Introduction to Tandem X.25 Capabilities

Glossary
Glossary–6 065307 Tandem Computers Incorporated
LIU. Line Interface Unit. A components of the 3650/6100 Communications Family.
Each LIU supports a single communications line. The 3650 CSS and 6100 CSS can have
1 through 15 LIUs. The 3605 and 6105 controllers can have 4 LIUs.
logical channel (LCN). Provides the logical connection between the user DTE and the
packet exchange.
logical channel number. Number assigned to a logical channel to uniquely identify it.
logical device. Device that can be accessed and addressed. It may not be equivalent to a
physical device.
manager process. A Tandem subsystem process that performs management services; a
process with which the SCP management process communicates to control a particular
subsystem. (For instance, an application controls SNAX/XF by issuing requests to the
SCP, but the SSCP process actually services the requests. The SCP is the management
process, and the SSCP is the manager process.)
M bit. More data bit. Part of the packet header for a data packet. The M bit identifies a
series of related data packets passing through the network.
message. Complete communications sent as a unit, able to be queued and assigned
priorities.
message handling (or messaging). The computing function that allows the exchange of
electronic messages among users in a network. Electronic mail and electronic data
interchange (EDI) are examples of message-handling applications.
modem. Modulator Demodulator. Hardware that converts digital data to an analog
signal for transmission over a telephone channel, or vice versa.
modem eliminator. Device that allows data communications equipment to be connected
without modems and telephone lines.
modifier. SYSGEN modifiers for Tandem IOPs are specified in the Peripherals
paragraph of the CONFTEXT file. They are used to customize the X25AM line to suit
a particular configuration.
modulo. A repeating packet-numbering sequence on layer 3, or a repeating
frame-numbering sequence on layer 2. In modulo-8 sequencing, the sequence
numbers go from 0 to 7, and then back to 0 again. In modulo-128 sequencing, the
sequence numbers go from 0 to 127, and then back to 0 again.
NAM protocol. Network Access Method protocol. Used by X25AM to connect Tandem
communications subsystems by running Expand over the X25AM line.
NETID. A set of network characteristics that can be specified as either a SYSGEN
modifier or an SCF attribute for an X25AM line. In the past, these sets were given
network-specific names such as DATAPAC, because they pertained to only one
network. Now, more general names are used, because each set of characteristics can
sometimes pertain to more than one network.