Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-24
Negotiating Path Time Factors
RSIZE n has a range of 0 to 186 to designate the line time factor in selecting the best
path to other nodes in the network. A smaller number indicates a more desirable path
for routing.
As always, the actual time factor used for a path between two immediate neighbors is
negotiated and the larger of their respective calculations is used.
Time Factors and Pathchange Messages
When a line comes up, Pathchange messages are exchanged to verify and negotiate
various parameters between the line handlers on each side of the line. One of the
parameters negotiated is the line’s time factor, the larger time factor being used by
both sides.
Time Factors and Netmap Messages
Netmap messages are exchanged between the NCPs of neighboring systems to
spread network topology information. Netmap messages contain the total time factor
and number of hops from the sender to each other system in the network.
Time Factors and Line Status Messages
The EXPLH_EXPNCP_LINE_STATUS message is sent from the line handler to NCP
to report both a change in line status and various parameters of a line that has come
up, such as nextsys, time factor, and delay factor.
Negotiating Path Time Factors
During connection to a remote node, the calculated path time factors are negotiated to
the higher time factor. $NCP is informed of this negotiated time factor and updates its
NETMAP table information. This negotiated time factor is used by $NCP to calculate
the route time factor.
If a line in the path fails, $NCP updates its NETMAP table to reflect the decrease in
path bandwidth. Reactivation of the line updates the NETMAP table to reflect the
increase in bandwidth. If a communications device fails, $NCP updates its NETMAP
table to reflect the decrease in bandwidth for all lines connected to the failed
communications device. (Note, however, that if PATHTF n is used to set the time
factor, this does not apply; instead, the time factor is constant.)
Best-Path Route Selection
Although $NCP may be aware of several routes to a destination node, only a single
route is active at any one time. This single route, which is the most efficient route at a
given point in time, is called the best-path route.
$NCP uses the following criteria to select the best-path route to a specific node:
•
The route must have the lowest TF of all possible routes.