Specifications

ShoreTel Voice Switches Overview
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ShoreTel 14 Maintenance Guide 62
Overview
ShoreTel Voice Switches provide physical connectivity for the PSTN and analog phones, and logical
connectivity for IP endpoints on a reliable, highly scalable platform for the ShoreTel call control
software. The call control software runs on the operating system of the switch, for example Linux or
VxWorks
®
.
The ShoreTel Voice Switches have flash memory that allows permanent storage of the call control
software and configuration information. The voice switches have no moving parts (that is, no hard
drive) other than a highly reliable fan. The switches include the necessary DSP technology to enable
toll-quality voice with features like echo cancellation, voice compression, and silence suppression.
TMS propagates configuration data from the database to each switch upon reboot of either TMS or the
switch. The data sent is a subset of configuration data specific to that switch. TMS also maintains this
data by propagating changes to the database to those switches affected by the change. The TMS/
Switch configuration interface uses the same Network Call Control protocol that is used for other TMS/
Switch communication. The TMS/Switch configuration interface uses the same Network Call Control
protocol that is used for other TMS/switch communication. The NCC protocol is based on Sun RPC.
You can obtain the configuration data that TMS sends to any specific switch with a CLI command. For
more information, see Commands Available Through VxWorks® CLI on page 76.
Switches share their switch-specific configuration with other switches in the system using the UDP-
based Location Service Protocol (LSP). Switches keep current with other switches by propagating
their changes and receiving them from other switches. For information about viewing switch-to-switch
communications, see Commands Available Through VxWorks® CLI on page 76.
The ShoreTel Voice Switches communicate call control information on a peer-to-peer basis. When
Distributed Routing Service (DRS) is enabled, switches exchange LSP messages only with other
switches at the same site. DRS communicates directly with the database to keep the database
configuration current. TMS tells each switch how to find DRS as part of the configuration process
described earlier. When DRS is enabled, switches generally give DRS an opportunity to resolve
numbers, so that its more complete view of the system can be leveraged to find the best contact. If the
switch knows where an intra-site extension is, it does not involve DRS.
For analog phones, the switch detects whether the phone is on or off hook, collects digits from the
phone, and (based on digits collected) determines when a call is established. If necessary, the switch
communicates with other switches (in some cases this may not be necessary, such as when the call is
to an endpoint directly on the switch) to establish a call between the appropriate endpoints.
The switch acts as a media gateway for the PSTN and analog phones by encoding the analog voice
and transmitting it to the other endpoint over the IP network using RTP. The switch also uses NCC to
send events to TMS about digit collection, caller ID, call establishment, and so forth. TMS makes this
information available to the server applications. These applications are not necessary for many calls
(such as those between two phones or a trunk and a phone, which can be established with only the
switches controlling the phones and trunks), but they can enhance the user experience. For example,
Communicator can provide information about the call to the user's desktop.
Note
Switch-specific configuration is in FLASH but configuration for other switches is in RAM. After
rebooting, the switch syncs with LSP to keep current with these configuration changes.