NTP Server General Questions

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.

Why should I synchronize my network?
Many operational processes (business and IT related) 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 1 millisecond to 1 second. Sometimes it is difficult to appreciate why one millisecond can make much difference. Usually it is because it is necessary to establish the order of events.

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.
Atomic Clock Upgrade Upgrading to an internal Rubidium atomic oscillator to keep the time server accurate if the GPS signal is lost or jammed.  This allows the time server to provide extremely accurate time while the GPS related issue is resolved.
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.
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.

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).
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.

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 Linux. 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.

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. The current version can be found here: http:/www.ntp.org/

How does NTP work?
Superficially, NTP is a software daemon operating in a client mode, server mode, or both.

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.

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 compute the 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.

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, 1 to 10 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.

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, 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 0.5 to 3 milliseconds typically. The algorithm can be configured to obtain time from an alternate source in case the original time server fails or gets out of synchronization.

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.

The NTP daemon for *nix systems can be found at http:/www.ntp.org. 

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.

Do I have to run *NIX computers to use NTP?
No. NTP client software is needed on machines wishing to synchronize to the time server. We offere Domain Time II software for time client synchronization, monitoring and management. Many operating systems include an NTP client built in.

I am already running NTP on a Linux 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 business operation, you can’t afford to leave time synchronization in the hands of a generic server or a clock outside of your control on the Internet. There is a risk of invalid time and denied access to the time either deliberately by the operator of the remote server or a network disruption.

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. The beauty of the many monitoring aspects of the Symmetricom dedicated time servers is the reliability and reporting features



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