APS overview

Overview

CAUTION Service Disruption

An NE transmits data only on the working line.

For a single failure, this configuration can cause a delay of up to 100 ms during an APS switch.

On the NFM-P, the main APS elements are the following:

• APS groups

  An APS group is an aggregation of one or two SONET/SDH ports and the associated logical ports, known as APS channels. The first port is known as the working channel and must be configured in the APS group. The second port is the protection channel, which is optionally configurable. In a 1+1 optimized APS group, the protection channel is replaced with a second working channel.

• APS channels

  APS channels are logical and model the physical ports. The set of associated data for an APS channel includes the corresponding physical port identifier, the role, which is working or protection, and the name of the APS group to which the port belongs. If a protection channel is configured, it carries the traffic of the failed working channel. If the protection channel fails, the working channel carries the traffic.

• APS bundles

  APS bundles protect multilink PPP and IMA bundles on channelized ASAP MDAs. All the members of a working or protection APS bundle must belong to the same working or protection line of the APS group.

• APS common port configurations

  All SONET/SDH port parameters on the working and protection channels in an APS group must be identical except for the following:

  • Clock Source

  • Loopback

  • Report Alarms

  • BER Signal Degradation Threshold

  • BER Signal Failure Threshold

  • SONET Section Trace Mode

• APS commands

  Each APS channel has one APS operational command associated with it. The APS operational command is determined by the last command that is issued to both APS channels and the signal condition of the working and protection ports. APS commands affect the APS operational states but do not affect the configuration. The operational state does not persist through an NE restart.

Table 38-1, Events affecting 1+1 protection The following table describes the events that affect 1+1 protection and their relative priority.

Table 38-1: Events affecting 1+1 protection

Priority	Event	Event type
1	Lockout of protection	User initiated
2	Signal failure on protection line	Automatically initiated
3	Forced switch	User initiated
4	Signal failure on working line	Automatically initiated
5	Signal degradation	Automatically initiated
6	Manual switch	User initiated
7	WTR time (revertive switching only)	User initiated (state request)
8	No reversion (non-revertive switching only)	User initiated (state request)

Consider the following when configuring APS:

• A port can belong to only one APS group.

• Two ports that belong to the same APS group must be of the same port type and have the same traffic speed.

• An APS group has one set of APS channels. The set can contain one or two APS channels.

• An APS channel can belong to only one APS group.

• A SONET/SDH port can either belong to only one APS channel.

Bidirectional mode

In 1+1 system bidirectional mode, a signal failure in either direction causes both the near-end and far-end NEs to switch to the protection channels. The highest-priority local request is compared with a remote request; the request that has the greater priority is selected. See Table 38-1, Events affecting 1+1 protection for the list of events that affect 1+1 protection.

Unidirectional mode

In a 1+1 system unidirectional mode, the working interface switches to the protection interface only for the direction in which a signal failure occurs. For example, if there is a signal failure in the transmit direction, the working interface switches to the protection interface for transmission but not for the receipt of data.