Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

312 Glossary
Glossary
extended packet sequence
numbering One of the optional
Network Subscribed Facilities
that provides packet sequence
numbering using modulo 128. If
not subscribed, modulo 8 is used.
F
facility An optional service
offered by a packet switching
network’s administration and
requested by the user either at
the time of subscription for
network access or at the time a
call is made. Also known as user
facility.
facility set A facility set defines
the various X.25 connection
parameters and X.25 facilities
that can be negotiated for each
virtual circuit on a per-call basis.
first select An optional packet
switching network facility by
which user data can be
transmitted as part of the control
packets that establish and clear a
virtual connection.
FCS Frame Check Sequence. A
sequence of bits generated by
X.25 at Level 2 that forms part of
the frame and guarantees the
integrity of its frame’s contents.
The FCS is also used by the
IEEE802.3 protocol to check the
validity of frames.
file equation An assignment
statement used to associate a file
with a specific device or type of
device during execution of a
program.
file number A unique number
associated with a file when the
file is opened. The file number is
returned in the FOPEN or
HPFOPEN call used to open the
file. It can be used to access that
file until the file is closed.
file specification The name and
location of a file. The full
specification for a file includes the
file name, group, and account.
file system The part of the
operating system that handles
access to input/output devices
(including those connected
through the DTC), data blocking,
buffering, data transfers, and
deblocking.
flow control A means of
regulating the rate at which data
transfer takes place between
devices to protect against data
overruns.
flow control negotiation One
of the network subscribed
facilities selected at subscription
time. This facility allows the Flow
Control parameter to be
negotiated at call set-up time, as
opposed to having a predefined
value.
formal file designator A name
that can be used
programmatically or in a file
equation to refer to a file.
FOS Fundamental Operating
System. The programs, utilities,
and subsystems supplied on the