Abstract:
A communication system is provided that includes a plurality of remote terminal units (RTUs) that communicate with a server via a network. The network provides communication paths to the RTUs via both a sessionless protocol and a switched connection protocol. Generally, the RTUs communicate via the network using the sessionless protocol. The network also includes a server. The RTUs share at least one account identifier that is coordinated by the server. Short messages are sent via the sessionless protocol. Longer messages are sent via the switched connection protocol using a shared account identifier. A corresponding method of operating the network is also provided. The use of a shared account identifier avoids the requirement of obtaining access accounts to the switched connection protocol for each of the RTUs, and is especially efficient and economical when the need to communicate longer messages is infrequent, but where each of a large number of RTUs require this capability.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U. S. Provisional Application No. 60/093,706, filed Jul. 22, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods and apparatus for communicating via a communication network, and more particularly to methods and apparatus for efficiently and economically communicating via a public network utilizing a shared account. 
     Public networks offer specialized, low-cost communication modes for the delivery of small packets of alarm and status information such as from remote industrial facilities. For example, networks operating in the Advanced Mobile Phone Service (AMPS) cellular network provide such communication modes via a cellular control channel, while networks operating in the Personal Communications Service (PCS) and Global System for Mobiles (GSM) offer Short Messaging Services (SMS) or equivalent services. Small data packets from remote terminal units (RTUs) are delivered via the low cost communication modes utilizing a sessionless, store-and-forward protocol. The maximum message length permitted by the protocol varies from system to system, but is typically equivalent to between 14 and 256 alphanumeric characters. Typical uses for SMS protocol in an industrial setting include the communication of alarm signals, switch closures, and event counts to a central computer via the network. 
     Occasionally, it is necessary in some applications to communicate more voluminous amounts of data to or from an RTU than can be efficiently handled using these low-cost communication modes. This need may arise, for example, hen an event logging function associated with an RTU is to be reprogrammed, or when a data history of a dynamometer associated with an RTU is to be uploaded to a central computer. In such cases, the need for wider bandwidth could be fulfilled by the RTU resorting to a switched connection protocol, e.g., placing a regular cellular or PCS call, to more rapidly and efficiently communicate larger data volumes. However, to be permitted to place a regular cellular or PCS call, a cellular or PCS subscriber account agreement is required. All such subscriber agreements have heretofore involved a monthly fee arrangement, the cost of which has hampered the development and spread of remote data collection applications. Network carriers have, in some instances, discounted the monthly cost of the service, but to date have still required an account for each RTU in a system. Where large numbers of RTUs need access to switched connection services for high volumes of data only occasionally, a large number of monthly service fees must be paid. 
     It would thus be desirable to provide methods and apparatus for utilization of low volume, low cost network data communication modes when feasible, and efficient and low cost use of high volume network data communication mode in systems in which the latter mode is infrequently required, in systems with multiple RTUs. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment of the invention, a communication system is provided that has a plurality of remote terminal units (RTUs) that communicate via a network using a sessionless protocol and a switched connection protocol. RTUs communicate with a centralized server via the network. Short messages are communicated between the RTUs and the server utilizing the sessionless protocol. Examples of suitable sessionless protocols are cellular control channels, and the SMS protocol provided by GSM and PCS, or equivalent protocols in other systems. To communicate longer messages, the RTUs are configured to use at least one account identifier in a coordinated manner to communicate the longer messages via a switched connection protocol of the network. 
     In another embodiment of the invention, an RTU is provided that is configured to communicate data via a network using both a sessionless protocol and a switched connection protocol. The RTU is also configured to identify itself to the network using a first account identifier when communicating via the sessionless protocol, and to use a second account identifier different from the first account identifier when communicating via the switched connection protocol. In one embodiment of the RTU, the second account identifier is a shared account identifier identified by a server via the network, using the lower cost sessionless protocol. 
     In yet another embodiment of the invention, a method of operating a communication system including a plurality of remote terminal units communicating via a network is provided. Each RTU identifies itself to the network utilizing a unique account identifier to communicate in a first communication mode, and each RTU identifies itself to the network utilizing at least one shared account identifier to communicate in a second communication mode. The use of the shared account identifier is coordinated by a centralized server. In one embodiment, the first communication mode is a sessionless protocol mode, and the second communication mode is a switched connection protocol mode. 
     In still another embodiment of the invention, a server is provided for controlling access by a plurality of RTUs to a network. The server is configured to communicate commands to an RTU to conduct a switched connection protocol session via the network. The server is also configured to assign a shared network account identifier to the RTU for switched connection protocol access to the network and to coordinate usage of the shared network account identifier among the plurality of RTUs. A corresponding method of operating a server is also provided. 
     It will be seen that the various embodiments of the invention provide users of low cost modes of public communication networks to economically deploy large, widely dispersed, low-volume data networks while retaining a low-cost method for handling occasional high-volume data transfers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an embodiment of a communication system. 
     FIG. 2 is a flow chart of a method of operating a remote terminal unit (RTU) in accordance with the present invention. 
     FIG. 3 is a flow chart of a method for delivering alarm status information from an RTU. 
     FIG. 4 is a flow chart of a method for setting up an RTU for a data session via a switched connection protocol. 
     FIG. 5 is a flow chart of a method for exchanging data between an RTU and a server after a data session is established, and for taking down the data session after its completion. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of an embodiment of a communication system  10  in accordance with the invention. In the represented embodiment, a number of remote terminal units (RTUs), for example, RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24 , are in communication with a wireless network  26 . Examples of digital wireless networks are Personal Communications Services (PCS) networks, Global System for Mobile Communications (GSM) networks, time division multiple access (TDMA) networks and code division multiple access (CDMA) networks. Messages communicated by RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  are communicated via wireless links such as radio links  28 ,  30 ,  32 , and  34 . It will be understood that communication system  10  generally coexists in an environment in which many other devices (not shown), including mobile telephones (not shown), are in communication or are capable of communicating with network  26 . It will also be understood that the number of RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  shown in FIG. 1 is exemplary only. A communication system  10  in accordance with the invention may comprise any number of RTUs. 
     Each RTU  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  monitors a device or a system, for example, devices  36 ,  38 ,  40 ,  42 ,  44 ,  46 , and  48 , respectively, generally at different and possibly widely-spaced locations. Devices  36 ,  38 ,  40 ,  42 ,  44 ,  46 , and  48  infrequently generate alarms, switch closures, status messages or other signals that can be encoded as a short message and transmitted by a respective RTU  12 ,  14 ,  16 ,  18 ,  20 ,  22 ,  24  in a sessionless protocol with network  26 , which is typically a limited capacity, low cost service such as SMS. In the typical industrial application shown in FIG. 1, messages are relayed via the sessionless protocol by network  26  to a central server  50 . Central server  50  includes an RTU database  52 , a shared account database  54 , a processor  56 , and a network interface  58 . RTU database  52  maintains the location and status of all RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24 . Shared account database  54  includes information about at least one switched connection account that is shared among RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24 . Processor  56  processes information from shared account database  54  and RTU database  52  and communicates with network  26  via network interface  58 , such as via radio links  60  and  62 . It will be understood that central server  50  also comprises means (not shown) to render information received from RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  into a useful form for the application in which communication system  10  is used. For example, data may be stored in a storage device, displayed visually or audibly, or used for generation of automatic control signals. The wide applicability of the invention will suggest other forms of data utilization to those skilled in the art. 
     The embodiment represented in FIG. 1 utilizes wireless transmission modes. In other embodiments, other types of transmission modes are used. For example, in one embodiment, a wire network having both sessionless and switched connection communication modes is utilized as network  26 . In other embodiments, combinations of wired and wireless communication transmission modes are used. In each embodiment, network  26  has both a sessionless and a switched communication protocol mode. Network  26  not necessarily be a digital network, inasmuch modems may be used for communication of digital data over analog networks. 
     FIG. 2 is a flow chart of an embodiment of a method used in communication system  10  by an RTU, for example RTU  12 , to communicate with central server  50 . Starting at  100 , RTU  12  monitors  102  one or more input channels, such as a serial channel  64  (see FIG. 1) between RTU  12  and device  36 . For example, device  36  monitors a flow, level, temperature or pressure and communicates an alarm to RTU  12  when the monitored parameter exceeds a certain threshold. If an unreported alarm is detected  104 , an alarm status is reported  106  to central server  50  using low cost, sessionless control channel or SMS communication protocols. In one embodiment, alarm events require acknowledgment from server  50 , or else RTU  12  will repeatedly attempt to communicate the alarm status to server  50  at intervals until an acknowledgment is received. It will be understood that data other than alarm status can be communicated in this manner, and that what is said herein about RTU  12  and its associated remote device  36  and serial channel  64  may be generalized to any RTU in communication system  10  and its associated remote device and electronic coupling thereto. 
     RTU  12  determines whether query or poll information has been received  108  from server  50 , for example, via sessionless control channel or SMS communication protocols. When such a query or poll is received  108 , RTU  12  sends its current status  110  via sessionless control channel or SMS communication protocols and then returns to monitoring of the input channels  102 . If server  50  does not receive a current status response  110  from RTU  12  within an anticipated time period, server  50  can repeat the query or poll. 
     RTU  12  also determines  112  whether a command has been received  112  from server  50  to set up an end-to-end data session using a switched circuit channel rather than sessionless control channel or SMS channel protocols. When such a command is received  112 , a data session is set up  114 . This data session allows communication of a higher volume of data to or through RTU  12  (for example, to initialize or reprogram device  36 ) than sessionless control channel or SMS techniques can effectively or economically accommodate. If no data session is to be set up, RTU  12  returns to the monitoring  102  of alarm input channels. 
     It will be appreciated that RTU  12  itself can be provided with the ability to request that a data session utilizing a switch circuit channel be set up by configuring RTU  12  to deliver  106 , in appropriate circumstances, an alarm status recognized by server  50  as a code for such a request. Server  50  then responds to the alarm status code by issuing the command  112  to set up an end-to-end data session. 
     In one embodiment and referring to FIG. 3, delivery of alarm status  106  is performed by transmission  200  of the alarm status via low cost, sessionless control channel or SMS communication protocol using a mobile identification number (MIN) assigned to RTU  12  to identify a service account and to access network  26 . RTU  12  next determines  202  whether network  26  has acknowledged that the transmitted alarm has been received, indicating that it is successfully en route to server  50 . If no acknowledgment is received and a predetermined number of retries is not exhausted, RTU  12  will wait  204  a predetermined period of time to retransmit  200  the alarm. If a selected number of retries is attempted without success  206 , other retry strategies, for example, adjustment  208  of the retry attempt interval, are implemented. 
     If an acknowledgment from network  26  is received that the alarm message is en route to server  50 , RTU  12  then checks  210  for an acknowledgment from server  50 . If an acknowledgment is received, RTU  12  returns to start  100 . Depending upon service limitations placed upon use of the sessionless control channel or SMS communication protocol by the carrier, RTU  12  may be required to wait some period of time before initiating further alarm messages or responding to messages from server  50 . 
     If an acknowledgment is not received from server  50 , RTU  12  will wait  212  a predetermined amount of time, for example, five minutes, until an acknowledgment is received. If an acknowledgment is not received within that time, it will attempt to send  200  another alarm message, unless RTU  12  determines  214  that a predetermined number of retry attempts have been exhausted. If the predetermined number of retry attempts has been exhausted, RTU  12  enters an error condition  216 , which, in one embodiment, requires manual intervention. 
     In one embodiment and referring to FIG. 4, setting up a data session  114  begins by RTU  12  receiving  300  a shared account identifier transmitted by server  50 . For example, the shared account identifier transmitted by server  50  and received by RTU  12  is a valid MIN/equipment serial number (ESN) combination. In another embodiment, each RTU  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  is provided with an list of valid, pre-established account identifiers, and server  50  transmits an indication of a shared account identifier. For example, when controlling RTU  12  for switched circuit access, server  50  transmits a code to RTU  12  that points to a pre-established valid account identifier stored in a memory of RTU  12 . In this manner, the transmitted code indirectly identifies an account identifier. The total number of different valid, pre-established account identifiers is less than the total number of RTUs in communication system  10  to effect a reduction in the number of different switched circuit access accounts that must be opened with the network carrier in accordance with the invention. However, embodiments of the present invention can utilize more than one account in cases in which more than one account is available. 
     It should be noted that it will suffice in at least one embodiment for server  50  to transmit a only a control signal to RTU  12  without any account identifier or indication thereof, if RTU  12  has one or more account identifiers stored in memory and appropriate measures are taken to prevent simultaneous use of the same account identifier by more than one RTU. For example, server  50  can coordinate use of shared account identifiers by ensuring that no more than one RTU is engaged in a switched circuit session at a time, or by ensuring that only one RTU in any group of RTUs having identical account identifiers stored in memory are engaged in simultaneous switched circuit sessions. 
     Again referring to FIG. 4, in one embodiment, the received MIN/ESN is stored or loaded  302  into a circuit switched radio component (not shown) of RTU  12 , placing RTU  12  into a circuit switched mode, for example, Advanced Mobile Phone Service (AMPS) cellular mode, or PCS mode. RTU  12  then dials  304  a switched circuit cellular link to server  50 , or, in other words, places a phone call to server  50 . Shared account database  54  is also updated by server  50  to coordinate usage of the shared account or accounts. In one embodiment, shared account database  54  is updated by server  50  to indicate that the MIN/ESN combination temporarily assigned to RTU  12  is exclusively assigned and is therefore not currently available for assignment to any other RTU. As a security measure to prevent unauthorized access, RTU  12  then logs  306  into server  50 . RTU  12  is then ready for higher volume data transfer with server  50  via this circuit switched mode call than is possible using the sessionless control channel or SMS communication protocol. 
     In one embodiment, server  50  requests an external session with equipment  36  external to RTU  12  or an internal session with RTU  12  itself Thus, RTU  12  determines  308  what type of session is being requested by server  50 . If an external session is requested, an external routine  310  is executed by RTU  12  as described below in more detail. Otherwise, an internal data session is conducted  312  in which RTU  12  and server  50  exchange data. Server  50  also interacts with RTU  12  by issuing commands that pertain only to RTU operation. For example, these commands include a code that instructs RTU  12  to terminate  314  the session and disconnect  316  the switched circuit link so that RTU  12  returns to start  100 , ready for communication of alarms. When RTU  12  logs off  314  server  50 , server  50  updates shared account database  54  to make the MIN/ESN combination that was used by RTU  12  available for assignment again. RTU  12  also returns to sessionless control channel or SMS communication protocol and no longer uses the MIN/ESN combination temporarily assigned by server  50 , unless and until the MIN/ESN combination is assigned by server  50  again at some later time. 
     In one embodiment and referring to FIG. 5, when an external session  310  is requested by server  50 , RTU  12  readies serial channel  64  to external device  36 . RTU  12  then enables  400  serial channel  64  and sends a response code back to server  50 . Subsequent communication over the switched circuit path will then be between server  50  and device  36  until a preassigned trap code or string from server  50  is detected  402  by RTU  2 . A trap code or string is sent by server  50  to regain the attention of RTU  12 , for example, to discontinue the session or to perform other tasks involving server  50  and RTU  12 . After the trap string is detected  402 , RTU  12  determines  404  whether a log off command has been received. If a logoff command has been received, the circuit switch link is disconnected  406  and RTU  12  returns to start  100 , ready for communication of alarms. When RTU  12  logs out, server  50  updates shared account database  54  to make the MIN/ESN combination that was used by RTU  12  available for assignment again. RTU  12  also returns to sessionless control channel or SMS communication protocol and no longer uses the MIN/ESN combination temporarily assigned by server  50 , unless and until the MIN/ESN combination is assigned by server  50  again at some later time. 
     Before a log off command is received  404 , RTU  12  processes, if required, other commands  408 . For example, in one embodiment in which a code that points to a pre-established valid MIN/ESN combination in a memory (not shown) of RTU  12  is communicated from server  50  to RTU  12 , an instruction to update the valid, pre-established MIN/ESN combinations in the memory of RTU  12  is sent from server  50  to RTU  12 . 
     If serial communication between external device  36  and server  50  (through RTU  12 ) ceases for more than a predetermined period of time, RTU  12  determines  410  that a time-out has occurred and automatically disconnects  406  the switched circuit link to prevent excessive link times when serial communication is disrupted. 
     It will be recognized that the herein described methods and apparatus provide efficient and economical use of networks, for example wireless digital and cellular networks, that offer reduced cost, low-volume sessionless communication protocols and higher cost, switched connection protocols. 
     Although various embodiments of the invention have been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. For example, it is not necessary that network  26  be a cellular or even a wireless network, or that RTUs  12 ,  14 ,  16 ,  18 ,  20 ,  22 , and  24  and server  50  communicate via radio links. Other modifications and variations of the invention will also become apparent to those skilled in the art. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims, and equivalents thereto.