Network Synchronization; Switch Availability; Node Redundancy - Cisco BPX 8620 Installation And Configuration Manual

Network Synchronization

Network Synchronization
Cisco WAN switching cell relay networks use a fault-tolerant network synchronization method of the
type recommended for Integrated Services Digital Network (ISDN). You can select any circuit line,
trunk, or an external clock input to provide a primary network clock. Any line can be configured as a
secondary clock source in the event that the primary clock source fails.
All nodes are equipped with a redundant, high-stability internal oscillator that meets Stratum 3 (BPX)
or Stratum 4 requirements. Each node keeps a map of the network's clocking hierarchy. The network
clock source is automatically switched in the event of failure of a clock source.
There is less likelihood of a loss of data resulting from reframes that occur during a clock switchover or
other momentary disruption of network clocking with cell-based networks than there is with traditional
TDM networks. Data is held in buffers and packets are not sent until a trunk has regained frame
synchronism to prevent loss of data.

Switch Availability

This section describes some of the features that contribute to network availability. Cisco WAN hardware
and software components are designed to provide a switch availability in excess of 99.99 percent.
Network availability is impacted by link failure, which has a higher probability of occurrence than
equipment failure.
Cisco WAN network switches are designed so that connections are automatically rerouted around
network trunk failures, often before users detect a problem. System faults are detected and corrective
action taken often before they become service affecting.

Node Redundancy

System availability is a primary requirement with the BPX switch. The designed availability factor of a
BPX switch is 99.99 percent based on a node equipped with optional redundancy and a network designed
with alternate routing available. The system software, as well as firmware for each individual system
module, incorporates various diagnostic and self-test routines to monitor the node for proper operation
and availability of backup hardware.
For protection against hardware failure, a BPX switch shelf can be equipped with the following
redundancy options:
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If redundancy is provided for a BPX switch, when a hardware failure occurs, a hot-standby module is
automatically switched into service, replacing the failed module. All cards are hot-pluggable, so
replacing a failed card in a redundant system can be performed without disrupting service.
Cisco BPX 8600 Series Installation and Configuration
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Redundant common control modules
Redundant crosspoint switch matrixes
Redundant high-speed data and control lines
Redundant power supplies
Redundant high-speed network interface cards
Redundant service interface cards
Chapter 1 The BPX Switch: Functional Overview
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005