References
The standards documents referenced are linked to from the relevant tutorial pages.
FarSite Communications X.25 Tutorial is a helpful tutorial on the subject.
WAN Design with Frame Relay , by David Horton
Credits
The image of a red post box on this page is provided courtesy of Graeme Weatherston / FreeDigitalPhotos.net.
The packet switching applet was written by two students in 1998 (an oldie, but a goodie). The X.25 applet was was written by a group of students in 2004. An applet is worth a thousand words - thanks!
