Individual Call Services

5.5 Individual Call Services

Individual call services are available through the Dimetra IP system. The controlling zone is determined in a manner different from that used for group-based calls for this type of call service. In an individual call, the controlling zone is determined by the first radio to transmit audio.

The following describes the call process operations for individual-based calls.

In individual calls, the initial call request goes over the control channel. An audio channel is not assigned until the target radio responds to the initial request. Audio channel resources are assigned once the target radio responds to the call request.

5.5.1 Private Call Request

The below figure graphically represents a private call request within a single zone. Note that it is also possible to make private calls across zones.

Figure 5-7 Private Call

Gateway Router BTS Patch Panel Core Router BTS Zone Controller LAN Switch

A private call begins with a call request. The call request resolution determines whether the call is set up or not. Requests are rejected if the target radio does not respond to the request or if the target radio is not registered with the system. Other reasons for a call to be rejected would be configuration-related (one of the radios blocked from private calls, site not allowed, and so on).

5.5.1.1 Private Call Request Flow

When and where to use:

Process Steps

1 A private call request is initiated when the caller selects the appropriate mode on the radio, and then enters the target radio's ID or selects it from a list.

2 When the caller presses the PTT button (semi-duplex) or presses the send button (full-duplex), the call request is sent over the control channel to the current site. The information is passed to the Site Controller for processing and routing to the Zone Controller at the initiator's MSO.

3 The Zone Controller receiving the call request checks its VLR to see if the requesting individual is configured to make private calls.

4 If the call is allowed, the Zone Controller checks its individual VLR to see if the target radio is currently registered in the zone, and if it is, at which site.

5 If the target radio is active (registered) in the same zone, the Zone Controller sends it a private call request over the control channel at its current site.

If the target radio is not in the current zone, the caller's Zone Controller determines the target radio's home zone by checking its individual-to-home zone map.

6 The caller's Zone Controller sends a message to the target radio's home Zone Controller requesting the current location of the target radio (which the home Zone Controller gets from its individual HLR).

7 Once the target radio's current zone is known, the receiving Zone Controller sends the call request to the Zone Controller in that zone.

8 The target radio's Zone Controller checks its individual VLR for the target's site location and sends the call request to the target radio through the control channel at its current site.

9 If the target radio is not registered with the system, the requester receives a call reject. Otherwise, the requester hears a ringing tone. If the target radio does not respond within the time-out period, the call request is ended.

5.5.1.3 Roaming During a Private Call

Process Steps

1 Audio is received by the assigned traffic channel at the local site and is routed to the RP at the zone.

2 The RP routes the audio packets through the exit routers where they get encapsulated as Frame Relay packets for transmission to the participating sites.

3 When the target user responds, the same path is used, but the source and destination of the audio are swapped.

4 For semi-duplex calls, the call is terminated when neither party responds within the defined message hang-time. Full-duplex calls are terminated when either party presses the end button.

5.5.1.3 Roaming During a Private Call

The Dimetra IP system supports call continuation during roaming for private calls. When a non-transmitting radio user roams to a new site during a call, the audio is redirected automatically to the new site. The radio user experiences a brief interruption of the audio when moving to another site within the same zone. The audio interruption when moving to a site in a new zone may be slightly longer.

A transmitting radio user in an active individual call cannot roam automatically. When a transmitting radio fades out (due to moving away from the current site), the system detects the loss and begins the call termination process.

5.5.1.4 Full-Duplex Private Calls

Radios or dispatch consoles can initiate full-duplex private calls, allowing both parties to simultaneously transmit and receive audio. Full-duplex private calls are supported for radio-to-console, console-to-radio, and radio-to-radio. For a radio to initiate a full-duplex private call, it must be configured with permission to do so through UCM. For full-duplex private calls, there is no hang timer that determines when the call is terminated. The call is initiated when the radio presses the send button, and the call terminates when one of the parties presses the end button. Full-duplex operation is simulated in the radio by switching between the uplink and downlink channels within each TDMA frame.

5.5.2 Telephone Interconnect

Telephone interconnect capability allows radio users to initiate and receive full-duplex calls through a connection to the Public Switched Telephone Network or customer Private Automatic Branch Exchange. Besides the usual system infrastructure, telephone interconnect service requires a Motorola Telephone Interconnect Gateway, and customer-supplied Private Automatic Branch Exchange.

Figure 5-8 Telephone Interconnect in E1 networking Gateway Router BTS Dispatch Console Zone Controller Patch Panel Core Router MTIG-E1 EC T o P A B X LAN Switch

The telephone interconnect feature builds upon all of the configuration and infrastructure discussed up to this point. With talkgroup calls and unit-to-unit calls, all parties to the conversations all reside somewhere on the Dimetra IP system.

For telephone interconnect calls, one of the parties is outside of the Dimetra IP system and is connected through landline telephone to the radios in the system.

The Dimetra IP system supports radio-to-landline and landline-to-radio interconnect calls. It does not support interconnect calls to and from talkgroups.

5.5.2.1 Relationship between Components

The Zone Controller uses call control client software to interface with call control server software running on the Motorola Telephone Interconnect Gateway. The call control server software translates the Zone Controller’s

5.5.2.2 Configuration

5.5.2.2 Configuration

Radios must be properly programmed to make and receive telephone interconnect calls.

5.5.2.2.1 Limiting Access to Interconnection Services

Telephone interconnect services are intensive users of system resources. Each call requires a single channel which is dedicated for the duration of the call, and telephone calls typically last longer than talkgroup calls. Because of this fact, and because of direct toll costs, it is essential that you have the ability to limit the use of this feature.