INTRODUCTION:

The Multi-Site Dispatch (MSD) Hub provides the capability to send half-duplex group calls to groups of radios, which are distributed, across several sites within the network. MSD calls originating at a DT-2000 switch will be directed to the hub and on to the appropriate switches. MSD operation requires audio and data connections between the hub and all switches that are part of the MSD network. Utilizing the "Call Linking" capability inherent in all DT-2000 subscriber units, mobiles and portables radios roaming through the network can receive and initiate calls on their programmed MSD group, without prior specification of which cell sites they may be operating in.

The MSD will support up to 32 sites. MSD Groups and corresponding GIDs may be defined at the MSD hub. A total of 1000 MSD groups will be available for network communication. Each MSD group requires a dedicated GID at each cell. The hub will be limited to 96 audio connections, which can be any configuration of Audio links such as POTS and 2W/4W E&M interfaces are supported. For fast access time, static audio connections (IP, microwave, or PSTN) will be required. Multisite dispatch calls are transmission trunked, which maximizes the channel efficiency of the entire system. The MSD as well as the DT2000 employ a digital matrix switching technique which means that any radio group on any channel can be dispatched across the network to any other group. This allows networked dispatch radios to co-exist with non-networked radios.

HARDWARE AND SOFTWARE REQUIREMENTS:

MULTI-SITE DISPATCH OPERATION EXAMPLE

Figure 1: Multi-Site Dispatch Network HUB with 4 Sites

OPERATION SEQUENCE:

A MSD call is initiated from a radio. The radio communicates with a switch, using a repeater, broadcasting a GID (Group ID) to the switch. The switch received the GID and determines whether the call is intended for MultiSite Dispatch. If so, the call is routed to the hub. The hub then determines which switches in the network will receive the dispatch call. The system then connects the incoming dispatch call to the appropriate switches. The switch receiving the initial MSD call from the radio will also direct the call to appropriate radios within its own service range. See the operational example in Figure 1.

The MSD hub is pre-configured to support multiple GIDs (Group IDs). In the example shown in Figure 1, let's say the Texas Energy Company encompasses a group of mobile vehicles and stations in San Antonio, Houston, Ft. Worth and Dallas. All their radios are then programmed with a set of MSD GIDs including combinations of the cities that they might want to call. In Figure 1, a division of the Texas Energy Company in San Antonio wants to send a dispatch to members of the divisions at Ft. Worth and Dallas. He selects the call group that is defined to talk to radios in cells 1, 2 & 3 (San Antonio, Fort Worth and Dallas) and presses the Push-To-Talk (PTT) on his radio. The pre-programmed GID is sent to the San Antonio Cell Site #1, which transmits the GID to the MSD Hub (which could be located in any of the four cities or in some other location). The MSD Hub receives the MSD GID and bridges pre-established voice lines from the San Antonio cell to cells #2 and #3 in Ft. Worth and Dallas. When the bridge activity is complete, the MSD Hub sends an acknowledgment back to the initiating cell #1 in San Antonio. Cell #1 in turn signals the initiating radio with a proceed tone, alerting the user that all radios are collected and the user can now talk to all radios in San Antonio, Ft. Worth and Dallas. The elapsed time from initial key-up to the time the user can talk to the networked sites is typically on the order of 600 ms. Users in the Ft. Worth and Dallas sites as well as in the San Antonio cell area will receive the dispatch call as they would any other call.

MULTI-SITE DISPATCH SPECIFICATION SUMMARY:

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