwidth usage at Carnegie Mellon?

The limits are as follows:



Inbound OR Outbound Usage Limit

Wired /Wireless Network Bandwidth Usage


No individual service or system running on the wired network should use more than 10 gigabytes (10GB) of bandwidth per day (inbound OR outbound).

To review the appropriate guideline in its entirety, read the Network Bandwidth Usage Guideline.

How is bandwidth usage monitored?

The total amount of bandwidth to and from a particular computer is monitored on a daily basis and follows the machine's hardware address (MAC address).

Note: A hardware address (also referred to as a "MAC" or "Media Access Control" address) consists of twelve hexadecimal values, sometimes in a continuous string, other times separated by dashes or colons (e.g., 00-00-0C-03-F3-55 or 00000C03F355). This address is unique to each network device on a computer--no two computers will have the same MAC address. Computers having more than one network card (e.g., one for wireless and one for wired) will also have one MAC address for each
network card.

What actions are taken to enforce the Network Bandwidth Usage guideline?

Users who are found to exceed the bandwidth guidelines are notified via email and are given an opportunity to correct the problem before network access is suspended. Users are considered to have exceeded the guidelines for the first time only if the average of their bandwidth usage over a five-day period exceeds the guideline. Users are then given two additional warnings each time their usage on a single day exceeds the guideline limits. Between each notification is a 72 hour (three days) "grace period" within which the user is expected to correct the problem that is causing the excessive use of bandwidth.

After a user has been notified and given opportunities to bring bandwidth usage under the establish limits, network access is suspended the next time bandwidth limits are exceeded within a single day. For details of the entire notification and enforcement process, read How Computing Services Monitors and Enforces Network Bandwidth Usage.

Is there any way to gain an exception to the usage guidelines?

Owners of servers or services who exceed the usage guideline and feel they have legitimate cause to do so, may request an exemption; in rare cases an exemption may be granted. In all cases, solutions for fair use of the Commodity Link bandwidth will favor those services that support the research and educational goals of the university. To request an exemption from the bandwidth guidelines, complete the the Bandwidth Exemption Request Form. The Network Security team will review your request and determine if an exemption should be granted.

What types of files require greater amounts of bandwidth to download or upload?

The size of specific files varies, but as an example, the size of a 5 minute long MP3 music file would be approximately 5 MB. The size of a full length DVD movie might be as large as 2.5 GB. A simple email message could be as little as 2K. Program and image files vary greatly in size. When possible, check the size of the file before you download.

Note: Remember that Carnegie Mellon University policy prohibits the distribution of materials owned by anyone other than the person engaged in such distribution (whether officially copyrighted or not) without the permission of the owner. The distribution of copyright protected files without the permission of the copyright holder is illegal. For more information, review the Copyright Violation Guideline in its entirety.

How can I monitor my own bandwidth usage?

You can monitor your bandwidth usage by visiting the Bandwidth Enforcement web page. The bandwidth web page shows the previous 5 days usage on a per day basis. Note that it does not provide up-to-the minute usage details.

How can I reduce my bandwidth usage?

Adhere to the following advice as appropriate to your computing practices:

  • Turn off or uninstall the filesharing component of peer-to-peer applications such as Kazaa, Morpheus, Limewire, Bittorrent, BearShare, skype, abcast, etc. Even if you aren't downloading much, it doesn't mean that a file sharing program isn't running as a server and sharing files with the world. Also, simply turning off or disabling file sharing does not always turn off ALL file sharing. The safest bet is to uninstall peer-to-peer file sharing programs. If you need help, the University of Chicago provides detailed instructions for disabling file sharing for many popular peer-to-peer clients.
  • Many services allow you to limit the number of computers that can be connected to the server at any given time. Limiting the number of simultaneous connections allowed might help to reduce the amount of data that other people retrieve from your computer.
  • Some programs may allow you to specify the amount of bandwidth that is available to the application (probably measured in bits per second). If your program has such a setting, try reducing the amount.
  • Monitor the amount of data transmitted by your service (FTP, Peer-to-Peer, etc.). Many programs provide status or usage reports that will tell you how much data is transmitted by that service in a given amount of time. You can also monitor your bandwidth usage by visiting Computing Services Bandwidth Enforcement web page.
  • Protect your machine from vulnerabilies Whether you're running special services or not, make sure your computer is not vulnerable to viruses or attacks. If you download software from a web site, be careful of your source. The software may be couterfeit or illegal, and even if the software download failed, it may have resulted in a virus, worm, some spyware, or trojan infiltrating your machine. Always install the latest patches or upgrades for your operating system or programs that allow people to retrieve data from your machines. For specific recommendations, refer to Securing Your Computer.

Last Updated: 07/16/10
Last Reviewed: 8/19/11