MODEL 844
4-Port Intersite Link

Expand a Multi-Site MPT 1327 Network
The Model 844 4-Port Intersite Link provides enhanced linking capacity to a Zetron Model 827- based MPT 1327 trunked radio system. It provides four 4-wire audio ports and four RS-232 serial data ports. The 4-wire audio and data ports provide a gateway for linking conversation audio and call setup data essential for roaming trunked network operation. Multisite operation allows mobile units to roam throughout the network without losing any system functionality. Roaming units are located and can receive calls from a telephone or another radio unit. In addition, multisite operation allows a group call to include up to six sites.

INTRODUCTION

The Model 844 4-Port Intersite Link provides enhanced linking capacity to a Zetron Model 827-based MPT 1327 trunked radio system. It provides four 4-wire audio ports and four RS-232 serial data ports. The 4-wire audio and data ports provide a gateway for linking conversation audio and call setup data essential for roaming trunked network operation.

Multisite operation allows mobile units to roam throughout the network without losing any system functionality. Roaming units are located and can receive calls from a telephone or another radio unit. In addition, multisite operation allows a group call to include up to six sites.

MULTISITE � A BRIEF OVERVIEW

The unique advantage of Zetron�s MPT 1327 trunking solution is the capability to build small to medium-sized multisite networks (up to 12 sites) without the need for an expensive central hardware switch. This unique Zetron �switch-less� architecture is made possible by two features implemented in the M827 Trunking Controller and the Model 844:

1. Internal PCM audio and data bus that all M827 and M844 units share

2. Call setup data packets and conversation audio are routed via a simple audio link between sites Multisite operation is implemented by a software option accompanied by the installation of the internal telco option card in at least one M827, or the addition of a M844, in each site to be linked. The M827 optional telco card can be configured as either a PSTN/PABX interface or 4-wire audio link interface. In network applications, sites are connected by leased 4-wire E&M lines provided by the telephone company, or by a multiplexer line shelf card connected to privately owned microwave links or fiber optic backbone.

OPERATION

The M844 easily interfaces to other M827s and M844s in a system over the PCM audio, subscriber, and repeater buses. Each M844 appears on a given Zetron MPT 1327 system as four separate units with the telephone interface enabled and repeater interface disabled. System control data passes between controllers via two data buses. The repeater bus passes real-time call setup information between the control units. Conversely, the subscriber bus transfers database, call detail records, statistics, and other less time sensitive data.

One M827 at the repeater site operates as the bus master to control and synchronize all communications between controllers at a given site. The M844 always functions as a slave signalling unit; as it does not operate in standalone mode. Any radio channel has access to any telephone or intersite link port via the PCM audio bus, regardless of which unit the port is physically located on. Each 4-wire port is equipped with a 1200 baud FFSK modem used to pass call setup, roaming, and registration information between sites. When a dedicated serial link is paired with a 4-wire link, the serial link is used instead to communicate initial call setup and registration information. Each 4-wire link operates independently from the others. The result is that a M844 appears to be four separate telco interfaces to the rest of the system.

SYSTEM CONFIGURATION
AND DATABASE MANAGEMENT

Statistics and Billing
Each M827 and M844 gathers and records statistical information to assist the operator in monitoring the traffic and loading of the system. Statistics are collected on an hourly basis for the current and previous days and are in accordance with MPT 1318. This information can be retrieved from any M827 at the site and stored on the office computer.

Call Detail Records (CDRs)
Each M844 and M827 stores a record of every call placed on the system. This information provides the detailed data needed to generate customer bills. Call records can be stored for the following types of transactions:

• Registration
• Status
• Short Data Messages (SDM)
• Mobile-to-Mobile
• Mobile-to-Landline
• Landline-to-Mobile

Buffer Space
Each M844 and M827 contains storage for up to approximately 7000 call records depending on the type of records stored. If the buffer storage area in one unit becomes full, it looks for storage available in another controller at the site. Records storage capacity can be altered by modifying the minimum call time to store for speech (mobile to mobile) and land-line calls.

Record Retrieval
Records are retrieved and stored on the office computer via an option in the M827 Database Program. Each time the billing records are retrieved, a user file is also created containing ASCII information on the fleets, units and groups programmed in the database.

ALARM REPORTING AND MONITORING
The M844 provide internal alarm condition monitoring and reporting. Internal system operation is monitored by a digital �watchdog� that alarms for the following conditions:

• Call detail storage buffer full
• Repeater serial bus failure
• Subscriber (database) serial bus failure

Features

• Integrates with the Zetron Model 827 to supports regional networks of up to 12 sites in a variety of different configurations
• Supports multiple Model 844s at each site, for up to 32 intersite links
• Provides additional storage capacity for system call detail records
• Supports internal system alarm detection and reporting
• Provides four analog speech/data ports to directly connect two or more Zetron MPT 1327 sites
• Uses 4-wire audio or 4-wire audio with E&M signaling to link multiple sites
• Supports four configurable RS-232 data linking ports for enhanced network performance

Specifications