IEICE Electronics Express, Vol.4, No.23, 717–723 One-way delay estimation without clock sychronization Dongkeun Kim a) and Jaiyong Lee Department of Electrical and Electronic Engineering, Yonsei University, 120–749, Seoul, Korea a) neurok@yonsei.ac.kr Abstract: One-way delay measurement requires end-to-end hosts to be synchronized in clock time on network. However, there is the relative or absolute difference between two clock times by reason of clock offset, clock skew and so on. In this paper, we present a theorem, methods and simulation results of one-way delay and clock offset estimations between end-to-end hosts. The proposed theorem is a relationship between one- way delay, one-way delay variation and round-trip time, and we show that the estimation error is mathematically smaller than a quarter of round-trip time. Keywords: clock synchronization, one-way delay, clock offset, clock skew Classification: Science and engineering for electronics References [1] D. Mills,“Improved algorithms for synchronizing computer network clocks,” IEEE/ACM Trans. Netw., vol. 3, no. 3, pp. 245–254, June 1995. [2] V. Paxson,“On Calibrating Measurements of Packet Transit Times,”in Proceedings of ACM SIGMETRICS, June 1998. [3] G. Almes, S. Kalidindi, and M. Zekauskas,“A One-way Delay Metric for IPPM,” RFC2679, IETF, Sept. 1999. [4] C. Demichelis and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” RFC3393, IETF, Nov. 2000. [5] J.-H. Choi and C. Yoo, “One-Way Delay Estimation and Its Application,” Elsevier Computer Communications, vol. 28, no. 7, May 2005. [6] A. Varga, OMNeT++: Discrete Event Simulation Environment. [Online] http://www.omnetpp.org [7] S. Floyd and V. Jacobson, “Random Early Detection Gateways for Con- gestion Avoidance,” IEEE/ACM Trans. Netw., vol. 1, no. 4, pp. 397–413, Aug. 1993. 1 Introduction One-way delay measurement requires a guarantee of clock synchronization between end-to-end hosts on network. However, the hosts have the relative or absolute difference in clock time by reason of clock offset, clock skew and clock adjustment. Although there are many other issues [1, 2], we focus on c  IEICE 2007 DOI: 10.1587/elex.4.717 Received October 26, 2007 Accepted November 09, 2007 Published December 10, 2007 717