Πλοήγηση ανά Συγγραφέας "Ntallaris, Efstratios"

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  • Μικρογραφία εικόνας
    Τεκμήριο
    One-way delay computations for real time clock synchronization.
    (Τ.Ε.Ι. Κρήτης, Τεχνολογικών Εφαρμογών (Σ.Τ.Εφ), Τμήμα Μηχανικών Πληροφορικής Τ.Ε., 2019-04-08) Ntallaris, Efstratios; Νταλλαρής, Ευστράτιος
    Global time agreement and clock synchronization in a network of nodes are important issues which cannot be easily measured due to unstable delays and asymmetric paths. An important metric used to obtain an estimation of the network delays is round-trip time. Round-trip time is often for approximating one-way delay. Specifically, under a common, assumption that the path is symmetric, one-way delay is estimated as half the round-trip time. However, very often this estimation is not very accurate. For example, the path that the packet follows to reach its destination is not always the same as reaching its source. Even if the reverse path is symmetric, unstable delays due to operating system intervention, such as interrupts while the packet is waiting at the socket buffer, and/or asymmetries in the processing time of messages make this estimate inaccurate. The aim of this thesis is to review and implement more accurate one-way delay estimation methods. We implement Yoo and Choi’s technique that focuses on measuring round-trip time on both sides with a ping pong procedure to estimate one-way delay using network calculus. We compare divergence of this method to the common practice of using “half the round-trip time”. We also implement Aoki, Oki, and Cessa’s model to measure one-way delay variation by relating it to inter-packet delay, providing linear regression to remove the clock skew. Experiments were performed on CAN Bus with two AVR microprocessors, and on Ethernet with two Odroid XU4 connected to a fast Ethernet router. Results show that one-way delay can, be computed much more accurately than earlier approximations. Moreover, CAN network offers a much smaller one-way delay variation than Ethernet. Notice that further more complex experiments related to computing one-way delay (and especially round trip time) in the presence of other CAN bus traffic in a 6-node configuration have been reported independently at the APPLEPIES conference “Applications in Electronics Pervading Industry, Environment” in Pisa, Italy (September 26-27, 2018). Proceedings are to appear in Lecture Notes in Electrical Engineering.