Providers of network appliances for small- and mid-size companies.

Cuckoo FAQ

Click here for specifications about Cuckoo.

Who needs Cuckoo?

Really anyone who needs accurate time, and wants the security and control of having their own time server. And Cuckoo is significantly less expensive than just about any NTP time server out there.

For a list of some companies and organizations who have relied on Cuckoo for their time, please see our testimonials page.

What is SNTP (compared to NTP)?

Cuckoo is an SNTP server, not an NTP server. Some basic terms and concepts:

• NTP stands for Network Time Protocol, and is the industry standard method of synchronizing computer time.
• SNTP stands for Simple Network Time Protocol.
• Any machine on your network that needs to get accurate time is an NTP or SNTP Client.
• SNTP servers and clients are fully compatible with NTP servers and clients. The protocol used between the NTP and SNTP is identical.

The "Simple" part of SNTP refers to the fact that the server operates in a standalone mode, and does not apply the NTP filtering algorithms to the clock source. Unlike NTP, SNTP does not rely on (and in fact cannot use) external NTP servers, or "peers". NTP specifies a number of filters and calculations required to gather those independent times from multiple servers, sift good time sources from bad time sources, and regulate the clock. SNTP consults and trusts a single time source. Cuckoo relies on its ability to always have a connection with its time source (the GPS receiver) to provide consistent time.

How does Cuckoo time accuracy compare?

This diagram shows actual time requests from Cuckoo and several major NTP servers on the Internet. The data collected for this chart comes from our YellowBill application.

Several important facts can be gleaned from this chart.

• PC Clock Drift - Over the course of the test run (about one day), this PC's clock drifted about 800 milliseconds, or almost one second. This is represented by the upward sloping line from left to right--the further the distance from 0, the further the PC's clock is from true time. This is pretty typical performance of most new commercial PCs. Older or off-brand machines can often be much worse.
• Latency - Notice that all of the Internet servers (not Cuckoo) have periods where their time readings are significantly skewed. This primarily comes from Internet routing latency. The NTP protocol is designed to correct for this by slowly slewing your computer's clock to match the average time. But the more discrepencies, the longer this process can take.
• Repeatability - You'll notice on the chart that some of the servers time requests appear to jump up or down by tens of milliseconds over long periods. Although your time requirements may not be that precise, it is troublesome to think that not all time servers are created equal. This effect is independent of network latency, since not all servers are subject to it. The effect may be related to other tasks that the server is responsible for during those periods, such as system backups or other periodic tasks. Or it may be an effect of the server not being directly connected to a reliable source of UTC time. For example, look at the blue server, which although "high" between 12 and 15 hours, drops "low" between 15 and 18 hours. This "jumping" represents a sudden skewing of that server's time results, where the reported times change from one packet to the next by 30 milliseconds or more.
• Cuckoo - In the center of the pack, you'll find a steady white line. This represents the time responses sent back by our Cuckoo device. Because Cuckoo doesn't have to contend with variable Internet routing, massive client requests, or service other tasks, it can deliver consistent time, every time.

Why is accurate time important?

Computer clocks drift, sometimes seconds per day. And keeping consistent and accurate times across your network is critical in a large number of applications:

Why buy Cuckoo when you can get NTP for free?

This is a very good question, because there are NTP servers on the Internet run by people who generously allow others to access them. There are several reasons why you might want to consider owning your own time server.

• Reliability - Because Internet routing can vary, so can the latency of the timestamps. See the diagram below for a comparison of some very popular NTP servers against Cuckoo.
• Independence - With your own time server, you are not making your companies vital functions dependent on outside organizations. Anyone providing a free time server is not contractually bound to provide you with continuous, uninterrupted service. Servers may go down for maintenance, be moved, or decommissioned without you knowing it.
• Security - You can keep your own time server completely behind your firewall. There is no possibility of someone blocking or corrupting time packets being sent to your network, as there is when using an external server. NTP timestamps are delivered using the UDP protocol, which means they are subject to IP address spoofing. By running your own time server, you remove a possible means for malicious interference in your businesses operation. Because a SNTP server (like Cuckoo) operates without any peers, it can be fully isolated behind a network firewall unlike an NTP server.
• Congestion - External time servers often have many clients to service. The more clients there are, the more jitter there is in the round-trip latency, which directly affects the time's accuracy. This is something over which you have no control or knowledge.
• Unconnected - Systems that are either sporadically connected to the Internet or are using a dial-up connection cannot reliably use Internet NTP servers. And believe it or not, some systems are not connected to the Internet at all, either by choice or necessity. All of these are perfect candidates for Cuckoo.

How does it work?

Cuckoo is an SNTP (Simple Network Time Protocol) server. Simply stated, this means that Cuckoo delivers the same timestamps used by any other NTP or SNTP client software, but does not consult with other NTP servers first. Instead, Cuckoo gets its time directly from the Global Positioning System, better known as GPS. Everyone knows that GPS satellites can be used to get an accurate location. But those same GPS satellites can give you an accurate time as well. Cuckoo uses its built-in GPS receiver to track time, and by constant monitoring of the GPS time signals can deliver timestamps accurate to +/- 1 millisecond.

Where does it go?

Cuckoo can be plugged directly into your network, just like any other Ethernet-based device. Because Cuckoo needs to track GPS satellites, it does need to have visible access to the sky. We provide a marine-grade antenna with a pole mount and 50 feet of cable for outside installations. In some instances, if you have a good orientation you may be able to avoid an outside mount by placing the antenna next to a window.

We don't have roof or outside access; will Cuckoo still work indoors?

We do offer a low-profile antenna instead of the larger outdoor mast-mount version. The antenna cable length on the low profile antenna is about 15 feet, and it can be placed on a windowsill. This antenna option can be substituted for the pole mounted antenna for the same price.

Any inside antenna placement, even in a window location, prevents the receiver from seeing more than 180° of the sky. Airchitex recommends an external mounted antenna for that reason. Whether or not you are able to still get a strong enough GPS signal from a windowsill depends on several factors. The orientation of the window, whether or not there are obstructions around the window (trees, other buildings, etc.), and the window itself (some solar reflective glazes can reduce the GPS signal to unreadable levels) are all factors.

Our location needs an antenna cable longer than 50 feet. Can we extend the antenna?

Airchitex is now providing a special order antenna that is 100 feet long; please call for details.

Airchitex does not provide GPS antenna extenders, although you can provide one of your own. The extra cable and connectors will introduce some amount of signal loss. The GPS receiver expects between 15dB and 30dB of signal gain, and the marine mount antenna under optimal conditions has a gain of roughly 40dB. To reduce the signal attenuation as much as possible, use high quality cable and connectors (SMA male one one end, SMA female on the other).

Note: The GPS receiver is actively powering the antenna. We do not recommend use of any amplified in-line devices. Voltage from these devices may interfere with or even damage your antenna or your Cuckoo.

What are the specifications of the marine antenna?

Can you install a lightning suppressor on the antenna?

Although this is not something we have tested at Airchitex, we have had a customer try this with success. Tim Hodges of Triangle Telephone Cooperative was kind enough to share with us his setup and some very helpful advice.

Antenna:	PCTEL Maxrad AGPS26
Lightning arrestor:	Polyphaser IS-MR50LNZ+6
Cable:	About 65' of Times Microwave LMR-240-MA

All equipment was purchased from Tessco. His average signal strength is about 52. He also mentioned that proper installation of the lightning suppressor requires a good ground attached to the suppressor, and pointed us to this whitepaper about GPS lightning protection.

Thank you Tim for all your help!

How many GPS satellites must be visible to get accurate time?

There are 24 operational GPS satellites with orbits distributed so that at least 4 of them are always visible from any point on the Earth at any given instant. There may be up to 12 visible at one time. Cuckoo needs to receive signals from at least 4 satellites to maintain a time fix.

Does Cuckoo report when it loses synchronization with GPS time? Can I detect this condition externally?

If Cuckoo does lose GPS sync, it will continue to operate on an internal clock but will report its non-synchronized status to all clients requesting time. A status LED on the front of Cuckoo blinks when there is not a good fix. Although Cuckoo will continue to run without GPS sync, the internal clock is not a precise time keeper, and eventually will drift from UTC time.

To remotely determine a GPS synchronization loss, there are a number of methods you can use.

• SNTP Protocol: NTP Resolution field. This is set to a number that indicates a power of 2 resolution in seconds. Normally when Cuckoo is in sync it reports -10 or 2^-10 seconds (which translates to about 1 ms resolution). Immediately after it loses sync, it will report a less accurate number to indicate the new resolution with the loss of sync state.
• SNTP Protocol: The NTP Reference field. This is the last time that the unit received a GPS signal. This tells you how long of a GPS signal outage there has been.
• SNTP Protocol: The NTP Transmit field. The protocol demands that if the primary reference isn't operating, you also must set the Transmit field to 0 (i.e. no timestamp). Note: Cuckoo provides an override to this behavior to allow the unit to report "okay" times in a GPS outage if your situation can tolerate non-reference derived time for a stretch of time. Although the default is to zero out Transmit immediately, the duration of outage before the problem is reported is user-configurable.
• DAYTIME Protocol. Using NTP protocol requires forming binary packets of a specific structure, but Cuckoo also supports the DAYTIME protocol. DAYTIME is just plain text over a TCP socket, which makes it very easy to script with a simple command-line utility like "netcat". The administrator has complete control over configuration of the DAYTIME string, so you can put whatever information you want in Cuckoo's response. The "normal" types of things that one would include are time, date, timezone, etc. One of the fields we provide is one that indicates the state of the GPS lock. (GPS lock state can be displayed on the LCD as well--the LCD display is completely user configurable.)

What is network latency, and why does it matter?

Network latency is a measurement of two times: the time required to send a packet from your computer to the time server, and the time required to send a packet from the time server back to your computer. These two times added together are round-trip network latency (or just "latency" for short in this description).

Each Network Time Protocol (NTP) packet contains timestamps that are used to compute the exact time that your PC needs. But the round-trip time is required to compute the true time, and the larger the latency, the more uncertainty that is introduced into the result. This means that more NTP packets may be required to hone in on the true time, and it will take even longer to gradually adjust to the correct time.

Because of limitations in the Internet, only the round-trip time can be measured. The round-trip time is assumed (for lack of any other information) to consist of half of the time is in sending the packet and half of the time in receiving it. However, packet routing times are often asymetrical (e.g. upload bandwidth is often smaller than download bandwidth), and halving the round-trip time does not always result in an accurate measurement. So its always beneficial when possible to have the lowest possible latency to your time server.

How does Cuckoo latency compare?

This chart shows latency comparision over the same data as the first chart. You'll notice that where Cuckoo's latency is less than 2 milliseconds, it is orders of magnitude higher for many commonly used NTP servers. This shows how geographic location and other factors affect Internet routing latencies. This is an example only--although typical for smaller networks, not all networks will have Cuckoo latencies this low.

This data was measured on a system with the following characteristics:

What do your computers need to use Cuckoo?

All computers and devices on your network that need accurate time must be running a NTP or SNTP client to synchronize their time with Cuckoo. NTP client software is platform specific, but in many cases will already come with the operating system.

Most versions of Microsoft Windows (XP, ME, 2000, and NT) provide a NTP client, accessible by right-clicking on the time in the status bar, and choosing Adjust Date/Time; and selecting Internet Time. All known Unix and Linux distributions include NTP support either in the default installation, or as an available package.

The provided Windows NTP client provides very little control, and it may not be suitable for more demanding applications. Because of this, Airchitex provides a free SNTP client for Windows called YellowBill. Although YellowBill can be used with any NTP server, it was designed for use with Cuckoo.

Finally, there are many implementations of NTP and SNTP clients that are available as freeware, public-domain software or as low-cost shareware.

How many computers can Cuckoo support?

There is no actual "maximum" of devices that Cuckoo can support. As you add more devices, the time requests will incur more and more latency. The individual circumstances of your situation dictates the maximum latency that you can tolerate, and hence, the maximum effective number of clients.

It takes Cuckoo roughly 250 microseconds to receive an NTP request, prepare an outgoing packet, and send the reply. That means the maximum theoretical rate of NTP packets is about 4000 packets per second.

For planning purposes, the number of computers that Cuckoo can support depends on the speed of the network in use, what type of client time software is used, the client's latency tolerance, the clients accuracy requirements, and the synchronization of the requests. For example, if each client is programmed to send out a request exactly at the minute rollover, then all clients will be sending their requests at the exact same time. The other 59 seconds in a minute, Cuckoo will be doing nothing.

Here are some possible use cases, but please remember that your mileage may vary.

• Realistic Case 1. The clients requests are not perfectly synchronized with UTC time, and that the time requests are once per minute. You are also using NTP clients (not SNTP clients) on the requesting machines. If you are using an NTP client, it will average out any error over time unlike an SNTP client. And your latency requirements are 100 milliseconds or less. Under these conditions, the maximum number of supportable clients is probably somewhere between 150 and 200.
• Realistic Case 2. Same conditions as above, but your latency requirements are much more strict: you can tolerate a maximum latency of only 10ms. The maximum number of supportable clients is probably less than 100.
• Worst Possible Case. All clients are asking simultaneously, and each client can only tolerate 5ms latency (typical latency for a roundtrip on a 100MBit ethernet). Under those circumstances, Cuckoo can only handle about 20 simultaneous client requests (and hence, 20 clients) before the latency exceeds 5ms.
• Unrealistically Optimistic Case. If every time client was designed to minimize their interference with their neighbors, you could have each client interleave its request perfectly with each other. In that case, the theoretical maximum packet rate could be reached while still keeping minimal latency. For one client time request every minute, the theoretical maximum is 240,000 clients! This is almost certainly impossible to achieve in reality, and would require an extremely careful and special design of the time clients and a completely dedicated network. With the expense of the software engineering and IT infrastructure required, it would be much cheaper and easier to just buy more Cuckoos! (This use case is provided for entertainment value--under no circumstances would Airchitex actually recommend having more than 256 clients per Cuckoo.)

What NTP Stratum does Cuckoo report?

Cuckoo is an NTP stratum 1 device.

Stratum 0 is the reference clock (in this case the GPS satellites) receiving a reliable source of UTC. Stratum 1 is a time server with a direct link to the reference clock. Cuckoo has a direct link to the GPS time via the GPS receiver.

Why is it called Cuckoo?

"Cuckoo" is named after the Cuckoo clock, another user-friendly timepiece.

Please Note:

Airchitex has been acquired by Intuitive Circuits as of August 16th, 2008. All Airchitex products will now be supported by Intuitive Circuts. For sales and support for any Airchitex products, please contact Intuitive Circuits at (248) 588-4400.

Copyright © 2008 Airchitex, Inc. All Rights Reserved.

No portion of this site may be reproduced in any manner without express permission of Airchitex, Inc.