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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
When two parallel links are available along the route, the controller chooses a link based on the
configuration of the switch. The link selection options are:
• AW —Selects the link with the least AW in the egress direction. This is the default.
• AvCR—Selects the link with the largest AvCR in the egress direction.
• maxCR—Selects the link with the largest maxCR in the egress direction.
• loadbalance—Selects links randomly so that one link does not become overburdened while the
other is idle.
Additional Routing Features in MGX and SES Nodes
The following sections describe additional routing features you might want to consider when planning
a PNNI network.
Preferred Routing
Preferred routes allow the switch administrator to define a specific route between the source and
destination nodes, and then specify this route as the preferred route when defining SPVCs. If the
connection is configured as a directed route, no other route is allowed, even if the route fails. If the
connection is not configured as a directed route, other routes are considered when the preferred route is
not available. When other routes are required, the switch can use the pre-calculated routing tables or
on-demand routing.
Preferred 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 preferred routing on SES nodes.
Note Preferred routes created with Release 3 software cannot be gracefully upgraded to Release 4 or later
preferred routes.
Table 4-3 Link Selection Parameters Required for Various Classes of Service
Service
Class Address AW maxCR AvCR CTD CDV CLR
0
1
1. CLR
0
is the cell loss ratio for cells with the Cell Loss Priority bit set to 0.
CLR
0+1
2
2. CLR
0+1
is the cell loss ratio for all cells with the Cell Loss Priority bit set to either 0 or 1.
CBR
Required Required Required Required Required Required Required Required
rt-VBR
Required Required Required Required Required Required Required Required
nrt-VBR
Required Required Required Required Required — Required Required
ABR
RequiredRequiredRequiredRequired————
UBR
RequiredRequiredRequired—————