Cisco ASR 900 Series Configuration Guide

SONET VT Configuration Parameters
The following parameters affect SONET VT configuration:
• BERT — Starts the BERT test.
CEM Group — Specifies the time slots for CEM group mapping.
• Clock — Specifies the clock source for VT.
• Description — Specifies the description of the controller.
• Loopback — Sets the VT in the loopback mode.
• Overhead — Configures VT line path overhead flags.
• Shutdown — Disables the VT interface.
• Threshold — Configures the VT threshold values.
SONET Protection Switching
Automatic protection switching (APS) is a protection mechanism for SONET networks that enables SONET
connections to switch to another SONET circuit when a circuit failure occurs. A protection interface serves
as the backup interface for the working interface. When the working interface fails, the protection interface
quickly assumes its traffic load.
The SONET protection schemes comply with GR-253 and ITU-T G.783. It allows Optical Interface Module
to work seamlessly as SONET Add or Drop Multiplexers (ADMs). The implementation of the above protection
schemes allows a pair of SONET lines or paths to be configured for line or path redundancy. In the event of
a fiber cut, the active line or path switches automatically to the standby line or path up to 60 milliseconds
(2/5/10 millisecond for holdover and 50 millisecond switchovers).
Optical Interface Module supports the following SONET protection switching schemes:
•
Linear Bidirectional 1+1 APS
•
Linear Unidirectional 1+1 APS
1+1 APS
In the 1+1 architecture, there is one working interface (circuit) and one protection interface, and the same
payload from the transmitting end is sent to both the receiving ends. The receiving end decides which interface
to use. The line overhead (LOH) bytes (K1 and K2) in the SONET frame indicate both status and action.
The protection interfaces need to be configured with an IP address of the chassis that has the working interface,
using APS commands. The APS Protect Group Protocol, which runs on top of UDP, provides communication
between the process controlling the working interface and the process controlling the protection interface.
Using this protocol, interfaces can be switched because of a chassis failure, degradation or loss of channel
signal, or manual intervention. In bidirectional mode, the receive and transmit channels are switched as a pair.
Two SONET connections are required to support APS.
The following option is available for linear bidirectional 1+1 APS:
1-Port OC-192 or 8-Port Low Rate CEM Interface Module Configuration Guide, Cisco IOS XE Everest 16.7.x
(Cisco ASR 900 Series)
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Configuring SONET
SONET VT Configuration Parameters

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English