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What is a Network Time
Server?
The general descriptive term
'network time server' can apply to any instance of the Network Time
Protocol (NTP) server software running on a computer/server platform.
The product term, 'Network Time Server' generally applies
to a network appliance (rack or tray mount), that acquires time
from an external source, maintains time in its internal local clock,
and supplies time to a connected network using the network time
protocol NTP. TrueTime's NTS-150, NTS-200 and TimeVault™ are
'Network Time Servers'.
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Why should
I synchronize my network?
Many processes that occur within the network
depend on accurate network timing. Further, more and more applications
that support eBusiness and other enterprises are dependent on conducting
their functions over the Internet. In summary:
| Network Operations |
Applications |
| Log file accuracy, auditing &
monitoring |
Transaction processing |
| Network fault diagnosis and recovery |
Software development |
| File time stamps |
Email |
| Directory services |
Legal and regulatory requirements |
| Access security and authentication |
Password and digital ID |
| Distributed computing |
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| Scheduled operations |
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| Real-world time values |
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Network operations typically require the most accuracy,
on the order of one to 10 milliseconds. Network synchronization
provides a solid infrastructure and helps avoid costly downtime
problems.
Applications typically require time stamping accuracy on the order
of 100 milliseconds to 10 seconds. Sometimes it is difficult to
appreciate why one second can make much difference. Usually it is
because it is necessary to establish the order of events.
For a complete discussion see the white paper, The
Importance of Network Time Synchronization (PDF - 53k)
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What's
important in selecting a Network Time Server?
As in selecting any product or service
there can be a long list of attractive features and TrueTime network
time servers are no different. However, the list usually can be
reduced to a few critical features that make a world of difference
in installing and using the server, as well as some that may seem
important but are not.
| Important
features to consider: |
| 100Base-T Ethernet |
Having a time server that supports
both 10Base-T and 100Base-T accommodates modern networks as
well as ones destined to be upgraded at some future point in
time. If your network is going to grow you want your time server
to keep pace with it. |
| Redundant time sources |
A dedicated network time server
keeps the network synchronized to a Reference Clock Source.
Redundancy provides the confidence you need to know that your
network has accurate time. The NTS-200 relies on GPS for time.
If for any reason GPS is not available it will revert to retrieving
time from other NTP servers. The TimeVault relies first on GPS,
then ACTS dialup, then on other NTP servers. |
| Time cross check |
There is no substitute for automatically
checking the system clock against a third party clock. If the
time is out of bounds, you are notified automatically. |
| NTP request throughput
and accuracy |
While the ability to synchronize
tens of thousands of clients is catchy marketing, the real test
is in the ability of the time server to handle coincidental
peak loading. Performance, or the ability to service a high
volume of NTP requests and maintain accuracy and availability,
is the key. |
| Easy to use: Keypads,
SNMP, Browser interface |
Keypads make for quick and easy
setup.
SNMP provides peace of mind.
Browser interface makes remote access intuitive. |
| Antenna cabling |
GPS synchronized time servers
require a cable to connect the antenna on the roof to the server
inside the building. Consider the cable type, cost to run and
length. TrueTime servers use inexpensive cable and we offer
a GPS Down/Up Converter for the especially long cable runs. |
| GPS receiver location |
Keep in mind the location of the
GPS receiver. After lightning strikes the antenna you will find
it cheaper to replace a GPS antenna than one with a combined
antenna and receiver. TrueTime GPS receivers reside in the chassis
and are protected from the elements. |
| Window Antenna/Single Satellite Timing |
In urban canyon environments where satellite visibility can be limited or when roof access is restricted, the automatic, single satellite timing mode provides accurate time with intermittent satellite coverage and can also track satellites using a window mounted antenna. |
| |
| Less important features:
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| GPS receiver accuracy |
The key attributes of the GPS
receiver in a network time server differ from those of other
more precise time and frequency devices. An NTP client's ability
to synchronize to the network time server is largely limited
by the network and the oscillator on the client server, workstation,
or PC. One to 10 milliseconds for client synchronization accuracy
is typical for servers and workstations. PC's are doing good
to get to 100 milliseconds. For this reason, the Coordinated
Universal Time (UTC) accuracy of the GPS receiver in a network
time server is not a critical specification and more often than
not is misleading with respect to the accuracy the customer
will observe in his own network. Having the GPS receiver accuracy
below the one millisecond level is all that is important. |
| Ancillary outputs |
TrueTime network time servers
are optimized to provide IT professionals synchronization over
a network using NTP. Our experience has shown that when more
timing outputs are added such as 1PPS, IRIG-B, 10 MHz, etc.,
the cost and complexity increases. As with any device, the more
complex, the higher the likelihood of failure somewhere in the
system. We have found that the majority of our customers prefer
reliability to outputs they have no real need for. |
| Price |
If you are considering a dedicated
network time server you must have compelling reasons to do so.
Part of your decision should be a consideration of product lifecycle
and the level of effort to install and maintain the server.
If you desire an easy-to-install, reliable, low maintenance
time server that can keep pace with your network for years to
come, you will find TrueTime network time servers to be the
best available. |
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What
is the difference between the NTS-200 and TimeVault™?
First, let's establish the similarities:
- GPS input: Acquire
time from the GPS satellite constellation.
- NTP Server: Synchronize
local servers, routers, and workstations with NTP running over
either 10 or 100 baseT networks.
- NTP Client: Obtain
time from local redundant servers or external public time servers.
- High Performance NTP:
Internal NTP Time Service architecture is very fast, supporting
the highest NTP request rates available on a 100baseT network.
- Excellent Remote Management:
They support SNMP MIB II variables and an HTML control and status
internal 'page'.
The NTS-200 Network Time Server
is intended to support Network Synchronization requirements where
'trusted time' is not a particular issue. It is the baseline product,
offering excellent cost/performance.
TimeVault™ is targeted to
eBusiness and enterprise customers that require not only accurate
time, but also 'trusted time'. It is uniquely able to synchronize
to any of three remote Reference Clock Sources; GPS (as per NTS-200),
the ACTS dialup directly to the National Institute of Standards
and Technology (NIST), and public NTP servers. When tracking GPS
or getting time from ACTS, TimeVault's time cross check processor
continually validates the selected source against a designated NTP
server (public or private). TimeVault has additional security access
features (password protection, function lockout, etc).
Click here for a detailed side by side comparison of the NTS-150,
NTS-200 and TimeVault
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TimeVault™
uses three Reference Clock Sources -- Why?
If accurate network synchronization
is of very high importance to your organization and a critical function
of network operations, TimeVault offers redundant reference clock
sources. If for any reason the GPS fails from events like antenna
failure, cable disconnect, lightning strike, etc. the unit will
dial the NIST ACTS time service for the time. If ACTS cannot be
reached then it will revert to user specified NTP servers. Users
are notified via SNMP of all changes in reference clock status.
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What
is ACTS?
It stands for Automated Computer Time
Service. It is a service provided by the National Institute of Standards
and Technology, NIST, in Boulder, Colorado. With this service, TimeVault
executes a time transfer over a dialup telephone link to UTC(NIST).
Further information can be found at http://www.bldrdoc.gov/timefreq/service/acts.htm
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What
does ACTS cost?
The only cost is of the telephone call
to (303) 494-4774 in Colorado or (808) 335-4721 in Hawaii.
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Who
are your customers for Network Time Servers?
Please see the partial
list.
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What is the Network Time Protocol?
The Network Time Protocol (NTP) is a UDP
protocol for IP Networks. It was designed to synchronize the clock
on client machines with the clock on network time servers. But NTP
is just the protocol. The implementation of NTP requires separate
client and server applications. TrueTime's NTS-200 is an excellent
example of the server implementation of NTP. The client application
runs on workstations such as Windows or Solaris. Using NTP packets,
the client and server exchange time stamp data, ultimately setting
the clock on the client machine very accurately to that of the time
server.
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Is
NTP an open source protocol?
Yes. It was developed at the University
of Delaware by Dr. David Mills; under contract to DARPA. Version
1 was distributed in 1985. Version 4 is current. Internet
RFC 1305: "Network Time Protocol (Version 3), Specification,
Implementation, and Analysis"; David L. Mills; March 1992;
is a 106 page description. Version 4 adds some secure authentication
features so, RFC 1305 is still an excellent guide.
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Where
do I get RFC 1305?
RFC 1305 is available in html
or many
other formats including PostScript and PDF.
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How
does NTP work?
Superficially, NTP is a software daemon
operating in a client mode, server mode, or both. The initial distribution
is for UNIX servers and workstations. There are many secondary distributions
for Windows NT, 2000 and other platforms. Regardless of the platform
and operating system, it always works over UDP/IP.
The purpose of NTP is to reveal the offset of the client's local
clock relative to a time server's local clock. The client sends
a time request packet (UDP) to the server which is time stamped
and returned. The NTP client computes the local clock offset from
the time server. But network latencies, the need to prioritize multiple
servers, and the requirement to be self-healing leads to a fairly
complicated, yet robust algorithm.
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Does
NTP supply the time to a computer or server?
Technically no. The purpose of NTP
is to reveal client clock offset; not deliver time. The operating
system (OS) delivers time. Processes within the NTP application
program use this offset to adjust the client clock. Since the hardware
implementation of computer clocks and the protocol to control them
varies from computer to computer; it is necessary to download computer
specific clock control software. If NTP is bundled with your computer
OS, this has already been done. If you are downloading and installing
NTP on a non-NTP aware OS; you will need to read the install instructions
carefully regarding this point. This really only applies to installing
NTP UNIX. The various third party NTP clients have clock control
built in.
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How
accurate is NTP?
It depends on how many hops occur between
client and server, and other network latency inducing factors. Over
Wide Area Networks, WANs, 10 to 100 milliseconds is typical. Within
a Local Area Network, LAN, 0.5 to two milliseconds is typical. However,
when operating an NTS-200 or TimeVault with GPS, their internal
accuracy is one microsecond. The NTS-200 and TimeVault synchronize
all of their clients to within 0.5 to ten milliseconds (assuming
the clock setting kernel permits this).
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NTP
is a UNIX daemon. What does that mean?
In the UNIX world, core operation programs
that operate in the background while other applications are running
are called daemons. NTP is such a daemon and as such,
operates without attention while a UNIX platform performs other
tasks.
By definition...
Daemon: <operating system>
/day'mn/ or /dee'mn/ (From the mythological meaning, later rationalized
as the acronym "Disk And Execution MONitor"); A program
that is not invoked explicitly, but lies dormant waiting for some
condition(s) to occur. The idea is that the perpetrator of the
condition need not be aware that a daemon is lurking (though often
a program will commit an action only because it knows that it
will implicitly invoke a daemon).
For example, using ITS to write
a file in the LPT spooler's directory would invoke the spooling
daemon, which would then print the file. The advantage is that programs
wanting files printed need neither compete for access to, nor understand
any idiosyncrasies of the LPT. They simply enter their implicit
requests and let the daemon decide what to do with them. Daemons
are usually spawned automatically by the system, and may either
'live forever' or are regenerated at intervals.
Unix systems run many daemons, mainly to handle requests for services
from other hosts on a network. Most of these get started as required
by a single real daemon rather than running continuously.
Examples are cron (local timed command execution), rshd (remote
command execution), rlogind and telnetd (remote login), ftpd, nfsd
(file transfer), lpd (printing).
Daemon and demon are often used interchangeably, but seem to have
distinct connotations. The term "daemon" was introduced
to computing by CTSS people (who pronounced it /dee'mon/) and used
it to refer to what ITS called a dragon.
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Where
can I get NTP daemons?
Determine if your operating system
has NTP built into it. If it does, then it is a simple matter of
either enabling the NTP capability or taking advantage of it.
Versions of operating systems that do not have NTP "built-in"
will require locating either freeware or shareware daemons. TrueTime's
NTP Client Software Resource page is an excellent repository.
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How
many clients can I serve?
The NTS-150, NTS-200 and TimeVault™
have demonstrated the ability to handle tens of thousands of clients
and still maintain millisecond level time stamp accuracy. And even
greater numbers of clients can be served with a slight degradation
in the time stamp accuracy.
While you probably won't have this many clients, it is important
that this level of performance be available to handle peak NTP packet
request loading conditions that can occur, and still maintain desired
synchronization accuracy and packet throughput.
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Do
I have to run UNIX computers to use NTP?
No. The NTP client/server software
runs in the NTS-150, NTS-200 and TimeVault™. Client software
is still needed on machines wishing to make use of the server. Client
software is much simpler. Third party NTP client programs are available
to run on any Windows (95/98, NT, 2000) or Linux platform. Selection
assistance is available from TrueTime, or at TrueTime's
NTP Client Software Resource page.
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I
am already running NTP on a UNIX general purpose server. Why do
I need your network appliance?
In brief, it comes down to the accuracy,
reliability, security and ease of use of the dedicated network time
server. If time is important to your network operations or accurate
timestamps are considered an important element of your eBusiness
participation, you can't afford to leave time synchronization in
the hands of a generic server. There is a risk of invalid time when
a new program is installed, the hard disk crashes, the power cycles,
or the clock resets.
Further, these network time servers have
convenient front panel time displays and controls. They have remote
management tools, like SNMP and an easy-to-use HTML interface you
can operate from a conventional browser, anywhere on the net.
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How
do I synchronize my network?
There isn't a quick answer to this.
TrueTime offers many resources to assist in this process:
In summary, follow these steps:
- Break your organization down into Timing
Dependent Entities (TDEs): departments, groups, subnets, and/or
functions having discernibly unique synchronization requirements.
- Determine the timing requirements for each
TDE: legal, operational, or mandated.
- Select the worst case scenario.
- Select Reference Clock Sources: i.e. UTC(NIST),
UTC(USNO), GPS, and synchronization methodology to satisfy the
worst case scenario.
- Establish hierarchical network timing topology:
| Stratum
0 |
Reference Clock Sources (like GPS) |
| Stratum
1 |
Primary Time Servers - the NTS-200
or TimeVault™. |
| Stratum
2 |
Secondary Time Servers; generally application
servers, NOS servers, and/or routers. |
| Stratum
3 |
Workstations, servers, Controlled Timed
Devices (CTDs). |
| Stratum
4-15 |
Further expands synchronization of workstations,
servers, and CTDs. |
- Install NTP client/server application
software:
Operating Systems, variants of UNIX,
Linux, Windows 2000, and others come with NTP. NTP can be
downloaded free from http://www.eecis.udel.edu/~ntp/
Many 3rd party workstation client software
packages are available. See TrueTime's NTP
client software resource page.
In many instances, workstations will
synchronize, on boot, with the NOS server, i.e. with Novell
ipx/spx; and later versions of MS Exchange Server.
- Develop a methodology for synchronizing
non-NTP synchronized CTDs.
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What
is Stratum?
The term "stratum" is
referenced in both the network world and the telecommunications
world.
Dr. David Mills, University of Delaware, is the author of the RFC
1305 that is NTP (Network Time Protocol). He developed a hierarchical
structure in which Stratum 0 is the USNO clock. Stratum 1 is a radio
receiver that receives the time from Stratum 0. Stratum 2 is a client
that receives the time over a network connection from a Stratum
1 clock. Stratum 3 is a client that gets the time from Stratum 2...
and so on to a theoretical Stratum 15.
In the telecommunications world, stratum refers to the holdover
performance of an oscillator in the event of loss of synchronization.
Stratum 1, Stratum 2, Stratum 3, and Stratum 4 are the most typical.
A Stratum 1 clock has an accuracy of 1.0 x 10-11, Stratum
2 has an accuracy of 1.6 x 10-8, Stratum 3 has an accuracy
of 4.6 x 10-6, and Stratum 4 has an accuracy of 3.2 x
10-5.
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What
type of network uses the NTS-150, NTS-200 or TimeVault™?
The term 'network' is really a topological
term that describes many types of systems: telecommunications, power,
or datacom. The NTS-200 and TimeVault strictly operate only with
datacom networks, and there, only over TCP/IP inter-networks. These
networks are characterized by passing information in packets using
IP addressing and routing. Internet, with a capital 'I', is the
pervasive TCP/IP network spanning the globe and incorporating millions
of connections.
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Will
an NTS-150, NTS-200 or TimeVault™ work on my network?
The NTS-150, NTS-200 and TimeVault conform
to the NTP specification. If the NTS-200 and TimeVault receive packet
requests that comply with the NTP specification, accurate time will
be provided. It does not matter where or from what platform the
NTP packet requests originate.
NTP is built around the User Datagram Protocol (UDP). If your network
supports Ethernet and UDP it should be compatible with TrueTime
network time servers.
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Where can
I learn more about NTP?
There is an excellent source of NTP material
at the University of
Delaware's web site. In addition, there is the NTP Usenet News
Group, comp.protocols.time.ntp.
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What about Factory Service?
Technical support and service is available
from 7:30 AM to 4:30 PM Pacific time, Monday through Friday. Call
(707) 528-1230 and ask for Service. We have skilled staff ready
to assist you.
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What about
local support in my area?
TrueTime has a nationwide network of local
representatives that can provide local design, installation, and
service support. Contact information
is available on the TrueTime website.
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How
do I buy TrueTime's Networking Products?
To purchase our products, please call
(800) 328-1230 and ask for Network Sales. Or, proceed to the Contact
Us page to find your local TrueTime representative.
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What
is your warranty?
Each new product manufactured by TrueTime
is warranted for defects in material or workmanship for a period
of one year from date of shipment ("Limited Warranty").
Defects in material or workmanship found within that period will
be replaced or repaired, at TrueTime's option, without charge for
material or labor, provided the customer returns the equipment,
freight prepaid, to the TrueTime factory under this limited warranty.
TrueTime will return the repaired equipment, freight prepaid, to
the customer's facility. This one year Limited Warranty does not
apply to any software or to any product not manufactured by TrueTime.
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What
does upgrade support cost?
TrueTime has Service Contracts available
for a variety of time periods. You can buy a Service Contract at
the time of original purchase, or you can purchase a Service Contract
at a later time (even after expiration of your warranty). Our Technical
Service Department can provide details for your particular requirement.
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How
are upgrades handled?
The standard feature of upgradeable
flash memory means that software upgrades can be accomplished via
the Internet.
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Can
I get a warranty greater than the standard one year warranty?
TrueTime has Service Contracts available
for a variety of time periods. You can buy a Service Contract at
the time of original purchase, or you can purchase a Service Contract
at a later time (even after expiration of your warranty). Our Technical
Service Department can provide details for your particular requirement.
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How do you set up a Network
Time Server?
Installation of the TrueTime Network
Time Server is a simple process. For GPS equipped units, the antenna
is a relatively small device. For window installations the antenna
is the size of large, thick coin and has a suction cup to hold it
fast to the glass. The roof mounted antenna (about the size of a
coffee cup) includes a threaded PVC pipe and hose clamps for attachment
to an upright stanchion on the roof. The Belden 9104 antenna coax
cable is relatively thin and flexible, making it easy to run to
the server.
After plugging in the server to AC power, the unit is ready (after
POWER ON) to receive the IP address, default gateway, and subnet
mask information from your Network Administrator. The unit will
automatically search for satellites and lock on to available signals.
Time is then automatically set in the unit, and it is ready to respond
to NTP client requests.
In the event of a loss of power, the unit maintains the original
setup parameters in nonvolatile memory, so there is no need for
operator intervention to restart the unit.
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How
far can I install the antenna from the Network Time Server?
The standard configuration supplied
with the NTS-150/NTS-200/TimeVault includes 50 ft. (15 m) of Belden
9104 Antenna Coax Cable with the L1 GPS Antenna (roof or window).
The antenna can drive up to 150 ft. (45 m) of antenna cable. For
longer cable runs we offer an optional GPS antenna inline preamplifier
that extends the cable length to 300 ft. (90 m) or a GPS Down/Up
Converter for cable runs up to 1500 ft. (457 m).
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What
if the roof or window is more than 150 ft. (45 m) away?
An optional GPS antenna inline preamplifier
that extends the standard cable runs up to 300 ft. (90 m) is available.
A GPS signal down/up converter and cable package is available that
can reach 1,500 feet (457 m).
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I can't
practically mount an antenna, what now?
Buy TimeVault™. Although it's
premier mode of operation is with GPS as the #1 Reference Clock
Source, without GPS connected, it dials into the US National Clock
in Boulder, Colorado, periodically synchronizing TimeVault to about
five milliseconds. This time is continually monitored by cross checking
the time against a user defined NTP server. TimeVault also functions
well using public NTP servers as a time source.
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Can I use
an existing GPS antenna instead of the one TrueTime supplies?
TrueTime strongly recommends the use of
the antenna that comes with the GPS Network Time Server. If you
have an installation that precludes use of the standard antenna,
please contact a Product Specialist at TrueTime, and we can evaluate
your application requirements, and make recommendations.
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How
big is the antenna?
The standard L1 GPS roof mounted
Antenna is 2.625 inches (6.67 cm) in diameter, and 3 inches (7.62
cm) in height. It weighs 0.55 pounds (.250 Kg) (including the mounting
nipple).
The standard L1 GPS window mounted antenna is approximately 2.00
inches (5.08 cm) in diameter, and 0.5 inches (1.27 cm) thick.
The optional GPS antenna inline preamplifier is approximately 3
inches long and 0.6 inches in diameter.
The optional GPS Down/Up Converter GPS Antenna is 4.4 inches (11.17
cm) in diameter and 2.1 inches (6.85 cm) in height. It weighs 0.60
pounds (.272 Kg) (including the mounting nipple).
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I need
to install the antenna over 150 ft. (45 m) from the receiver --
what do I do?
TrueTime offers an optional
GPS antenna inline preamplifier that extends the standard cable
run up to 300 ft. (90 m), or a GPS Down/Up Converter option for
use with antennas up to 1,500 feet (457 m) from the receiver.
Can I install
the antenna in a window?
TrueTime offers a window mount antenna in addition
to roof mounted antennas for the NTS-150, NTS-200 and TimeVault
servers. Mounting the antenna in the window will substantially reduce
the number of satellites visible to the antenna. To accommodate
for this and still maintain accurate time, the time server must have
the Single Satellite Timing mode. This mode is standard on all NTS-150,
NTS-200 and TimeVault models after November 2002 (firmware version
v008 or later). TrueTime NTS-150, NTS-200 and TimeVault models with
older firmware can upgrade at no charge to v008.
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Are your products Y2K compliant?
All of TrueTime's products performed
excellent into the year 2000. As part of our product development
process, we simulate major events such as leap years, leap second
changes, and millennia rollovers to assure proper operation.
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I
thought GPS was for position. Does it supply time?
Most definitely. Since the first
days of longitude determination in navigation, time is the REQUIRED
4th dimension. Although GPS was originally developed for precision
ballistic missile targeting, it is now the #1 source of precision
time in the world. Virtually all of our power, telecommunication,
and networking infrastructure depends on accurate GPS timing for
synchronization purposes.
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How accurate
is GPS for network timing?
The GPS Receiver used in the
NTS-150, NTS-200 and TimeVault provides 1 microsecond accuracy internal
to the units. Time out of these units is via NTP, which at best
delivers 0.1 millisecond accuracy; a factor of 100 coarser than
GPS accuracy. Network factors reduce client synchronization accuracy
to one to 10 ms typically. You can not get any better time synchronization
in a local network than you can from a GPS synchronized local time
server.
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What
do I need to track GPS satellites?
The NTS-150, NTS-200 and TimeVault™ are
supplied with a GPS antenna (roof or window mounted), mounting kit,
and 50 ft. (15 meters) of standard coaxial cable. The roof antenna
(all weather) is mounted such that it has a view of most of the
sky. The GPS satellite constellation consists of a minimum of 24
satellites with 12 hour inclined orbits. That means that there should
always be plenty of satellites within the hemisphere to satisfactorily
operate the system. Mount the antenna, string the cable, connect
the cable to the back of the Network Time Server and wait several
minutes for it to track satellites and obtain a time solution (note:
if only part of the sky is in view, it may take longer to get the
time).
For window mounted antenna installations it is best to use a window
that faces the equator or has the best view of the sky. Generally
more satellites will be in view toward the equator than away from
it, east or west facing windows will also work. Polar facing windows
will also work but in general are not preferred. Windows that have
the best view of the sky are preferred over those that don’t,
regardless of orientation. Attach the antenna above the window sill
versus at the top of the window. This will improve the upward visibility
from the antenna to the sky. Note that some window glazing treatments
may reduce or block the GPS signals preventing the time server from
acquiring the time.
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Will GPS work
inside a building?
The GPS signal is a relatively low strength
signal (~ -132dBm) at an extremely high frequency of 1,575 Megahertz.
In order for the antenna to receive such a signal, it is necessary
to have a relatively unobstructed view of the sky to view satellites
within the GPS constellation. You can track satellites with a window
mounted GPS antenna.
The primary concern with reception in a building window is that
you effectively block off at least a 180° azimuth viewing angle
for available satellites. The time server can accommodate this by
deriving the time from as little as one intermittent satellite signal.
However, the solar reflective coating found on many buildings today
effectively reflects the GPS signal and may reduce the signal strength
to a level the time server cannot track.
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Other TrueTime Time
and Frequency Products
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