Specifications

ShoreTel Architecture System Reliability
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ShoreTel 14 Maintenance Guide 27
System Reliability
System reliability is ensured at several levels, including:
 Distributed Switch Control
 Distributed Database
 Client Application Service (CAS)
 Public Switched Telephone Network (PSTN) Failover
 CDR Data Storage
These areas are described in the following sections. For more information about failover for IP phones,
see IP Phone Failover on page 163.
For configuration details about PSTN failover configuration, CDR data, or IP phone configuration, see
the ShoreTel System Administration Guide.
Distributed Switch Control
The ShoreTel Telephony Management Service (TMS) runs on every ShoreTel Distributed Voice Server
(DVS), ensuring switch control even if there a WAN outage between a remote DVS and the
Headquarters site. Because multiple servers share the task of switch management, if a server fails,
only the extensions it controls may be affected by a disruption in service.
Distributed TMS enables applications to handle calls on the switches at remote sites during a loss of
network connectivity between the remote server site and the headquarters site. The co-located TMS
provides local control of switches and local control by applications such as the Communicator client
and IP Phone displays using Client Application Services (CAS). Applications are able to provide all of
the features they normally provide (during full WAN connectivity) for extensions on locally controlled
switches. Monitoring and control of extensions on remotely controlled switches without a local DVS are
still affected by WAN outages.
Distributed TMS also reduces the affects of a particular TMS/Server outage to just those extensions
controlled by that TMS instance.
Overall system scalability is increased with this feature because TMS instances control a subset of the
switches in an entire system rather than all the switches in the system. Scalability is also increased
because TMS instances handle a subset of Communicator clients rather than all clients in the entire
system.
WAN Outage
Distributed Telephony Application Service (DTAS) is responsible for routing call control and events
between applications and the TMS instance responsible for a given extension.
When there is a loss of connectivity between the HQ database and a local DVS, DTAS continues to
operate, except that additions and deletions to the configuration database are not seen by local
applications. DTAS services involving the local TMS are available. DTAS operations involving remote
TMS instances not reachable because of WAN outage are not available.