Tag Switching 9-39
cnfrsrc
Details of More Rigorous Allocations
More rigorous allocations are possible when default values are not applicable. For example, the LCN
allocations for a port group must satisfy the following limit:
In this expression, “a (x)” represents AutoRoute LCNs, “n
1
(x)” represents the guaranteed minimum
number of VSI LCNs, “t” is the number of ports in the port group that are configured as AutoRoute
trunks, and “g” is the total number of LCNs available to the port group. Figure 9-10 shows the
relationship of these elements.
The “270” value reflects the number of LCNs which are reserved on each AutoRoute trunk for
internal purposes. If the port is configured in port rather than trunk mode, “t” = 0, and t*270 drops
out of the expression.
Figure 9-10 Port VSI Partition LCN Allocation Elements
Note Tag switching can operate on a BXM card configured for either trunk (network) or port
(service) mode. If a BXM card is configured for port (service) mode, all ports on the card are
configured in port (service) mode. If a BXM card is configured for trunk (network) mode, all ports
on the card are configured for trunk (network) mode. When the card is configured for trunk mode,
the trunks reserve some connection bandwidth.
In the following expression, “z
1
“ equals the number of unallocated LCNs in the common pool of
LCNs available for use by the port VSI partitions. The value of “z
1
“ is the number of LCNs available
after subtracting the AutoRoute LCNs [sum ( a (x) ], VSI LCNs [sum (n
1
(x) )], and LCNs for trunk
use [t*270] from the total number of LCNs “g” available at the port. For a BXM card with ports
configured in “port” mode, “t” = 0.
z
1
= (g - sum ( a(x) ) - sum ( n
1
(x) -t*270)
sum ( a (x) ) + sum ( n
1
(x) ) +t*270 <= g
Port group LCNs
(e.g. 8192)
t*270
Unallocated LCNs in common pool "g"
available on a FIFO basis to port VSI
partitions that exceed their configured
guaranteed minimum LCN settings.
sum n(x)
z =
g = port group
common pool,
e.g., 8192
sum a(x)
12144
