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Home | Support | FAQs | Network Timing FAQs

Network Timing FAQs

 

Product Specific FAQs
SyncServer S200
SyncServer S250
SyncServer S300
SyncServer S350
SyncServer S100

Network Time Servers
What is a Network Time Server?
Why should I synchronize my network?
What's important in selecting a Network Time Server?
What is ACTS?
What does ACTS cost?
Who are your customers for Network Time Servers?

Network Time Protocol
What is the Network Time Protocol?
Is NTP an open source protocol?
Where do I get RFC 1305?
How does NTP work?
Does NTP supply time to a computer or server?
How accurate is NTP?
What are the main differences between SNTP and NTP clients?
NTP is a UNIX daemon. What does that mean?
Where can I get NTP daemons?
How many clients can I serve?
Do I have to run UNIX computers to use NTP?
I am already running NTP on a UNIX general purpose server or my router. Why do I need your network appliance?
How do I synchronize my network?
What is Stratum?

GPS for Time & Frequency
I thought GPS was for position. Does it supply time?
How accurate is GPS for network timing?
What do I need to track GPS satellites?
Will GPS work inside a building?

What are the key differentiating features and benefits of the SyncServer S200?
The S200 sets the standard which is shared by Symmetricom's other SyncServer network time servers.

  • Stratum 1 Operation Via GPS Satellites
  • 3 Independent 10/100Base-T Ports
  • High-Resolution Vacuum Florescent Display
  • Full numeric keypad
  • IPv6 and IPv4 Compatible
  • Secure Web-Based Management
  • SSH, SSL, SCP, SNMP v3, Custom
  • MIB, HTTPS, Telnet, and more
  • Stratum 2 Operation via NTP Servers
  • Nanosecond time accuracy to UTC
  • Dedicated Sysplex Timer output
  • Email Alerts for Alarms or Error
  • Single Satellite Timing
  • Dual USB ports
  • Rubidium & OCXO Oscillator Upgrades

Like other SyncServers, the S200 is the easiest to set up and maintain network time server in the world. The front panel is designed to quickly bring the server online with a few front panel keystrokes or DHCP. To fully configure the unit, use the very intuitive web interface or the step-by-step wizards for the most common operations.

The S200 provides very reliable and secure network synchronization technology by combining multi-port network interfaces with multiple time reference technology and enhanced security protocols.

Multiple ports provide the flexibility to adapt to different network topologies as networks grow and change. They support a wide range of network protocols including IPv4 and IPv6, for easy management and seamless integration into your existing and future network. The high speed processor and a nanosecond clock assure high bandwidth NTP performance for hundreds of thousands of network clients.

The Stratum 1 level S200 derives extremely accurate time directly from the atomic clocks aboard the GPS satellite system. Reliability is further enhanced via Stratum 2 operation by retrieving time from other user-designated time servers. Like all SyncServers, the S200 can be upgraded to an internal Rubidium atomic oscillator to keep the time server accurate if the GPS signal is lost.

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What are the key differentiating features and benefits of the SyncServer S250?

    Multiple and Versatile Timing Configurations

  • In addition to GPS, the S250 can use IRIG B AM, 1PPS, and 10 MHz inputs as references.
  • The S250 also outputs IRIG B AM, 1PPS and 10 MHz signals.

    Key Features Next generation, High-Bandwidth NTP Time Server

  • Stratum 1 Operation Via GPS Satellites
  • 3 Independent 10/100Base-T Ports
  • High-Resolution Vacuum Florescent Display
  • Full numeric keypad
  • IPv6 and IPv4 Compatible
  • Secure Web-Based Management
  • SSH, SSL, SCP, SNMP v3, Custom
  • MIB, HTTPS, Telnet, and more
  • Stratum 2 Operation via NTP Servers
  • Nanosecond time accuracy to UTC
  • IRIG B AM, 1PPS, 10 MHz input/output
  • Dedicated Sysplex Timer output
  • Email Alerts for Alarms or Error
  • Single Satellite Timing
  • Dual USB ports
  • Rubidium & OCXO Oscillator Upgrades
  • All features of the SyncServer S200

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What are the key differentiating features and benefits of the SyncServer S300?

    Four Ports including Gigabit Ethernet - Unmatched High Performance with Unparalleled Flexibility and Security

  • The S300 has four dedicated and isolated Ethernet ports, one of which is Gigabit Ethernet - more than enough to meet the need of servicing thousands of NTP requests per second while maintaining microsecond caliber timestamp accuracy.
  • Multiple ports provide the flexibility to adapt to different network topologies as networks grow and change.

    Enhanced Security - Secure and Easy Network Integration and Management

  • RADIUS, SSL, Autokey, MD5, passwords, access control lists and more are standard for maximum security.
  • All of the expected network management and monitoring protocols are standard in the S300.

    Redundancy and Time Assurance

  • Internal modem is standard to connect directly to legal time provided by national time authorities.
  • An optional AM radio is available to synchronize to national time broadcasts, which can be an alternative to GPS when GPS is not viable option.

    Alarm Relays for Monitoring Systems

  • Aside from extensive software based alarms, the hardware based alarm relays further enhance Alarming choices.

    Key Features of the S300 Ultra High-Bandwidth NTP Time Server

  • Stratum 1 Operation Via GPS Satellites
  • Gigabit Ethernet port plus 3 additional Independent 10/100Base-T Ports
  • Internal Dial-up Modem for Time Reference Redundancy
  • Stratum 2 Operation via NTP Servers
  • RADIUS, NTPv4 Autokey, MD5 authentication
  • Secure Web-Based Management
  • SSH, SSL, SCP, SNMP, Custom MIB, HTTPS, Telnet, and More
  • High-Resolution Vacuum Fluorescent Display
  • Full Numeric Keypad
  • IPv6 and IPv4 Compatible
  • Nanosecond Time Accuracy to UTC
  • Dedicated Sysplex Timer Output
  • Alarm Relays
  • Single Satellite Timing
  • Rubidium & OCXO Oscillator Upgrades
  • Optional IEEE-1588 / PTP Grandmaster option
  • Upgrade to AM radio broadcast time sync
  • All features of the SyncServer S200

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What are the key differentiating features and benefits of the SyncServer S350?

    Multiple and Versatile Timing Configurations

  • In addition to GPS, the S350 can use timecodes, 1PPS, and 10 MHz inputs, NTP peering to other time servers over the network and the built-in modem to periodically dial national time services.
  • Time code inputs/outputs include IRIG A/B/E/G/NASA36/XR3/2137 in AM and DCLS formats.
  • An optional AM radio is available to synchronize to national time broadcasts, which can be an alternative to GPS when GPS is not viable option.

    Four Ports including Gigabit Ethernet - Unmatched High Performance with Unparalleled Flexibility and Security

  • The S350 has four dedicated and isolated Ethernet ports, one of which is Gigabit Ethernet - more than enough to meet the need of servicing thousands of NTP requests per second while maintaining microsecond caliber timestamp accuracy.
  • Multiple ports provide the flexibility to adapt to different network topologies as networks grow and change.

    Enhanced Security - Secure and Easy Network Integration and Management

  • RADIUS, SSL, Autokey, MD5, passwords, access control lists and more are standard for maximum security.
  • All of the expected network management and monitoring protocols are standard in the S350.

    Alarm Relays for Monitoring Systems

  • Aside from extensive software based alarms, the hardware based alarm relays further enhance Alarming choices.

    Key Features of the S350 Ultra High-Bandwidth NTP Time Server

  • Stratum 1 Operation Via GPS Satellites
  • Gigabit Ethernet port plus 3 additional Independent 10/100Base-T Ports
  • Internal Dial-up Modem for Time Reference Redundancy
  • Stratum 2 Operation via NTP Servers
  • RADIUS, NTPv4 Autokey, MD5 authentication
  • Secure Web-Based Management
  • SSH, SSL, SCP, SNMP, Custom MIB, HTTPS, Telnet, and More
  • Independent Time References: GPS, Timecodes; 1PPS, 10 MHz
  • Versatile Timing Outputs: IRIG A/B/E/G/NASA36/XR3/2137 AM or DCLS; 1PPS, 10 MHz, Sysplex
  • High-Resolution Vacuum Fluorescent Display
  • Full Numeric Keypad
  • IPv6 and IPv4 Compatible
  • Nanosecond Time Accuracy to UTC
  • Alarm Relays
  • Optional IEEE-1588 / PTP Grandmaster option with Time Interval Measurement capability
  • Rubidium & OCXO Oscillator Upgrades
  • Upgrade to radio broadcast time sync
  • All features of the SyncServer S300.

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What are the key differentiating features and benefits of the SyncServer S100?

  • The SyncServer S100 is a cost effective GPS network time server that accurately synchronizes enterprise servers, workstations, and routers. The SyncServer S100 also includes a single satellite timing mode for versatile antenna mounting options.
  • In cases such as in skyscrapers or in urban canyons, roof mounted antenna installation costs can be prohibitively expensive or unfeasible. Using a small window mounted GPS antenna eliminates extensive multi-floor and through-roof cabling, and in some cases, costs associated with renting roof top antenna space.

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Network Time Servers

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.

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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 E-mail
Directory services Legal and regulatory requirements
Access security and authentication Password and digital ID
Distributed computing  
Scheduled operations  
Real-world time values  

Network operations typically require the most accuracy, on the order of 1 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 1 second. 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 papers, The Importance of Network Time Synchronization and 5 Dangers of Poor Network Time Keeping.

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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 Symmetricom 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:
Multiple NTP ports Having a time server that supports offers multiple NTP ports accommodates modern networks as well as ones destined to be upgraded at some future point in time. If your network is going to grow, or security is important, 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.
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, NTP will change to the next best reference. (You are notified of course via SNMP).
NTP request throughput and accuracy While the ability to synchronize many hundreds of thousands of clients is useful on very large networks, the real test is in the ability of the time server to handle coincidental peak loading of NTP requests. Performance, or the ability to service a high volume of NTP requests and maintain very high 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.
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. Symmetricom 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.

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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, a NTP server 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
Dial up time services also available European countries as well as Japan. The built-in modem on the S300/S350 is compatible with all of these services.

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What does ACTS cost?
The only cost is of the telephone call.

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Who are your customers for Network Time Servers?
Please see the partial list.

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Network Time Protocol

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. Symmetricom's time servers are excellent examples of 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 and makes an adjustment. 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 with the SyncServer® models with GPS, the internal clock accuracy is less than 50 nanoseconds and the NTP time stamp accuracy at the NTP port is less than 14 microseconds.

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What are the main differences between SNTP and NTP clients?
SNTP is a Simple Network Time Protocol. It is based on RFC 1361/2030: it gets its time from the specified time servers of the machine on which it is installed. This protocol cannot be configured to obtain time from an alternate time server if the primary server is down. This could be called a short version of NTP client software.

NTP, Network Time Protocol, is based on RFCs 1305 and 1119 which can be configured to obtain and distribute the time on the network. It has a built-in algorithm that calculates the time accurately up to 1-10 milliseconds. The algorithm can be configured to obtain time from an alternate source in ca

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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: /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, Symmetricom’s NTP Client Software Resource page is an excellent repository.

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How many clients can I serve?

Symmetricom's NTP time servers have demonstrated the ability to handle many hundreds of thousands of clients and still maintain microsecond level 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. NTP client software is needed on machines wishing to synchronize to the time server. Symmetricom offers SymmTime, a very popular freeware NTP time client for Windows. Symmetricom also offers Domain Time II software for time client

 
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