Timing and synchronization are critical for many aerospace and defense systems. Historically TDM transport (e.g. E1/T1 SDH/SONET), dedicated wires (e.g. IRIG-B) and GPS are used for preforming the synchronization function in aerospace and defense systems. TDM transport enables frequency synchronization only, while the others enable frequency and time synchronization.
The requirements for accurate synchronization over packet networks in aerospace and defense systems are derived from many applications including:
- GPS backup or replacement
- Military cellular infrastructure
- Frequency or time distribution in:
- Vehicles – aircrafts / ships / cars
- Sensor synchronization
- Network performance monitoring
- Location services
Packet networks replace the TDM networks, thus eliminating the ability to relay on TDM transport for synchronization purposes.Due to cost and efficiency, dedicated wires are also being widely replaced. While GPS can deliver accurate frequency, phase and time, it introduces major problems. Among them, the need for GPS antenna, performance degradation due to poor weather conditions, vulnerability to jamming and spoofing, poor GPS signal reception in case of limited sky view, and requirement for high quality holdover oscillator. As a result of all those major limitations, in many aerospace & defense applications, GPS is no longer the solution of choice. The solution is to form a reliable packet network based synchronization, that delivers frequency, phase and time. This solution can replace the GPS or work simultaneously with GPS as a backup. The IEEE 1588 Precision Time Protocol, also known as PTP, can accomplish that.
IEEE 1588-2008 is a two-way packet-based communications protocol designed to precisely synchronize clocks to sub-microsecond accuracy. The PTP standard incorporates hierarchical master-slave architecture for clock distribution. Under this architecture an ordinary clock is a device with a single network interface and is either a master or a slave. A boundary clock (BC) is a device with multiple network interfaces. One of them acts as the slave clock and the other acts as the master. A Transparent clock (TC) is a device that measures the time taken for PTP message to transit the device and provides this information to clocks receiving this PTP message.
The root timing source is called the grandmaster. The grandmaster is the prime master which transmits synchronization information to the other devices on the network. The synchronization information is timestamp carried by PTP UDP or Ethernet packets. The protocol defines events and general PTP messages. Event messages are messages with timestamp. An accurate timestamp is generated at both transmission and receipt. General messages do not require accurate timestamps. The PTP event messages are: Sync, Delay Req, PDelay Req and PDelay Resp. The PTP general messages are: Follow Up, Delay Resp, PDelay Resp Follow Up, Announce, Management and Signaling.
IPClock’s standard compliant PTP products have been widely deployed by equipment vendors in various markets and applications. The products leverage IPClock’s innovative clock recovery technology and provide high immunity to packet switched network impairments. The Timing accuracy in IPClock’s products is better than ±1µsec, and frequency accuracy is better than 16ppb on none-PTP aware, 10-switch GbE network under ITU-T G.8261 conditions. IPClock offers standalone products as well as IP core products. All IPClock products are adaptive to network impairments, enable zero touch approach, and eliminate the user’s need to configure servo in accordance to the network conditions. IPClock’s products enable significant cost reduction without compromising on clock synchronization accuracy, taking advantage of IPClock support of low cost oscillators. IPClock’s off-the-shelf products are designed to support future enhancements and field upgrades.