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Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5
Part Number OL-3847-01 Rev. D0, April, 2004
Chapter 4 Planning Intermediate Route Selection
Additional Routing Features in MGX and SES Nodes
Note In all Release 3 software, the preferred routing feature specifies a route within a single peer group.
Release 3 software does not support preferred routes that span multiple peer groups. Release 4 and later
software does support preferred routes that span multiple peer groups.
The preferred route and directed route for an SPVC or SPVP is defined when the connection is created.
Although you can change the preferred route configuration after a connection is created, you can
eliminate reconfiguration by planning for preferred routes before creating connections.
Priority Routing
Priority based routing allows you to specify a priority for each SPVC or SPVP connection. High priority
connections are established before low priority connections. During failures, the high priority
connections are also released and reestablished before low priority connections.
Priority routing was introduced in Release 3.0.00 and is supported on the MGX 8830, MGX 8850
(PXM1E), MGX 8850 (PXM45), and MGX 8950 switches and the MGX 8880 Media Gateway. Release
3.0.20 and later support priority routing on SES nodes.
The routing priority for an SPVC or SPVP can be defined with either the addcon or the cnfcon
command. For SVCs and SVPs, the routing priority is assigned using the cnfpnportsig command. This
routing priority also applies to the priority bumping feature. Although you can change the routing
priority after a connection is created, you can eliminate reconfiguration by planning for priority routing
before creating connections.
Tip The priority routing feature allows administrators to influence the order in which connections are routed
or rerouted when network events require connection rerouting. The priority routing feature does not
change the criteria for selecting routes. It controls the sequence in which connections are routed or
rerouted.
Grooming
Connection grooming is the process of checking each connection to determine if a more efficient route
is available. If a prospective new route is significantly better than the incumbent route, the connection is
rerouted.
Grooming is also used to return a connection to its non-directed preferred route (if configured) after it
has been rerouted due to failure along its preferred route. Connections will only return to their
non-directed preferred routes when one of the following occurs:
• The connection is manually groomed.
• Automatic grooming is enabled and the grooming operation completes.
• The current connection route experiences a failure.
Grooming may be needed, for example, if a link fails along the most desirable route, and then returns to
service. When the link fails, the connection is rerouted to another route, which may be a less desirable
route. To return the connection to the more desirable route, you can use manual grooming or scheduled
grooming. The advantage to scheduled grooming is that is can occur automatically at times when the
network is not busy.