TACACS (Terminal Access Controller Access Control System) is an authentication protocol that was commonly used in UNIX networks. TACACS allows a remote access server to communicate with an authentication server in order to determine if the user has access to the network. TACACS is an encryption protocol and therefore less secure than TACACS+, the later version of TACACS. For more information, please refer to this page
http://www.networksorcery.com/enp/protocol/tacacs.htm

TACACS+ (Terminal Access Controller Access Control System plus) protocol is the latest generation of TACACS. TACACS+ provides access control for routers, network access servers and other networked computing devices via one or more centralized servers. The separation of authentication, authorization and accounting is a fundamental component of the design of TACACS+. A very important benefit to separating authentication from authorization is that authorization can be a dynamic process. TACACS+ uses TCP for its transport. For more information, please refer to this page
http://www.networksorcery.com/enp/protocol/TACACS+.htm

TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. In other words, IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

For example, when an HTML file is sent to you from a Web server, the Transmission Control Protocol (TCP) program layer in that server divides the file into one or more packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, it may get routed differently through the network. At the other end (the client program in your computer), TCP reassembles the individual packets and waits until they have arrived to forward them to you as a single file. For more information, please refer to this page http://www.networksorcery.com/enp/protocol/tcp.htm.

Telnet is a terminal emulation protocol commonly used on the Internet and TCP/IP-based networks. It allows a user at a terminal or computer to log onto a remote device and run a program.

On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer. Telnet enables you to control the server and communicate with other servers on the network. To start a Telnet session, you must log in to a server by entering a valid username and password. For more information, please refer to this page
http://www.networksorcery.com/enp/protocol/telnet.htm

A device that enables you to communicate with a computer. Generally, a terminal is a combination of keyboard and display screen.

Token-ring network is a type of computer network in which all the computers are arranged (schematically) in a circle.

Topology is the shape of a local-area network (LAN) or other communications system. Topologies are either physical or logical. There are four principal topologies used in LANs.

a. bus topology
b. ring topology
c. star topology
d. tree topology

A wireless communications device usually attached to a satellite. A transponder receives and transmits radio signals at a prescribed frequency range. In other words, a transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal. After receiving the signal a transponder will at the same time broadcast the signal at a different frequency.

Tunneling is a technology that enables one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. Tunneling is also called encapsulation.