An Ideal Quota System for Multi-Tenant (Cloud) Data Centre Networks


Cloud data centres typically sell processing by the second, storage by the GB and network capacity by the Gb/s; plus sometimes data volume sent and/or received as well. However, each node on the network is shared in highly variable proportions so the ideal unit of the quota would be congested-bytes, ie. the amount of bytes of traffic that arrive at a queue when it is too long. Such a quota system should keep queues very short and encourage virtual machines to migrate to locations that spread the load evenly througout the network.

A highly practical design of such a quota system has been designed. However, it needs to be implemented and tested. It is based on the idea of a congestion policer that has been used in other scenarios. A congestion policer does not monitor the amount of traffic, it monitors the amount of congestion caused by traffic. The policer would replace the current scheduler under the hypervisor, which arbitrates access to the network. 


The goal of this project is to implement a congestion policer within a hypervisor and to test its ability to control a data centre network. The project builds in stages, so that some success can be assured at each step. Step #1: test a congestion policer arbitrating a single network interface; Step #2: Test a network with congestion policers at every incoming network interface (which are the only bottlenecks); Step #3: If a really successful student completes all that, the case where there may be bottlenecks at any switch in the network could be tackled.

Learning outcome:

  • Xen or KVM hypervisor internals 
  • Kernel programming
  • Cloud business models
  • Internet traffic and congestion control techniques
  • Traffic test scripting techniques
  • Data Centre protocol designs: DCTCP (Data Centre TCP), ECN (Explicit Congestion Notification), Ethernet, VXLAN, Layer-3 switching, iSCSI etc.
  • Writing a top-flight research paper


  • Good programming and scripting skills
  • Good grounding in operating systems
  • Good grounding in network protocols and technologies
  • Willingness to break new research ground and take risks


Communications Systems/Media

Contact person:

Bob Briscoe,