LAN :
www.marconi.com/html/education/webbasedlantheory.htm
https://ictglobal.com/tutorials.html
www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introlan.htm#xtocid2

WAN :
www.marconi.com/html/education/webbasedwantheory.htm
www.rad.com/networks/1994/networks/wan.htm
www.alliancedatacom.com/wan.asp
www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introwan.htm

TCP/IP :
www.yale.edu/pclt/COMM/TCPIP.HTM
https://oac3.hsc.uth.tmc.edu/staff/snewton/tcp-tutorial/sec1.html
https://oac3.hsc.uth.tmc.edu/staff/snewton/tcp-tutorial/sec2.html
www.cisco.com/warp/public/cc/techno/protocol/iprout/tech/tcpip_pc.htm
www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ip.htm#xtocid2

WIRELESS :
https://wireless.java.sun.com/getstart/
www.proxim.com/learn/library/whitepapers/wp2001-06-what.html
https://net-services.ufl.edu/~ns/provided_services/wireless/wireless-draft.html
https://student.csumb.edu/dh/diciucciorobert/world/cst311/html/wireless.html
https://www.bell-labs.com/technology/wireless/

OPNET :
www.opnet.com
Other Universities' Opnet Sites

NETWORK CORPORATIONS LINKS:
Alcatel
Cisco Systems
3Com
Nortel Networks
Novell