Abstract:
A wireless terminal or other type of terminal in a communication system is controlled in a bandwidth-efficient manner using commands associated with a terminal protocol supported by a switch of the system. In an illustrative embodiment, a set of command symbols are generated by: (i) resizing a command space associated with a wired terminal protocol to obtain a reduced command space suitable for use with a wireless terminal; (ii) generating a representation in which a first portion of the reduced command space is correlated with a second portion of the reduced command space; and (iii) assigning command symbols to valid entries in the representation, such that a given one of the command symbols uniquely identifies a particular combination of commands in the reduced command space. The switch transmits a given command symbol to the wireless terminal, and the wireless terminal decodes the symbol and executes the corresponding commands specified by the symbol. Since the command symbols can be represented using significantly fewer bits than would otherwise be required using the complete wired terminal protocol, the invention allows the switch to control the wireless terminal in a bandwidth-efficient manner, while still providing substantially the full functionality of the wired terminal protocol at the wireless terminal.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to communication systems, and more particularly to communication systems which support wireless mobile telephones or other types of wireless user terminals. 
     BACKGROUND OF THE INVENTION 
     Communication system switches frequently deploy multifunction voice or voice-and-data terminals which generally require a complex multi-octet terminal protocol to drive the terminal interface and to control transport services. Such a multi-octet protocol is typically field oriented, and may include, e.g., a header field, a command pointer field, a command data field interpreted according to the contents of the command pointer, and an integrity check field. Each field is usually defined as a collection of one or more bits, and certain bits or collections of bits are dedicated to certain functions. This creates fixed relationships between bits and command interpretations. In addition, the deskset terminal design is such that a large number of bits are assigned or reserved for numerous feature keys and feature indicator controls. When such a system is upgraded to support wireless terminals, use of the existing wired terminal protocol is desirable from a switch software point of view, since re-use of the protocol is generally a low-cost implementation. Unfortunately, this conventional approach requires excessive bandwidth, and fails to optimize the control protocol for the wireless voice terminal. 
     There are a number of issues associated with use of an existing wired terminal protocol to support wireless terminals. For example, the wireless terminal by its very nature is designed to be small and easily portable. The direct consequence of this is that there is an extremely limited area on the terminal user interface for feature access presentation. This implies that the wireless terminal control protocol requires many fewer codepoints for feature button and associated feature indicator pairs. Further, the area for a switch-controlled display on the wireless unit may be much smaller, and therefore only a subset of the normative wired terminal display control functionality is required to support the wireless terminal. In addition, a significant portion of the information displayed by a wireless terminal relates to the condition of the terminal itself, e.g., battery charge remaining, signal strength, etc., and is not commanded by the switch. Conventional techniques for utilizing a wired terminal protocol to support wireless terminals have failed to adequately address these and other important issues, and as a result these techniques suffer from the above-noted problems of excessive bandwidth consumption and lack of optimization. 
     A need therefore exists for techniques which allow an existing wired terminal protocol to be custom-fit to a wireless terminal interface, in order to capitalize on the existing switch software codebase, to reduce the amount of bandwidth consumed for terminal control, and to preserve the functionality of the system as represented to the user via the wireless terminal. 
     SUMMARY OF THE INVENTION 
     The invention allows a switch or other communication system device to direct a system terminal to perform a set of command-based operations using a compressed symbol-based command format. The format in an illustrative embodiment is the result of cross-coding a collection of individual commands from an existing wired terminal protocol into a bandwidth-efficient set of command symbols, such that a particular combination of multiple wireless terminal commands are executed upon the transmission of a given symbol from a commanding switch. In other words, a given transmitted symbol is interpreted by the wireless terminal as corresponding to the particular combination of commands in the wired terminal protocol. The invention is not restricted to use in applications in which a wired terminal protocol is supported by a wireless terminal, as in the illustrative embodiment, but is instead more broadly applicable to any application in which an existing terminal protocol is used to support a terminal having a valid command space which is less than the full available command space of the terminal protocol. 
     In the illustrative embodiment, the set of command symbols may be generated by: (i) resizing a command space associated with the wired terminal protocol to obtain a reduced command space suitable for use with the wireless terminal; (ii) generating a tabular representation in which specific bit values from a first portion of the reduced command space correspond to columns and specific bit values from a second portion of the reduced command space correspond to rows; and (iii) assigning command symbols to valid entries in the tabular representation, such that a given one of the command symbols uniquely identifies a particular combination of commands in the reduced command space. In operation, the switch transmits a given command symbol to the wireless terminal, and the wireless terminal decodes the symbol and executes the corresponding commands specified by the symbol. Similar techniques may be used for terminal-to-switch communications in accordance with the invention. 
     The above-described illustrative embodiment of the invention significantly reduces the command field associated with supporting the operation of a wireless terminal using an existing wired terminal protocol. This results in a proportional bandwidth consumption reduction when communicating over wireless communication channels, thereby preserving this scarce resource. The full functionality of the system, as expressed by the wired terminal protocol, is made available to the wireless terminal to the extent implementable in that terminal. In addition, there is no need to subject the command symbols to bitwise encryption, since their field mapping conventions in accordance with the wired terminal protocol are eliminated during the symbol generation process of the invention. These and other features and advantages of the present invention will become more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a portion of an exemplary communication system in which the invention may be implemented. 
         FIG. 2  shows a wired terminal protocol packet format that may be utilized to support a wireless terminal using the techniques of the invention. 
         FIG. 3  shows an illustrative embodiment of a wireless terminal configured in accordance with the invention. 
         FIG. 4  is a table illustrating symbol generation in an illustrative embodiment of the invention. 
         FIGS. 5A through 5G  are tables illustrating field-based commands and associated parameters of the wireless terminal, after resizing of the command space associated with the wired terminal protocol. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be illustrated below in conjunction with an exemplary wireless communication system. Although particularly well-suited for use with, e.g., a telephone system which supports both wired deskset terminals and wireless terminals, the invention is not limited to use with any particular type of system or terminal. The disclosed techniques may be used in any communication application in which it is desirable to utilize a given terminal protocol to provide bandwidth-efficient support of a terminal which uses less than the full available command space of the terminal protocol. For example, the invention may be applied to handsets for use in cellular and personal communication services (PCS) systems, and to other types of communication terminals, such as wired ISDN terminals. The word “terminal” as used herein should therefore be understood to include not only portable wireless handsets as in the illustrative embodiment, but also other types of communication devices, including personal computers, wired and wireless desksets, optical communication terminals, or any terminal supported by a message-oriented command structure. It should be noted that the invention does not require any particular type of information transport medium, i.e., the invention may be implemented with any desired transport type. The term “switch” as used herein should be understood to include enterprise switches and other types of telecommunication switches, as well as other types of processor-based communication control devices such as servers, computers, adjuncts, etc. The term “table” as used herein is intended to include not only tabular representations as in the illustrative embodiments, but any other type and arrangement of data from which information can be extracted using one or more identifiers. For example, information stored in an addressable memory may be viewed as an example of one type of table. 
       FIG. 1  shows a portion of an exemplary communication system  100  in which the invention may be implemented. The system  100  includes an enterprise switch  110  which receives as an input a trunk  114 . The trunk  114  supplies incoming calls to the switch  110  for processing. The switch  110  in this embodiment includes a central processing unit (CPU)  115 , a memory  116 , at least one interworking function (IWF)  117 , and a system database  118 . The CPU  115  may be a microprocessor, an application-specific integrated circuit (ASIC) or other type of digital data processor, as well as various portions or combination of such elements. The memory  116  may be a random access memory (RAM), a read-only memory (ROM) or combinations of these and other types of electronic memory devices. 
     The IWF  117  is used to provide necessary format conversions pertaining to signaling and transport, in a known manner. The IWF  117  may in other embodiments be incorporated into other elements of switch  110 , such as the CPU  115  and memory  116 . The system database  118  may be used to store, e.g., feature assignments to particular feature buttons, directory number assignments to corresponding call appearances or direct facility termination keys, access restrictions, and other known administrative information regarding the configuration of the system  100 , as well as other types of information. 
     The switch  110  in this example further includes four port cards  120 A,  120 B,  120 C and  120 D. Port card  120 A is coupled to a wireless base station  121  which communicates with a first wireless terminal (WT)  122  designated WT 1  and a second wireless terminal  123  designated WT 2 . The terminal WT 1  may be a mobile telephone, and the terminal WT 2  may be a wireless deskset. Port card  120 B is connected to a broadband wireless base station, e.g., a National Information Infrastructure (NII) wireless base station  124 , which communicates with a wireless personal computer (WPC)  125 . Port card  120 C is connected to a wired deskset (DS)  126 . Port card  120 D is connected to an advanced terminal (AT)  127 , which may be, for example, a video telephone operating in accordance with the H.320 standard. It should be noted that the switch  110  may include additional port cards, and may be connected to other types and arrangements of user terminals. The switch  110  is also connected to an administrator terminal  128  which may be used to program the operation of the switch  110  during a system administration, e.g., an initial set-up and configuration of the system or a subsequent system-level or user-level reconfiguration. 
     The system  100  of  FIG. 1  includes an adjunct feature server  129 . The adjunct feature server  129  may be directly connected to the switch  110  or connected thereto over a network or other suitable transport medium. The adjunct feature server  129  may be used, e.g., to implement various aspects of a symbol-based control technique in accordance with the invention. Although shown as separate from the switch in the embodiment of  FIG. 1 , an adjunct such as adjunct feature server  129  is considered to fall within the general definition of the term “switch” as given previously. Such an adjunct may be physically incorporated within the switch in other embodiments of the invention, and may be partially or completely implemented using other switch elements such as CPU  115  and memory  116 . 
     The present invention in the illustrative embodiment allows an existing wired terminal protocol, such as a protocol used to control wired deskset terminal  126  in the system of  FIG. 1 , to be extended in a bandwidth-efficient manner to support wireless terminals, such as the mobile wireless terminal  122 . More particularly, the invention allows the wireless terminal  122  to operate using an existing wired terminal protocol of system  100  but at a substantially reduced bandwidth consumption and with a high degree of optimization for the specific characteristics of the wireless terminal. A typical wired terminal protocol supports a large number of commands, e.g., for controlling a deskset or other type of multifunction business telephone. In the illustrative embodiment to be described below, a set of command symbols are created to replace the conventional multi-octet, field-based, bit-oriented command structure of the existing wired terminal protocol. A mechanism is defined for creating the command symbols, e.g., on the wireless port card in the serving switch, and for decoding and executing them in the served wireless terminal. Note that in the process, individual bits lose their assigned identity in the wired terminal protocol to that of the generated command symbol, and that overall bit utilization is reduced while performing equivalent command functions. The invention is illustrated herein by way of example using the downlink, i.e., switch-to-terminal, symbol generation procedure. The terminal-to-switch procedure can be implemented in a similar manner, as will be apparent to those skilled in the art. 
       FIG. 2  illustrates a standard wired terminal protocol which serves as the basis for the symbol generator in the illustrative embodiment. In accordance with the protocol, a given fixed-length 24-bit packet  130  includes a header field  132  and a command portion  134 . The header field  132  contains four bits of control information, including a primary switchhook (PSH) state bit  135 , a secondary switchhook (SSH) state bit  136  (bit B 2 ), an extended protocol (XP) indicator bit  137 , and a test bit (TST)  138 . The PSH state bit  135  indicates the state of the wired terminal handset-related switchhook, the SSH state bit  136  indicates the state of the wired terminal intercom service, the XP indicator bit  137  is used to support datagrams via an adjunct interface of the wired terminal, and the TST bit  138  is used to indicate to the serving switch that the wired terminal has entered a user-commanded self-test mode. The command portion  134  in this embodiment contains a 4-bit command pointer field  140 , which indicates the type or category of command the terminal is to execute, two 4-bit command data segments  142 - 1  and  142 - 2  which specify the particular command within a given category, and an 8-bit cyclic redundancy code (CRC) field  144  to ensure command integrity. The command pointer  140  generally addresses a particular terminal element, and pointers are available for categories such as, e.g., audio path control, alerter control, user interface condition control, and display control. 
       FIG. 3  shows a wireless terminal  122  to which the above-described wired terminal protocol will be applied in the illustrative embodiment of the invention. The terminal  122  includes a housing  150  with a speaker  152 , a microphone  154 , a display  156  and an audio alerter  158 . The display  156 , which may be an LCD display or other suitable type of display, includes a display area  160 , a set of local icons  162 - 1 ,  162 - 2  and  162 - 3 , a system icon  164 , and a set of SLK labels  170 - 1 ,  170 - 2 ,  170 - 3  and  1704  which indicate the functions associated with SLKs K 1 , K 2 , K 3  and K 4 , respectively. A given physical SLK can have multiple function assignments which vary in accordance with the feature labels, based on the symbol-based control techniques of the invention to be described in greater detail below. 
     The local icons  162 - 1 ,  162 - 2  and  162 - 3  indicate locally-generated status information associated with the wireless terminal, e.g., battery charge remaining, signal strength, etc. The system icon  164  conveys system information supplied to the terminal by the switch. Alternative embodiments could include multiple switch-driven system icons. The wireless terminal  122  further includes buttons P 1 , P 2 , P 3  and P 4 , LED indicators  172 - 1 ,  172 - 2  and  172 - 3 , and a conventional set of touch-tone dialpad buttons  174 . It should be emphasized that the configuration of wireless terminal  122  as shown in  FIG. 3  is for purposes of illustration only, and should not be construed as limiting the invention to any particular type of wireless terminal. 
     The command symbol generation procedure in the illustrative embodiment of the invention is as follows. First, the command space is resized according to the requirements of the wireless terminal user interface application, e.g., the wireless terminal of FIG.  3 . This involves determining all command elements which are not of use to the button and indicator fields available on the wireless terminal  122 . These fields are relatively small as compared to the more complex wired terminal for which the  FIG. 2  protocol is designed.  FIG. 4  shows a table illustrating the resizing process. Bits B 1  and B 2  in the  FIG. 4  table correspond to the PSH bit  135  and TST bit  138 , respectively, in the  FIG. 2  packet format. Bits B 3  and B 4  correspond to the two bits of the command pointer  140 . Bits B 5  through B 8  may correspond to one of the four-bit data segments  142 - 1  or  142 - 2 . All entries in the  FIG. 4  table that are not applicable to the function of the wireless terminal are shaded. For example, the maintenance test operation is not permitted when the wireless terminal is active in a call. Therefore, all command entries which have the wireless terminal both “off-hook” on the primary switchhook and in test mode are shaded. Similar command field reductions are made against other command space entries in the wired terminal protocol. Also, bits corresponding to functions which are irrelevant to the wireless terminal, e.g. the SSH bit  136  for an intercom function and the XP bit  137  for a datagram service, are eliminated from the wireless terminal command space, and are thus not shown in the  FIG. 4  table. 
       FIGS. 5A through 5G  show tables illustrating the resulting field-based commands and associated parameters of the wireless terminal, after the above-described resizing of the command space.  FIGS. 5A and 5B  show the interpretation of bits B 1  and B 2 , respectively, which as previously noted correspond to the PSH and TST bits, respectively.  FIG. 5C  shows the interpretation of the pointer bits B 3  and B 4 . These bits specify a particular command category in the wireless terminal, and include visual indicator, audio alerter, display predetermined string, and display data string command categories.  FIGS. 5D through 5G  illustrate the specific commands for each of these command categories. 
       FIG. 5D  shows that the visual indicator includes a two-bit indicator ID, one for each of the system icon  164  and the three LEDs  172 - 1 ,  172 - 2  and  172 - 3 . For the system icon  164 , the available attributes are on, off, and reverse video. For the LEDs, the available attributes are on, off, flash and fast blink.  FIG. 5E  shows that the audio alerter  158  supports eight patterns: no alert, alert patterns 1 to 5, call waiting alert, and test alert pattern for maintenance. When the wireless terminal is active in a call, the audio alerter  158  can have only two patterns: no alert, or call waiting alert.  FIG. 5F  indicates that the pre-determined display string commands include eight system-defined display strings, and three supplementary display commands: clear display, load display string, and display test pattern. When the system initiates the test operation at the wireless terminal, the audio alerter has a dedicated alerting pattern for test, and the display has the display test string. The system will not send the display data to the display during the test operation. With regard to the predetermined sting display functions of  FIG. 5F , system-defined display strings can be downloaded to the wireless terminal via the “load string” command as follows:
         load string   string N   string character  1  (upper 4-bit)   string character  1  (lower 4-bit)   string character  2  and so on.   string character NULL   string character NULL (as terminator)
 
The data string display functions of  FIG. 5G  may be used to display multiple characters, e.g., a telephone number, on the display of the wireless terminal. A telephone number may thus be supplied from the system to the wireless terminal for display.
       
     The tables of  FIGS. 5A through 5G  represent the essential and sufficient functions required to control the wireless terminal  122  of  FIG. 3  using the wired terminal protocol of FIG.  2 . These tabulations demonstrate the sufficiency of the reduced command set, and the command points available to drive the wireless terminal in a fashion substantially equivalent to, e.g., that with which the system users are familiar based on their wired terminals. As shown in  FIG. 4 , the applicable combinations of commands for this wireless terminal can be reduced to a total of only 103 combinations, each corresponding to a unique symbol. 
     In the next step of the symbol generation process, the reduced command field is cross-coded, as illustrated in the diagram of FIG.  4 . In the illustrative embodiment, bits B 5 -B 8  are orthogonalized against the balance of the frame structure, i.e., bits B 1 -B 4 . Particular values of bits B 5 -B 8  are assigned to rows of the  FIG. 4  table, and particular values of bits B 1 -B 4  to columns as shown. Other orthogonalization arrangements may also be used, and yield similar results. As the final step in the symbol generation process, command symbol values are assigned, in this case serially and sequentially, to the valid, i.e., non-shaded, entries in the table of FIG.  4 . In other words, symbol numbers are assigned starting with the valid entry in the right-most and upper-most position in the table, and subsequent valid entries are numbered serially and sequentially, i.e., in order continuing down the first column, then from the upper-most valid entry in the next column down that column, and so on. This results in 103 assigned symbols, labeled as shown in FIG.  4 . Other techniques may be used to assign symbol numbers to valid entries in the command space, including random assignment techniques. 
     Note that the command space in this illustrative embodiment has been reduced from a 24 bit structure, with 2 24  symbol possibilities, to one which can be represented using less than 2 7  symbols, and thus only 7 bits. As is apparent from  FIG. 4 , each of the symbols corresponds to a particular entry in the table, and thus a particular combination of commands. In general, the total number of valid entries in the reduced command space is less than or equal to 2 N , where N is the number of bits in a given symbol. A parity bit may be added in the illustrative embodiment as an additional integrity check, and to preserve an octet-based format, which is assumed by most commercially available hardware components. The eighth bit in the illustrative embodiment may alternatively be used to expand the symbol count if mandated by system requirements. The need for an integrity check generally depends on the particular medium used in a given application. For example, in the wireless domain, primary integrity checks may be executed by the Media Access Control (MAC) function, such that the CRC is not needed. Other applications could utilize a shortened CRC or other type of integrity check. 
     The symbol generation process in the illustrative embodiment may be implemented in whole or in part in a port card in the serving switch, e.g., in port card  120 A associated with wireless base station  121  in system  100  of  FIG. 1 , elsewhere in the enterprise switch  110 , e.g., using CPU  115  and memory  116 , in the wireless terminal  122 , in the adjunct feature server  129 , or in various combinations of these and other system elements. Other suitable arrangements of hardware and/or software may be used to implement the symbol generation process in accordance with the invention. The wireless terminal  122  includes suitable circuitry for receiving symbols, decoding a given received symbol, and executing the corresponding combination of commands uniquely specified by that symbol. Such receiving, decoding and execution circuitry may include, e.g., a conventional processor and memory, and may be implemented in a straightforward manner. 
     The above-described illustrative embodiment of the invention significantly reduces the command field associated with supporting the operation of a wireless terminal using an existing wired terminal protocol. This results in a proportional bandwidth consumption reduction when communicating over wireless communication channels, thereby preserving this scarce resource. The fill functionality of the system, as expressed by the wired terminal protocol, is made available to the wireless terminal, to the extent implementable in that terminal. In addition, there is no need to subject the command symbols to bitwise encryption, since their field mapping conventions in accordance with the wired terminal protocol are eliminated during the symbol generation process of the invention. As previously noted, the above-described embodiment of the invention is intended to be illustrative only. For example, the invention is not restricted to use in applications in which a wired terminal protocol is supported by a wireless terminal, as in the illustrative embodiment, but is instead more broadly applicable to any application in which an existing terminal protocol is used to support a terminal which utilizes less than the full available command space of the terminal protocol. In addition, although illustrated for downlink, i.e., switch-to-terminal communication, the invention can also be used for uplink, i.e., terminal-to-switch, communications. These and numerous other alternative embodiments within the scope of the following claims will be apparent to those skilled in the art.