Installation guide

392 Planning and Installation Guide ShoreTel 14.2
Session Initiation Protocol Overview
D
Overview
The protocol, which works at the application layer, allows users to initiate interactive sessions between
any network devices that support the protocol. SIP is capable of initiating or terminating Internet
telephony calls and other multimedia applications such as video or gaming.
The protocol is based on a client-server model. With support for redirection services, networked users
can initiate a call or receive a call, regardless of their physical location.
In its networking negotiations SIP takes into account the following pieces of information:
 The address of the end system
 The physical media
 The call recipient's acceptance to the invitation
The protocol then configures the parameters for the session and handles the call setup and tear-down.
SIP allows two discrete ShoreTel systems to be integrated with any IP connection, without the need for
physical tie trunking. (Note that care should be taken to make sure that the extension numbering plans
in the two systems do not overlap, and that if they do overlap, translation tables need to be used to
resolve conflicts.)
In the current release of the ShoreTel system, the SIP trunks and SIP tie-trunks support the SIP
capabilities. Like other trunk, the SIP trunk assignments are switches, so that SIP calls into and out of
the ShoreTel system traverse these SIP trunks. However, up to five SIP trunks can be associated with
one analog switch port, meaning that there will be no physical channel/port associated with each SIP
trunk. The SIP trunk is a logical trunk end point which only handles call control responsibilities. The
media flows directly between the end-point SIP devices (i.e. call initiator and the call terminator),
freeing the switch from the burden of controlling media flow.
General SIP Comments
Conferencing
 Ports for MakeMe conferences must be available on the initiating side of a 3-way conference call
involving a SIP end-point.
 On ShoreTel IP800 models or third-party SIP phones, MakeMe conference ports are needed even
for 3-way conferences. Note that configuration of any Make Me conferencing support in ShoreTel
Director requires at least 4 available conference ports.
 ShoreTel SIP trunks support from 4-way up to a maximum of 6-way conferences. This
conferencing relies on ShoreTel’s MakeMe capability. End-users can set up MakeMe conference
calls by using their ShoreTel Communicator. Like extensions with support of Media Gateway
Control Protocol (MGCP), SIP extensions require permissions and a minimum of 4 MakeMe ports
to set up MakeMe conference call.