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`US005396537A
`5,396,537
`[11] Patent Number:
`United States Patent [19]
`Schwendeman
`[45] Date of Patent:
`Mar. 7, 1995
`
`
`[54] RELIABLE MESSAGE DELIVERY SYSTEM
`
`[75]
`
`Inventor: Robert J. Schwendeman. Pompano
`Beach’ Fla’
`[73] Assignee: Motorola, Inc., Schaumburg, I11.
`
`5,133.31]
`5,151,899
`5,315,535
`
`[21] Appl- No: 963,370
`[22] Filed:
`03- 19: 1992
`
`8/1992 Weinberg .
`31-'0/94.1
`9/1992 Thomas etal.
`5/1994 Kane et al.
`............................ 379/57
`OTHER PUBLICATIONS
`_
`EMBARC Advanced Messaging by Motorola, Bro-
`chure No. RC—5—6O Sep. 1992.
`Primary Examine.»-—Curtis Kuntz
`Assistant Examfner—G. .T. Oehling
`Attorney. Agent. or FI'rm—Keliy A. Gardner; John H.
`Related U-S- Alllilication Data
`Continuation-in-part ofSer. No. 954,106. Sep. 30, 1992. M00”
`Pat. NO. 5,315,635.
`Int. CL6 ............................................
`US. Cl. ........................................
`340/325-44
`_
`[531 Fm” °f Search ----------------------- 379/56» 57» 53» 93=
`379/97' 98’ 993 340/82544! 311-1’ 32107’
`825.15, 825.17; 370/94.1; 358/437, 439, 441
`References cited
`
`[63]
`
`[55]
`
`and apparatus for reliably deliyering -Ines-
`A
`from 8 central
`ta 3 communi-
`sages
`cation receiver (130) in a communication system (100),
`such as an electronic mail system. The central terminal
`(102) transmits messages (1300) to the communication
`receiver (130) and the communication receiver (130)
`receives transmitted messages (1300) over a first com-
`munication medium (l22). The communication receiver
`(130) reconciles messages that it failed to receive over
`the first communication medium (122) with the central
`terminal (102) over a second communication medium
`(152). The reconciliation process between the commu-
`nication receiver (130) and the central terminal (102)
`utilizes cyclic redundancy codes (CRCS) transmitted
`with the messages (1300) to identify the messages (1300)
`bang 1”°°°n°11ed-
`
`12 Claims, 11 Drawing Sheets
`
`us‘ PATENT DOCUMENTS
`4,644,351 2/ 198? Zabarsky et al. ................. 379/5'! X
`4,803,437 2/ 1989
`er al.
`.
`4:3-"5~033 10/1939 5'W131‘ 9‘ 31-
`-
`4,882,5';'9 ll/1989 Siwiak .
`4,914,649 4/1990 Schwendeman etai..
`4,918,431? 4/1990 Jusinskj era].
`.
`4,952,929
`3/1990 Danica et a1_ _
`4,991,197 2/1991 Morris ................................. .. 379/53
`5,043,721 8/1991 May .
`5,051,992 9/1991 DeLuca et al.
`
`.
`
`114
`102
`
`
`124
`
`
`
`SECTIONS
`
`
`
`NON-
`
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`PSTN
`INPUTS
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`136
`
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`140
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`
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`U.S. Patent
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`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 2 of 11
`
`5,396,537
`
`
`
`
`
`MESSAGE
`DATA
`
`MESSAGE
`SEQUENCE REPETITION
`NUMBER
`COUNT
`
`
`
`
`3
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 3 of 11
`
`5,396,537
`
`CENTRAL MEMORY
`
`REMOTE UNIT MEMORY
`
`RECONCILE TX MSGS AGAINST RX MSGS
`
`FIGC5
`
`4
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 4 of 11
`
`5,396,537
`
` Y
`
`PREVIOUS
`SG MISSING IN
`SEQUENCE?
`
`FLAG
`MISSING
`MSGS
`
`612
`
`5
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 5 of 11
`
`5,396,537
`
`
`REMOTE UNIT
`REACHABLE VIA PATH
`
`YES
`IS MODE
`2 WAY PATH (E1;
`
`
`CONNECTED AND OPERATING
`
`
`OR UNIT
`
`ACKTNG?
`INCREMENT MESSAGE
`COUNTER FOR THIS
`
`UNTPS ADDRESS
`
`
`ON PATH A
`
`
`INCREMENT MESSAGE
`COUNTER ON
`
`APPROPRIATE ADDRESS
`FOR PATH B
`
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`
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`
`SEND MESSAGE (INCLUDING ID
`AND CRC) VIA APROPRIATE PATH
`
`£36
`
`Q4
`
`
`
`DISCARD
`MESSAGE
`_“lE¥:"*YES
`
`OR PUT IN
`
`
`HISTORY
`FILE
`
` SAVE MESSAGE IN
`
`RETRANSMISSION MEMORY
`FOR THIS ADDRESS
`
`6
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 6 of 11
`
`5,396,537
`
`N0
`
`
`IS
`A REMOTE
`UNIT CONNECTED TO PATH
`A REQUESTING
`UPDATES?
`
`
`
`
`YES
`
`1004
`
`FOR IT'S ADDRESSES, CHECK FOR
`ENTRIES IN RETRANSMISSION MEMORY FILE
`
`
`OOEP
`55”“ "END
`CREgEED
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`”S?§E8“E°
`°'i»a‘é‘%?«’<‘s’5"
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`VIA PATH A
`ID
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`
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`
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`
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`
`
`
`
`
`
` DELETE FROM
`RETRANSMISSION
`MEMORY FILE
`
`
`REMOTE UNIT HAVE
`
`THIS ID/CRC IN IT'S ID/CRC
`
`FILE AND MARKED
`
` 1012
`NO (ACK'D AS "BAD")
`
`SEND MESSAGE
`TO REMOTE UNIT K33
`VIA PATH A
`
`N0
`1022
`3RD
`
`
`YES
`NO ACK
`
`FOR THIS MESSAGE,
`
`
`THIS CYCLE?
`
`1020
`
`N0
`
`ACK
`Rgcglvgo?
`
`
`
`YES
`
`.Z5§ZZ3E.ZZ7
`
`7
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 7 of 11
`
`5,396,537
`
`T 1102
`
`WAIT FOR
`MESSAGE
`
`'
`
`H30 ME$§?sEM
`UPDATE
`‘ROUTINE
`
`
`IS
`IT NEW?
`
`(NO COPY MARKED
`"GO0D"
`IN ID/
`CRO FILE)
`
`
`YES
`
`“08
`DISCARD AND
`MARK OLD
`MESSAGE A3
`DUPLICATE
`RECEIVE
`
`
`
`
`
`
`
`
`
`nos
`
`PUT MESSAGE
`IN MEMORY
`
`1110 1112
`
`
` PUT ID/CRC IN YES
`
`RECEIVED
`ID/CRC MEMORY
`ON PATH
`AND MARK “GOOD”
`
`A?
`
`
`
`1118
`
`
`
`
`PUT ID/CRC IN
`SEND
`ID/CRC MEMORY AND
`MESSAGE
`DON"T MARK "GOOD
`BACK
`
`
`
` SEND
`RECEIVED
`MESSAGE
`on PATH
`ACK
`
`
`"0
`
`
`
`
`
`WAS
`MESSAGE
`FROM UPDATE
`
`ROUTINE?
`
`
`YES
`RETURN TO
`UPDATE ROUTINE
`
`JF§?Z33.Z]?
`
`IE5
`
`8
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 8 of 11
`
`5,396,537
`
`1201
`
`CONNECT PATH A AND
`LOG IN BY ADDREss(Es)
`
`
`
`1202
`
`REQUEST UPDATE
`(3t$T‘i«'i?aBIA‘iWY
`
`RECEIVE
`“END OF UPDATE’
`MESSAGE
`
`1204
`YES
`
`_fl28
`RETURN mow:
`REEEETGENI
`ROUTINE
`
`
`
`1295
`
`
`
`NOTIFY USER
`OF ERROR
`AND WAIT
`
`ROUTINES
`
` TO OTHER
`N0
`(A)
`1208
`RECEIVE
`ID/CRC?
`
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`
`s
`
`1
`
`214
`
`
`13
`ID/CRC IN
`MEMORY AND MARKED
`GOOD?
`
`
`
`
`
`
`1216
`fig§03§
`
`YES
`
`
`
`
`
`
`1222
`
`1130
`
`“NO” ACK
`
`
`No
`
`1218
`
`ACK As "BAD"
`
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`
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`MESSAGE
`
`DELETED FROM
`MESSAGE
`MEMORY
`
`N0
`
`
`
`
`
`MESSAGE WITHIN
`X SECONDS?
`
`
`YES
`
` Ygg 1220
`
`
`
`DELETE FROM
`ID/CRC
`MEMORY
`
`GO TO MESSAGE
`RECEPTION ROUTINE
`
`4Z;}?2:;{—2:£?
`
`9
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 9 of 11
`
`5,396,537
`
`1302
`
`49999 $0
`
`I3
`
`MESSAGE
`
`1402
`
`
`REMOTE UNIT
`CONNECTED TO PATH
`
`
`A REQUESTING
`
`UPDATE
`
`
`
`
`SEND
`NO "END UPDATE"
`
`
`
`UNCHECKED CRC IN
`MESSAGE
`
`VIA PATH A
`
`
`
`
`
`
`
`REMOTE
`DELETE FROM
`UNIT HAVE
`RETRANSMISSION
`THIS CRC MARKED
`MEMORY
`
`"GOOD"?
`
`
`10
`
`10
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 10 of 11
`
`5,396,537
`
`ENTER
`
`1502
`
`1504
`
`CONNECT PATH A.
`LOG IN BY ADDRESSES
`
`1506
`
`
`
`
`REQUEST UPDATE (AUTOMATICALLY
`OR MANUALLYL SET TIMER
`
`mo
`EXIT
`
`YES
`
`
`
` RECEIVE 1508
`
`
`"END UPDATE"
`
`MESSAGE?
`
`
`NO
`
`3RD
`
`UNSUCCESFUL
`TRY?
`
`1512
`
`"53 1516
`
`"0
`
`1513
`
`1520
`
`“O
`NOTIFY USER
`oR ERROR M
`
`AND WAIT
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` 1522
`
`
`F I3 CARc?E
`1524 YES
`
`MEMORY AND
`S§'g%03.9K
`MARKED
`
`"GOOD"?
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`1530
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`
`IN
`
`1526
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` WAS
`N0
`
`MESSAGE
`
`DELETED?
`
`
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`
`1528
`
`DELETE CRC
`FROM MEMORY
`
`SEND
`ACK "BAD"
`
`FYGJ5
`
`11
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 11 of 11
`
`5,396,537
`
`
`
` MESSAGE WITHIN
`
`SEND
`NACK
`
`X SECONDS?
`
`FYGJ6
`
`12
`
`12
`
`

`
`1
`
`5,396,537
`
`2
`nication receiver reconciles messages that it failed to
`receive, e.g., missed messages and erroneously received
`messages, over the first communication medium with
`the communication system over a second communica-
`tion medium. The reconciliation process between the
`communication receiver and the communication system
`utilizes message identifiers transmitted with the mes-
`sages to identify the messages being reconciled.
`
`RELIABLE MESSAGE DELIVERY srsraru
`
`This is a continuation-in-part of U.S. patent applica-
`tion Ser. No. 07/954,106, now U.S. Pat. No. 5,315,635,
`filed Sep. 30, 1992 by Kane et aI., entitled “Reliable
`Message Communication System”.
`
`5
`
`FIELD OF THE INVENTION
`
`This invention relates generally to message delivery
`systems, such as for electronic mail systems, and more
`specifically to a method and apparatus for reliably de-
`livering messages to one or more remote units from a
`central communication system utilizing a paging trans-
`mitter system.
`
`BACKGROUND OF THE INVENTION
`
`Communication systems, such as paging systems,
`typically communicate messages from an originating
`device to one or more destination devices. These mes-
`sages can include numeric and alphanumeric informa-
`tion for a user of the destination device. The destination
`device, e.g., a selective call receiver or pager, typically
`presents the information received to the user by display-
`ing the information on a display.
`Contemporary paging systems offer a limited mes-
`sage length for communicating information. For exam-
`ple, an alphanumeric message may be typically 80 1
`characters or less. These typical message lengths have
`provided reasonably reliable delivery Of messages to the
`users of the communication system.
`On the other hand, a distinct trend in the market is for
`customers desiring much longer messages, such as from
`ten to one hundred times longer messages or more.
`Transmission of these messages over a paging channel
`can encounter a number of obstacles to reliable delivery
`of the longer messages, such as different types of inter-
`ference, fading, noise, and other phenomena detracting
`from error-free and reliable communication of the mes-
`sages to the destination devices.
`This difficulty in reliable transmission of the longer
`messages is especially frustrating to customers that are
`used to communicating long messages over a more
`reliable communication medium, such as direct wire
`line or dial-up telephone communication. Tl:u's:is partic-
`ularly the case for electronic mail system users which
`typically desire to send relatively long messages with a
`high degree of certainty that the messages are received
`error free. Typically, an originating device, such as a
`personal computer or workstation, can send long mes-
`sages to one or more destination devices, such as other
`personal computers or workstations, over a direct wire
`line interface, or over a local area network (LAN), or
`over a dial-up telephone line connection using the pub-
`lic switched telephone network (PSTN).
`Therefore, a need exists to enhance the reliability of
`transmitting messages, including long messages, in com-
`munication systems that utilize paging systems for de-
`livering the messages.
`
`SUMMARY OF THE INVENTION
`
`According to an embodiment of the present inven-
`tion, there is provided a method and apparatus for reli-
`ably delivering messages to a communication receiver
`in a communication system. The communication system
`transmits messages to the communication receiver and
`the communication receiver receives transmitted mes-
`sages over a first communication medium. The commu-
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a communication system
`in accordance with the preferred embodiment of the
`present invention.
`FIG. 2 is a message block diagram illustrating a trans-
`mitted inessage according to the preferred embodiment
`of the present invention.
`FIG. 3 is a message sequence diagram illustrating a
`first example of received messages being stored in the
`memory of a remote unit of the communication system
`according to the preferred embodiment of the present
`invention.
`
`FIG. 4 is a message sequence diagram illustrating a
`second example of received messages being stored in
`the memory of a remote unit of the communication
`system according to the preferred embodiment of the
`present invention.
`FIG. 5 is a block diagram illustrating messages stored
`in the memory of a central terminal of the communica-
`tion system and messages stored in the memory of a
`remote unit before a reconciliation of messages between
`the central terminal and the remote unit, in accordance
`with the preferred embodiment of the present inven-
`tion.
`
`FIG. 6 is a flow diagram illustrating an operational
`sequence for a remote unit, according to the preferred
`embodiment of the present invention.
`FIGS. 7 and 8 are message sequence diagrams illus-
`trating a timing aspect of the second example of FIG. 4»,
`in accordance with the preferred embodiment of the
`present invention.
`FIGS. 9 and 10 are flow diagrams illustrating opera-
`tional sequences for the central terminal of FIG. 1,
`according to the preferred embodiment of the present
`invention.
`
`FIGS. 11 and 12 are flow diagrams illustrating opera-
`tional sequences for the remote unit of FIG. 1, accord-
`ing to the preferred embodiment of the present inven-
`tion.
`
`FIG. 13 is a message block diagram illustrating a
`transmitted message according to an alternative em-
`bodiment 15 of the present invention.
`FIG. 14 is a flow diagram illustrating an operational
`sequence for the central terminal of FIG. 1, according
`to the alternative embodiment of the present invention.
`FIGS. 15 and 16 are flow diagrams illustrating an
`operational sequence for the remote unit of FIG. 1,
`according to the alternative embodiment of the present
`invention.
`
`DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`FIG. 1 shows a communication system 100 utilizing a
`paging transmitter system 120, I22, 124, 126, for deliv-
`ering messages to at least one portable remote unit, e.g.,
`a portable selective call receiver 130, in accordance
`with the preferred embodiment of the present inven-
`tion. A central terminal 102 comprises input sections
`110, 112 for receiving inputs from a number of different
`
`I5
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`13
`
`13
`
`

`
`3
`devices 104, 106, 103, including receiving page requests
`for initiating pages that are transmitted by the paging
`transmitter system 120, 122, 124, 126, to the at least one
`portable remote unit 130. The central terminal 102 has
`input sections 110 that interface with the telephone
`company equipment, such as the public switched tele-
`phone network (PSTN) 107. Personal computers or
`other computing devices 104 can access the input sec-
`tions 110 through the PSTN using a dial-up telephone
`line and modern communication. Other calling devices,
`such as telephone input devices 106 can access the input
`sections 110 of the central terminal 102 through the
`PSTN 107. Typically, these input devices 104, 106, can
`remotely initiate page requests through the central ter-
`minal 102 by calling up the input sections 110 of the
`central terminal 102 over dial-up telephone lines of the
`PSTN 10?.
`Alternatively, other input sections 112 of the central
`terminal 102 can receive inputs, such as page requests,
`from local computing devices 198, such as a local per-
`sonal computer or console or other terminal device.
`Typically, the one or more local input devices 108 inter-
`face with the input sections 112 of the central terminal
`102 via direct wire line connections using standard
`RS-232 or RS-422 interface.
`The input sections 110, 112, communicate page re-
`quests to a controller 114 through a communication bus
`116. The controller 114 may comprise controller cir-
`cuitry and associated memory such that an incoming
`page request may be accepted and stored into available
`memory for subsequent transmission to one or more
`selective call receivers 130. Additionally, a non-volatile
`memory device 118, such as battery backed up RAM,
`one or more disc drive units, or other non-volatile stor-
`age medium, is utilized by the controller 114 for longer
`term storage of messages destined for the one or more
`selective call receivers 103. The controller 114 typically
`couples the message information and other associated
`information to the memory device 118 via the bus 116.
`The message information, which can include numeric,
`alphanumeric, or binary information, and other associ-
`ated infonnation stored in the memory 118 can be used
`by the controller 114 for reliable delivery of the mes-
`sage to the destination or remote unit 130, as will be
`more fully discussed below.
`The controller 114 oouples messages to the paging
`encoder 120 over the bus 116 for encoding the messages
`for transmission over a paging channel. The paging
`encoder 120 then couples the encoded messages over a
`communication path 122' to one or more paging trans-
`mitter systems 124, 126, for transmission over a paging
`communication channel. The communication path 122,
`in this example. will be labeled path B which routes the
`messages from the central
`terminal 102 to a paging
`transmitter system 124, for transmission and over a
`paging communication channel for reception by the one
`or more selective call receivers 130. The general opera-
`tion of a communication system including a paging
`system of the type shown in FIG. I is more fully de-
`scribed in U.S. Pat. No. 5,138,311, issued Aug. 11, 1992,
`entitled, “Communication System Having adaptable
`Message Information Formats”, which is assigned to
`the same assignee as the present invention and is incor-
`porated herein by reference.
`The selective call receiver 130 preferably incorpo-
`rates a paging receiver 134 that operates to receive
`messages transmitted over the paging communication
`channel through the antenna 132. The operation of a
`
`5
`
`10
`
`IS
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`S0
`
`55
`
`65
`
`14
`
`5,396,537
`
`4
`paging receiver 134 of the general type shown in FIG.
`1 is well known and is more fully described in U.S. Pat.
`No. 4,513,961 issued May 21, 1985, entitled, “Universal
`Paging Device With Power Conservation", which is
`assigned to the same assignee as the present invention
`and is incorporated herein by reference.
`The paging receiver 134 couples a received message
`to the controller 136 through the bus 138. The control-
`ler 136 address information in the received message and
`then match predetermined address in the selective call
`receiver 130. In this way, the controller 136 can deter-
`mine whether the received message is intended for the
`particular selective call receiver 130. Further, a mem-
`ory 140 is coupled to the paging receiver 134 and the
`controller 136 through the bus 138 for storing the re-
`ceived message in the memory 140. A user can access
`user input means 141, such as buttons or switches, at the
`remote unit 130 to cause the message data of a received
`message to be displayed on a display, e.g., a liquid crys-
`tal display (not shown). The user can then read the
`message that is visible on the display. User input at the
`remote unit 130 can also cause the remote unit 130 to
`perform other functions that are well known to users of
`selective call recvers and portable personal comput-
`ing devices.
`A real time clock 142 is also coupled through the bus
`138 to the controller 136 for providing time information
`thereto. The remote unit 130 is then capable providing
`time information to the user by displaying the time
`information on the display (not shown). Additionally,
`the controller 136 can utilize the, time information pro-
`vided by the real time clock 142 to keep track of the
`time when messages were received at the remote unit
`130 and to perform and other useful operations that will
`be more fully discussed below.
`Furthermore, the selective call receiver 130 includes
`a modem transmitting unit and a modern receiving unit
`144 and the associated telephone interfacing circuitry or
`other suitable communications apparatus (e.g., packet
`radio modem) which allows the user of the selective call
`receiver 130 to connect the selective call receiver to a
`telephone interface 150, such as may be provided by an
`M11 plug 148 and associated wiring 146 at the selective
`call receiver 130 and the complimentary wall jack 150
`and associated wiring 152 thereof. This telephone inter-
`face 144, 146, 148, 150, 152, allows the controller 136 of
`the selective call receiver 130 to remotely access the
`central terminal 102 through a dial-up telephone line
`and the PSTN 107. At the central
`terminal 102, a
`modem transmitting unit and a modem receiving unit
`111 is capable of communicating with the modem 144 at
`the selective call receiver 130. In this way, the selective
`call receiver 130 can communicate with the central
`terminal 102 and receive message information there-
`from through a separate communication path which, in
`this example, is labeled path A 152. Therefore, the selec-
`tive call receiver 130 cab receive message information
`from the central terminal 102 via path A 152 and via
`path B 122. The path A 152 communication medium
`and the path B 122 communication medium can com-
`prise any communication paths, such as direct wired
`line path, telephone line path, or wireless communica-
`tion path including at least one radio communication
`channel preferably path A 152 is different than path B
`122.
`
`In the preferred embodiment, path A 152 is a dial-up
`telephone line using modem communication between
`the central terminal 102 and the remote unit 130. Also,
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`preferably path B includes a paging communication
`channel for transmitting messages to the selective call
`receiver 130. Alternatively, path A may be a one-way
`or two-way radio frequency communication channel
`between the remote unit 130 and the central terminal
`102, and path B can be a paging communication chan-
`nel. Additionally, in another alternative, path A and
`path B can be one-way or two-way radio frequency
`communication channels. An advantage of delivering
`messages to the remote unit 130 through the paging
`communication channel Over the two-way radio fre-
`quency communication channel is that typically more
`messages can be delivered through the medium in the
`paging communication channel. This in turn enhances
`the commercial viability of the communication system.
`However, using two-way radio frequency communica-
`tion channels for both path A and path B may be per-
`fectly acceptable in some systems.
`By using a dial up telephone line interface for path A
`152, and utilizing modem communication between the
`remote unit 130 and the central terminal 102 in the
`preferred embodiment,
`the reliability of transferring
`messages between the central terminal 102 and the re-
`mote unit 130 is relatively high and approaches the
`reliability that users of conventional computing systems
`have previously experienced. Hence, it is advantageous
`to transfer messages over the dial-up telephone line
`interface 152 because it is a more reliable communica-
`tion medium than transmission over the paging commu-
`nication channel 122, e.g., over a radio paging channel.
`On the other hand, the dial-up telephone line interface
`152 has several draw backs. First, dial-up telephone line
`interfacing typically interfaces between one originating
`and one receiving device which significantly reduces
`the number of remote units that can subscribe to any
`type of communication system. Second, the telephone
`line interface 152 normally requires that the remote unit
`130 connect to a telephone line interface which may not
`always be available. Third, the remote unit is not as
`portable due to the requirement that it be intercon-
`nected with the telephone interface. In the case of a
`paging communication channel
`transmission,
`the re-
`mote unit 130 is portable and can receive messages
`transmitted over the paging communication channel
`while the remote unit 130 is being carried by a user.
`Hence, although the telephone line interface communi-
`cation tends to be more reliable than the paging channel
`communication, it can significantly limit the number of
`subscribing remote units 130 in the communication
`system, and it tends to inconvenience users by requiring
`them to connect their remote units 130 to a telephone
`line interface I52 for communication with the central
`terminal 102. Therefore, the preferred embodiment of
`the present invention utilizes both path A and path B
`communication of messages in a manner that signifi-
`cantly increases the reliability of transmission of mes-
`sages between the central terminal 102 and the remote
`units 130 while allowing large numbers of portable
`remote units 130 to be serviced in the communication
`system, as will be more fully discussed below.
`The communication system 100 of the preferred em-
`bodiment of the present invention allows high through-
`put of messages between the central terminal 102 and
`the portable remote units 130 by transmitting messages
`over the path B 122, e.g., a radio frequency paging
`channel, for normal communication of new messages
`between the central terminal 102 and the remote units
`130. Additionally, for a higher grade of service, the
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`terminal 102 can transmit messages multiple-
`central
`tinges over path B 122 to better guarantee that the re-
`mote unit 130 will receive at least one of the transmis-
`sions of the same message. For example, the central
`terminal 102 can transmit a message three separate times
`over the paging channel 122 where each subsequent
`transmission of the same message is delayed by a prede-
`termined time interval from the previous transmission,
`e.g., three minutes. In this way, the remote unit 130 has
`a higher probability of receiving the message transmit-
`ted over the paging channel 122.
`Nonetheless, there may be times when the message is
`not received by the remote unit 130. In such event the
`communication system 100 provides a means at
`the
`remote unit 130 for determining that a message was
`missed and further for reconciling with the central ter-
`minal 102 to receive at least the message information of
`a missed message over a more reliable communication
`medium, such as provided through path A 152. How-
`ever, the required throughput of path A 152 can be
`much lower than the throughput of messages through
`path B 122 because the number of missed messages will
`be much lower than the number of new transmitted
`messages for the communication system 100. Hence, the
`bulk of communication transmission including the trans-
`mission of new messages can be handled through path B
`122, e.g., the radio frequency paging channel. The rec-
`onciliation of missed messages between the remote units
`130 and the central terminal 102 can be handled over
`the more reliable communication medium provided
`through path A 152. Further the portable remote units
`130 can be carried by a user while receiving new mes-
`sage transmissions over the paging channel 122. The
`users of the remote units 130 will be minimally inconve-
`nienced by requiring that the remote unit 130 be con-
`nected with the telephone line interface 152 to perform
`reconciliation of missed messages because messages
`typically will be missed relatively infrequently. Option-
`ally, as mentioned earlier, path A 152 can be configured
`as a one-way or two-way radio frequency communica-
`tion channel between the central terminal 102 and the
`remote units 130. In this case. the message reconcili-
`ation can be performed while the users carry the remote
`selective call receivers 130 such that. Hence, the users
`are minimally inconvenienced.
`PIG. 2 is a message block diagram illustrating a trans-
`mitted rnessage according to the preferred embodiment
`of the present invention. The transmitted message 200
`typically includes identification and control information
`202, as well as message data information 204. The mes-
`sage data 204 normally is the information that is com-
`municated between an originating party and the destina-
`tion remote unit 130. That is, the message data 204 is the
`message information communicated to the user of the
`selective call receiver 130. The message data 204- can
`include numeric information, alphanumeric informa-
`tion, and binary data. The identification and control
`information 202 included with the message 200 nor-
`mally is required for delivering the message in the com-
`munication system 100. Such information 202 includes
`address information 206 which identifies one or more
`remote units 130 as the destination of that message data
`204. Hence, when a remote unit 130 receives a message
`200 that was transmitted from the central terminal 102,
`the remote unit 130 can determine whether that particu-
`lar message 200 was intended for reception by the par-
`ticular remote unit 138. Normally, the address informa-
`tion 206 included with the message 200 is decoded by
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`the remote unit 130 and compared to a predetermined
`address in the remote unit 130. If the address informa-
`
`tion 206 in the message 200 matches the predetermined
`address in the remote unit 130 then the message 200 was
`intended for that particular remote unit 130. The remote
`unit 130 can then store the received message data 204 in
`a memory 140 in the remote unit 130, or optionally in a
`computer memory of a computing device associated
`with the remote unit 130 for later processing. A user of
`the remote unit 130 can subsequently review the mes-
`sage data 204 to communicate the message to the user.
`Typicaily, the user reviews the message on a display on
`the remote unit 130. That is, for example, the user can
`read the message on a display screen such as commonly
`available on portable personal computers and portable
`selective call display receivers.
`Additionally,
`in the preferred embodiment of the
`present invention, the message 200 includes other iden-
`tification information fox enhancing the reliability of
`delivering the message from the central terminal 102 to
`the portable seiective call receiver 130. For example,
`each message 200 can include a message sequence num-
`ber 208 which identifies the relative sequence of the
`message 200 in a transmission sequence for messages
`transmitted from the central terminal 102 to the remote
`unit 130 for a particular address information 206. That
`is, each message that includes the same address informa-
`tion 206, i.e., that is destined for reception by the same
`one or more remote units 130, can be tagged with a
`message sequence number 208 that identifies to the one
`or more remote units 130 when a transmitted message
`200 is received out of’ sequence or when a transmitted
`message was not received by the remote unit 130.
`When a transmitted message 200 is received by the
`remote unit 130 and the address information 206 in the
`message 200 matches a predetermined address for the
`remote unit 130, then, if the message sequence number
`208 identifies the message 200 as being out of sequence
`with a transmission sequence established by previously
`received messages, the remote unit 130 may determine
`that one or more messages were transmitted by the
`central terminal 102 and not received by the remote unit
`130. Those transmitted messages that intervened be-
`tween the last received message in the transmission
`sequence and the received message being out of se-
`quence may have been missed by the remote unit 130.
`However,
`the intervening messages may not always
`have been missed.
`For example, the communication system 100, as dis-
`cussed earlier, can transmit messages multiple times
`over the paging communication channel 122 to provide
`a higher grade of service for the destination remote
`units 130. In this case a message 200 can be received by
`the remote unit 130 and the message sequence number
`208 may indicate that the received message 200 is out of
`sequence with a transmission sequence established by
`previously received messages at the remote unit 130.
`However, this may only indicate that one transmission
`of a message was missed by the remote unit 130 and that
`subsequent re-transmissions of that message may be
`received by the remote unit 130, thereby reestablishing
`the transmission sequence of received messages at the
`remote unit 130.
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`Preferably, a message repetition count 210 is included
`with each transmitted message 200 to identify to a re-
`ceiving remote unit 130 the relative position of the
`received message 200 in a repetition sequence. For ex-
`ample if under a grade of service, messages are repeat-
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`edly transmitted three times for delivery to a receiving
`remote unit 130, where the repeatedly transmitted mes-
`sages have the same destination address 206, a received
`message 200 including a message repetition count 210 of
`two may identify to the receiving remote unit 130 that
`the received message 200 was the second transmission
`of that message from the central terminal 102.
`Other information can be transmitted with a transmit-
`ted message 200, such as error detecting and/or correct-
`ing code. For example, a cyclic redundancy code
`(CRC) 212 can be included with each transmitted mes-
`sage 200 to help identify at the receiving remote unit
`130 when received message data 204 has been errone-
`ousiy received, e.g., when the message data 204- has
`been received with errors included therein. In this cage,
`although the message 200 has been received by the
`remote unit 130, the message data 204 may not ba com-
`pletely and correctly communicated to the user of the
`remote unit 130. Hence, the remote unit 130 has failed to
`receive the message 200 accurately enough to commu-
`nicate the message information to the user of the remote
`unit 130. Hence, two possible conditions can identify
`when the remote unit 130 has failed to receive a trans-
`mitted message. The first is when the remote unit re-
`ceives a transmitted message