Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-22
Routing and Time Factors
Routing and Time Factors
This subsection explains how $NCP implements its routing scheme. It describes the
following topics:
•
Setting Time Factors on page 18-23
•
Negotiating Path Time Factors on page 18-24
•
Best-Path Route Selection on page 18-24
•
Network Routing Table (NRT) and Multiple Path Table (MPT) on page 18-25
•
Calculating Route Time Factors on page 18-27
•
Routing Algorithms on page 18-28
•
Multi-CPU Paths on page 18-31
•
Multi-CPU Routing Examples on page 18-34
$NCP provides a sophisticated automatic routing scheme to ensure that a message
gets to its destination in the most efficient way possible. This most efficient way is
called the best-path route. $NCP determines the best-path route based on the time
factors (TFs) and hop counts (HCs) of available routes. $NCP maintains routing
information in the network routing table (NRT) and, for multi-CPU paths, in the
multiple path table (MPT) and reverse pairing table (RPT).
A time factor of 1 represents the best path and a time factor of 186 represents the
least-favorable path.
A path is one or more lines between two nodes.
Paths to a neighbor are called direct paths or single-hop paths. A direct path can be a
single-line path, a multi-line path, or a multi-CPU path that is made up of one or more
multi-line or single-line paths.
How the path time factor is determined depends on the type of path, as follows:
•
If a path consists of only one line—as in the case of single-line path—the time
factor for the path is the same as the time factor for the line. The time factor
setting, regardless of how it is set, is used directly to calculate the path’s time
factor.
•
If a path consists of more than one line—as in the case of a multi-line path—the
path time factor is derived from a composite of the time factors for the single lines
that make up the multi-line path. Accordingly, the path time factor can possibly
change as lines go up or down. (Note, however, that if you set PATHTF n, it sets
the path time factor directly, regardless of the line time factors and line states.)
The formula for calculating a path time factor from the line time factor is as follows
(the ROUND function rounds to the nearest integer):
PATHTF = ROUND(224000 / (224000 / LINETF1 + 224000 / LINETF2 + …))