Info about Remote Access
Implementation of PAD
When one computer on an X.25 network wants to communicate with another computer in a remote location, the first computer sends a signal to its attached PAD requesting a connection to the remote computer. The remote computer responds by either accepting the request and initiating full-duplex communication or rejecting the request. Either computer can then terminate the link at any time. Note that this communication link is for data only-X.25 does not support voice transmission. Note also that PADs are DCEs, and even though they are located at the customer premises, they are actually considered nodes on the X.25 network and are therefore drawn within the cloud in the diagram.
When PADs are used for providing remote access through dumb terminals over X.25 to mainframe or minicomputer hosts, the terminals require PADs but the mainframe hosts do not-they are directly connected to the X.25 network. To configure the PAD, the administrator must specify a number of PAD parameters such as echo control, data forwarding, break signals, line folding, and binary speed. The PAD parameters (usually 22 for each terminal that the PAD services) are defined by an International Telecommunication Union (ITU) protocol called X.3. Communication between terminals and PADs is governed by the protocol X.28, and communication between the PAD and the remote host is governed by X.29.