·         Selecting the Right WAN: http://docs.rinet.ru/NeHi/ch11/ch11.htm

·         PSTN: http://www.ericsson.com/support/telecom/part-b/index.shtml

·         X.25: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.htm

·         Frame Relay: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm

·         Frame Relay Tutorial Center: http://www.alliancedatacom.com/frame-relay-tutorials.asp

·         ISDN: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm

·         CSU/DSU White Paper (pdf): http://www.gdc.com/inotes/pdf/sc5000wp.pdf

·         DSL Forum: http://www.dslforum.org/

·         The SONET Homepage: http://www.sonet.com/

·         WLANs versus Wireless WANs White Paper (pdf): http://www.sierrawireless.com/news/docs/2130273_WWAN_v_WLAN.pdf

·         WiMAX forum: http://www.wimaxforum.org/technology

·         Securing Remote Access Connections: http://www.windowsecurity.com/articles/Securing_Remote_Access_Connections.html

·         VPN White Paper: http://www.microsoft.com/windows2000/techinfo/howitworks/communications/remoteaccess/vpnoverview.asp

Network General's Protocol chart   (you need Adobe acrobat reader to view)  This is a great view of TCP/IP and it's rich suite of support protocols

Radcom's Protocol chart  a colorful and up-to-date view of LAN and cellular protocols

Protocol Encapsulation chart a very different look at LAN protocols in terms of encapsulation, this chart is worthy of study!