As part of a broader organisational restructure, data networking research at Swinburne University of Technology has moved from the Centre for Advanced Internet Architecture (CAIA) to the Internet For Things (I4T) Research Lab.

Although CAIA no longer exists, this website reflects CAIA's activities and outputs between March 2002 and February 2017, and is being maintained as a service to the broader data networking research community.

Incast congestion control


Transmission Control Protocol (TCP) carries the bulk of all traffic across most common types of data networks, including those in today's high-speed, low-latency datacenters. A key problem faced by commodity datacenters is incast congestion. Client queries are distributed by front-end nodes over TCP connections to multiple back-end servers, and the replies coming back tend to be highly correlated in time. This correlated reply traffic causes microsecond-timescale congestion (which we call microburst congestion) in the multi-gigabit Ethernet switch buffers along the return path.

TCP reacts far too slowly to packet losses in the context of high-speed and low RTT networks. Consequently, any packet loss caused by incast (microburst) congestion will stall the higher layers' data gathering pipeline (potentially for many tens of milliseconds) and unnecessarily increase client response times as a result.

We propose to evaluate emerging reactive (e.g. faster control loops) and proactive (e.g. burst de-correlation) techniques for managing incast TCP congestion events.

Project Goals

  • To identify and statistically characterise microburst congestion events common in data centres
  • To create a real and/or simulation testbed capable of emulating different types of microburst congestion events
  • To empirically evaluate at least one (and possibly more) TCP modification(s) for reducing (and hopefully eliminating) the occurrence of TCP-triggered microburst congestion events in the emulated testbed environment.

Project Outcomes

In September 2013 we released a FreeBSD9-based VirtualBox VM appliance containing NS-3 and a version of NSC (Network simulation cradle) patched to work with the actual TCP stacks from FreeBSD9 and FreeBSD-HEAD. This enables researchers to perform simulations of incast topologies using the same TCP algorithms as implemented in real FreeBSD systems.

Program Members

cisco logo

This project has been made possible in part by a gift from The Cisco University Research Program Fund, a corporate advised fund of Silicon Valley Community Foundation, for a project titled "Exploring possible mitigation for incast TCP congestion in data centres".

Last Updated: Sunday 5-Jan-2014 07:01:58 EST | Maintained by: Lawrence Stewart ( | Authorised by: Grenville Armitage (