The Perceptus Back Story

In theory, Windows XP in a home (i.e. non-domain) setting should have no troubles keeping its time accurate. All you need to do is enable the “Internet Time” option so that it synchronizes with a network time protocol (NTP) server. It looks so easy, but it turns out that it’s really not bullet proof.

Most users should try a different NTP server first. The default time.windows.com server is heavily overloaded, and it’s hard to consistently get a sync. Try pool.ntp.org – that’s actually a network of machines that share the load.

But that’s not the solution in this blog post. IMHO, NTP is unusable in many small network environments because of firewalls and network address translation (NAT). Even the built-in Windows firewall can block NTP traffic which operates on UDP port 123.

Most home PCs connect to the Internet through a small, inexpensive router from the likes of D-Link, NetGear, Linksys, etc. Many of these block NTP or don’t work with it properly. This used to be a common problem with NATs. Port forwarding UDP port 123 to a computer works for some people, but that only works for one computer. And it didn’t work on the two routers I tested with today.

My solution that is generally bullet proof? Use a protocol that is TCP based. I don’t want to get too technical, suffice it to say that the chances of a TCP protocol working with all NATs is higher than that of UDP. Luckily, I found a perfectly good protocol and client (my backup plan was to write a crazy script to screenscrape a web page). It’s called DAYTIME it’s actually older and technically inferior than NTP, but what’s a second or two of accuracy if it works?

Now for a basic client, one might as well go to the source: http://tf.nist.gov/service/its.htm. It’s free, as functional as it needs to be, open source, and provided courtesy of a US government agency.

I setup a this as a weekly time update job on 10 small retail store POS networks through a generic maintence scripting system that is already in place: “nistime-32bit.exe Once -s5”. That’s it. It runs the time client, fixes the time, then exits. There are other options, but for this client, one time synchronizaton per week should be more than enough.

The moral of the story? UDP is over-rated in an Internet that is flooded by little home routers.