Network Traffic Control Policy

Background

Pembroke College, like many other colleges, operates a network traffic control policy. The purpose of our policy is to ensure that sufficient of our finite total network capacity is available to each user. With no controls in place, records show that the top 10 students in terms of network usage are responsible for 90% of the total traffic.

In recent years we have operated three schemes to attempt to control this minority of users:

  • Peer-to-peer detection. Peer-to-peer software used to be almost exclusively used for illegally downloading and distributing copyright CDs and DVDs. It is now used for legitimate purposes so it is no longer appropriate to prohibit its use. At the same time, the major media companies (eg Sony, AOL Time-Warner) who hold most of the relevant copyright have developed more sophisticated methods of detecting users who are distributing illegal material (the ‘pushers’), and stiff financial penalties, so most colleges rely on receiving alerts from outside, rather than attempting to detect it themselves.
  • Peer-to-peer networks depend on re-distribution of data to others after receipt.  This necessitates an implied offer by the downloader to make University bandwidth available to a third party – an offer that no user is entitled to make.
  • Escalating warnings for high traffic. Firstly a warning was sent by email, then a severe warning in person, and finally a disciplinary hearing with the Tutor, which often resulted in disconnection or a drastic speed reduction for several weeks.

 

It was clear that many students found it difficult to predict the impact on their traffic quota of certain activities, and receiving a warning the following day was too late to be helpful. The current system allows us to set multiple quotas using different thresholds for different time slots, and to warn by automatic email or by reducing network speed, or both, if any quota is exceeded.

Different colleges operate policies aimed at controlling different types of traffic. The University charges colleges for what approximates to ‘Internet’ traffic. There is no explicit charge for traffic within College or within Cambridge. However, this charge is only a small part of what it costs to provide ethernet connections to student rooms. By far the greater part is the cost of implementing the network infrastructure – cabling, routers etc – and regularly upgrading it as demand rises inexorably.

So while some colleges operate policies aimed at their bill from the University for ‘Internet-only’ traffic, Pembroke’s policy is aimed at total network traffic – intra-College, CUDN, JANET and Internet. And while other colleges may attempt to recover the cost, our preferred solution is to prevent the problem by monitoring and control.

The scheme for academic year 2015-2016
  • Each student is allocated a quota of 10GB per day of intra-Cambridge traffic (ie to and from addresses ending in “cam.ac.uk”), plus 10GB per day of internet traffic.
  • This quota applies to the total of incoming and outgoing traffic, to and from the sum of all computers registered to that student.
  • Traffic is calculated approximately every 10 minutes on a rolling basis.
  • If a student’s network traffic over the preceding 18 hours is at such a rate that the daily quota is likely to be exceeded, an ‘Early Warning’ email is sent. No other action is taken.
  • If traffic over the preceding 24 hours exceeds the daily quota, a different email is sent, and a more severe speed reduction is imposed – this time to 100 kbit/s. Experience in previous years of imposing speed reductions down to 30 kbit/s after disciplinary action shows that this still allows email clients to retrieve and send (though large attachments will cause some delay), and browsers will be able to view most web pages. Several students who experienced problems at 30 kbit/s were found to have network-hungry background processes running on their computers – in itself a possible reason for repeatedly going over quota.
  • As soon as a subsequent 10-minute calculation no longer shows a problem for that student, the speed restriction is removed. The process is entirely automatic and – failures excepted – will operate the same at night and at weekends as during the working week.
  • It is up to each student to decide how best to use his/her daily quota – for academic work, or for a 24-hour Skype voice call or a 10-hour Skype video call, or for downloading the equivalent of many CDs of music from iTunes, or for watching several of the latest episodes of a favourite soap using video-on-demand. Note that these illustrations are alternatives – using the whole of a day’s quota on any one of them will leave no quota left for any other activity.
  • All students are also provided with accounts for use in Pembroke’s computer rooms, where this quota does not apply. The facilities in these computer rooms, and in connected systems across the University, are designed to satisfy the academic IT needs of any student. Not everyone has a personal network connection, after all – it’s certainly very useful but it remains non-essential.

 

Appeal

The College will always consider appeals if the system is thought to have calculated usage incorrectly. This usually involves making a detailed analysis of a given day’s traffic and an inspection of the relevant computer. Students are advised to consult the IT Department in the first instance (by email to help@pem.cam.ac.uk, by telephone to 01223 339804 or in person to room U10). They are also happy to discuss any problems a student has in keeping within quota, as there are technical solutions in most cases.