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.

Synthetic Packet Pairs (SPP) - Tool for passive round trip time measurement


Regular and frequent measurements of round trip time (RTT) are important in test networks or overlay networks (e.g. to evaluate network protocols), and they are also becoming increasingly important in operational networks, such as the Internet (e.g. to assess the quality of service for highly interactive real-time applications). Active probing techniques are possible but problematic. The extra packet traffic imposed by active probes along a network path can modify the behaviour of the network under test. In addition, estimated RTT results may be misleading if the network handles active probe packets differently to regular IP packets.

In contrast, SPP provides frequently updated RTT measurements using IP traffic already present in the network. SPP measures the RTT between two measurement points without requiring precise time synchronisation between each point. SPP accurately measures the RTT experienced by any application's traffic without needing modifications to the application itself or the routers along the path. In addition, SPP works with applications that do not exhibit symmetric client-server packet exchanges (such as many online multiplayer games) and applications generating IP multicast traffic.

This website provides a standalone open source implementation of SPP in C, which works on Linux and FreeBSD.

SPP is also in the FreeBSD ports tree under benchmarks/spp, and post-v0.3.6 development is now publicly available on Bitbucket.

Program Members

(Alumni: Lutz Mark, Thuy Nguyen, Brandon Tyo, Amiel Heyde, Atwin O. Calchand, David Hayes)
Last Updated: Friday 13-Nov-2015 13:39:46 EST | Maintained by: Sebastian Zander ( | Authorised by: Grenville Armitage (