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High Availability

The Cisco AS5850 Universal Gateway is designed to meet the high-availability requirements found in carrier-class environments.

Redundancy, hot-sparing, call-management, and self-management features are all part of the carrier-class attributes available in the

Cisco AS5850.

Dual load-sharing redundant Gigabit Ethernet packet interfaces provide a highly available backhaul method to the IP core. Dual redundant

Fast Ethernet provides reliable links to the management systems and the call agents.

Enhanced RSC Redundancy

The Cisco AS5850 ERSC hosts the centralized functions of Layer 3 packet switching, bus clock, and Stratum 3 timing generation, as well

as external connections, including egress interface to the IP or packet-based network. Hardware is present on the ERSC to detect critical

faults and provide an autoreboot capability. Each ERSC provides dual redundant Gigabit Ethernet backhaul interfaces, and dual Fast

Ethernet interfaces for management and call agent traffic. These interfaces can be connected to the same core device or different core

devices, depending on the type of interface resilience required.

When two ERSCs are installed, chassis-management functions such as clock control and environmental monitoring benefit from redundant

circuitry on the ERSCs. Chassis management redundancy is automatically enabled any time two ERSCs are present in a Cisco AS5850

Universal Gateway. Health monitor functions on redundant ERSCs allow a redundant pair to determine if failover should be preformed,

assuring that failovers occur only to a healthy ERSC and preventing failover flapping.

High Availability with RPR+

High availability on the high-end universal gateway is an increasingly important customer requirement, particularly with the Cisco AS5850

Universal Gateway because it is deployed into the traditional telecommunications-carrier space with voice over IP (VoIP) and other packet-

based converged services at higher (and increasing) port and trunk densities.

The Cisco AS5850 can use dual enhanced ERSCs with Route Processor Redundancy Plus (RPR+) to increase network availability. RPR+

takes advantage of redundancy by establishing one of the ERSCs as the active processor while the other ERSC is designated as the standby

processor. Following an initial synchronization between the active and standby ERSCs, RPR+ dynamically maintains configuration

information between the two RSCs, meaning that the standby ERSC does not need to be reloaded and reinitialized if the active ERSC fails.

The Cisco AS5850 provides unique functions when in RPR+. The active CPU controls resources on the active ERSC card as well as on the

standby ERSC card, allowing the active CPU to use many of the resources on the standby card in a redundant or load-sharing configuration

such as the standby card switch fabric, Gigabit Ethernet and Fast Ethernet interfaces, and Stratum 3 clocking system.

A switchover from the active to the standby processor occurs when the active ERSC fails, is removed from the Cisco AS5850 chassis,

or is manually taken down for maintenance. When the active ERSC fails, all active calls are dropped. After the switchover, new calls are

accepted in less than one second plus any route convergence time.

Fault Tolerance

The Cisco AS5850 Universal Gateway achieves fault tolerance through the use of hot-swappable DSP cards, power supplies, redundant

ERSCs, fan units, and redundant Gigabit Ethernet and Fast Ethernet links. ERSC redundancy enables a system to keep running if a failure

occurs. Additional mechanisms enable redundant components to be built into the system and used when required without resulting in

active call loss.

Call Admission Control

CAC allows the platform to gracefully refuse calls based on local call-processing resources, such as CPU load, memory usage, bandwidth

availability, or measured congestion on the IP network. Such call control dramatically improves the reliability of the Cisco AS5850

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