Specifications

ShoreTel Architecture Call Control
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ShoreTel 14 Maintenance Guide 21
In ShoreTel’s implementation of SIP call control, functions are split among the following software
modules:
 User Agent
 Location Service
 Admission Control Service
 Bandwidth Manager
SIP architecture deploys a peer-to-peer model in which endpoints can function either as clients or
servers.
User Agents
User agent objects represent call endpoints—an extension or a trunk. Each user agent is addressable
by a SIP URL.
For extensions, the URL syntax is:
sip:nnn@ip_addr:5441, where:

nnn – extension number

ip_addr – IP address

5441 – UDP port number used by ShoreTel Call Control
For trunks, the URL syntax is:
sip:TGrp_xxxpyy@ip_addr:5441, where:

xxx – trunk group number

yy – port number

5441 – UDP port number used by ShoreTel Call Control
In ShoreTel’s call control protocol, user agents representing endpoints on an IP network operate as
peers, functioning as clients when initiating requests and as servers when responding to requests.
Location Service
Endpoint location exchange is performed via ShoreTel’s proprietary Location Service Protocol (LSP).
When switches first connect, they exchange all known SIP URLs. Afterwards, only configuration
updates are transmitted.
LSP is based on UDP. The service relies on keep-alive pings (sent every 30 seconds) to detect
switches that are unreachable.
Admission Control Service
Admission Control Service instructs Bandwidth Manager to reserve bandwidth for intersite calls. If a
request is successful, updates are sent to Bandwidth Managers running on other switches at the same
site.