X25AM Programming Manual

Glossary
X25AM Programming Manual—527201-001
Glossary-4
fast select.
fast select. Optional network facility allowing user data to be put into call request, call
accepted, clear, and clear request packets.
flow control. Mechanism by which the recipient of incoming data notifies the sender to stop
or start transmitting data depending on the state (full or empty) of the recipient's
incoming data buffer.
frame. Message unit consisting of a sequence of bits bracketed by beginning and ending
flag sequences. It can contain packets.
frame layer. Also called the link level. It is the X.25 protocol description for the link access
procedures for the link between the network and the computers, terminals, or other
devices.
framing. Selecting bit groupings representing characters and establishing a reference so
elements can be identified within the frame.
Guardian operating system. The operation system that runs on an NonStop system.
hex. Hexadecimal. Base-16 numbering system.
high PIN. A PIN that is greater than 255. See also low PIN.
I. Information frame. Link-level frame containing a packet.
incoming call packet. Packet that the network sends to a remote entity in response to
receiving a call request packet addressed to that entity.
INSTALL. Program that allows a user to load all of the system software from a tape and
create an operating-system image from it.
interface. Shared boundary defined by common interconnection characteristics.
International Organization for Standardization (ISO). An organization established to
oversee remote development of standards to facilitate the international exchange of
goods and services.
interrupt. Signal used by a device to stop the current task of a subordinate device. Once
stopped, the subordinate device waits for the primary device to send information to it.
Example: CPU and controller.
invitation-to-clear packet. Sometimes sent as the last data packet or after the last data
packet to request the disconnection of the call, to solve the problem of having a clear
packet overtake a data packet (causing a call to be disconnected before all of the data
is received).
IOP. I/O process. System process that controls input and output, usually to and from a
device.
ISO. See International Organization for Standardization (ISO).