Expand Configuration and Management Manual (H06.03+)

Glossary
Expand Configuration and Management Manual—529522-002
Glossary-9
Layer 3
Layer 3. A term that is used to refer to the Network Layer of the Open Systems
Interconnection (OSI) Reference Model. Layer 3 governs the switching and routing of
information between systems in the network and is responsible for error checking and
recovery. The Expand line-handler process’s Network Layer, or path functions,
corresponds to the PATH object referred to by the Expand Subsystem Control Facility
(SCF) interface.
Layer 4. A term that is used to refer to the Transport Layer of the Open Systems
Interconnection (OSI) Reference Model. Layer 4 accepts data from the OSI Session
Layer (Layer 5) and passes it to the OSI Network Layer (Layer 3). Layer 4 provides
end-to-end data integrity between processes and checks that messages received are
correct. The Expand line-handler process’s Layer 4, or path functions, corresponds to
the PATH object referred to by the Expand Subsystem Control Facility (SCF) interface.
Layer 4 send window. A data structure that determines how many Expand packets are
sent before an acknowledgment is required on a single end-to-end (Layer 4)
connection.
line. A single physical connection between two systems. See also route and path.
line buffer. A portion of the Expand line-handler process data space used to buffer
incoming and outgoing messages after they have been formatted into packets by the
Expand line-handler process.
line function. One of the two functions of an Expand line-handler process. A single-line
Expand line-handler process performs both line and path functions with a single logical
device. A multi-line path requires a logical device to manage the path function and a
separate logical device for each line in the path.
line handler. See Expand line-handler process.
line logical device. A logical device that manages a line in a multi-line path. One line
logical device is required for each line in a multi-line path.
LNP. See logical network partitioning.
load. (1) To transfer the operating system image or an application from a disk into a
computer’s memory so that the operating system or application can run. (2) To insert a
tape into a tape drive, which prepares it for a tape operation (read or write).
load balancing. A term used to refer to the balancing of traffic on multi-CPU paths. $NCP
periodically runs a rebalancing algorithm that reconsiders the pairings of Expand line-
handler processes on each multi-CPU path. If the load is unbalanced, $NCP changes
some Expand line-handler process pairs. You can initiate an immediate rebalance
using the SCF RESET PROCESS command or specify when rebalancing should occur
using the SCF ALTER PROCESS command. See also rebalancing algorithm and
Expand line-handler process pair.