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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

DESCRIPTION OF A PREFERRED
EMBODIMENT

SUMMARY OF THE INVENTION

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

3

nication system (12). A second fleet (18) has a first subgroup (18a) contained in the coverage area of the first communication system (10) and a second sub-group (186) contained within the coverage area of the second communication system (11). Lastly, a third fleet (19) 5 includes a first sub-group (19a) contained within the coverage area of the first communication system (10) and a second sub-group (19b) contained within the coverage area of the third communication system (12).

So configured, members of the first sub-group (17a) 10 of the first fleet, all being located within the coverage area of the first communication system (10), can communicate amongst one another using the resource controller (13a) and repeaters (14a, 15a, and 16a) of the first communication system (10) in accordance with well 15 understood prior art technique. Similarly, the members of the second fleet (18a) and of the third fleet (19a) can also communicate with one another within the coverage area of the first system (10).

If, however, the members of the second fleet (18) 20 wish to conduct a group wide communication, then an intersystem communication path must be established, since, as depicted, the two sub-groups (18a and 186) of this fleet are located within two separate communication systems (10 and 11) and the infrastructure of which 25 communication systems will not, by service limitations, be able to include those communication units that are located outside the service coverage area of their infrastructure, respectively. A dial up line (20) provides this path. Referring momentarily to FIG. 2, the resource 30 controller (13a and 13b) of the two systems (10 and 11) along with the various repeaters (14a-b, ISa-b, and 16a-b) are coupled to a multiplexer (21a and 21b, respectively), such that the output from each can be appropriately compressed and/or packetized for transmis- 35 sion over the dial up link (20), and subsequently demultiplexed and provided to an appropriate corresponding repeater or resource controller at the receiving end. Each system also includes an appropriate dialer (22a and 22b) to allow access to the dial up line as provided 40 through a PSTN or other landline resource provider.

In this embodiment, the dial up line can be, for example, a 56 kbps DDS dial up line or a 64 kbps ISDN link. The bandwidth of either link can simultaneously carry more than a single digitized voice circuit, particularly 45 where compression and packetizing methods are used. With momentary reference to FIGS. 5a and b, the multiplexers (21a and 21b) provide a voice packet (31) that includes an address field (32), a voice type field (33) (to identify the packet as a voice packet), a compressed 50 voice field (34), and a Cyclic Redundancy Check (CRC) field (35). The particular form of voice compression selected will of course depend upon the needs of a particular application. In addition, or in the alternative, a variety of voice compression methodologies can be 55 accommodated in a single system, with higher quality techniques being utilized for higher priority and/or higher cost services. The data packet (41) similarly includes an address field (42), a type field (43) to identify the packet as a data packet, and a CRC field (44). In 60 substitution for the compressed voice field, intrasite supervisory data information (45) allows an appropriate exchange of control information between systems. For example, this field can accommodate call establishment information, auto registration information, dynamic 65 regrouping information, and so forth.

With reference to FIG. 6, compressed voice frames for different communications are seen multiplexed with

4

one another and with supervisory data packets. These multiplexed packets are what the system transports to the dial up connection (20).

Importantly, this invention does not require constant maintenance of a dedicated landline between communication systems. Furthermore, this system obtains maximum effective use of those landline links that are established from time to time. For example, referring now to FIG. 3, intersystem communication path establishment procedures will be described.

The resource controller (13a-c) of each communication system includes a significant amount of processing capability. Pursuant to this embodiment, these processing abilities are supplemented to allow the following determinations and actions to be made. Upon initiation (50), the process first determines whether new data exists for intersystem transmission (51). If not, the process simply monitors for new data to appear. Once new data exists, a destination site ID is obtained (52) to identify the particular system with which a communication link must be utilized. (This site ID can be obtained, for example, from the requesting unit itself, or by referring to a local or remotely maintained look-up table that associates the requesting unit and on target units with destination site IDs.) With the destination identified, the process then determines whether an existing connection to that site already exists (53). If such a link does not already exist, then the dialer (22o-Z>) will be utilized to establish a new connection via known dial up methodologies, and a connection timer will be initiated for the newly established line (56). Subsequently, the information can be provided to the destination site in packetized form as described above.

If a communication path already exists to the destination site (53), the process then determines whether the existing path has capacity to support the new communication (54). If not, then again a new path is established and a connection timer initiated for the newly established line (56). Otherwise, presuming sufficient capacity, the new message will simply be multiplexed with other messages currently being supported by the link (55).

With reference again to FIG. 1, therefore, if an existing link (20) has bandwidth sufficient to support three communications, and if two of those sub-channels (61 and 62) are already in use to support communications, and the first sub-group (17a) initiates a communication that must include the members of the sub-group (lib) located in the second communication system (11), the first system (10) will first determine that an existing intersystem link (20) already exists, and will then determine that the existing link (20) has sufficient capacity to support the desired communication by use of the third sub-channel (63). By way of further example, if the three sub-channels (61-63) of the first communication path (20) are all in use at the time the first group communication initiates, the above described process will allow the establishment of a new communication path (67) to supplement the intersystem capacity of the already established link (20). When newly established, any of the three sub-channels (64-66) of the second link (67) can be utilized to support the new communication.

In a similar manner, and by way of further example, the above activities can be further enhanced through establishment of yet additional intersystem links to other systems. For example, the first system (10) could establish a link to the third system (12) to support the communication between the first group communication units (17o-c). Once this link (68) has been established, however, and one of its sub-channels (69-71) dedicated to servicing the latter communication, a subsequent communication need between the two systems, for example, to support a communication of third group com- 5 munication units (19a-b), the above described process will allow the new communication to automatically be supported by the existing link (68) without necessitating the dial up of a new link.

In an alternative embodiment, a dedicated line (20) 10 could be maintained between two sites (10 and 11) that have a need for particularly frequent intersystem communications. The bandwidth resources of this dedicated link could be utilized in the same manner as described above, such that when the dedicated link had sufficient 15 capacity to support a current communication, dial up of an additional line could be obviated, whereas when the dedicated link was fully loaded, a dial up non-dedicated link could be established to support the additional communications. 20

In addition to allowing automatic establishment of dial up lines to support current needs for communication paths, this embodiment also supports automatic disconnect procedures for previously established lines as appropriate. As depicted in FIG. 4, upon initiation 25 (90), the process determines whether the connection timer previously initialized upon establishment of this particular line has expired (91). If not, connection timer monitoring continues. If expiration has occurred, however, the process then determines whether the commu- 30 nication being supported has concluded (92). If not, the process monitors for termination of the communication. Once termination occurs, the process determines whether there are any other communications currently in progress between the two sites (again, these commu- 35 nications may be either voice communications or an exchange of control information between the sites). If no other communications are then being supported, the line is dropped (96). If other communications are in progress, the process determines whether these addi- 40 tional communications can be served notwithstanding termination of a link. For example, in FIG. 1, presume that both links (20 and 67) are established, and that the first (20) supports two communications and the other (67) supports only one communication. With only a 45 total of three communications being supported, all three communications could be supported by a single path if the communications were appropriately merged to a single line (94). If the additional communications cannot be served by fewer lines, the process continues to moni- 50 tor for termination of additional communications. If, however, fewer lines can suitably support the existing communications, the remaining conversations will be merged on to fewer lines (95) and the unused line will be dropped (96). 55

As described, this system ensures that adequate resources are available to support intersystem communication needs, both in support of communication unit to communication unit conversations and in support of system to system communications, per se. These re- 60 sources are provided in an efficient and economical manner. Dial up lines are only utilized when necessary, and only for so long as absolutely required.

In another embodiment, the establishment of new lines can slightly precede the actual need for such lines, 65 and/or the disconnect of existing lines can be slightly postponed, to accommodate a likely need to support a communication between systems. For example, histori

cal analysis of loading by system operators may indicate that a greater need for intersystem connections exist during certain hours of the day. The system can modify its processing as described above to maintain a predetermined intersystem capacity excess in order to quickly meet likely communication needs. For example, the above process can be modified slightly to assure that at least one sub-channel always remains vacant and available. Therefore, if all three sub-channels of an established link are suddenly allocated, a second dial up line can be established even though no immediate need for those resources currently exist, in order to be able to quickly accommodate a likely communication need. What is claimed is:

1. A method of conducting a voice communication between a first communication unit serviced by a first radio frequency communication system and a second communication system serviced by a second radio frequency communication system, comprising the steps of:

A) determining whether a first multi-channel communication path exists between the first and second radio frequency communication systems;

B) when the first multi-channel communication path so exists, determining whether the first multi-channel communication path has at least one channel to support the voice communication;

C) when the first communication path has at least one channel, initially establishing the voice communication using only one channel of the first multichannel communication path;

D) when either the first multi-channel communication path does not exist or the first multi-channel communication path has insufficient capacity;

i) automatically establishing a new multi-channel communication path to support the voice communication;

ii) initially establishing the voice communication using only one channel of the new multi-channel communication path.

2. The method of claim 1, wherein step C further includes the step of:

CI) compressing the voice communication prior to using the one channel of the first multi-channel communication path.

3. The method of claim 1, and further including the step of:

CI) using the first multi-channel communication path to also support exchange of system control information between the first and second radio frequency communication system.

4. The method of claim 1, and further including the step of:

CI) when the voice communication has concluded, determining whether the first multi-channel communication path should be maintained.

5. The method of claim 4, wherein step CI further includes the steps of:

Cla) determining whether the first multi-channel communication path then supports any other communications between the first and second radio frequency communication systems;

Clb) when the first multi-channel communication path does not then support any other communications, dropping the first multi-channel communication path.

6. The method of claim 5, wherein step CI further includes the step of:

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