Based on obscure ARPANET access control system for terminal servers, later documented and extended by Cisco

Forwards username and password to TACACS server, returns authorization response

XTACACS, Extended TACACS

Adds support for multiple TACACS servers, logging, extended authorization

Can independently authorize access via PPP, SLIP, telnet and ssh

TACACS+

Separation of authentication, authorization, and accounting functions with extended functionality

Password information is encrypted using RADIUS-style encryption

Password forwarding allows use of one password for multiple protocols (PAP, CHAP, telnet and ssh)

Extensive accounting support (connect time, location, duration, protocol, bytes sent and received, connect status updates, etc)

Control over user attributes (assigned IP addresses, connection timeout, etc.)

https://www.bestitdocuments.com/Samples