Distributed Voice Servers

Share This

ShoreTel – Distributed Voice Servers


The ShoreTel system supports not only distributed call control, but also distributed voice application servers.

Distributed servers are extremely valuable for two purposes:

• Reducing WAN bandwidth by providing local voice mail and auto-attendant services

• Increasing the scale of the system


Even though there are multiple servers, the ShoreTel system provides a single image of your entire network.

The system is currently certified to support up to 21 servers, one main server and up to 20 distributed servers.

Consider adding a server at a site when the site exceeds 100 users. Add a new server for every 1,000 users.


The distributed servers run the following voice applications:

Voice Mail – Each server supports 254 simultaneous voice mail or auto-attendant connections. The voice mail system uses SMTP to transport composed messages between the distributed servers. The ShoreTel system also supports linking to legacy voice mail systems using AMIS protocols.

Auto-Attendant – The system supports up to 1000 menus that are hosted on every server, and each server provides 64 voice mail/auto-attendant connections.

Configuration – The system enables users to log in and make configuration changes (call handling modes, etc.) from their ShoreTel Communicators client or from the Communicator for Mobile call handling mode client (if supported).

Maintenance – The system provides a web site accessible through ShoreTel Director for maintenance of all the remote servers. The distributed voice applications use a Remote TAPI Service Provider that relies on the call control information from the main server. Using redundant network paths to the main

server can improve reliability of the remote server.


Distributed Voice Mail

The ShoreTel system uses Distributed Voice Mail (DVM) to provide greater voice mail availability. Each ShoreTel remote server has an instance of the telephony platform included, allowing voice mail and auto-attendant services to maintain full functionality during WAN short-term outages. The enhanced DVM included with the ShoreTel remote server allows users with mailboxes on the remote server to receive and pickup voice mail

messages without depending on WAN connectivity to the headquarters server. The message waiting indicator (MWI) lights will correctly update with or without WAN connectivity.


Additionally, incoming calls can still reach the automated attendant, access the dial-byname directory, and reach their intended local party during a WAN outage. If a party cannot be reached directly due to a WAN outage and his or her call handling would send unanswered calls to voice mail, the call is handled by the local voice mail server. The caller hears a generic greeting including the intended party’s recorded name and can leave a

message. This message will be forwarded at a later time to the home voice mail server for the addressee via SMTP.


Similarly, the enhanced DVM provides greater Communicator availability during WAN outages. If the WAN loses connectivity, users will retain full Communicator functionality as long as there is a DVM server at the same site as the users, the users voice mailboxes are on that server, and the DVM server is managing the switch that manages the users’ phones.


Although each voice mail server is autonomous in delivering voice services, it still must have connectivity to the configuration data stored on the headquarters server in order to make configuration changes. Specifically, users on an isolated remote server would not be able to change call handling modes or make other changes that require modification to the configuration data on the headquarters server.


IP Phone Limitations/Requirements

Connectivity is required between the phone and the switch that is controlling the phone (this will be referred to as “basic connectivity”). All aspects of the phone’s operation are functional when this basic connectivity exists, with the following exceptions:


Directory feature: In addition to basic connectivity, the directory feature also requires connectivity between the switch and a headquarters (HQ) server or distributed voice mail (DVM) server that controls that switch.

Options features, Changes to Call Handling Mode (CHM), Wrap-Up: In addition to basic connectivity, these features require either connectivity between the switch and an HQ server or DVM server that controls that switch. In addition, if the aforementioned switch is a DVM server, connectivity is required between that server and the HQ server or Distributed Database (DDB) services must be enabled for the

DVM. Further, connectivity between the DVM server and the HQ server is required for successful synchronization between the Replication Master and Slave databases.

Switch-to-switch extension monitoring: This condition exists when a programmed button requires monitoring activity on an extension that is serviced by a different switch than the one that controls the phone.


For example, if switch A (the phone’s switch) is controlled by server X, and switch B (the monitored extension’s switch) is controlled by server Y., then servers X and Y may be a DVM or the HQ server.


For proper functionality of the switch-to-switch extension monitoring, the following conditions must exist:

— Switch A must be able to talk to server X.

— Server X must be able to talk to server Y.

— Server Y must be able to talk to switch B.

— If X and Y are the same, connectivity is, of course, assumed to exist.

• Auxiliary information on incoming calls, such as trunk information and called workgroup (WG) information, requires connectivity between the switch and a headquarters (HQ) server or distributed voice mail (DVM) server that controls that switch.


Communicator Limitations/Requirements

Communicator: Communicator utilizes two communications channels, TAPI and CSIS. TAPI is used to communicate with the server that manages the switch that manages the user’s phone (regardless of whether the phone is an analog or IP phone). CSIS is used to communicate with the user’s voice mail server. (These two servers are often the same device.) As long as the client can reach these two servers, Communicator is fully functional.

First-time Communicator users: When a user logs into Communicator for the first time, CSIS and TAPI both communicate with the HQ server in order to find out which server they need to use. Thus, for first-time users, a connection is required between the client and the HQ server regardless of where their VM and extensions are being serviced.

Workgroup functionality: If users are configured to have workgroup functionality, they can access the mailboxes of all workgroups to which they belong. This requires connectivity to the server(s) on which those mailboxes reside.




CSIS (Client Server Internet Service), is a ShoreTel proprietary protocol that uses HTTP messages to communicate between Call Manager (client) and ShoreWare servers. The CSIS protocol communicates configuration updates such as call handling mode settings and Outlook integration. The CSIS client holds “open a pending HTTP request” in order to receive notifications from the CSIS server.


TAPI (Telephony Application Programming Interface) allows applications to control telephony functions between a computer and telephone network for data, fax, and voice calls. It includes basic functions, such as dialing, answering, and hanging up a call. It also supports supplementary functions, such as hold, transfer, conference, and call park found in IP phones telephone systems.

Related Blogs

As teams become more mobile, working across multiple locations and in-field environments...
How companies do business has fundamentally changed post-pandemic. Many organizations have moved...
  If you don’t have one already, there’s a good chance that...
  At its core, a firewall acts as a barrier between a...
How Does Teams Play In Today’s Evolving Work Environments? Increasing pressures on...
Mitel Product Updates for UCaaS When Mitel announced its strategic partnership two...

Join Our Newsletter & Learn

Get our latest content delivered to your inbox.