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Claims  |
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What is claimed is:
1. A communications system, comprising:
one or more digital communication units for conducting digital
communications;
one or more analog communication units for conducting analog
communications; and
a digital switch including:
a time division multiplex (TDM) bus for transferring digital information
between dedicated interface modules and one or more digital interface
modules connected to the bus during preassigned time slots, wherein the
dedicated interface modules interface communications between the TDM bus
and the digital and analog communications units, and the one or more
digital interface modules interface the analog communication units in
digital communications with the digital communications units.
2. The communications system according to claim 1, wherein the digital
communications include digitally encrypted audio information.
3. The communications system according to claim 2, further comprising:
digital interface units connected to each digital interface module, wherein
each digital interface unit includes:
means for encrypting information originating from the analog units, and
means for decrypting information from the digital units.
4. The communications system according to claim 3, wherein each digital
interface unit includes a predefined cryptographic key for encrypting or
decrypting communications information retrieved from the TDM bus by the
digital interface unit via a corresponding digital interface unit.
5. The communications system according to claim 3, the digital switch
further comprising:
a message control bus for transferring control signals between all
interface modules to set up and take down communication paths through the
digital switch over the TDM bus,
wherein the one or more digital interface modules includes means for
monitoring the message control bus to detect when an analog communication
unit is to transmit or receive encrypted communications and assigning a
digital interface unit to the encrypted communication to interface the
analog communication unit in encrypted communications.
6. The communication system according to 3, wherein each digital interface
unit includes a digital signal processor including:
means for storing a cryptographic key;
means for selectively encrypting information from the analog communication
units retrieved from the TDM bus by a corresponding digital interface
module using the cryptographic key; and
means for selectively decryting information to be received by the analog
communication units via the corresponding digital interface module and TDM
bus using the cryptographic key.
7. The communications system according to claim 2, wherein the analog
communication units include telephone sets of landline telephone
subscribers and wherein a landline telephone subscriber initiates and
receives encrypted communications using the one or more digital interface
modules by pressing a single key on the subscriber's telephone set.
8. The communications system according to claim 1, wherein each dedicated
interface module includes:
means for digitizing communications received from the analog and digital
communications units and placing the digitized information on the TDM bus
during a corresponding preassigned time slot, and
means for retrieving digitized information during particular time slots and
converting the retrieved information into a format for communication with
the analog and digital communications units.
9. The communications system according to claim 1, wherein the analog
communication units include one or more dispatch units for monitoring
communications involving digitally encrypted audio information from one or
more digital communication units using the one or more digital interface
modules.
10. The communications system according to claim 9, wherein the dispatch
unit monitors multiple communications on a single speaker by summing
communications involving groups of analog and digital communication units.
11. The communications system according to claim 1, wherein the digital
communication units include mobile or portable radio transceivers.
12. The communication system according to 1, wherein the one or more
digital interface modules dedicates time slot channels for digitally
encrypted communications involving an analog communication unit and groups
of digital communication units.
13. The communication system according to 1, wherein the one or more
digital interface modules dynamically assigns time slot channels from a
pool of available time slots.
14. A digitally trunked radio frequency communications system comprising:
mobile or portable digitally trunked radio transceivers;
plural digital repeater sites having corresponding coverage areas and
serving mobile or portable digitally trunked radio transceivers disposed
within the coverage areas, the radio transceivers supporting digitally
encrypted communications; and
a distributed switch for routing communications between digital repeater
sites and analog communication sources and destinations including a
digital interface module for encrypting communications originated from an
analog communication unit and decrypting encrypted communications to be
received by the analog communication unit, wherein the digital interface
module permits the analog communication unit to originate and participate
in encrypted communications with one or more radio transceivers.
15. The switch according to claim 14, further comprising:
a plurality of digital interface units connected to the digital interface
module, wherein unencrypted information from the analog communications
unit is encrypted by one of the plurality of digital interface units under
the control of the digital interface module before being transmitted by a
digital repeater site to a receiving radio transceiver and information
encrypted by a transmitting radio transceiver and intended for the analog
communication unit is decrypted by one of the digital interface units
under the control of the digital interface module.
16. The system according to claim 14, wherein the analog communications
unit includes a dispatch console.
17. The system according to claim 14, wherein the analog communications
unit includes a telephone set of a landline telephone subscriber and
wherein the landline telephone subscriber initiates encrypted
communications by activating a switch on the telephone set.
18. The system according to claim 14, wherein encrypting of communications
includes digital encryption with a cryptographic key and decrypting of
communications includes digital decryption with a cryptographic key.
19. The system according to claim 18, wherein each digital interface unit
is assigned a cryptographic key and corresponds to a communications
channel over the distributed switch.
20. The system according to claim 19, further comprising:
means for dedicating at least one dedicated digital interface unit to a
particular radio transceiver or a group of transceivers, wherein encrypted
communications conducted via the dedicated digital interface unit and
involving at least one analog communication unit are encrypted and
decrypted using the same cryptographic key.
21. The system according to claim 19, further comprising:
means for dynamically assigning an encrypted communication involving at
least one analog communication unit to an available digital interface unit
from a pool of nondedicated digital interface units.
22. A method where an analog communications unit participates in digitally
encrypted communications with digital RF transceivers located in different
geographical sites over a distributed time division multiplex (TDM)
digital switch, comprising:
(a) providing each site and the analog communications unit with a
corresponding interface to the switch;
(b) providing a digital interfacing module on the switch;
(c) routing digitally encrypted communications involving the analog unit
through the digital interfacing module;
(d) digitally encrypting communications routed from the analog unit to the
digital interface module; and
(e) sending the digitally encrypted communications from the digital
interface module to at least one rf transceiver.
23. The method according to claim 22, further comprising:
(f) retrieving from the TDM switch digitally encrypted communications
directed to the analog communications unit in the digital interface
module,
(g) decrypting the communications retrieved in step (e), and
(h) sending the decrypted communications to the analog communications unit.
24. The method according to claim 23, wherein the analog communications
unit is a dispatch console unit.
25. The method according to claim 23, wherein the analog communications
unit is a telephone set of a landline telephone subscriber. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The invention relates to a network of trunked radio transmission systems in
which and audio signals from one system are switched through a distributed
digital switching network to another transmission system. More
particularly, the invention relates to providing the distributed switching
network with the capability to permit different types of users of the
network, including for example individual and groups of radio unit
subscribers, dispatch console operators, and landline telephone
subscribers, to process and participate in digitally encoded
communications.
BACKGROUND AND SUMMARY OF THE INVENTION
Trunked RF repeater systems have become a mainstay of modern RF
communications systems and are used, for example, by public service
organizations (e.g., governmental entities such as counties, fire
departments, police departments, etc.). Such RF repeater systems permit a
relatively limited number of RF communications channels to be shared by a
large number of users--while providing relative privacy to any particular
RF communication (conversation). Typical state-of-the-art RF repeater
systems are "digitally trunked" and use digital signals conveyed over the
RF channels (in conjunction with digital control elements connected in the
system) to accomplish "trunking" (time-sharing) of the limited number of
RF channels among a large number of users.
Briefly, such digitally trunked RF communications systems include a
"control" RF channel and multiple "working" RF channels. The working
channels are used to carry actual communications traffic (e.g., analog FM,
digitized voice, digital data, etc.). The RF control channel is used to
carry digital control signals between the repeater sites and user RF
transceivers (radio units) in the field. When a user's transceiver is not
actively engaged in a conversation, it monitors the control channel for
"outbound" digital control messages directed to it. User depression of a
push-to-talk (PTT) switch results in a digital channel request message
requesting a working channel (and specifying one or a group of callees) to
be transmitted "inbound" over the RF control channel to the repeater site.
The repeater site (and associated trunking system) receives and processes
the channel request message.
Assuming a working channel is available, the repeater site generates and
transmits a responsive "outbound" channel assignment digital message over
the RF control channel. This message temporarily assigns the available
working channel for use by the requesting transceiver other callee
transceivers specified by the channel request message. The channel
assignment message automatically directs the requesting (calling)
transceiver and callee transceivers to the available RF working channel
for a communications exchange.
When the communication terminates, the transceivers "release" the
temporarily assigned working channel and return to monitoring the RF
control channel. The working channel is thus available for reassignment to
the same or different user transceivers via further messages conveyed over
the RF control channel. An exemplary "single site" trunked RF repeater
system is disclosed in the commonly-assigned U.S. Pat. Nos. 4,905,302 and
4,903,321.
Single site trunked RF repeater systems may have an effective coverage area
of tens of square miles. It is possible to provide one or more satellite
receiving stations (and a single high power transmitting site) if a
somewhat larger coverage area is desired. However, some governmental
entities and other public service trunking system users may require an RF
communications coverage area of hundreds of square miles. In order to
provide such very large coverage areas it is necessary to provide multiple
RF repeater sites and to automatically coordinate all sites so that a
radio transceiver located anywhere in the system coverage area may
efficiently communicate in a trunked manner with other radio transceivers
located anywhere in the system coverage area.
FIG. 1 is a schematic diagram of a simplified exemplary multiple-site
trunked radio repeater system having three radio repeater
(transmitting/receiving) sites S1, S2, and S3 providing communications to
geographic areas A1, A2, and A3, respectively. Mobile or portable
transceivers within area A1 transmit signals to and receive signals from
site S1; transceivers within area A2 transmit signals to and receive
signals transmitted by site S2; and transceivers within area A3 transmit
signals to and receive signals transmitted by site S3. Each repeater site
S1, S2, S3 includes a set of repeating transceivers operating on a control
channel and plural RF working channels. Each site may typically have a
central site controller (e.g., a digital computer) that acts as a central
point for communications in the site, and is capable of functioning
relatively autonomously if all participants of a call are located within
its associated coverage area.
To enable communications from one area to another, however, a switching
network referred to herein as a "multisite switch", must be provided to
establish control and audio signal pathways between repeaters of different
sites. Moreover, such pathways must be set up at the beginning of each
call and taken down at the end of each call. For example, the site
controller (S1) receives a call from a mobile radio in A1 requesting a
channel to communicate with a specific callee. A caller requests a channel
simply by pressing the push-to-talk (PTT) button on his microphone. This
informs the site controller S1 via an "inbound" digital control message
transmitted over the RF control channel that a working or audio channel is
requested. The site controller assigns a channel to the call and instructs
the caller's radio unit to switch from the control channel to the audio
channel assigned to the call. This assigned channel is applicable only
within the area covered by the site.
In addition, the site controller sends the channel assignment to the
multisite switch 200 which assigns an internal audio slot to the call. The
switch 200 also sends a channel request to other site controllers having a
designated callee within their site area. Audio signals are routed such
that audio pathways are created to serve the callee(s) and one or more
dispatcher consoles 202 involved in the communication. Upon receiving a
channel request, these "secondary" site controllers (in the sense they did
not originate the call) assign an RF working channel to the call. Each
secondary channel is operative only in the area covered by the secondary
site controller. The secondary site controller(s) also sends the channel
assignment back up to the multisite switch.
Thus, the caller communicates with a unit or group in another area via the
multisite switch. The call is initially transmitted to the primary site
controller, routed through an assigned audio slot in the switch, and
retransmitted by the secondary sites on various assigned channels in those
other areas. When the call ends, the primary site controller deactivates
the assigned channel for that site and notifies the multisite switch 200
that the call is terminated. The multisite switch 200 propagates an end of
call command ("channel drop") to all other site controllers. This releases
all working channels assigned to the call and breaks the associated audio
rating pathways.
In addition to providing communications between mobile radio units in
different areas, the multisite switch 200 provides communications between
land-line telephone subscribers and radio units as well as dispatchers and
mobile radio units. Land-line telephone subscribers can communicate with
radio units by dialing an access number as well as a radio unit (or group)
identification number which is routed to the trunked communications system
through a central telephone interconnect switch (CTIS) and the multisite
switch 200. One or more dispatch consoles 202 is connected to the
multisite switch 200 in the same manner as the site controllers 102. Both
land-line subscribers and dispatch console operators can issue a channel
call request through the multisite switch 200 to a site controller 102 to
call for example a mobile radio unit.
Each dispatch console 202 may participate in calls in its area. Thus, when
a call comes through the multisite switch 200 from another area to a
mobile radio, the switch informs the dispatch console 202 of the call in
addition to notifying the corresponding site controller 102. The dispatch
operator can then listen or participate in the call. The multisite switch
200 also handles calls to groups of mobile units and/or dispatch consoles
by ensuring that the site controllers for all of the callees in the group
assign a channel to the group call.
The multisite switch 200 has a distributed architecture. The logical
functions and computational workload of the multisite switch 200 are
shared by various distributed microprocessor "nodes". Each node is
connected either to a site controller 102, dispatch console 202, public
and/or private landline telephone exchanges and other components of the
overall radio system. The nodes are referred to herein as interface
modules and include, for example, Master Interface Modules (MIMs) for the
nodes coupled to site controllers and Console Interface Modules (CIMs) for
the nodes coupled to dispatch consoles. Each interface module of the
multisite switch is supported by a switch controller card operated by
microprocessors. All of the cards have substantially the same hardware and
are interchangeable. Each card acts as a gateway interface into the
distributed switch network.
One of the significant advantages digital communications systems afford is
the capability to digitally encode (e.g. encrypt) voice/data
communications. This capability is particularly desirable and necessary
for calls over RF channels which can be monitored by any suitably tuned
radio receiver. Agencies and departments such as local police departments,
in particular, require secure private RF communications. Mobile units
and/or groups of mobile units can communicate securely over RF
communications links using one or more assigned encryption/decryption
"keys" in accordance with an encryption/decryption algorithim, (e.g. the
DES) to encrypt the voice/data to be transmitted and decrypt the received
information. Only those users having digital encryption/decryption
capabilities and the necessary "key" can monitor or participate in the
encrypted communication.
The interface modules in the multisite switch do not perform any encryption
and decryption, instead, these operations occur at the radio units.
Typically, the information is digitally encrypted/decrypted at the radio
unit and communicated in that form directly over the audio network to/from
the sites through the MIM modules. Unfortunately, some users of the
multisite switch, such as dispatch console operators and land-line
telephone subscribers, do not have digital encryption and decryption
capabilities. As a result, a dispatch operator can not monitor,
participate in or originate digitally encrypted calls. Similarly, even
though a land line subscriber can access the trunked RF communication
system for unencrypted or "clear" calls, that subscriber is unable to
receive or originate encrypted calls.
The present invention overcomes these drawbacks by permitting users lacking
digital encryption capabilities to nonetheless participate in encrypted
communications over the multisite switch. More particularly, one or more
digital voice interface modules (DVIM) similar in architecture and
operation with other switch interface modules (e.g., CIM's and MIM's) are
employed to digitally encode and decode calls for multisite switch
"analog" type users lacking that capability.
Each DVIM includes plural digital voice interface units (DVIU) with each
DVIU having a digital signal processor that digitally encodes information
received from analog communications units over the switch via the DVIM and
decodes digitally encoded information on the switch audio network to be
received by those analog units. For encryption/decryption, each DVIU
stores an assigned cryptographic "key" corresponding to a key employed by
a particular radio unit or group of radio units to digitally
encrypt/decrypt communications. One or more (including multiple pools of)
DVIU's may be dedicated to a particular group or groups of radio units, or
a DVIU may be assigned dynamically from a pool of available DVIUs. The
DVIM selects (1) the DVIU with the appropriate key to handle a particular
encrypted communication and (2) whether that DVIU should encrypt or
decrypt the received information.
The present invention therefore permits one or more analog communication
units to originate and receive digitally encoded calls without themselves
each having digitally encoding/decoding capabilities. In other words,
analog communication units do not need to be individually retrofitted with
digital encoding/decoding hardware and software to participate in
digitally encoded calls over the multisite switch. This is particularly
advantageous to dispatch console operators because it allows plural
communications, some of which may be digitally encoded, to be summed and
monitored on a single speaker. Landline telephone subscribers also benefit
from digitally encoded communications (e.g. by enhanced security) with
radio units in the field simply by dialing, in addition to a system access
number, a single key such as a # key to originate and participate in a
digitally encoded call.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention will
become better and more completely understood by referring to the following
detailed description of presently preferred exemplary embodiments in
conjunction with the sheets of Figures, of which:
FIG. 1 is a schematic illustration of an exemplary "multi-site" trunked RF
communications system;
FIG. 2 is a schematic of an exemplary architecture for a distributed
digitally trunked radio frequency communications system multisite
switching network;
FIG. 3 is a detailed block diagram of a single exemplary interface module
(providing multiple audio sources/destinations) shown in FIG. 2;
FIG. 4 is a general block diagram of an exemplary architecture of the
controller portion of the interface module shown in the FIG. 3;
FIG. 5 is a more detailed block diagram of an exemplary audio module shown
in FIG. 3;
FIG. 6 is a detailed schematic diagram of the circuitry associated with an
exemplary audio channel section shown in FIG. 5;
FIG. 7 is a block diagram of a digital voice interface module (DVIM);
FIG. 8 is a detailed block diagram of an exemplary digital voice interface
unit (DVIU) shown in FIG. 7; and
FIGS. 9(a)-9(c) are flow diagrams outlining processing procedures followed
in accordance with the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
In the following description, for purposes of explanation and not
limitation, specific details are set forth, such as particular circuits,
circuit components, interfaces, techniques, etc. in order to provide a
thorough understanding of the present invention. However, it will be
apparent to one skilled in the art that the present invention may be
practiced in other embodiments that depart from these specific details. In
other instances, detailed descriptions of well known methods and
programming procedures, devices, and circuits are omitted so not to
obscure the description of the present invention with unnecessary detail.
An exemplary trunked radio repeater system 100 in accordance with the
invention is generally depicted and was described above in conjunction
with in FIG. 1. In the preferred multisite system 100, for example, the
site controller (S1) receives a call from a mobile radio in coverage area
A1 requesting a channel to communicate with a specific callee or group of
callees. The caller requests the channel simply by pressing the
push-to-talk (PTT) button on the microphone of his remote RF transceiver.
This informs the site controller (e.g., via an "inbound" digital control
message transmitted over the RF control channel) that an audio working
channel is needed. The site controller assigns a working channel to the
call and instructs the caller's radio unit to switch from the control
channel to the assigned working channel. This assigned working channel is
thus ready to support communications within the area covered by the site.
In addition, the site controller sends a message indicating the channel
assignment to the multisite network switch 200. The switch 200, in turn,
sends a channel request to all other site controllers and routes audio
signals such that an audio signal pathway is created between the RF
repeater servicing the caller and the RF repeater(s) servicing the
callee(s). Additional audio signal pathways may also be established in
similar fashion such that one or more dispatch consoles 202 and land-line
subscribers may become involved in the communication. Upon receiving a
channel request, these "secondary" site controllers may each assign an RF
working channel to the call (e.g., if a callee designated by the caller's
channel request message happens to be physically located within the
coverage area serviced by the associated RF transceiving site). Meanwhile,
the switch 200 ensures that the caller's audio has been routed from the
active RF receiver of site S1 to active transmitters of each of the other
sites participating in the call.
FIG. 2 is a detailed schematic diagram of the architecture of multisite
switch 200 provided by the presently preferred exemplary embodiment of
this invention. The multisite switch 200 communicates with each site
controller 102 and dispatcher console 202 via data and audio communication
lines.
The multisite switch 200 establishes and removes audio connections between
sites 102 and dispatch consoles 204 using a local area network of
interface modules (or nodes). As shown in FIG. 2, the interface modules
are labelled corresponding to whether they interface with a site
controller, dispatch console, landline telephone switch or other system
component. For example, MIMs 203 are interface modules in the switch that
interface with site controllers and CIMs 204 are interface modules that
interface with dispatch consoles. There are other interface modules such
as a Monitor Module (MOM) 205, Logging Recorder Interface Module (LRIM)
206, Central Telephone Interconnect Module (CTIM) 207, a Digital Voice
Interface Module (DVIM) 250, and a Network Interface Module (NIM) 252. The
MOM 205 is the interface for the system manager 211 and the MOM PC
(personal computer) 252 that have supervisory responsibility for the
switch 200 and overall radio system.
Each interface module in the multisite switch is supported by a
microprocessor based controller module. All of the modules (the MIMs,
CIMs, CTIM, MOM, RIM, SWIM, DVIM, and NIM) have the same hardware and are
interchangeable. The modules have different "personalities" to indicate
that they are assigned to, for example, a site controller or a dispatch
console, etc. Each module can be easily configured to be a MIM, CIM, etc.
by setting a few switches.
The interface modules of the switch 200 are connected to a digital message
bus 209 and a digital audio (TDM) network 210. The message bus 209 is
shown in FIG. 2 as a message network using a conventional GSC digital
messaging protocol as implemented by the Intel 80C152 Global Serial
Channel (GSC) microprocessor. Such a GSC microprocessor is used as the
communications controller the controller module in each interface module.
The message bus 209 is a high speed data bus that interconnects the
interface processors in the controller of each interface module.
The audio bus 210 comprises 32 time division multiplexed (TDM) buses in the
preferred embodiment. Each bus contains 32 slots, each slot corresponding
to a single audio channel. A maximum of 1024 audio slots may be routed
through the switch (32 buses.times.32 slots), although some of the slots
are used for other purposes (e.g. signalling). In the preferred
embodiment, 240 channels of digitized audio are carried by audio TDM
network 210.
The MOM 205 is the interface module for the system manager 211 and the MOM
PC (personal computer) 250. The system manager 211 updates databases
maintained in all of the interface modules. The MOM 205 maintains certain
centralized databases including databases for smart calls and confirmed
calls. Smart calls relate to the operation of the dispatch console 202. A
call is "smart" if the call is selected by the dispatcher via a select
speaker in the console 202. A confirmed call is one for which the audio
channel and slot assignments must be confirmed before the caller begins
talking. The system manager 211 sets which calls are to be confirmed and
provides this information to the site controllers 102. The channel
assignment message for the originating call from the primary site
controller instructs the multi site switch that the call is to be
confirmed. When the MOM 205 receives a message that a confirmed call is
requested, it tells the primary MIM which secondary MIMs must confirm the
call by sending a "site mask" to the primary MIM. The site mask identifies
each secondary MIM to participate in the confirmed call.
The LRIM 206 interfaces recorders to the switch assigned to log calls for
various groups or units. The CTIM 207 functions much the same as a MIM
does with respect to interfacing a site to the switch except that it
interfaces to landline telephone lines from the CTIS to switch 200. NIM
252 interfaces one switch 200 to another multisite switch to provide even
greater coverage. Using NIM 252 any number of switches can be connected.
As part of the switch initialization procedure, the interface modules
connect their assigned TDM bus slots to the module's external channel
inputs. For example, a MIM will assign each channel from its site
controller to a separate audio TDM bus slot on audio network 210. Once the
TDM bus slot is linked to the site channel, the bus slot continuously
receives the output from the channel through the host node without further
channel setup required. Of course, the site channel has no intelligible
signal until it is assigned to a call by the site controller. Although a
TDM bus slot is linked to a corresponding site channel, no other interface
modules (MIM, CIM, etc.) listens to that bus slot until the host interface
module sends a slot assignment message throughout the multisite switch 200
over the message network 209 notifying the interface module nodes that an
active call from the site has been assigned to that bus slot.
FIG. 3 is a high level block diagram of a single (multiple audio channel)
exemplary MIM 203 provided by the presently preferred exemplary embodiment
of this invention. The architecture of other interface modules, e.g. CIM,
DVIM, and CTIM, is virtually the same as that for the MIM. As mentioned
above, the "highway" used to communicate signals between interface modules
includes an audio (TDM) network 210 and a control message network ("GSC")
209. The audio TDM network 210 handles digitized audio signals
irrespective of whether they are unencrypted (e.g. "clear voice") or
digitally encrypted. The TDM audio bus simply transfers whatever digital
information is placed on the TDM bus slot. Because each TDM bus provides
multiple time "slots", MIM 203 typically services multiple RF channels
providing multiple audio source/destinations each of which are connected
independently to a TDM bus slot.
MIM 203 includes a controller module 410, a backup controller module 412,
and plural (preferably eight) audio modules 400 (only four are shown for
purposes of illustration). Each audio module 400 in the preferred
embodiment is connected to a maximum of four RF repeaters of an RF
trunking site, or in the case of a CIM and a CTIM (for console and
landline communications) to four bidirectional audio links. For example,
audio module 400(A) includes bidirectional audio links 402(1)-402(4)
serving associated first through fourth trunked RF repeater site
"channels" (i.e., RF transceiving/repeating decks associated with
particular trunked RF channels). As described in more detail below, the
audio modules 400 act as source gateways ("entrance/exit ramps") which
convert analog audio signals generated by MODEMs from the trunked repeater
sites into digitized audio signals (PCM) and place the digitized audio
signals onto the audio TDM network 210. These same audio modules 400 act
as audio destinations by taking selected signals from the audio TDM
network 210, converting them from digital into analog form, and providing
the resulting analog signals to the RF repeater site "channels" for
transmission via RF links.
The controller module 410 communicates with each of the four audio modules
400 via a common HDLC link 500 and an audio control link 600. The HDLC
link 500 is used, for example, to carry fault indications and messages
relating to RF "channel" status between the audio modules 400 and the
controller module 410. Audio control link 600 permits the controller
module 410 to set low-level parameters (e.g., level adjustment, TDM slot
assignment, etc.) within each audio module 400.
FIG. 4 shows a block diagram of an exemplary architecture for controller
410. Each controller 410 includes a communications controller 301, a
dual-port random-access-memory (RAM) 302 and an interface processor 303.
The communications controller 301 routes and receives control messages
between the control message bus 209 and the interface processor 303. The
dual-port RAM 302 is used to communicate between the communications
controller and the interface controller 303. The communications controller
301 may be an Intel 80C152 GSC microprocessor. Messages received from the
site controller 102 over the serial port 304 are translated into a format
usable by the multisite switch. The communications controller also
translates switch messages into a format that the site controller or
console understands.
The interface processor 303 performs substantially all the logical
functions for the interface modules MIM, CIM, DVIM, etc. and is
effectively the "intelligence" of the MIM 203. Interface processor 303
(which may be an Intel 80C186 microprocessor) initially assigns TDM bus
slots channels to the individual RF transceivers associated with audio
links 402(1)-402(4) of audio modules 400 using parallel audio control bus
600. The interface processor 303 connects audio slots to the site
controller, dispatcher console, or CTIS to establish a communications link
for a call and also terminates that link when a call ends. As previously
described, each MIM is preassigned a set of TDM bus slots for outputting
audio signals onto the TDM bus, and these slots are not assigned and
de-assigned during the course of normal call routing.
Each call through the switch is patched to its assigned TDM bus slot on the
audio bus 210. When the call ends, that slot is made available for
assignment to another call. Since the interface controller 303 for each
interface module assigns slots, connects audio slots to the site
controller or dispatch console to establish a communications link, and
terminates calls, the interface modules must continually inform each other
of their slot assignments. Accordingly, the interface modules send control
messages regarding slot assignments, slot updates and slot idles over the
control message network 209 to other interface modules.
The communications controller 301 for each interface module initially
processes all of the messages on the message network. Slot assignments are
forwarded to the interface processor 303 through the dual-port RAM 302.
The communications controller 301 processes slot update and slot idle
messages by referring to a slot bit "map" or database located and
maintained in the dual-port RAM 302 for all TDM bus slots on the audio bus
210. By referring to the slot bit map, the communications controller 301
determines whether the slot status message conveys information already
known, or if the slot status message conveys new information about a TDM
bus slot. Update messages are sent regularly by the interface modules
hosting calls to confirm to the other interface modules the active status
of a slot. When a host interface module terminates a call, it sends a slot
idle message to the other nodes and also periodically resends idle
messages until the slot is reassigned to another call. Thus, all interface
modules are continually informed of the status of all TDM bus slots that
have been assigned at least once. A more detailed description of the slot
bit map and slot status messages is provided in application Ser. No.
07/658,640 filed on Feb. 22, 1991 entitled "Message Bus Slot Update/Idle
Control and RF Trunking Multisite Switch" which is incorporated herein by
reference.
Each MIM is coupled to its site controller through a standard serial
telephone line. MIMs receive digital command signals from their site
controllers 102 through a downlink line as is described in commonly
assigned U.S. Pat. No. 4,835,731, entitled "Processor-To-Processor
Communications Protocol For A Public Service Trunking System" also
incorporated by reference.
Each MIM also maintains a radio unit database that identifies the radio
units within its | | |
