NTP servers are generally supplied as 1U high rack mountable network devices. They obtain an accurate time from an external time reference, such as GPS or radio, and provide an accurate timing resource for a computer network. NTP or Network Time Protocol is a protocol designed for distributing time to client computers over an IP network. The protocol is UDP based and as such requires the TCP/IP network infrastructure to be installed.
Hardware InstallationStratum 1 NTP time servers rely on an external timing reference to obtain accurate time. Various external timing references are available. Options may vary with the installations regional location.
GPS (Global Positioning System) is a popular timing reference. The advantages of a GPS reference are that it is highly accurate and can be utilised anywhere in the world. A typical GPS NTP server installation can synchronise to within a few microseconds of UTC time. The disadvantage of GPS is that ideally a roof-mounted external antenna is required with a good view of the sky. The maximum cabling distance between an NTP server and GPS antenna is governed by the quality of coax utilised. Relatively low-quality coax, such as RG58 can be used to around 50m. Higher quality coax, such as LMR200 can be utilised to around 80m. Very high quality coax, such as LMR400 can be utilised to around 200m. Additionally, GPS amplifiers can be used to amplify the GPS signal and extend cable runs. It is also good practise to install a surge suppressor to externally mounted GPS antennas, to protect against the possibility of damage caused by lightning strikes.
Local radio time references are available in many countries. Radio time references tend to be local to the country of origin and maybe neighbouring countries. The advantage of radio is that generally a good signal can be obtained indoors, close to the NTP server installation. However, radio time services are less accurate than GPS and reception areas are regional. A typical radio NTP server installation can synchronise to within a few milliseconds of UTC time. A number of factors can affect radio reception, including: locating the radio antenna underground or in a basement; locating the antenna inside a metal cage (including metal cladding) and locating the antenna close to electrically noisy equipment.