Distributed Call Control Chapter 2: System Overview
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2.3 Distributed Call Control
The heart of the ShoreTel 8 system is the distributed call control software, which runs on
the ShoreGear voice switches on top of VxWorksTM, a real-time operating system. Each call
control element manages the call setup and call teardown, including features such as
transfer, conference, forward, call permissions, and call routing. The voice switches
communicate on a peer-to-peer basis, eliminating any single point of failure. For instance,
if one ShoreGear voice switch goes offline, all other ShoreGear voice switches continue
operating. When the voice switch comes back online, it rejoins the voice network with no
impact on system operation. There is no server involved with the basic telephony, so the
system delivers levels of availability unmatched by even legacy vendors.
2.3.1 Distributed Routing Service
Distributed Routing Service (DRS) allows larger systems to scale beyond 60 switches up to
a total of 200 switches (including SoftSwitches). The Distributed Routing Service is
optional on systems up to 60 switches, but must be enabled on systems with 60 or more
switches.
When the Distributed Routing Service is disabled, ShoreGear switches build an internal
routing database from the peer-to-peer communication with other switches. Each
ShoreGear switch contains routing information for all endpoints in the system, including
information regarding trunk selection for outbound calls. When a user places a call from
any extension, each switch can route the call to the correct ShoreGear switch based on its
internal routing database.
When the Distributed Routing Service is enabled, ShoreGear switches only exchange
routing information with other switches at the same site, rather than exchanging the
information with every switch in a multi-site system. Although each ShoreGear switch only
maintains routing information within its site, each ShoreWare server also includes an
instance of the Distributed Routing Service, which maintains system-wide routing
information. When calls are initiated, ShoreGear switches contact the Distributed Routing
Service in order to find the ShoreGear switch or switches necessary to complete the call.
Figure 2-1 The Distributed IP Voice Architecture of the ShoreTel 8 System
Open API Layer
Open
Applications
Voice Endpoints
Integrated
Applications
Open Third-Party
Applications
Open Protocol Layer
Distributed Applications Platform
Single System
Management
Distributed Call Control
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