I am Richard Clegg a Senior Research Fellow in the Department of Electronic & Electrical Engineering at UCL. I gained a PhD in Mathematics and Statistics from the Univeristy of York in 2005. My current research interests centre around networks: mainly computer networks but anything where things are associated with other things can be viewed as a network. My ErdÅ‘s number is three.

This site has been on the web in some form or another continuously since late 1994. You can find the previous version of the site here and the previous previous version here.

Along with Keith Briggs I run the Mathematics of Networks meetings. These (approximately) yearly meetings have been running since 2003.

I organise the networks seminars for the networking group at EE in UCL. Please contact me if you're interested in speaking, attending or suggesting a speaker.

When not in work I enjoy diving (I am a diving instructor with the British Sub Aqua Club) and brewing.

My research interests include:

- Network topologies
- Statistical nature of traffic
- Distrubted and overlay networks
- Software defined networks

In general I'm interested in:

- Data analysis, machine learning
- Statistically rigorous analysis
- Graph theory
- Queu(e)ing theory

I have acted as a reviewer for a number of journals including:

- Journal for Selected Areas in Communications Systems
- Physica A
- Performance Evaluation
- Computer Communications
- IEEE Network
- Electronics Letters
- Transactions on Parallel and Distributed Systems
- Computer Networks
- Networks and Spatial Economics
- The Journal of Complex Networks
- New Generation Computing

I am on various Technical Program Committees including:

- SIMPLEX -- Simplifying Complex networks.
- UKPEW -- the UK Performance Engineering workshop.
- AICT -- the IEEE Application of Information and Communication Technologies
- PMECT -- Performance Modeling and Evaluation of Computer and Telecommunication Networks
- SNS -- the Workshop on Social Network Systems
- EWSDN -- the European Workshop on Software Defined Networking
- NetSciCom -- the IEEE International Workshop on Network Science for Communication Networks

This talk is an updated version of this talk at QMUL. The difference is two slides at the end which provide insight into the sampling issues related to the data.

The key message of this paper is that TCP/IP does not work in the real world as it is generally taught. The idea of a connection when one side sends data as fast as possible controlled by loss to fill a pipe is not what happens in the real world.

This work joins the two papers

A longitudinal analysis of Internet rate limitations (INFOCOM 2014)

and

On the relationship between fundamental measurements in TCP flows (ICC 2013)

The talk analyses passive traces with the aim of explaining what are the root causes of bandwidth on a connection. Theoretical results show that in equilibrium an unconstrained TCP flow has a bandwidth proportional to 1/RTT and 1/sqrt(p) where p is probability of packet loss. The experimental results here show different results, however. In particular, while the relationship with RTT is upheld, the relationship with loss is not found. A strong relationship with the length of flow is found. Longer flows have faster throughput in proportion to sqrt(L) where L is the length of the flow in packets.

A follow up analysis looks at the causes of throughput. It is found that less than half of flows are governed by loss. Flow bandwidth is very often governed by applications -- for example you tube deliberately throttles traffic so that users do not download too far ahead. Some flows are governed by operating system restrictions which do not scale window sizes. Some flows are governed by middleboxes which manipulate the window size. It is these restrictions which, the network studied, are the primary method which restricts bandwidth on connections.