ShoreTel 8 Planning and Installation Guide 291
Session Initiation Protocol
This chapter provides detailed information about the Session Initiation Protocol (SIP). You
should refer to this chapter for help in planning a SIP deployment on your ShoreTel system.
Session Initiation Protocol (SIP - RFC 3261) is a newer protocol that is still being fine
tuned by the IETF and that is regarded as having the potential to become the global
signaling standard that will enable all switches, gateways, and phones to talk to one
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
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
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.)
Further, the addition of SIP obviates the need to support other trunking standards, such as
BRI, through use of a SIP gateway.
In ShoreTel 7.5, SIP is supported via SIP trunks. SIP trunks will be assigned to a particular
switch as with any other trunk, so that SIP calls into and out of the ShoreTel system will be
routed through these 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
WARNING We do not recommend placing Emergency 911 calls from SIP devices.
ShoreTel supports SIP trunks, but does not directly support SIP extensions with this