IEEE 1588 Conference and Plug-fest Winterthur, October 10-12, 2005 Using PTP for Synchronizing Legacy Networks Heiko Gerstung, Martin Burnicki, Udo Maltzahn Meinberg Radio Clocks

Synchronizing Legacy Networks Overview Motivation Todays Solutions Differences between PTP and NTP Solutions Combined PTP GMC/NTP Time Server with GPS Using PTP to synchronize a “slave” Time Server with a GPS based Time Server Comparing NTP and PTP Clients

Synchronizing Legacy Networks Motivation Time Synchronization over Network Links with an accuracy of <1ms Use an already existing stable time source for PTP networks Provide a high-precision time using standard network infrastructure (standard cable systems) Maximize the distance between GPS antenna location and time server location (e.g. underground installations)

Synchronizing Legacy Networks Today‘s Solutions Network Time Synchronization: Network Time Protocol (NTP) Simple Network Time Protocol (SNTP)

Synchronizing Legacy Networks Today‘s Solutions Single Node Synchronization: using dedicated hardware references GPS Longwave Radio Frequency Standards High Quality Oscillators IRIG

Synchronizing Legacy Networks Main Differences between PTP and NTP Network Infrastructure NTP: LAN/WAN,Unicast,Broadcast,Multicast PTP: LAN,Multicast Time Sources NTP: multiple servers, weighted average PTP: One single GMC at a time Accuracy NTP: under 1ms possible, 1-10ms typical in LAN, <100ms over the Internet PTP: Sub-Microsecond Security NTP: Symmetric Keys, Public Keys PTP: Work In Progress

Synchronizing Legacy Networks Main Differences between PTP and NTP Different Target Audiences: PTP Applications with high demands on accuracy Relative synchronization Dedicated Networks NTP Applications with low/medium demands on accuracy Synchronization using absolute time (UTC) Corporate LAN/WAN and Internet

Synchronizing Legacy Networks Applications Time Server talking both PTP and NTP  both NTP and PTP clients use the same time source  reducing equipment Using PTP for synchronizing NTP servers  using PTP as a „time backbone“ for NTP infrastructures  reduce network related time error by using PTP instead of NTP for synchronization between two NTP servers

Synchronizing Legacy Networks Solutions

Synchronizing Legacy Networks Time Server talking both PTP and NTP both NTP and PTP clients use the same time source, e.g. GPS, IRIG, Long Wave radio… all NTP and PTP clients are using comparable time stamps Eliminates the need to purchase, install, configure and maintain two different systems for each client community

Synchronizing Legacy Networks Combined PTP GMC/NTP Time Server

Synchronizing Legacy Networks Combined PTP GMC/NTP Time Server

Synchronizing Legacy Networks Combined PTP GMC/NTP Time Server Design Overview: The 50 Mhz clock of the TSU is derived from the internal Oscillator of the GPS receiver This oscillator is constantly disciplined using the GPS signal At start-up the absolute time of the TSU is set to the GPS time The TSU has an additional input with which the nanosecond part can be zeroed. The PPS output of the GPS receiver is connected to this pin and is used to reset the ns part once the internal oscillator of the GPS receiver has warmed up By using this mechanism, the timestamp offset from the GPS PPS is <20 ns

Synchronizing Legacy Networks Applications

Synchronizing Legacy Networks Using PTP for Synchronizing NTP Servers Combined PTP GMC/NTP servers use PTP to achieve a highly accurate inter-server synchronization („time backbone“) and NTP to provide synchronization to „leaf nodes“ (which are only compatible with SNTP/NTP) Provide special purpose outputs (10Mhz, PPS, IRIG, E1/T1) without the need to install GPS receivers

Synchronizing Legacy Networks Using PTP for synchronizing NTP Servers

Synchronizing Legacy Networks Using PTP for Synchronizing NTP Servers Design Overview: At start-up the system waits until it is synchronized by PTP (PTP_SLAVE state has been reached) Now the system clock is set to the time of the TSU Afterwards, NTP is started. The NTP daemon has been modified with an additional refclock driver NTP reads the TSU‘s time by using a kernel device driver The TSU looks like a hardware reference clock to the NTP daemon

Synchronizing Legacy Networks Comparing NTP and PTP Clients

Synchronizing Legacy Networks Thank You Questions? heiko.gerstung@meinberg.de http://www.meinberg.de