Contention ratio

In computer networking, the contention ratio is the ratio of the potential maximum demand to the actual bandwidth. The higher the contention ratio, the greater the number of users that may be trying to use the actual bandwidth at any one time and, therefore, the lower the effective bandwidth offered, especially at peak times.^[1]

A contended service is a service which offers (or attempts to offer) the users of the network a minimum statistically guaranteed contention ratio, while typically offering peaks of usage of up to the maximum bandwidth supplied to the user. Contended services are usually much cheaper to provide than uncontended services, although they only reduce the backbone traffic costs for the users, and do not reduce the costs of providing and maintaining equipment for connecting to the network.

In the UK, an RADSL (Rate Adaptive Digital Subscriber Line) connection usually has a contention ratio between 20:1 and 50:1 per BT guidelines, meaning that 20 to 50 subscribers, each assigned or sold a bandwidth of "up to" 8 Mbit/s for instance, may be sharing 8 Mbit/s of uplink bandwidth.^[2]

In the US and on satellite internet connections, the contention ratio is often higher, and other formulas are used, such as counting only those users who are actually online at a particular time.^{[citation needed]} It is also less often divulged by ISPs than it is in the UK.^{[citation needed]} The connection speed for each user will therefore differ depending on the number of computers using the uplink connection at the same time because the uplink (where all the low bandwidth connections join) will only handle the speed that has been implemented on that line.

See also

• Quality of service

References

1. ^ UK OFCOM research report annex on broadband [1]
2. ^ A good account of the state of the issue in the UK is found in a 2004 OFCOM report on wireless internet.