High Bandwidth, Low Network Performance?

In the mail titled “Network Problem Caused by P2P Applications in Student Halls”, officer of PolyU Student Halls of Residence (in short, SHR) warned hallmates that using peer-to-peer (P2P) applications will result in termination of network socket. This triggered the many complaints from hallmates, who need these P2P applications in daily life. Let’s see what P2P is and how will it affect the network as well as hallmates’ daily life.

BitTorrent, an example of peer-to-peer (P2P) application

BitTorrent, in short BT, is both the protocol and the name of the P2P file distribution application created by programmer Bram Cohen that makes it possible to massively distribute files without incurring the corresponding massive consumption in server and bandwidth resources.

The BT protocol achieves this goal by breaking down a file into smaller fragments. Peers download missing fragments from each other and upload those that they already have to peers that request them. The protocol is 'smart' enough to choose the peer with the best network connections for the fragments that it’s requesting. To increase the overall efficiency of the ad-hoc P2P network temporarily created to distribute a particular file, the BT clients request from their peers the fragments that are most rare. The file fragments are not usually downloaded in sequential order and need to be reassembled by the receiving machine. It is important to note that clients start uploading fragments to their peers before the entire file is downloaded. Sharing by each peer therefore begins when the first complete segment is downloaded and can begin to be uploaded if another peer requests it. This scheme is particularly useful for trading large files. This is contrasted with conventional file serving where high demand can lead to saturation of the host's resources as the consumption of bandwidth to transfer the file to many requesting downloaders surge.

It seems that it is a great technology that everybody should use it. In fact, BitComet is elected to be one of the 21st century inventions. BT has bright future, but SHR is going to forbid it.

Are Peer to Peer (P2P) applications allowed to use in Student Halls?

After the mail was issued, we send a letter to the office of SHR via e-mail to ask for the details of the action taken by SHR. The reply was as follow:

… Please note that hall network cannot support P2P software. In fact, P2P softwares cause a high data packet rate problem rather than data transfer rate problem. Such high data packet rate problem (abnormal packet rate) will dominate most of the hall network and affect other network users … Residents are therefore advised not to use any P2P applications without thoroughly understanding their impact on the network … Please understand that the measure is for the welfare of all residents. Thank you for your understanding.

But in fact, it is not always true. To prove this we have logged some data from P2P software. The average traffic is not more than 5KB/s and it is far less than what ITS defined limit. It is because Information Technology Services Office (ITS) had already blocked the bandwidth usage of P2P applications without any notice. Here are some average data rates of some commonly used P2P applications:

BitComet (BT): ~10KB/s

Emule: ~1-2KB/s

WinMX: totally blocked

How can such data rate cause ‘High Bandwidth’? Some download actions from websites result more packet rate transfer than those P2P applications. Try to download any software from download.com, you will discover the transfer rate is more than 10KB/s, always. Normal use of P2P applications will not harm the network. Therefore, we seek for further clarification.

The reply from SHR is rather disappointing. It claimed that all users using hall network should agree not to produce excessive traffic. For protecting the normal operation of the Network, the Hall or ITS will suspend the user's access privilege to the Network with immediate effect and without prior notice when deemed necessary. The spokesman quoted the hall network regulation section 2.2.iii to prove their rights.

The Hall Network user shall NOT produce excessive network traffic (such as programmatic and continuous download of on-line journals and information of any type from internet), massive emailing for whatever reasons,broadcasting, developing or distributing material of obscene and pornographic nature which will violate the laws of Hong Kong.

Does the use of P2P applications include in the above regulation? The ‘programmatic and continuous download’ mentioned above is too vague to define. If a hallmate uses ICQ around the clock, does he violate the above regulation? ICQ occupies bandwidth continuously and it is a P2P application, thus using ICQ violated the above regulation. Yet I think the regulation does not intend to block ICQ users; the regulation is not clearly defined only.

SHR kept its stance firmly, making us hard to follow the complaints. We then asked the officers on G/F, they said they could do nothing about the action as all actions were taken by ITS. When we tried to ask ITS for further details, the hall website suddenly add the followings in the Q&A section in the late October:

Are Peer to Peer (P2P) applications allowed to use in Student Halls?

Yes, P2P applications with proper license are allowed to use in Student Halls. However, when upload/download materials, students must ensure that their actions do not infringe the copyright laws. Any communication which violates applicable laws and regulations, including but not limited to those related to copyright, data privacy and transmission of obscene and indecent materials, is not allowed. Residents concerned will have their IT access suspended for a week without prior notice.

It is totally contradicting from the letter issued at the very beginning. If the above is the final answer of SHR, we are safe to use P2P applications. Of course, we hope it is the final one.

Written by Shivan Raptor