one then determines whether this existing path has suffi
METHOD FOR SUPPORTING VOICE cient capacity to support the voice communication.
COMMUNICATIONS BETWEEN When the above proves true, the method utilizes the
COMMUNICATION SYSTEMS established path to support the voice communication.
5 In one embodiment of the invention, when either
This is a continuation of application Ser. No. such a communication path does not already exist, or
07/656,360, filed Feb. 15, 1991 and now abandoned. has insufficient capacity, the method provides for auto
CICI „ ... matic establishment of a communication path that will
FIELD OF THE INVENTION support the voice communication.
This invention relates generally to communication 10 In another embodiment, the communication paths
systems, including but not limited to a method that will also support an exchange of system control infor
allows land mobile radio systems to be linked together mation in addition to the voice communication.
in an efficient manner. In yet another embodiment, the method provides for
. T.T_ __ _IT_ ,T,,,^.T T at least occasional determination as to whether the es
BACKGROUND OF THE INVENTION ]5 ... path shou]d continue tQ be maintained( and/or
The basic operation and structure of a land mobile whether many established paths between two systems
radio system is well known. Land mobile radio systems can be reduced in number while continuing to accom
typically comprise one or more radio communication modate an identical number of ongoing communica
units and one or more repeaters that transceive informa- tions.
tion via the RG communications channels. These com- 20 „„„„„„„rT,I,^,.T „^ ^„ . ,,ITV„_
munitions channels are typically narrow band fre- BRIEF DESCRIPTION OF THE DRAWINGS
quency modulated channels. Further, trunked commu- FIG. 1 comprises a block diagram depiction of a
nication systems are organized so that a group of users plurality of RF communication systems intercoupled in
are served by a set of repeaters that support trunked accordance with the invention;
communication resources within an RF coverage area. 25 FIG. 2 comprises a block diagram depiction of two
When a subscriber unit leaves the RF coverage area RF communication systems intercoupled in accordance
of one communication system, another communication with the invention;
system may therefore provide necessary service. A well FIG. 3 comprises a flow diagram depicting a path
known technique for establishing a link between two establishment mechanism;
users served by different communication systems is by 30 FIG. 4 comprises a flow diagram depicting a line
means of a telephone interconnect call. In order to place disconnect mechanism;
a call, dual-tone multiple-frequency signalling is often FIGS. 5a-b depict packet formating for voice and
used. This technique is cumbersome in the dispatch data messages; and
environment because it requires several seconds of FIG. 6 comprises a timing diagram depicting multidelay to establish the connection, as compared with the 35 plexing of packet information, conversation which itself may only last a few seconds.
Another method of interconnecting communication systems relies upon dedicated lines that link the communication systems continuously. These lines may be ei- In FIG. 1, a first, second, and third RF communicather analog or digital lines that are leased from a public 40 tion system (10,11, and 12) are depicted. These systems utility, or that are privately owned. In a dispatch envi- may be separated from one another by a significant ronment traffic is characterized by extreme burstiness geographic distance, or may have overlapping coverwith very low average utilization. Nevertheless, the age areas, depending upon the needs of a particular infrastructure guarantees service to worst case traffic application. Furthermore, the systems themselves may rather than average traffic. As a result, most of the time 45 be different one from the other, according to the needs the infrastructure remains idle. Therefore, this method of a particular application. As depicted, each system eliminates an initial connection delay, but only at the here comprises a trunked communication system having expense of maintaining connection for significant peri- a resource controller (13c-c) and three repeaters (14a-c, ods of time when not in use. ISa-c, and 16a-c). In this embodiment, it will be preA third method of interconnecting communication 50 sumed that one of the repeaters (14<2-c) for each system systems is by means of a packet data network. This constitutes a control resource that supports various method provides an efficient method for intercommuni- system functions, such as call assignments and the like, cation system communication; however, the transmis- The remaining two repeaters (15a-c and 16a-c) collision delay can be several seconds long, making this prise voice channels that may be allocated on an as unacceptable for voice communication. 55 needed basis to support desired communications beTherefore, current methods of interconnecting com- tween communication units serviced by the resource munication system sites are inefficient, cumbersome to controller (13a-c).
use, and do not allow an integrated solution. The general nature and functionality of the above
described elements of each system are well known and
60 understood by those skilled in the art. Therefore, no
These problems and others are substantially resolved further description will be provided here,
by a method for conducting voice communications For purposes of illustration, three groups or fleets are
between a first communication unit serviced by a first illustrated in FIG. 1. The first group (17) includes a
RF communication system and a second communica- sub-group (17a) located within the coverage area of the
tion unit served by a second RF communication system. 65 first communication system (10), a second sub-group
Pursuant to this method, one determines whether a first (176) contained within the coverage area of the second
communication path already exists between the two communication system (11), and a third sub-group (17c)
communication systems. When such a path does exist, contained within the coverage area of the third commu