Beta Draft Confidential
Configuring Trunks
About APS
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/057-13
Unidirectional APS Over PNNI
There are two directional switching modes in APS 1+1 architecture: unidirectional
mode and bidirectional mode. In unidirectional mode, the head end makes a decision
on the selector position without regard to the K1/K2 bytes received from the tail end.
In bidirectional mode, the head end will consider the K1/K2 bytes received from the
tail end in deciding the selector position. Unidirectional APS is less disruptive and is
the default mode for the Bellcore GR-253-CORE standard.
APS over PNNI in unidirectional mode is supported for the 4-port OC-3c/STM-1,
1-port OC-12c/STM-4, and OC48/STM-16 modules on the GX 550 BIO1 module.
Special Considerations
Fast APS 1+1 on a CBX 500 — Configure the working and protection physical ports
on different IOMs. (See the Switch Module Configuration Guide
for CBX 3500, CBX
500, GX 550, and B-STDX 9000
for more information.) Configure an APS trunk between
ports on different IOMs in a CBX 500 switch.
Fast APS 1+1 on a GX 550 — Configure the working and protection physical ports
on different modules. (See the Switch Module Configuration Guide
for CBX 3500, CBX
500, GX 550, and B-STDX 9000
for more information.) Configure an APS ATM direct
cell trunk between ports on different modules in a GX 550 switch.
Physical Port Provisioning
You provision Fast APS 1+1 on the physical port as follows:
• Configure the physical port attributes on the working port. (The protection port is
automatically configured with the corresponding values.)
• See the Switch Module Configuration Guide
for CBX 3500, CBX 500, GX 550, and
B-STDX 9000
for more information on configuring Fast APS 1+1 on CBX 500 and
GX 550 switches.
Note – See the Switch Module Configuration Guide for CBX 3500, CBX 500, GX 550,
and B-STDX 9000
for a listing of the minimum software and hardware versions that
support these Fast APS 1+1 options.
As traffic is rerouted from a working trunk to a protection trunk during a failure, the
switchover speed may be less than that provided by Intra-card APS 1+1.
Note – Point-to-multipoint (PMP) circuits are not supported by The Fast APS 1+1
option.
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