Hardware Support for Clock Synchronization in Distributed Systems Martin Horauer University of Technology Vienna Department of Computer Technology

Objectives LANs (hardware) Internal Clock Synchronization: | C p (t) - C q (t) |   External Clock Synchronization: | C p (t) - t |   1ns distance10m 100m 1 km 1s1s 1ms precision, accuracy NTP LANs (software) GPS PLL LANs (hardware)

Requirements  Hardware Clock  small oscillator drift  good stability  fine grained  rate and state adjustable  Access to an external time reference  Timestamp Messages  tight coupling of timestamp mechanisms to the network medium Hardware Support OCXO or XO + Rate Synchronization Clock ASIC UTCSU

Software Timestamping C q (t) - C p (t)  T R – T S - [  -  ]  =  max -  min

Timestamping with Hardware Support

C q (t) - C p (t)  T R – T S - [  -  ]  =  max -  min

Hardware Support for Clock Synchronization

Clock Synchronization Packet Timestamping Preamble SFDDest. Addr.Src. Addr.TF User DataFCS Transmit TS FCS Transmit Timestamping: Preamble SFDDest. Addr.Src. Addr.TF User Data FCS Transmit TS FCS Receive TS Receive Timestamping: Transmit TS FCS Dest. Addr.Src. Addr.TF User Data Transmit TS FCS Receive CRC check: = FCSReceive TS

Hardware Support for Clock Synchronization

Prototype Implementation