Service Availability Versus High Availability - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x Service Availability Configuration Guide
Figure 1 illustrates the multiple layers of JUNOSe Software service availability
99.999%
The security layer protects the network from DoS attacks.
The network resiliency layer protects against port, link, and node failures. You can
configure IEEE 802.3 ad link aggregation for Ethernet, and Virtual Router Redundancy
Protocol (VRRP) to improve network resiliency.
The software availability layer protects against software failures by using hot-fixes
or installing a higher-numbered software release. You can perform a unified in-service
software upgrade (ISSU) instead of the conventional software upgrade to reduce
outage. You can eliminate or reduce single points of failure by configuring stateful
SRP switchover (high availability). Any network component with an uptime of 99.999
percent is considered highly available with a downtime of less than 5 minutes in a
year.
The hardware redundancy and design layer introduces redundancy in the network
in the form of multiple power supplies, cooling devices, line modules, and sometimes
even a router. For instance, you can install a backup line module in your router to
protect against line module failure. You can also configure a router as a backup router
that accepts subscriber login requests when the master router fails.

Service Availability Versus High Availability

High availability is a measure of the uptime of a network or network component. A
network component that has a downtime of 5 minutes is accessible or available 99
percent of the time. If a failure occurs, a backup component is available within 5
minutes. A highly available network is a network that has components that either
have high reliability or have the ability to recover very quickly from a failure, or both.
Service availability refers to the ability to provide uninterrupted delivery of services.
For example, from the time when a component fails to the time when the backup
component is accessible, the delivery of services is interrupted. To provide
uninterrupted delivery of services, highly available components must maintain session
details and other data across failures. Service availability can thus be defined as the
ability to provide uninterrupted delivery of services using a highly available network.
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Service Availability Overview
Protects infrastructure against DoS attacks
Network Resiliency
Protects against port, link (fiber cuts), and network node failures
Software Availability
Protects against software crashes and minimizes downtime from software upgrades
Hardware Redundancy and Design
1:1 or N:1 component-level protection
Security