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Chapter 2 Campus Infrastructure Considerations

High Availability

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Cisco IP Telephony Network Design Guide

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as power and supervisor modules. Network redundancy, however, is achieved

with a combination of hardware, software, and intelligent network design

practices.

Network redundancy is achieved at many levels (see Figure 2-2). Physical

connections exist from the edge devices where IP phones and computers are

attached to two spatially diverse aggregation devices. In the event that an

aggregation device fails, or connectivity is lost for any reason (such as a broken

fiber or a power outage), failover of traffic to the other device is possible. By

provisioning clusters of Cisco CallManagers to provide resilient call control,

other servers can pick up the load if any device within the cluster fails.

Advanced Layer 3 protocols such as Hot Standby Router Protocol (HSRP) or fast

converging routing protocols, such as Open Shortest Path First (OSPF) and

Enhanced Interior Gateway Routing Protocol (EIGRP), can be used to provide

optimum network layer convergence around failures.

Advanced tools are also available for the MAC layer (Layer 2). Tunable

spanning-tree parameters and the ability to supply a spanning tree per virtual LAN

(VLAN) allow fast convergence. Value-added features such as uplink-fast and

backbone-fast allow intelligently designed networks to further optimize network

convergence.

High availability of the underlying network plays a major role in ensuring a

successful deployment. This translates into redundancy, resiliency, and fast

convergence.

Further Information

For more information on high availability, see the “Additional Information”

section on page xvii.

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Cisco WS-X4604-GWY - VoIP Gateway Especificaciones Pagina 42