DESC:SYSTEM FOR CONNECTING MULTIPLE COMMUNICATION UNITS OVER A SINGLE MODEM
Field of invention:
The present invention relates to an audio communication system and more particularly relates to a system for connecting multiple communication units over a single modem line.
Background of the invention:
Normally, in a communication system the connection between different data communication units on field and central modem is star or point to point architecture. This means a separate modem link or cable exists between a controller and each of data communication units to establish data communication. Additionally, different power cables are used for connecting power, to the data communication units from a local or central source.
Referring to the figure1, it shows a communication system (50), in accordance with an existing prior art. The communication system (50) consists of a central exchange (51), field communication stations (52) desk mounted station and /or wall mounted station (53) and loud speakers (54). A variety of cables are employed in the communication system (50).
The central control exchange (51) is connected to different field communication stations (52 or 53), with individual signal cables (5). The signal cables used are typically 3 pair twisted 0.5 Sq mm. The power supply is fed locally through separate individual cable (6), typically 3 core 1.5 Sq mm. The loud speaker (54) is connected to the field communication stations (52 or 53) with cables (7). The loud speaker cables used are 1pair twisted 0.5 Sq mm. The signal cable (5) uses one pair for modem communication and one or more pairs for carrying audio signal.
Normally, the industrial communication system comprises hundreds of field communication units. A star architecture of communication between the controller and the communication units requires; laying individual signal cables (5) over a large distance for each field communication station, apart from power cables (6). This results in notable demerits of:
a. Huge cabling costs and maintenance issues,
b. For physical relocation or addition of a communication unit; one requires re-routing and laying of cables all the way from the controller (51) to the desired location,
c. Further, failure at controller (51) results in complete failure of the system.
Accordingly, there exists a need of a system for connecting multiple communication units over a single modem cable that overcomes the above mentioned drawbacks of the prior art.
Object of invention:
An object of the present invention is to reduce the cabling quantity and cost by connecting multiple communication units over a single MODEM cable (system cable) instead of star type cabling.
Another object of the present invention is to provide a signaling protocol for a plurality of communication units connected over the same modem line.
Still another object of the present invention is to enable use of a Bus with branched, cabling architecture for complicated sites with complex routing requirement.
Yet another object of the present invention is to enable use of common signal cum power supply cable to reduce the cabling, where distances are not high between the stations.
Summary of the invention
The present invention provides a system for communication with multiple communication units over a single modem. The system comprises of a controller provided with plurality of modems. The modem is a frequency shift key modem. A plurality of communication units is divided into groups according to their geographical location. The communication units in a group are connected in a bus architecture through the connecting means and at least two such groups are connected to a junction box in a loop-in-loop-out fashion. The junction box is then connected to a single modem from the controller. Thus, each single modem of the controller is connected to at least two groups of communication units through a junction box. Each communication unit is provided with a predefined physical address and a master-slave control communication protocol is provided for communication between the controller and the plurality of communication units. In an embodiment, the connecting means is a signal cable configured for carrying a modem signal, audio signals and power there through. With the communication protocol, the controller is configured to communicate a single communication unit or the multiple communication units at a time.
The master slave protocol consists of packets of multiple bytes. The central controller through the modem polls each of the communication units connected on the modem bus periodically using the unique address allocated to each communication unit. In response, the communication units send a specific request to the central controller or just send the “status” or “alive” data packet to the central controller. The controller can send a response to the individual communication unit by sending a packet containing the physical address of the communication unit. All the communication units on the signal cable receive polling packets (two bytes), but only the communication unit with the specific address accepts the packet and responds, while others discard the packet. Response from polled station may vary from two or more bytes, depending on the response or request to be made by the station.
Brief description of the drawings:
Figure 1 shows a perspective view of an existing communication system, in accordance with a prior art; and
Figure 2 shows a perspective view of a system for connecting multiple communication units over a single modem, in accordance with the present invention.
Detailed description of the invention:
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments.
The present invention provides a system for connecting multiple communication units over a single modem. The system provides master slave signaling protocol used with a frequency shift key (FSK) modem and multiple communication units connected over the same modem line, with serial communication to a communication controller.
The present invention is illustrated with reference to the accompanying drawing throughout which reference numbers indicate corresponding parts in the system. These reference numbers are shown in bracket in the following description and in the table below.
Table:
Component No Component name
100 Communication system
1 Signal cables
2 Loudspeaker cables
3 Mains cable
11 Controller/ server rack
11A MODEM
12 Communication units
13 Loud speaker
14 Power Supply cum Branching Junction Box
Referring to the figure 2, there is shown a system (100) for connecting multiple communication units over a single modem (hereinafter referred to as “the system (100)”), in accordance with the present invention.
The system (100) comprises a controller (11), a plurality of communication units (12), plurality of junction boxes (14) and a plurality of cables. The plurality of cables includes signal cables (1), loudspeaker cables (2) and mains cables (3). The system (100) operates at power supply of 230V AC (alternating current) with a frequency of 50Hz.
The controller (11) consists of a plurality of modems (11A) therein. In a specific embodiment, the modem (11A) is a FSK modem (Frequency shift key). The central controller is supplied with a power of 230v 1F 50Hz via the mains cable (3). The modem (11A) and the individual communication units (12) are in hybrid bus cum star configuration. This hybrid bus cum star configuration is repeated for all the modem (11A) at central controller (11).
A junction box (14) from the plurality of junction boxes (14) is connected to a single modem (11A) from the plurality of modems (11A), through a signal cable (1). The junction box (14) is a branching cum power supply junction box and receives a mains supply of 230 V AC with a frequency of 50Hz through the mains cable (3).
Each communication unit (12) is given a predefined physical address and the communication units are divided into groups according to their geographical location. In a group, the communication units are connected in a bus architecture through the signal cable (1). Each communication unit (12) is in communication with other fields units (12) in the group. At least two such groups of communication units (12) are connected to a junction box (14) in a loop-in-loop-out fashion. Connection between a junction box (14) and plurality of communication units is through the signal cable (1). The communication units (12) are also provided with a rectifier (not shown), a regulated power supply (not shown) to cater to its needs thereof and a loudspeakers (13). A loudspeaker cable (2) connects the loudspeaker with the communication unit (12).
In an embodiment the signal cables (1) are feeder communication means configured for carrying the signal and power to the individual communication units (12). The signal cables (1) carry modem signals and audio signals from the central controller (11) to the junction box (14) and from the junction box (14) to the plurality of communication units (12) connected in a hybrid bus cum star architecture. Each signal cable (1) carries modem signals, audio signals and power at low voltage AC (30V ac.) to the plurality of communication units (12). In a specific embodiment, the signal cable (1) is 20 pair 0.5mm solid conductor telephone cable, the mains cable is 3 core 2.5 Sq.mm ATC multi strand conductor cable, and the loud speaker cable is 1 pair 0.75 Sq.mm multi strand conductor cable.
Again referring to the figure 2, the communication between the modem (11A) in the central controller (11) and the communication units (12) is based on a communication protocol (a master-slave protocol). The master/slave communication protocol is implemented so that the communication units (12) can communicate with the controller over a common bus without any corruption of data. The master slave protocol consists of frames/ packets of multiple bytes. The central controller (11) through the modem (11A) polls each of the communication units (12) connected on the modem bus periodically using the unique address allocated to each communication unit (12). In response, the communication unit (12) sends a specific request to the central controller (11) or just sends the “status” or “alive” data packet to the central controller (11).
The controller (11) can send a response to an individual communication unit (12) by sending a packet containing the physical address of the unit. The central controller and field stations have capability to interpret the information contained in the frame/ packets and take appropriate actions. All the communication units (12) on the signal cable (1) receive polling packets (two bytes) from the controller, but only the communication unit with the specific address will accept the packet and respond. Others will discard the packet. Communication from Field station to the controller; is similarly received by all other field stations connected on the common signal cable, but it is discarded by them. Response from polled station may vary from two or more bytes, depending on the response or request to be made by the station. Any communication common to all the communication units (12) can be sent with a broadcast header. This packet will be accepted by all the communication units (12), in this case. The system provides facilities to communication units (12) to make
? one way announcements,
? open communication within a group(Open-line’ calls),
? point to point communication, and
? calling all the communication units (12) in the system (100).
For this purpose one of the pairs for audio signals is utilized for each call, under instructions from central controller and as per pre-determined program. As per the system architecture, all the signal pairs are looped through to all the communication units (12). The communication units (12) can continue to communicate within their groups in ‘Open-line’ calls, even when the central controller (11) fails to operate. To improve reliability, the signal cables (1) can be looped back to the junction box (14). In this case the system will continue to work even when the signal cable has a single break.
In electrical terms, the effect of imbalance of impedance on the modem line for different number of communication units (12) has to be overcome, where the number may change for each situation. This is taken care of, in the present invention by incorporating bi-directional hybrid current source stage (four wire to two wire) in the modem with a low termination impedance across the lines. Similar stage is incorporated in the field station.
Advantages of the invention:
1. Reduced cabling costs (Typically by a factor of two and above)
? Multiple communication units (12) in a group get connected with same signal cable (1) instead of individual cable from the central controller (11).
? Powering from the same cable eliminates need for separate power cable for each communication unit (12).
? For adding a communication unit (12), one can connect it to the nearest communication unit (12) by extending the signal cable, instead of drawing a cable all the way from central controller (11).
2. Increased reliability
? In case of a cut in signal cable (1) at one location, the communication units (12) still remain connected and communication is uninterrupted due to the loopback connection possibility.
? In case of failure of central controller (11), the communication units (12) connected on a hybrid Bus cum Star cable can still communicate in groups (Open-line’ calls). Through a special facility, the communication units can switch from one group to another group as well.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the claims of the present invention.
,CLAIMS:CLAIMS
We Claim:
1. A system (100) for communication with multiple communication units (12) over a single modem (11A), the system (100) comprising:
a controller (11) consisting of plurality of modems (11A);
a connecting means (1) configured for carrying a modem signal, an audio signal and power there through;
a plurality of junction boxes; each junction box (14) connected to a single modem (11A), through the connecting means (1);
a plurality of communication units (12) connected to the junction box (14) in a loop-in-loop-out fashion, through the connecting means (1), wherein the plurality of communication units (12) is divided into groups according to the geographical location thereof, communication units (12) in each group are connected in a bus architecture through the connecting means (1), and at least two groups of communication units (12) are connected to the junction box (14) through the connecting means (1); and
a communication protocol implemented for communication between the controller (11) and the plurality of communication units (12).
2. The system (100) as claimed in claim 1, wherein the connecting means (1) is a solid conductor signal cable.
3. The system (100) as claimed in claim 1, wherein each communication unit (12) is provided with a predefined physical address.
4. The system (100) as claimed in claim 1, wherein each communication unit (12) is in communication with other communication units (12) in the group.
5. The system (100) as claimed in claim 1, wherein the modem (11A) is a frequency shift key modem.
6. The system (100) as claimed in claim 1, wherein the controller (11) is configured to communicate with any one selected from: the single communication unit (12) and the plurality of communication units (12).
7. The system (100) as claimed in claim 1, wherein the communication protocol is a master-slave protocol.
Dated this 28th day of December 2017

Ashwini Kelkar
(Agent for the applicant)
(IN/PA-2461)