The glossary is your easy-to-use reference to familiarize yourself with the most common terms and definitions for time systems, clocks, and time reference.


AFNORAssociation français de nermolisation (AFNOR) is the French national organisation for standardisation.
AFNOR NFS 87-500AFNOR NFS 87-500 is a standardized French time code similar to IRIG, but it contains additional information about day, month, day of month, and year. All of this time information is submitted every second with the aid of a modulation frequence of 1kHz.
ASCIIThe American Standard Code for Information Interchange (ASCII) is a 7-bit character encoding scheme for numbers, letters and control characters used in PCs with DOS. Windows-based PCs use the ANSI character encoding. All numbers and letters of the ASCII code are integrated within the ANSI code from positions 32 to 127.
BroadcastIn a network, Broadcast means a message will be sent to all members of the network.
Cat 5/6/6ACat5/6/6A are the most commonly used cables for networks these days. They differ in their maximal working frequency:
Cat5 up to 100MHz
Cat6 up to 250MHz
Cat6A up to 500MHz
CESTMESTThe Central European Summer Time (CEST) is used as the summer daylight saving time in most countries
of central Europe. The difference to UTC is +2 hours.
CETThe Central European Time (CET) is the official time in most countries of central Europe. The difference to
the Coordinated Universal Time (UTC) is +1 hour. The difference of the Central European Summer Time
(CEST) to UTC is +2 hours.
Clock changeClock change means the change from Daylight Saving Summer Time to winter time and vice versa.
Crystal oscillatorA crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating quartz
crystal to create an electrical signal with a very precise frequency.
Current LoopFor data communication, a Current Loop is a serial communication interface that uses current drops instead of voltage changes to transmit data.
DCF 77The time signal transceiver DCF 77 is a long-wave radio in Mainflingen (D), which is used by most radio-controlled clocks in western Europe to synchronize to an accurate time and date. The amplitude of the 77.5kHz carrier signal is reduced for 0.1s or 0.2s to 15% on the beginning of the seconds 0-58. The resulting binary-coded second stamps contains the time and date data. As a special case, the last second of every minute is marked with no carrier reduction to introduce a new minute.
DCF-FSKDCF - Frequency Shift Keying (DCF-FSK) is a proprietary protocol to transmit DCF frames with FSK-modulation. Instead of the reduction of the amplitude by normal DCF transmission, the frequency of the carrier signal is decreased from 1.25kHz to 1kHz during the second mark. The content of the submitted frames is exactly the same as DCF.
DecibeldBDecibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base ten of the ratio of the two quantities.
DHCPWith the Dynamic Host Configuration Protocol (DHCP) the network configurations of a client, such as addresses, subnet masks, gateways, and DNS-addresses, can be set automatically from a server. This will normally be proceeded by a boot sequence.
DNSThe Domain Name System (DNS) is a service within a network, which translates domain names meaningful to human like into a IP address.
EthernetLAN-TechnologyEthernet is a technology for cable-based realization of a LAN. It is frame-based and enables data exchange between all members of the network. There are 10 Megabit/s, 100 Megabit/s (Fast Ethernet), 1-10 Gigabit/s (Gigabit-Ethernet) specified as transfer rate.
FirewallA Firewall is a system that supervises data traffic in a network and can block data based on send or destination address, currently used services, and other rules. In this manner it blocks unauthorized access while permitting authorized communication.
FirmwareFirmware is a software embedded in an electronic device to control this device.
GalileoGalileo is a global satellite-based navigation system built by the European Union (EU). It is similar to GPS or GLONASS.
GLONASSGLONASS is a global satellite-based navigation system built by the Russian government. It is similar to GPS or Galileo.
GMTGreenwich Mean Time (GMT) is a term originally used to refer to solar time at the zero meridian in Greenwich (UK). In the past it was used as worldtime, but it has been replaced by UTC. GMT is the same as UTC. Today this term is often used for the Western Europe time zone (WEZ/WET, UTC+0)
GPSNAVSTAR GPSThe Global Positioning System (GPS) is a globally available, satellite-based system for navigation. GPS was designed in 1970 by the United States Department of Defence (USDD)
GUIA Graphical User Interface (GUI) is the part of a software that enables the communication between humans and machines with graphical elements.
HTTPThe Hypertext Transfer Protocol (HTTP) is a networking protocol for data transfer. It is the foundation of data communication for the World Wide Web. HTTP is mainly used to load websites into a browser.
HubA Hub is a central allocator within a network. It sends received data via all other ports to all attached members.
I2CTwo-Wire Interface (TWI)The Inter-Integrated Circuit (I2C) is a serial databus developed by Philips mainly used for interdevice communication over a short distance with a small bandwidth. There are two signals used for communication: Serial Clock Line (SCL) and Serial Data Line (SDA). There are four specified modes with the following maximal clock frequencies: standard mode (100kHz), fast mode (400kHz), fast mode plus (1MHz), and high-speed mode (3.4MHz).
Impulse LineDepending on the number of impulse side clocks, a transmitter current can be connected to an impulse line and operated simultaneously. The impulse side clocks are controlled by the configurable number of pulses per minute (60, 8, 5, 2, or 1 pulse per minute).
IP addressAn Internet Protocol address (IP address) is an address in networks based on the Internet Protocol (IP). Every participant of the network is assigned an IP address, with which it is addressable. One IP address can stand for one or a group of devices, and a device can have more than one IP address.
IP-XYThe IP class (International Protection Rating) specifies usability of electrical equipment for different environmental conditions and the protection of users against potential damage. The code always consists of the two letters IP followed by two digits. The first digit indicates the level of protection against the ingress of solid objects. The second digit specifies the protection of the equipment against harmful ingress of water.
IRIG Time CodeThe Inter Range Instrumentation Group Time Code (IRIG Time Code) is group of serial time codes, which uses a continuous stream of binary data to transmit data like time and date. The name of the IRIG format contains one letter and three digits, each of which specifies a characteristic of the Code.
IRIG-AIRIG-A is a time code defined by the Inter Range Instrumentation Group (IRIG). Every second a frame with 1000 bits of data is transmitted.
See also: IRIG Time Code
IRIG-BIRIG-B is a time code defined by the Inter Range Instrumentation Group (IRIG). Every second a frame with 100 bits of data is transmitted.
See also: IRIG Time Code
LANA Local Area Network (LAN) is a cable-based network for internal data exchange. A LAN is always limited to a geographical area such as an enterprise, school, or laboratory.
LONLON (called LonWorks) is a fieldbus which is used for the automation of various function within buildings.
MAC AddressEthernet ID (Apple)
Airport ID (Apple)
Wi-Fi Address (Apple)
Physical Address (Microsoft)
The Media Access Control Address (MAC Address) is a global unique identifier assigned to a network interface. The MAC Address has the length of 48 bits and is stored permanently in the hardware of the network interface.

Main-clockMaster ClockThe main clock is the clock within a system of clocks, which controls and synchronises all slave clocks. The
main clock takes its time from an accurate time source.
MOBALine©MOBALine© is a two-wire interface designed for fail-safe data communication and can supply the connected devices. There are mainly slave clocks attached to MOBALine©.
MSF 60The time signal transceiver MSF-60 is a long-wave radio station in Anthorn (GB) that transmits time and date information with a 60kHz carrier and ON-OFF-amplitude modulation. Every new minute the carrier signal is switched off for 500ms. All other 59 seconds the carrier signal is switched off for 100ms or 300ms. The resulting second marks carry the binary-coded time and date information. All the information is transmitted once every minute:
Bit      Value
1-16    dUT1
17-24  Year (0-99)
25-29  Month (1-12)
30-35  Day (1-31)
36-38  Day of the week (0-6; 0 = Sunday)
39-44  Hour (00-23)
45-51  Minute (00-59)
58       Daylight savings (0 = no / 1 = yes)
MulticastIn a network Multicast means that the same message will be sent to a defined group of members within the network.
NATNetwork Address Translation (NAT) is a collective term for different methods that automatically exchange address information within a data package through others to connect two networks. There are two main methods: Source-NAT changes the sender address, Destination-NAT the one of the receiver.
Networktime Serversee NTP Server
NTPThe Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems on packed-based networks with variable latency.
NTP serverAn NTP server delivers a reference time in a network to its clients.
Optical fiberOptical linkAn optical fibre is a fibre that acts as a waveguide to transmit light between the two ends of the it. 
OscillatorAn oscillator is a module that generates electrical oscillation.
PoEPower over Ethernet (PoE) technology describes a system to pass electrical power safely, along with data, on Ethernet cable. The supply voltage is 48V with a maximum current of 350mA.
Polarized ImpulsesPulses which are put out at equal intervals with the same polarity.
PortA port is an external interface or connection on a device to connect it with another device through a cable (LAN, USB, serial) or to extend it with a card (PCI) to have additional functions.
In networks the port is software connection on computers by usage for different services such http, NTP, ftp, telnet.
PPMA Pulse Per Minute (PPM) is an electrical signal that very precisely indicates the start of a minute.
PPSA Pulse Per Second (PPS) is an electrical signal that very precisely indicates the start of a second.
PTPThe Precision Time Protocol (PTP) is a high-precision time protocol for synchronization used in measurement and control systems residing on a local area network. Different from NTP, focus is on higher accuracy and local networks. Implemented in hardware, PTP can achieve an accuracy in the range of nanoseconds and with software a few microseconds.
Puls per minutePPMsee PPM
Puls per Secondsee PPS
Radio controlled clockA radio controlled clock is a clock, which can receive a time signal from a time signal transmitter and
synchronise to the submitted time.
Radio transmissionIn telecommunications, radio transmission is the process of sending and receiving data without the need of
a cable.
RALRAL is a color-matching system used in Europe. Every color has its own unique number allocated.
Redundant SystemWith redundancy a system will be protected against failure. For this reason the system is often supplemented by a second similar system. In case the first system fails, the second system ensures full functionality.
RJ ConnectorA Registered Jack (RJ) is a standardized physical network interface. Common connecters are RJ45 (network) or RJ11 and RJ12 (telephone).
RouterA router connects or separates multiple networks. For this purpose the router analyzes the incoming data packets for its destination address. Depending on the result, the data packet will be blocked or forwarded.
RS-232EIA-232This is a standard for a serial binary interface. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pin-out of connectors.
The main characteristics are:
  • The transfer is done in words often as ASCII encoding.
  • It's a bit-serial interface, the bits are transmitted one after another on one line.
  • The data transfer is asynchronous, i.e. there is no common clock between the sender and receiver.
  • It's an asymmetrical voltage interface since the information is transmitted via a single wire per direction with different voltage levels.
  • The connector used today is commonly a 9-pin D-Sub connector.
RS-422EIA-422This is a standard for a differential symmetrical serial interface. The main difference to RS-232 is that data are transmitted differentially over two data wires. There is also the possibility of having multiple receivers for one transmitter (multidrop network).
RS-485EIA-485This is a standard for a differential symmetrical serial interface. Compared to RS-422, the RS-485 holds an additional protection against shorts and allows the connection of multiple transmitters and receivers (multipoint).
SelfsettingSelf-setting indicates that a clock that has a connection to a time signal (e.g. MOBALine) sets itself to the corresponding time.
SlaveclockA slave-clock is a clock which will be synchronised by the main-clock to the time of the main-clock.
Slaveclock lineIn a clock-system a slave-clock line is a path to control a group of connected slave-clocks. 
SNMPSimple Network Management Protocol (SNMP) is a standard protocol to manage IP-based devices such as routers, switches, servers, work stations, printers, and so on. The devices can be managed, controlled, and monitored by a central station.
SNTPThe Simple Network Time Protocol (SNTP) is a simplified version of NTP for synchronizing the clocks on computer-based systems. Due to the simplification, SNTP is less accurate than NTP.
SSHSecure Shell (SSH) is a network protocol that allows data to be exchanged using a secure channel between two network devices. It was developed to detach non-encrypted protocols like telnet.
Stepwise SecondA stepwise second is a second hand that jumps from second to second.
StrataStrata indicates the number of devices from the time source to the time server. Normally the time source has the value 1. Each device between them increases the value with n+1. The maximum allowed is 16, which means it is not synchronized or there is no reachable time source available.

Sweeping second

Means that the second hand moves continuous without any leaps.
SwitchA Switch or a network switch is a computer network device that connects network segments. It is responsible for the distribution of data packets in a network. The switch can do a direct link between connected devices, provided it has access to the ports of the receivers. To do so, it uses the MAC addresses in the submitted data packets.
Switching relaysA relay is an electrically operated switch which can be controlled with a small electrical current over
distance. For this reason the relay has an electromagnet.
SynchronisationSynchronization means adjustment of data between two devices.
TCPThe Transmission Control Protocol (TCP) is one of the core members of the Internet Protocol Suite. It's a convention for exchanging data between computers. Compared to UDP, TCP is an connection-orientated network protocol. It provides a connection between two endpoints in a network. With this connection, data can be exchanged in both directions. Many application protocols such as HTTP, FTP, or telnet need a permanent connection channel for data communication.
TCP/IPTransmission Control Protocol / Internet Protocol (TCP/IP) refers to a family of network protocols. Because of their great importance to the internet, they are also known as an internet protocol family. To identify the computers in the network, each device has its own IP address through which it is reachable. TCP or UDP is used for transporting the data.
TelnetTelnet is a character-orientated communication protocol for transferring data between two devices. It is typically used for remote device control. Since the communication is not encrypted, it is displaced by SSH.
TFTPThe Trivial File Transfer (TFTP) is file transfer protocol known for its simplicity. Generally it is used for automated data transfer of configuration or boot files between machines in a local environment, e.g. loading a new firmware.
TimeserverA time server is a server that reads the actual time from a reference clock and distribute it to its clients.
TimesynchronisationTime synchronization means the adjustment of local time with a external time-source. 
ToETime over Ethernet (ToE) means the distribution of time over Ethernet.
Twisted PairTwisted Pair cable is a type of wire in which two conductors (the forward and return) are twisted together. This is an additional protection against electromagnetic interferences.
UDPThe User Datagram Protocol (UDP) is one of the core members of the Internet Protocol Suite. It is a connectionless network protocol. As opposed to TCP, there is no logical connection between the endpoints. Common network applications that use UDP are NTP, DNS, TFTP, VoIP, and streaming media applications.
UnicastThis marks the transfer of a message between a transmitter and a single receiver.
UTCUTC is a time standard by which the world regulates clocks and time. Most computer-based systems use this time.
WANA wide area network (WAN) is a computer network that covers a large area.