High Availability Networks
Automatic Protection Switching
Features
- Disaster Recovery Capabilities
- Highly Reliable, Redundant Architecture
- Proactive Performance Monitoring
- End-to-End, Point-and-Click Provisioning
- Remote Management and Integral Diagnostics
- Environmentally Hardened Design
Introduction
When network availability is of utmost importance, the Automatic Protection Switching (APS) functionality of DNX platforms provides network operators with a proven-reliable solution. Increasingly stringent Service Level Agreements between service providers and customers demand high availability equipment and facilities solutions. APS is one of the most effective ways to protect hardware and facilities and guarantee high availability network services.
Automatic Protection Switching
APS is the capability of a transmission system to detect a failure on a designated working facility and switch to a designated protection facility to recover the traffic, thus increasing overall system availability. Protection switching may be initiated as a result of signal failure (hard failures such as Loss of Frame), signal degradation (soft failures such as an error rate exceeding a configured threshold), or user command (via local craft port or remote management).
Switching can be revertive, in which case service is automatically restored to the working facility as soon as the failure condition clears, or non-revertive, in which case the protection facility is treated as the working facility pending manual intervention.
DNX platforms provide two different APS schemes that enable service providers to deploy resilient network architectures: 1+1 (one-plus-one) APS and 1:1 (one-for-one) APS.
1+1 APS
1+1 APS
In 1+1 APS there is a protection link for each working link. The traffic is bridged onto both links producing a working signal and a protection signal that are identical. Near End and Far End DNX systems independently monitor the links to ensure traffic is received from the highest quality link. This is accomplished without the need for any special communications or handshaking between the two endpoints.
A DNX-1u Access Gateway configured with 1+1 APS interfacing to a DNX-11/88 Multiservice Access Concentrator with 1+1 APS is illustrated above. In one configuration, high availability service is delivered using diverse T1/E1 facilities. In the other, leased terrestrial lines and fixed wireless facilities are combined to ensure high availability service.
1:1 APS
In 1:1 APS there is also a protection link used to back up a working link. However, other traffic can be carried by the protection link during normal operation. This other traffic can be a mixture of low priority traffic and high priority, mission-critical traffic. As depicted in the following graphic, when the working link fails, its high priority traffic is automatically switched to the protection link, preempting any low priority traffic that might be present.
The flexibility of 1:1 APS requires close coordination between DNX endpoints. The DNX maintains a communication path between endpoints to ensure both ends select the same link for the high priority traffic. Duplicate communication paths embedded in the working and protection links ensure smooth operations.
During normal operation 1:1 APS functionality enables both high and low priority traffic to be transported over two transmission links.
When a facility failure occurs, high priority traffic moves to the protection link, preempting lower priority traffic.
Proven Reliability
With DNX platforms installed in mission-critical locations, virtually every remote device can be managed from a central location. By creating an IP-based telemetry channel within the payload facilities, the DNX delivers remote access to distributed elements of the network. This contributes to OpEx savings by enabling telemetry resources to be networked within the same IP-based channel. Extensive integral diagnostics enable swift resolution of service-affecting issues from central locations, reducing the need to dispatch technical personnel while increasing network availability.
Manageability
The ENvision Plus Element/Network Management platform further contributes to overall availability of the network. ENvision Plus provides traditional element management functionality and acts as a network management resource for all DNX equipment deployed, regardless of the transmission facilities used to interconnect the devices. Simplifying system configuration and providing centralized alarm reporting allows network operators to quickly diagnose and troubleshoot network outages using an intuitive graphical interface. ENvision Plus can optionally provide circuit-based disaster recovery rerouting that enables restoration of service on a network topology basis, in contrast to point-to-point APS functionality, or when redundant facilities between two points do not exist.
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