`
`USOU?3?2826B2
`
`(12; United States Patent
`Dahod et a].
`
`[IO] Patent No.:
`
`(45} Date of Patent:
`
`US 7,372,826 32
`May 13, 2008
`
`(54) PROVmING ADVANCED
`COMMUNICATIONS FEATURES
`
`(75)
`
`Inventors: Ashraf M. Dahud. Andover, MA (US);
`Michael Silva. East Sandwich. MA
`(US); Peter Higgins. Sandwich. MA
`(US); Rajat Gltai. West Yarmouth. MA
`(US); John Die-Pietro, Brewster, MA
`(US): Nick Lopez. Sleepy Hollow. IL
`(US); Paul Shieh. Westborough. MA
`(US)
`
`(73) Assignee: Starent Networks. Corp.. Tewksbury.
`MA (US)
`
`( ’3 ) Notice:
`
`Subject to any disclaimer. the term of this
`patent is extended or adjusted under 35
`use. 154(k)) by 0 days.
`
`(21) Appl. No.: 103210.897
`
`(22)
`
`Filed:
`
`Aug. 1.. 2002
`
`(65)
`
`Prior Publication Data
`US 2004t'0022208 Al
`Feb. 5. 2004
`
`(51}
`
`Int. Cl.
`(2006.01)
`HO4Q 7/00
`(52) U.S.CI.
`...................... 370I328;370t349;370t356:
`370889: 370t401: 455517
`(58) Field of Classification Search
`370t312.
`3702328, 335. 342. 352 353. 355. 356. 432.
`370t441. 466. 349. 390. 40]. 338. 389: 455t524.
`455542. 560. 404.1. 412.]. 412.2. 414.1.
`455517. 520: T05t’26. 27: 379t88.01. 88.03.
`379t88.04. 88.16. 265.01. 265.02; T09t’207.
`709t23l. 238
`See application file for complete search history.
`
`(56)
`
`References Cited
`U .S. PAT liN’l‘ IJOCUMIEiN'lS
`
`4.677.656 A ’l‘
`5.513.181 A *
`
`6:198? Burke et al.
`4-4996 Bresalier et' al.
`
`455-403
`37llt465
`
`5.634.|96 A "‘
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`5.838.748 A *
`
`55199? Alford
`2-"'19‘)8 Sigler el al.
`1151998 Nguyen
`
`455th
`.. 45534261
`
`3756?“
`
`(Continued)
`FOREIGN RATENT DOCUMENTS
`
`El’
`
`0 650 284
`
`4-1995
`
`[Continued]
`0T] HER PUBLICATIONS
`
`Schulzrinne. ii. ”The Session initiation Protocol." http:-'-'www.cs.
`coltunbisedn-‘ncomsfil8].-'s|icles-"l1.-’sip__longt'.pdf. May 2001.
`
`[Continued]
`
`Primary [:‘xcnitiner-
`Assistant Eromitter
`
`
`Joseph I’eild
`Inder Pal Mehm
`
`(74) Attorney. Agent. or Finn—Wilmer Cutler Pickering
`Hale and Dorr LLP
`
`(57}
`
`ABSTRACT
`
`Advanced communications features are provided in a mobile
`conununications network having at least one mobile switch—
`ing center and at least one mobile station subsystem. The
`mobile switching center and mobile station subsystem each
`communicate signaling mesmges according to a mobile
`signaling protocol. An indication is received that a half-
`duplex mobile communications session is to be initialed
`between a first mobile station subsystem and a second
`mobile station subsystem. The first and second mobile
`station subsystems include full—duplex communications
`apparatus for use in Tull-duplex mobile communications
`sessions. The half-duplex mobile communications session
`relies on the first and second mobile station subsystems. and
`all of tile reliance is onlyr on the lull-duplex communications
`apparatus. Mobile conuttunications telephone calls are
`established with the first mobile station subsystem and the
`second mobile station subsystem. One of the first and second
`[nubile station subsystems is selected as a voice signal
`source in the half-duplex communications session.
`
`27 Claims. 13 Drawing Sheets
`
`{4410
`
`
`
`GOOGLE 1017
`
`GOOGLE 1017
`
`1
`
`
`
`US 7,372,826 BZ
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`6. 1 12.0 83
`6.128.509
`6, 131 .121
`6.2 98.0 58
`6.3 66.7 82
`6.4 00.967
`6.449.496
`6.477.150
`6.570.871
`6.606.305
`5.754.180
`7.05 8.036
`200 1700462 34
`200 27007 5805
`200270075814
`200 27007 58 75
`200270077136
`200270078464
`200270085552
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`2003700 I 78 36
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`Sweet 31 a].
`Voijola et al.
`Maitaway et a1.
`Maker et a].
`Fumarolo ct al.
`Nilsson
`Beith et a1.
`Maggenti et al.
`Schneider
`Boyle el al.
`Christie
`Yu el al.
`Agrawal Ct at]
`Gupta ct 3].
`Based et al.
`Dravida et a1.
`Maggenli et al.
`Dravida el al.
`Tandon
`Dravirla e1 31.
`Maggenti et al.
`Vishwanathan or .11.
`Mohan et a1.
`Maes et al.
`Wengrovitz et al.
`
`45574261
`45575561
`7097227
`3707390
`4557457
`4557563
`4557563
`3707312
`3707356
`3707260
`3707236
`3707335
`
`200370156688 Al "‘
`200370185202 Al *
`200570286689 Al *
`200670002358 Al
`200670140151 Al ’1‘
`
`872003
`1072 003
`1272005
`172 006
`672 006
`
`McCarty et a1.
`Maenpaa
`Vuori
`Ray et :11.
`Damn eta].
`
`3797671
`...... 3707352
`379788.22
`
`
`
`370.7331
`
`FOREIGN PA'I‘IENT DOCUMENFS
`
`131’
`WO
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`W0
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`WO 01756236
`W0-Ul.-"76276 A2
`W0 02730010
`W0-02745440 Al
`W0~027054707 A2
`
`671998
`1071998
`472000
`672000
`872000
`972000
`1272000
`572001
`872001
`1072001
`472002
`672002
`772002
`
`OTHER PUBLICATIONS
`
`4557517
`3707338
`
`l-Iandlcy. M. et al.. “SIP Session
`letfiorg-"htmi-“rfc2543. Mar. 1999.
`
`Initiation Protocol.“ http:7.-"7tools.
`
`3707352
`
`“' cited by examiner
`
`2
`
`
`
`US. Patent
`
`May 13
`
`3
`
`2008
`
`Sheet 1 of 13
`
`US 7,372,826 B2
`
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`
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`
`
`
`
`
`US. Patent
`
`May 13,2003
`
`Sheet 2 of 13
`
`US 7,372,826 32
`
`
`
`FIG. 2
`PRIOR ART
`
`4
`
`4
`
`
`
`US. Patent
`
`May 13, 2008
`
`Sheet 3 of 13
`
`US 7,372,826 B2
`
`
`
`IO._._>>w._.n_Om
`
`(m.OE
`
`5
`
`
`
`US. Patent
`
`h4ayl3
`
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`
`Sheet4 of13
`
`US 7,372,826 B2
`
`New
`
`CD
`[-
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`
`
`
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`
`6
`
`
`
`US. Patent
`
`May 13,2008
`
`Sheet 5 of 13
`
`US 7,372,826 32
`
`USER
`
`USER
`
`530
`
`525
`
`m a
`
`PTI'
`
`DIRECTORY
`
`FIG.4
`
`517
`
`515
`
`7
`
`
`
`US. Patent
`
`May 13,2008
`
`Sheet 6 of 13
`
`US 7,372,826 32
`
`INDICATE THATA PTT SESSION SHOULD COMMENCE
`
`2010
`
`ESTABLISH VOICE CONNECTION TO INITIATOR MS
`AND INTENDED RECIPIENT MS
`
`REFER TO PTT DIRECTORY
`
`2020
`
`2015
`
`DEFAULT TO LISTEN MODE
`
`SWITCH TO TALK MODE ON SIGNAL
`
`
`
`
`
`
`
`
`
`
`
`
`
`2030
`
`
`
`
`
`CAUSE VOICE SIGNAL FROM MS TO BE
`TRANSMITTED TO ANOTHER MS
`
`2035
`
`IGNORE OTHER VOICE SIGNALS
`
`
`
`
`
`
`
`
`2040
`
`2045
`
`
`
`SIGNAL REVERSION TO LISTEN MODE
`
`HALT TRANSMISSION OF VOICE SIGNAL
`
`
`
`INDICATE THAT PTT SESSION SHOULD TERMINATE
`
`2055
`
`CLOSE VOICE CONNECTIONS
`
`2060
`
`FIG. 5
`
`8
`
`8
`
`
`
`US. Patent
`
`May 13, 2008
`
`Sheet 7 of 13
`
`US 7,372,826 B2
`
`
`
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`
`02.092
`
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`
`9
`
`
`
`
`
`US. Patent
`
`May 13,2008
`
`Sheet 8 of 13
`
`US 7,372,826 B2
`
`SIGNAL START OF RECORDING VOICE MESSAGE
`
`
`
`
`
`DETECT SIGNAL
`
`
`
`3020
`
`
`
`ESTABLISH VOICE CALL TO USER'S MS
`
`
`
`
`
`RECORD VOICE MESSAGE
`
`
`
`3040
`
`
`
`DERIVE INSTANT TEXT MESSAGE FROM VOICE
`
`MESSAGE
`
`
`
`
`
`
`
`CAUSE INSTANT TEXT MESSAGE TO BE DELIVERED
`
`TO ANOTHER IMG
`
`
`
`EXTRACT RECORDING FROM INSTANT TEXT MESSAGE
`
`
`
`
`
`3010
`
`
`
`3030
`
`
`
`3050
`
`
`
`
`
`3060
`
`3070
`
`PLAY BACK RECORDING
`
`3030
`
`FIG. 7
`
`10
`
`10
`
`
`
`US. Patent
`
`May 13,2008
`
`Sheet 9 of 13
`
`US 7,372,826 32
`
`SUBSCRIBER
`
`THE SUBSCRIBER DIALS '1-800-888—VIM1'
`
`IMG
`(ST—16)
`
`”ENTER I TO CREATEA NEW GROUP, ENTER 2 TO RECORD A MESSAGE OR 3 ACCESSING
`TO OBTAIN STATUS FROMA PREVIOUS VIM SESSION"
`SYSTEM
`
`H
`
`SUBSRIBER ENTERS 1
`
`—> - — -
`
`DEFINING
`A NEW
`VG
`
`RECORD
`AND PLAY
`OUT A
`MESSAGE
`
`— -
`
`OPTIONAL
`REIRIEII/il.
`
`"PLEASE ENTER EACH NUMBER FOLLOWED BY THEII KEY, WHEN
`FINISHED PLEASE PRESS THE STAR KEY'
`
`THE SUBSCRIBER ENTERS EACH NUMBER AND ENDS WITH THE STAR KEY
`
`THE SYSTEM WOULD THEN PLAY BACK THE NUMBERS FOLLOWED BY...
`"TO ACCEPT PRESS I, TO CHANGE PRESS 2"
`
`SUBSCRIBER ENTERS 1
`
`
`
`"IF YOU WISH TO RECORDA MESSA CE, START RECORDING AT THE TONE
`OTHERWISE STAY ON THE LINE FOR MORE OPTIONS. ONCE YOU'VE COMPLETED
`RECORDING, YOU MAY HANG UP TO SEND YOUR MESSAGE. '
`
`“PLEASE ENTER THE VIM GROUP ID TO RECORD A MESSAGE FOR."
`
`SUBSCRIBER ENTERS THE VIM GROUD ID
`
`”AT THE TONE START RECORDING YOUR MESSAGE. HANG-UP WHEN FINISHED"
`
`THE SUBSCRIBER RECORDS THE MESSAGE AND HANGS-UP
`
`THE SYSTEM STARTS PLACING OUT-BOUND CALLS TO
`THE MEMBERS OF THE VG.
`
`- 4-
`
`THE SUBSCRIBER DIALS ‘1-800—888-VIM1'
`"ENTER I TO CREATEA NEW GROUP, ENTER 2 TO RECORD A MESSAGE,
`
`OR 3 TO OBTAIN STA TUS FROM A PREVIOUS YIN SESSION”
`
`SUBSCRIBER ENTERS 3
`
`THE SYSTEM PLAYS OUT THE RECEIVE STATUS
`FIR} an H: :3 I
`
`FIG. 8
`
`11
`
`11
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`US 7,372,826 B2
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`US ?,372,826 B2
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`2
`
`1
`PROVIDING ADVANCED
`COMMUNICATIONS FEATURES
`
`BACKGROUND
`
`This invention relates to providing advanced communi-
`cations features.
`
`Wireless telecommunication systems are able to provide
`wireless versions of information services traditionally pro-
`vided by land-line or copper wire systems. Examples of
`wireless communications applications include Advanced
`Mobile Phone Service (AMPS) analog cellular service and
`Code Division Multiple Access (CDMA) and Advanced
`Mobile Phone Service (AMPS—D) digital cellular service in
`North America. and Group Speciale Mobile (GSM) cellular
`service in Europe.
`Although the particular application may vary. the com-
`ponents of a wireless communication system are generally
`similar. as described in more detail below. For example. a
`wireless communication system usually includes a radio
`terminal or mobile station. a radio base station, a switch or
`network control device. often referred to as a mobile tele-
`phone switching office (MTSO). and a network to which the
`wireless communications system provides access. such as
`the Public Switched Telephone Network (PSTN).
`The various wireless communication applications use any
`of multiple modulation techniques for transmitting in forum-
`tion to efliciently utilize the available frequency spectrum.
`For example. frequency division multiple access (FDMA),
`time division multiple access (TDMA). and code division
`multiple access modulation techniques are used to build
`high-capacity multiple access systems. Teleconmiunication
`systems designed to communicate with many mobile sta-
`tions occupying a common radio spectrum are referred to as
`multiple access systems.
`For example. in an FDMA analog cellular system, such as
`an AMPS analog cellular radio system. the available he
`quency spectrtun is divided into a large number of radio
`channels. e.g.. pairs of transmit and receive carrier frequen-
`cies. each of which corresponds to a message transmission
`channel. The bandwidth of each transmit and receive fre-
`quency channel is narrowband. generally 2530 kHz. Thus.
`the FDMA system permits information to be transmitted in
`a bandwidth comparable to the bandwidth of the transmitted
`infonnation. such as a voice signal. The cellular service area
`in the FDMA system is generally divided into multiple cells.
`each cell having a set of frequency channels selected so as
`to help reduce co-channel interference between cells.
`Frequency division is often combined with time division
`so that transmission circuits are distinguished in both the
`frequency and time domain. e.g.. in a FDFTDMA system. In
`a digital
`l-‘IJFI‘DMA (commonly referred to as TDMA]
`cellular system. a narrowband frequency channel is refor-
`matted as a digital transmission path which is divided into a
`nutnber of time slots. The data signals from diilerent calls
`are interleaved into assigned time slots and sent out with a
`correspondingly higher bit rate. the time slot assigned to
`each mobile station being periodically repeated. Although
`the TDMA bandwidth may be somewhat larger than the
`FDMA bandwidth, a bandwidth of approximately 30 kHz is
`generally used for AMPS-D digital TDMA cellular systems.
`Another approach to cellular multiple access modulation
`is CDMA. CDMA is a spread spectrum technique for
`transmitting infomiation over a wireless communication
`system in which the bandwidth occupied by the transmitted
`signal is significantly greater than the bandwidth required by
`the baseband information signal (cg. the voice signal).
`
`10
`
`2E]
`
`3n
`
`4E]
`
`45
`
`50
`
`55
`
`60
`
`65
`
`16
`
`Thus, CDMA modulation spectrally spreads a narrowband
`information signal over a broad bandwidth by multiplex
`modulation. using a codeword to identify various signals
`sharing the same frequency channel. Recognition of the
`transmitted signal takes place by selecting the spectrally-
`coded signals using the appropriate codeword. in contrast to
`the narrowband channels of approximately 30 kHz used in
`FDMA and TDMA modulation techniques, a CDMA system
`generally employs a bandwidth of appmximately 1.25 MI-lz
`or greater.
`Typically. the mobile communication systems described
`above are arranged hierarchically such that a geographical
`“coverage area” is partitioned into a ntunber of smaller
`geographical areas called “cells." Referring to FIG.
`1_. each
`cell
`is preferably served by a Base Transceiver Station
`(“HTS") 1020. Several B'I‘S 1020-» are centrally adminis-
`tered via fixed links 104a-n by a Base Station Controller
`(“BBC") 106a. The BTSs and BSC are sometimes collec-
`tively referred to as the Base Station Subsystem (“BS") 107.
`Several BSCTs 1065-): may be centrally administered by a
`Mobile Switching Center (“MSC”) 110 via fixed links
`IOSa—n.
`MSC 118 acts as a local switching exchange {with addi-
`tional features to handle mobility management require-
`ments. discussed below) and communicates with the phone
`network {“PSTN") 120 through trunk groups. U.S. mobile
`networks include a home MSC and a serving MSC. The
`home MSC is the MSC corresponding to the exchange
`associated with a Mobile Subscriber (also referred to above
`as a mobile station or “MS"); this association is based on the
`phone number. such as the area code. of the MS. Examples
`of an MS include a hand-held device such as a mobile phone.
`a PDA. a 2-way pager. or a laptop computer. or Mobile Unit
`Equipment. such as a mobile unit attached to a refrigerator
`van or a rail car. a container. or a trailer.
`The home MSC is responsible for a Home Location
`Register (“HLR”) 118 discussed below. The serving MSC.
`on the other hand. is the exchange used to connect the MS
`call to the PSTN. Consequently. sometimes the home MSC
`and serving MSC functions are served by the same entity.
`but other times they are not (such as when the MS is
`roaming). Typically. a Visiting Location Register (“VLR”)
`116 is co—located with the MSC‘ 110 and a logically singular
`HLR is used in the mobile network (a logically singular
`I-lLR may be physically distributed but is treated as a single
`entity). As will be explained below. the I-ILR and VLR are
`used for storing subscriber information and profiles.
`Radio channels 112 are associated with the entire cover-
`age area. As described above. the radio channels are parti—
`tioned into groups of channels allocated to individual cells.
`The channels are used to carry signaling information to
`establish call coimections and related arrangements. and to
`carry voice or data infonuation once a call connection is
`established.
`
`two significant
`least
`Mobile network signaling has at
`aspects. One aspect involves the signaling between an MS
`and the rest of the network. in the case of 2G (“26“ is the
`industry term used for “second generation”) and later tech—
`nology. this signaling coneems access methods used by the
`MS {such as TDMA or CDMA). pertaining to, for example.
`assignment of radio channels and authentication. A second
`aspect involves the signaling among the various entities in
`the mobile network. such as the signaling among the MSCs.
`BSCs. VLRs, and HLRs. This second part is sometimes
`referred to as the Mobile Application Part (“MAP") espe—
`cially when used in the context of Signaling System No. 7
`(“SS7“). SS? is a common channel signaling system by
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`which elements of the telephone network exchange infor—
`mation, in the form of messages.
`The various forms of signaling (as well as the data and
`voice communication) are transmitted and received in accor-
`dance with various standards. For example. the I'ilectronics
`Industries Association (“BIA") and Telecommunications
`Industry Association (“'l‘lA") help define rnany [1.8. stan-
`dards. such as IS-4l _. which is a MAP standard. Analogously,
`the CCI'IT and ITU help define international standards. such
`as (iSM-MAP. which is an international MAP standard.
`Information about these standards is well known and may be
`found from the relevant organizing bodies as well as in the
`literature. see. e.g.. Bosse, SIGNALING IN 'l‘l'iI..IiCOM-
`MUNICA’I‘IDNS Nli’l‘WORKS (Wiley 1998).
`To deliver a call from an MS 114. a user dials the number
`and presses “send" on a cell phone or other MS. The MS 114
`sends the dialed number indicating the service requested to
`the MSC 110 via the BS 107. The MSC‘ 110 checks with an
`
`associated VLR 116 (described below) to determine whether
`the MS 114 is allowed the requested service. The serving
`MSC routes the call to the local exchange of the dialed user
`on the PS'I‘N 120. The local exchange alerts the called user
`terminai. and an answer back signal is milled back to the MS
`114 through the serving MSC 110 which then completes the
`speech path to the MS. Once the setup is completed the call
`may proceed.
`To deiiver a call to an MS 114. (assuming that the call
`originates from the PS'I'N 120) the PS'I'N user dials the MS‘s
`associated phone number. At least according to U.S. stan-
`dards. the PSTN 120 routes the call to the MS’s home MSC
`
`(which [nay or may not be the MSC' serving the MS}. The
`MSC then interrogates the HLR 118 to determine which
`MSC is currently serving the MS. This also acts to inform
`the serving MSC that a call is forthcoming. The home MSC
`then routes the call to the serving MSC. The serving MSC
`pages the MS via the appropriate BS. The MS responds and
`the appropriate signaling links are set up.
`During a call. the BS 107 and MS 114 may cooperate to
`change channels or BTSs 102.
`if needed.
`for example.
`because of signal conditions. These changes are known as
`“handoffs.” and they involve their own types of known
`messages and signaling.
`One aspect of MAP involves “mobility management."
`Different 138s and MSCs may be needed and used to serve
`an MS. as the MS 114 roams to different locations. Mobility
`tnanagelnent helps to ensure that the serving MSC has the
`subscriber profile and other information the MSC‘ needs to
`service (and bill) calls correctly. To this end, MSCs use VLR
`116 and HLR 118. The HLR is used to store and retrieve the
`mobile identification number (“MIN"). the electronic serial
`number (“TEN"), MS status, and the MS service profile.
`among other things. "lhe VLR stores similar information in
`addition to storing an MSC identification that identifies the
`home MSC. In addition. under appropriate MAP protocols.
`location update procedures (or registration notifications) are
`performed so that the home MSC ofa Mobile Subscriber can
`locate its users. These procedures are used when an MS
`roams from one location to another or when an MS is
`
`powered on and registers itself to access the network. For
`example. a location update procedure may proceed with the
`MS 114 sending a location update request to the VLR 116
`via the BS 107 and MSC‘ 110. The VLR 116 sends a location
`
`update message to the HLR 118 serving the MS 114, and the
`subscriber profile is downloaded from the HLR 118 to the
`VLR 116. The MS 114 is sent an acknowledgement of a
`successful location update. The [HR 118 requests the VLR
`
`(ii'any) that previously held profile data to delete the data
`related to the relocated MS 114.
`
`FIG. 2 shows in more detail the signaling and user traflic
`interfaces between a BS 101Ir and an MSC 110 in a CDMA
`
`mobile network. The BS 107 communicates signaling in for-
`mation using an SSY-based interface for controlling voice
`and data circuits known as the “Al" interface. An interface
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`known as “A2" carries user traffic (such as voice signals)
`between the switch component 204 of the MSC‘ and the BS
`107. An interface known as “A5" is used to provide a path
`for user traffic for circuit-switched data calls (as opposed to
`voice calls) between the source BS and the MSCT. Informa-
`tion about one or more of A1, AZ, A5 may be found in
`CDMA lntemetworking—Deploying the Open—A Interface.
`Su—Lin Low. Ron Schneider. Prentice Hall. 2000. ISBN
`0-13-088922-9.
`
`Mobile conununications providers are supplying newer
`services, e.g., “data calls" to the lnternet. For at least some
`ofthese services. MSCs are not cost elfective because they
`we -’ primarily designed for voice calls. Integration of new
`services into the MSC is difficult or infeasible because ofthe
`
`proprietary and closed designs used by many MSC software
`architectures. That is. the software logic necessary to pro-
`vide the services is not easy to add to the MSC 110. Often.
`a switch adjunct
`is used to provide such services. For
`example. an Inter-Working Function (“IWF”) is an adjunct
`to route a data call
`to the Internet.
`[Either approach
`integrating functionality into the MSC or adding a trunk—side
`adjunct—involves the MSC in the delivery of service.
`Integrating new services via MSCT design changes or through
`trunk-side adjuncts can increase network congestion at the
`MSC and consume costly MSC resources.
`Data calls typically make use ofthe Internet. which is an
`example ofa packet-switching medium. A packet-switching
`medium operates as follows. A sequence ofdata is to be sent
`from one host to another over a network. The data sequence
`is segmented into one or more packets. each with a header
`containing control information. and each packet is milled
`through the network. A common type of packet switching is
`datagram service. which offers little or no guarantees with
`respect to delivery. Packets that may belong together logi-
`cally at a higher level are not associated with each other at
`the network level. A packet may arrive at the receiver before
`another packet sent earlier by the sender, may arrive in a
`damaged state (in which case it may be discarded}. may be
`delayed arbitrarily (notwithstanding an expiration mecha-
`nism that may cause it to be discarded). may be duplicated.
`and may be lost.
`to the Internet. multicast communication
`With respect
`refers to the transmission of identical data packets to
`selected multiple destinations on an Internet Protocol net—
`work. (In contrast, broadcast communication refers to the
`indiscriminate transmission of data packets to all destina-
`tions. and unicast comtnunication refers to the transmission
`of data packets to a single destination.)
`Each participant in a multicast receives information trans
`mitted by any other participant
`in the multicast. Users
`connected to the network who are not participants in a
`particuiar multieast do not receive the information transmit-
`ted by the participants of the multicast.
`In this way. the
`multicast communication uses only the network components
`(cg. switches and trunks) actually needed for the niulticast
`transmission.
`
`In tnulticast processing, when a potential participant
`(“host") is directed to join a particular IP multicast group,
`the host sends a “request to join" message to the nearest
`multicast-capable router to request
`to join the multicast
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`to this group. For
`group and receive information sent
`example. a host A sends a message to join multicast group
`‘1’, and a host B sends a message to join mu lticast group X.
`A router R propagates the request up to the multicast source
`if the data path is not already in place.
`Upon receiving an IP packet for group X. for example. the
`router R maps an IP multicast group address into an Iithernet
`multicast address. and sends the resultant Ethernet packet to
`the appropriate switch or switches.
`According to the Internet Group Management Protocol
`(“lGMP”), a host’s membership in a multicast group expires
`when the router does not receive a periodic membership
`report from the host.
`With respect to interaction among MSs, a Nextcl service
`(known as Nextcl Direct Connectfli‘. using Specialized
`Mobile Radio teclmology. and described at httpvfwwwnex-
`tel.comfphone_servicesfdirectconnect.shtm])
`having
`two
`versions has been proposed for special connection calls
`among MSs. Both versions of the special connection calls
`require special—purpose MSs. In the first version. a one to
`one conversation is allowed between two mobile telephone
`subscribers, e.g.. A and B. When A wishes to have special
`connection communication with B. A enters B’s private
`identification number. holds down a push to talk (“PTT”)
`button. waits for an audible alert signifying that B is ready
`to receive. and starts speaking. To listen. A releases the PTT
`button. If B wishes to speak. B holds down the PIT button
`and waits for an audible confirmation that A is ready to
`receive. The service alloWs a subscriber to choose private
`identification numbers from scrollable lists displayed on
`mobile telephone handsets or to search a list of pro-stored
`names of subscribers.
`
`In the second version, conversations are allowed among
`members of a predefined group of subscribers, known as a
`Talkgroup. which is identified by a number. The mobile
`telephone handset may allow Talkgroup numbers to be
`searched through the control surface of the handset. In order
`to place a group call. the initiating subscriber, e.g.. A. locates
`a Talkgroup number in the handset. holds down the PTT
`button, and. upon receiving an audible confirmation such as
`a chirp, can start speaking. All of the other Talkgroup
`members on the group call can only listen while A is holding
`down the P'l’l‘ button. IfA releases the P'I‘I‘ button. another
`member on the group call may hold down the P'l"I' button.
`acquire control signaled by the audible confirmation. and
`start speaking.
`Technology on the Internet includes instant text messag-
`ing (1M), which lets users receive text messages moments
`alter the messages are sent. IM provides a way to chat with
`friends and also provides a useful tool for business. IM
`provides the convenience of electronic mail (e—mail) and the
`immediacy of a telephone call. The text messages arrive in
`real time (or nearly so) because both parties are constantly
`connected to the network. Recipients receive messages as
`fast as the data can travel across the Internet. (Email is less
`immediate. E—rnai] technology sends messages to a server
`that stores the items until the messages are downloaded by
`the recipient‘s e-1nail software.) When a user logs on to an
`[M service, the software lets a server know that the user is
`available to receive messages. To send a message to some-
`one clse.
`the user begins by selecting that person‘s name.
`usually from a contact list the user has built. The user then
`enters the message and clicks a “Sen " button. A data packet
`is sent that contains address information for the recipient, the
`message. and data identifying the sender. Depending on the
`particular service. the server either directly relays the mes-
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`sage to the recipient or facilitates a direct cormection
`between the user and the recipient.
`An 1M service typically uses one of three mechanisms to
`transport messages: a centralized network. a peer-to-peer
`connection. or a combination of both a centralized network
`and a peer-to-pcer connection. In the case of a centralized
`network (used by, e.g.. MSN Messenger). users are con—
`nected to each other through a series of servers that are
`linked to form a large network. When a user sends a
`message. servers locate the recipient’s computer station and
`route the message through the network until the message
`reaches its destination.
`
`According to the peer-to-peer approach (used by, cg.
`ICQ). a central server keeps track of which users are online
`and the users‘ unique Internet Protocol (IP) addresses. (An
`IP address identifies a computer. which allows the computer
`to send and receive data via the Internet.) After a user logs
`on,
`the server provides the user's computer with the IP
`addresses of each other user on the user’s contact list who is
`
`currently logged on. When the user creates a message to
`send to another user, the user‘s computer sends the message
`directly to the recipient‘s computer. without involving the
`server. Messages traverse only the network portion between
`the sender’s and recipient’s computers, which speeds trans-
`fers by helping to avoid network traflic.
`America Online. Inc. (AOL) supplies AOL Instant Mcs-
`sengcr (AIM) which combines the centralized and peer-to-
`peer methods. When a user sends a text message,
`the
`message travels along AOL’s centralized network. However.
`when the user sends a file. the users‘ computers establish a
`peer-to-peer coimection.
`In another variation of Internet technology. at least one
`wireless Internet system has been proposed that provides
`reliable access to tens of megahertz of bandwidth across a
`wide geographic area, using local wireless transceiver tech—
`nology {e.g.. in a nanocell system). In contrast to the cellular
`wireless voice system. which relies on tens or hundreds of
`cells in a region. the local wireless transceiver system relies
`on thousands or tens of thousands of transceivers in the
`
`region. In such a system. each transceiver may cover, cg.
`0.05 square kilometers, which is about one-hundredth the
`coverage of a conventional cell. High spatial reuse of the
`radio frequency (RF) spectrum allows the local wireless
`transceiver system to accommodate many more active
`devices at a given data rate than a conventional cell system.
`In addition. since users are closer to access points. the local
`wireless transceiver system acconunodates lower-power
`transmissions. The local wireless transceiver system can
`support large numbers of devices. rurming at high speeds.
`with relatively little drain on the devices‘ batteries.
`For example,
`in a citywide local wireless transceiver
`system network of 10.000 transceiver access points {cell
`centers), if each point provides its users with l-bes co]-
`Icctive throughput. 10 active devices per transceiver can be
`supported at 100 kbi’s each, which amounts to 100.000 active
`devices in the city. If each device is active 10 percent of the
`time, such a network can support a million devices. although
`some accounting would need to be made for bandwidth
`consumed by overhead for channel access. handoffs. and any
`provision for asymmetric trafiic (e.g._.
`in which more bits
`flow toward a device than from it).
`Each local wireless transceiver system access point may
`be or resemble access points for wireless local area network
`(LAN) technology such as IEEE 802.11. An asynchronous
`digital subscriber line (ADSL). or a cable modem line may
`be used to provide a link between each access point and the
`Internet (a wireless link may be used as well or instead).
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`With respect to the siting of access devices. since each
`device requires electrical power and is preferably elevated
`for adequate radio frequency coverage. sites on utility poles
`and buildings are typical candidates, with the high-speed
`neighborhood Internet access infrastructure serving as a
`backbone.
`
`FIGS. 5. 7 are flow diagrams of procedures in corrunu-
`nications systems.
`FIGS. 8. 12 are call
`communications systems.
`
`flow diagrams of sequences in
`
`[)Ii'l‘AIllEI) DESCRIPTION
`
`SUMMARY
`
`Advanced communications features are provided in a
`mobile communications network having at least one mobile
`switching center and at least one mobile station subsystem.
`The mobile switching center and mobile station subsystem
`each conuntmicate signaling messages according to a mobile
`signaling protocol.
`to an aspect of the invention. an indication is received that
`a half-duplex mobile eonmiunications session is to be ini-
`tiated between a first mobile station subsystem and a second
`mobile station subsystem. (As used herein. “half-duplex"
`refers to a session in which at most one MS at a time is
`considered a transmission source; “halfdnplex” does not
`necessarily mean the sharing. alternating or otherwise. of
`any channel or medium for transmission and reception.) The
`first and second mo