Modestly demonstrating your technical expertise and industry experience lends creditability and trust. Stand your ground and make a case for your goals. Keep a clear head and rely heavily on logic and fact. You will generally get right down to business.
Keep the main things the main things! This is not the same as detail, which requires proper attention. Be clear, direct and consistent in your responses. Miscommunication happens easily and often with language barriers and industry jargon. Verbalize details in a couple of different ways to see if everyone still agrees. Use visuals, sketches, and drawings to clarify and document details.
ITM/PTTI addresses advances in GNSS technology, precise time
The meeting will likely delve into greater detail than you expect as an American. Start with the overall, and then go into the details, following a systematic approach, including costs, numbers, etc. Expect to work in the metric system. Do what you committed to do. Do it as quickly as possible! Jeff Hannah 0 Comments 2 Share it on: The low administration effort for this protocol is also significant.
As redundant masters are also supported, a PTP domain automatically configures itself using the best master clock algorithm and is also fault-tolerant, but the most important characteristic remains synchronism in the microsecond and sub-microsecond range.
The biggest interest in deterministic Ethernet is currently found in automation, particularly for motion control applications. Many drive manufactures are equipping their devices with Ethernet interfaces, but now have problems synchronising all connected drives as precisely as possible over the network. Several groups in this industrial sector have decided to use this protocol in their Ethernet based field busses.
Also, solutions by Beckhoff and Jetter are being developed to ensure time synchronisation with this protocol or a similar approach.
Precise Time and Time Interval
But interest is not only coming from the automation industry. Increasing demand is growing out of test and measurement - the origin of the timing protocol. Also initial projects have been started to use IEEE for military applications. Other groups which show interest are coming from telecommunications and electrical power distribution IEC -Communication networks and systems in substations. Before we focus on initial results, here is a short overview of the protocol function. The working of the protocol The basic function is that the most precise clock on the network synchronises all other users.
A clock with only one network port is termed an ordinary clock. There are two clocks, Master and Slave. In principle any clock can perform both the master and slave function. The precision of a clock, or to be more exact the time source used to set it, is categorised by the protocol in classes strata.
Here the highest class is an atomic clock which has the stratum value 1. The selection of the best clock in the network is performed automatically using the best master clock algorithm. The precision of the synchronisation depends heavily on the network and the components used in the network. For this reason the transition over less deterministic components such as routers and switches, is also made possible by the protocol through use of the boundary clock.
There is also a management protocol available for administration and configuration of clocks in the network. PTP is based on IP multicast communication and is not restricted to Ethernet, but can be used on any bus system that supports multicasting.
Timekeepers: How the World Became Obsessed With Time
Multicast communication offers the advantage of simplicity: IP address administration does not need to be implemented on the PTP nodes. Every slave synchronises to its master's clock by exchanging synchronization messages with the master clock. The synchronisation process is divided into two phases. First the time difference between master and slave is corrected - this is the offset measurement. During this offset correction, the master cyclically transmits a unique synchronization SYNC message to the related slave clocks at defined intervals by default every two seconds.
This sync message contains an estimated value for the exact time the message was transmitted. The mechanism provides for precise synchronisation determined by the transmission and reception time of PTP messages as sent over the specific network sector. The master clock measures the exact time of transmission, TM1 and the slave clocks measure the exact times of reception, TS1.
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In a second message, the follow-up sync message, the master sends the exact TM1 transmission time to the slave clocks. On reception of the sync message and for increased accuracy, on reception of the corresponding follow-up message the slave clock calculates the correction offset in relation to the master clock taking into account the reception time stamp of the sync message. The slave clock Ts must then be corrected by this offset. If there were to be no delay over the transmission path, both clocks would now be synchronous. The second phase of the synchronisation process, the delay measurement, determines the delay or latency between slave and master.
For this purpose the slave clock sends a so-called 'delay request' packet to the master and, during this process, determines the exact time of transmission of the message, TS3. The master generates a time stamp on reception of the packet and sends the time of reception, TM3, back to the slave in a 'delay response' packet. From the local time stamp for transmission, TS3, and the time stamp for reception provided by the master, TM3, the slave calculates the delay time between slave and master.
The delay measurement is only performed irregularly and at larger time intervals random value between 4 to 60 seconds by default than the offset measurement. In this way, the network, and particularly the terminal devices, are not too heavily loaded. However, a symmetrical delay between master and slave is crucial for the delay measurement and its precision, i.
Using this synchronization process, timing fluctuations in the PTP elements especially the protocol stack and the latency time between the master and slave are eliminated. PTP reference architecture As previously mentioned, what is so special about the architecture is the separation of the time-critical part which is implemented in hardware and the protocol itself, and is decoupled from hard real-time conditions - the software part. The hardware unit comprises a highly precise real-time clock and a time stamp unit TSU to generate the time stamp. The software part implements the actual IEEE protocol with the binding to the realtime clock and the HW time stamp unit.
The diagram below illustrates a co-operating of the hard- and software component of a IEEE synchronisation element. The intention behind this architecture is to offer operating system-independent modelling of the software component.
In order to achieve this, we introduced three layers with different abstraction level. The figure shows the interaction of the individual layers.
Precise Time – Global Exhibitor
The highest layer implements PTP for the synchronisation of clocks in a network and can be used on different communication elements PC, switch, router, etc. Here resides the actual intelligence located for synchronising the individual communication elements. This should allow protocol transfer to other platforms without too much interference into their functionality. The protocol dispatchers ensure the atomic execution of functions during an individual process. Communication between the protocol and the OS Abstraction Layer has been realised by a queue and three well defined interfaces. The middle layer encases operating system-dependent functions to which one must adapt, if necessary.