MAX Administration Guide
8-1
8
Administering PAD, X.25, and Frame Relay
You can manage the Packet Assembler/Disassembler (PAD), X.25 and Frame Relay functions
on the MAX unit through the unit’s terminal-server CLI. You can verify the settings of support
PAD through the VT100 interface’s Ethernet menu.
Administering X.25
X.25 is an international ITU-T protocol that enables users to transmit information over a
packet-switched network. It allows remote devices to communicate with one another across
high-speed digital links without the expense of individual nailed-up lines. The X.25 protocol
handles both high-volume data transfers and interactive use of host machines. As a full-duplex,
connection-oriented protocol, X.25 uses Virtual Circuits (VCs) and provides services such as
multiplexing, in-sequence delivery, transfer of addressing information, segmenting and
reassembly, flow control, transfer of expedited data, error control, reset, and restart. Allocation
of logical channels can be either static (using a Permanent Virtual Connection, or PVC) or
dynamic (using a Switched Virtual Connection, or SVC).
X.25 uses the first three layers of the OSI model. The Physical layer implements several
standards, such as V.35, RS-232 and X.21bis. The Data Link layer uses an implementation of
Link Access Procedure, Balanced (LAPB) and provides an error-free link between two
connected devices. The Network Layer uses the Packet Layer Protocol (PLP). PLP is primarily
concerned with network-routing functions and the multiplexing of simultaneous logical
connections over a single physical connection. X.25 exchanges packets between local Data
Terminal Equipment (DTE) and remote Data Circuit-Terminating Equipment (DCE).
Internet Protocol over X.25 is a method of transporting IP packets on X.25 facilities when the
circuit is established as an end-to-end X.25 connection. X.25/Transaction Processing Protocol
for Point-of-Service (X.25/T3POS) is a character-oriented, frame-formatted protocol designed
for an X.25 packet-switched network. The protocol provides reliable and efficient data
transactions between a host device and Data Terminal Equipment (DTE). The DTE is usually a
client device communicating through an asynchronous port, while the host is a mainframe
communicating by means of an X.25 packet network. The MAX converts data arriving from
the DTE to a format capable of being transmitted over a packet network. In addition,
Administering X.25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1