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Configuring Unidirectional Switching Mode Support

You can configure interoperation with SONET/SDH Line Terminating Equipment (LTE) that is provisioned for unidirectional linear APS in 1+1 architecture on the following interfaces:

Unchannelized OC3, OC12, and OC48 SONET/SDH interfaces on T-series platforms
SONET/SDH interfaces on the M40e routing platform
ATM over SONET interfaces

By default, APS supports only SONET/SDH LTE that is provisioned for bidirectional mode.

In bidirectional switching mode, the working interface switches to the protect interface for both receipt and transmission of data, regardless of whether the signal failure is in the transmit or receive direction.

In true unidirectional mode, the working interface switches to the protect interface only for the direction in which signal failure occurs; for example, if there is a signal failure in the transmit direction, the working interface switches over to the protect interface for transmission but not receipt of data. When the protect interface operates in unidirectional mode, the working and protect interfaces must cooperate to operate the transmit and receive interfaces in a bidirectional fashion.

The JUNOS software does not support true unidirectional mode. Instead the software supports interoperation with SONET/SDH LTE provisioned for unidirectional switching. This means that the SONET/SDH LTE on the router receives and transmits on one interface, even when you configure unidirectional support. The JUNOS implementation of unidirectional mode support allows the router to do the following:

Accept a unidirectional mode as valid
Trigger the peer (ADM) selector to switch receive from working interface to protect interface or the reverse
Not send reverse requests to the far end (ADM)

To configure unidirectional mode support, include the switching-mode unidirectional statement, at the [edit interfaces interface-name sonet-options aps] hierarchy level:



[edit interfaces interface-name sonet-options
aps]

switching-mode unidirectional;

Note: On interfaces with unidirectional APS support configured, revertive mode and load sharing between circuits are not supported.

To restore the default behavior, include the switching-mode bidirectional statement, at the [edit interfaces interface-name sonet-options aps] hierarchy level:



[edit interfaces interface-name sonet-options
aps]

switching-mode bidirectional;

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