Alcatel-Lucent 7950 XRS Series, Configuration Manual

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High Availability
Page 234 7950 SR OS Basic System Configuration Guide
• Redundant line cards — Failover to the backup within a minimum time interval,
preferably with no loss of traffic.
• Redundant power supply — A power module can be removed without impact on traffic.
• Redundant fan — Failure of a fan module without impacting traffic.
• Hot swap — Components in a live system can be replaced or become active without
taking the system down or affecting traffic flow to/from other modules.
Router hardware architecture plays a key role in the availability of the system. The principle router
architecture styles are centralized and distributed. In these architectures, both active and standby
route processors, XCMs and XMAs (also called line cards), fans, and power supplies maintain a
low MTTR for the routing system.
However, in a centralized architecture, packet processing and forwarding is performed in a central
shared route processor and the individual line cards are relatively simple. The cards rely solely on
the route processor for routing and forwarding intelligence and, should the centralized route
processor fail, there is greater impact to the system overall, as all routing and packet forwarding
will stop.
In a distributed system, the packet forwarding functionality is situated on each line card.
Distributing the forwarding engines off the central route processor and positioning one on each
line card lowers the impact of route processor failure as the line cards can continue to forward
traffic during an outage.
The distributed system is better suited to enable the convergence of business critical services such
as real-time voice (VoIP), Video, and VPN applications over IP networks with superior
performance and scalability. The centralized architecture can be prone to performance bottleneck
issues and limits service offerings through poor scalability which may lead to customer and
service SLA violations.
Service Redundancy
All service-related statistics are kept during a switchover. Services, SDPs, and SAPs will remain
up with a minimum loss of forwarded traffic during a CPM switchover.
Accounting Configuration Redundancy
When there is a switchover and the standby CPM becomes active, the accounting servers will be
checked and if they are administratively up and capable of coming online (media present, etc.), the
standby will be brought online and new accounting files will be created at that point. Users must
manually copy the accounting records from the failed CPM.