Good ol' X.25 (Sangoma Technologies update)

by Andy Oram

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Most of us remember X.25 as the first couple wasted days in courses on
computer networking, something we had to pay obeisance to before we
could get down to the TCP/IP stuff we needed to know. I had no idea
until recently that X.25 is still growing in use, and not just in
legacy applications.

X.25, actually, is one of an enormous series of protocols standardized
by the international body CCITT; X.500 is another one of the few that
are well-known.
I threw a joke about X.25 in to my recent weblog about the
history of computer
X.25 was on my mind thanks to a recent interview I conducted with
David Mandelstam, CEO of
Sangoma Technologies Corp.,
a company that has made telecommunications and routing equipment since
1984. (And I thought it would be ironically appropriate to post this
blog in the middle of our
Emerging Technology conference.)

Sangoma's earliest projects involved X.25, and they are still
developing X.25 enhancements, largely on Linux. Mandelstam says, "It
has been estimated that there is still over $10 billion invested
worldwide in X.25 hardware." Many legacy systems are used by such
large institutions as banks and phone companies, and serve them
well. In fact, new systems are still being built on X.25.

X.25 is noted for being slow (64 Kbs or less) and as having poor
latency, but for being very, very reliable. Its positive and negative
characteristics alike stem from the extensive error-checking it does
at each hop. It thus finds uses in applications where the amounts of
data to be transmitted are small and latency is not very important,
but it's critical that data not get lost. Examples mentioned by
Mandelstam include:

  • A lottery system being built in Spain. This is a completely new X.25

  • The SITA system, used to communicate information among carriers and
    between the carriers, airlines, and other institutions. This is a
    relatively new system that uses X.25 as the core protocol.

  • A cell phone system in India, where the gathering of billing data is

Currently, Sangoma encourages customers to base products on Linux
"whenever possible." He says, "An Open Source solution is the only
reasonable choice when developing a specialized communication
server. It's imperative to get control down to the lowest level of the
kernel, even to the hardware."

He illustrates the value of Linux for embedded and server applications
by pointing to a recent project that had to communicate with 32,000
automated teller machines. That meant a system that could run 32,000
networking processes at once. Sangoma did a great deal of tweaking and
rewriting of the kernel to let it scale. The automated teller machine
application, incidentally, used several protocols including X.25.

"In the old days when DOS was used for embedded applications,"
Mandelstam says, "programmers would just bypass the operating system
and write their drivers to go down to the hardware. You can't do that
with a modern operating system, but Linux gives you control over the
device drivers and kernel. Windows, being closed, cannot be
manipulated at this level." So Mandelstam has found in general that
"customers develop on Windows only when there is no choice."

What old networking technologies continue to seem to have lasting