Voice mail deposit for wireless mobile telephone networks

Upon determining that call redirection to a voice mailbox is required (based on receipt of redirection request message from the MSC-S serving the called mobile), the MSC-O transmits a transfer-to-number request (TRANUMREQ) signal to the called mobile's home location register (HLR). The HLR then transmits a routing request (ROUTREQ) signal to an adjunct mobile switching center (MSC-A) which supports direct trunk mobile's voice mailbox. The ROUTREQ message not only serves as an indication to the MSA-A that a TLDN is being requested, but it also provides the MSC-A with the mailbox number to which a call terminating to the TLDN is to be connected. The MSC-A allocates a TLDN for the call that will be redirected to voice mail and associates the mailbox number with this TLDN. The assigned TLDN is returned via signaling messages to the HLR via the routing request return result (routreq) which in turn relays the TLDN to the MSC-o via the transfer-to-number request return result (tranumreq). The MSC-O then redirects the call via either public or private voice transmission facilities to the MSC-A, then MSC-A uses the mailbox number provided by the HLR to connect to the called mobile's voice mailbox

BACKGROUND OF THE INVENTION
 1. Technical Field
 The present invention relates generally to mobile-to-mobile
 telecommunications and in particular to delivering calls from an
 originating mobile switching center (MSC-O) to a called mobile's voice
 mailbox. Still more particularly, the present invention relates to
 employing existing message definitions to obtain a temporary local
 directory number (TLDN) to facilitate call delivery from the MSC-O to the
 called mobile's voice mailbox.
 2. Description of the Related Art
 Mobile service subscribers may currently obtain both "roaming" access, or
 wireless service outside a home service area, in addition to many other
 services including incoming call redirection to voice mail. When a call
 attempts to terminate to a mobile, the home mobile switching center
 (MSC-H) handles the call and, if necessary, redirects the call to the
 serving mobile switching center (MSC-S) in a process known as call
 delivery. In the event that the called mobile cannot or does not accept
 the incoming call, the MSC-S may request, via signaling messages that the
 MSC-H redirect the incoming call to the called mobile's voice mailbox.
 Generally, the MSC-H will have a direct connect trunks to the voice mail
 system, thereby allowing a non-PSTN routable numbers to be used as the
 redirection number to steer the redirected call to the called mobile's
 voice mailbox. For example, the redirection number used for voice mail
 could be `#4258675555`. Since the use of such non-PSTN routable numbers
 requires special digit translations understood only by the MSC-H, all
 calls to a mobile must first route to the mobile's MSC-H before call
 delivery occurs to the MSC-S. This ensures that the MSC-H can redirect the
 call to the called mobile's voice mailbox if necessary.
 For reasons described in the paragraph above, mobile-to-mobile calls must
 also first route the called mobile's MSC-H. The originating mobile
 switching center (MSC-O) serving the originating mobile cannot redirect
 the call to the called mobile's voice mailbox based on a non-PSTN routable
 number. When the mobile switching center serving the called mobile (MSC-S)
 determines that call redirection to voice mail is required, a request to
 invoke redirection to voice mail is signaled to the MSC-H. In the ANSI-41
 wireless networking standard, this message is the Redirection Request
 (REDREQ) message; other wireless networking standards such as the Mobile
 Application Part signaling used for GSM networks implement a similar
 mechanism to redirect incoming calls to voice mail.
 The mechanism described above incurs substantial use of trunk resources. A
 call must be connected from the MSC-O serving the originating mobile to
 the called mobile's MSC-H and thence to the MSC-S serving the called
 mobile. A mobile in Seattle, Wash. calling Dallas-based mobile that
 happens roaming in Portland, Ore. involves a trunk from the Seattle MSC-O
 to the Dallas MSC-H and thence to the Portland MSC-S rather than routing
 directly from Seattle to Portland. The indirect routing through Dallas is
 required in order to ensure that the call can be redirected by the Dallas
 MSC-H to voice mail if requested by the Portland MSC-S. In addition to
 wasteful use of trunk resources, this type of call routing increases voice
 transmission delay which may be detrimental to perceived audio quality.
 Some MSC's implement digital mobile voice coder bypass techniques in which
 digitally encoded speech may be passed directly from mobile to mobile
 provided that the bit patterns not be altered by transmission equipment.
 Since long-haul trunks require echo cancellation equipment, such voice
 coder bypass techniques will not operate on long-haul trunk circuits,
 causing voice quality degradation because the MSC-O must decode the
 digitally compressed voice signal and then the MSC-S must re-encode and
 digitally recompress the voice signal.
 SUMMARY OF THE INVENTION
 It is therefore one object of the present invention to provide an improved
 method and apparatus for mobile-to-mobile telecommunications.
 It is another object of the present invention to provide an improved method
 and apparatus for delivering calls from an MSC-O to a called mobile's
 voice mailbox.
 It is yet another object of the present invention to provide a method and
 apparatus for employing existing message definitions to utilize a TLDN to
 facilitate call delivery from the MSC-O serving the calling mobile to the
 called mobile's voice mailbox.
 The foregoing objects are achieved as is now described. Upon determining
 that call redirection to a voice mailbox is required (based on receipt of
 redirection request message from the MSC-S serving the called mobile), the
 MSC-O transmits a transfer-to-number request (TRANUMREQ) signal to the
 called mobile's home location register (HLR). The HLR then transmits a
 routing request (ROUTREQ) signal to an adjunct mobile switching center
 (MSC-A) which supports direct trunk connections to the voice mail system
 that hosts the called mobile's voice mailbox. The ROUTREQ message not only
 serves as an indication to the MSC-A that a TLDN is being requested, but
 it also provides the MSC-A with the mailbox number to which a call
 terminating to the TLDN is to be connected. The MSC-A allocates a TLDN for
 the call that will be redirected to voice mail and associates the mailbox
 number with this TLDN. The assigned TLDN is returned via signaling
 messages to the HLR via the routing request return result (routreq) which
 in turn relays the TLDN to the MSC-O via the transfer-to-number request
 return result (tranumreq). The MSC-O then redirects the call via either
 public or private voice transmission facilities to the MSC-A, the MSC-A
 uses the mailbox number provided by the HLR to connect to the called
 mobile's voice mailbox.
 The capability of connecting to a called mobile's voice mailbox via a
 PSTN-routable TDLN number eliminates the requirement of routing
 mobile-to-mobile calls through the called mobile's MSC-H. Instead,
 mobile-to-mobile calls can be routed directly from the MSC-O to the MSC-S
 and, if call redirection to the called mobile's voice mailbox is required,
 the MSC-O is capable of connecting to the called mobile's voice mailbox
 via the PSTN. In addition to dramatically reducing transmission back-haul
 requirements (and thereby improving voice quality and reducing
 transmission costs), this invention allow the called mobile's carrier to
 centralize the special translations required to connect to voice mail
 systems at the MSC-A. Previously, the special translations required to
 handle voice mail redirection were distributed if the home carrier's
 network consisted of multiple MSC-H switches.
 The above as well as additional objectives, features, and advantages of the
 present invention will become apparent in the following detailed written
 description.

DETAILED DESCRIPTION
 With reference now to the figures and in particular with reference to FIG.
 1, a diagram of a communications system in which a preferred embodiment of
 the present invention may be implemented is depicted. Communications
 system 102 includes an originating mobile switching center (MSC-O) 104
 connected to a plurality of base transceiver stations (BTS's) 106. (Mobile
 switching centers are also frequently referred to as a mobile
 telecommunications switching office or "MTSO".) The calling subscriber's
 mobile unit 108 initiates wireless calls through BTS's 106, which are
 handled by MSC-O 104. MSC-O 104 is connected to a public or private
 land-line network 110, such as an integrated services digital network
 (ISDN) or a public switched telephone network (PSTN), with calls from
 mobile unit 108 to land-line terminals being routed through network 110.
 Calls placed from mobile unit 108 while located within the wireless
 network including MSC-O 104 to mobile units served by another wireless
 network are also routed through network 110.
 The called subscriber's mobile unit 112 has a home area served by BTS's 114
 connected to home mobile switching center (MSC-H) 116. However, mobile
 unit 112 may "roam" outside the home area and still receive wireless
 communications service, from BTS's 118 connected to serving mobile
 switching center (MSC-S) 120 in the exemplary embodiment. Each mobile
 switching center, MSC-O 104, MSC-H 116, and MSC-S 120, is connected to
 land-line network 110. Each mobile unit is associated with a home location
 register (HLR) for storage of subscriber data of mobile units provisioned
 by the wireless carrier. Each mobile switching center is associated with a
 visitor location register (VLR) for temporary storage of subscriber data
 of mobile units provisioned on an HLR but located within the area served
 by the respective mobile switching center. Mobile switching centers MSC-O
 104, MSC-H 116, and MSC-S 120 are shown as forming part of different
 wireless networks in the exemplary embodiment, but any two or more mobile
 switching centers MSC-O 104, MSC-H 116, and MSC-S 120 may be within a
 single wireless network. MSC-H 116, in particular, is connected to and
 forms part of the same wireless network as adjunct mobile switching center
 (MSC-A) 122, also connected to land-line network 110, which hosts the
 voice mailbox 124 within voice mail system 126 for the called subscriber
 and associated with the telephone number of called subscriber's mobile
 unit 112.
 In operation, MSC-O 104 routes a wireless call from mobile unit 108 to
 mobile unit 112 via MSC-S 120 in accordance with the known art. Upon
 determining that the wireless call to mobile unit 112 should be redirected
 to called subscriber's voice mailbox 124, such as by receiving a REDREQ
 message from MSC-S 120, MCS-O 104 transmits an IS-41 TRANUMREQ message to
 the HLR 128 associated with MSC-H 116. HLR 128 may be integrated with
 MSC-H 116 or a stand-alone network entity. The HLR 128 for MSC-H 116, in
 turn, requests a temporary local directory number (TLDN) from MSC-A 122 by
 transmitting a IS-41 ROUTREQ message to MSC-A 122. The ROUTREQ message
 includes the digits on which MSC-A 122 will translate to connect to the
 called subscriber's voice mailbox 124 when the wireless call to the
 allocated TLDN arrives. Those skilled in the art will recognize that the
 ROUTREQ message definition required to obtain a TLDN from MSC-A 122 as
 described above already exists within the IS-41 (ANSI-41) standard, but is
 currently utilized only for voice mail retrieval rather than voice mail
 deposit.
 In response to receiving the ROUTREQ message, MSC-A 122 allocates a TLDN at
 MSC-A 122 for the wireless call mobile unit 112 being redirected to voice
 mailbox 124. The TLDN is returned by MSC-A 122 to the HLR 128 associated
 with MSC-H 116. Once the HLR 128 has obtained a TLDN for the wireless call
 being redirected, HLR 128 relays the TLDN to MSC-O 104 in the TRANUMREQ
 return result. MSC-O 116 then translates on the TLDN in accordance with
 the known art to route the wireless call via land-line network 110 to
 MSC-A 122. When the redirected wireless call arrives, MSC-A 122
 retranslates on the digits provided in the VoiceMailboxNumber parameter of
 the ROUTREQ message and connects the redirected call to the voice mail
 system, and specifically to voice mailbox 124 associated with called
 subscriber's mobile unit 122. MSC-H 116 is thereby relieved of
 responsibility for redirecting the wireless call to voice mailbox 124.
 The present invention allows call redirection to take place from the
 origination mobile switching center rather than the home mobile switching
 center. Thus, for example, a mobile unit in Seattle calling a Dallas
 mobile unit located in Portland may connect directly from the Seattle
 MSC-O to the Portland MSC-S without first having to route the call to the
 home mobile switching center in Dallas. When call redirection to voice
 mail is required, a Dallas TLDN will be provided is provided by the
 adjunct mobile switching center in Dallas and the call may be completed to
 voice mail via the MSC-A. This dramatically reduces trunk backhaul,
 thereby lowering costs associated with the call and permitting faster call
 setup times.
 Referring to FIG. 2, a data flow diagram for a process of redirecting a
 wireless call to a subscriber's voice mailbox in accordance with a
 preferred embodiment of the present invention is illustrated. The
 originating mobile switching center, which may be located for this example
 in Seattle, transmits a locate request (LOCREQ) message 202 to the called
 mobile's home mobile switching center HLR, located in this example in
 Dallas. The HLR transmits a route request (ROUTREQ) message 204 to the
 serving mobile switching center MSC-S, located in this example in
 Portland. The MSC-S returns a route request response (routreq) message 206
 containing a TLDN for routing the the call to the HLR. The HLR then
 returns a locate request response (locreq) message 208 to the MSC-O. Call
 setup 210 from MSC-O to MSC-S then occurs.
 If a busy signal or no answer is received and the called party has
 voicemail, a redirection request (REDREQ) message 212 will be transmitted
 from MSC-S to MSC-O followed by a redirection request response (redreq)
 message 214 from NSC-O to MSC-S. The MSC-O will then transmit a transfer
 number request (TRANUMREQ) message 216 to the HLR. Up to that point, no
 change in existing IS-41/ANSI-41 signaling occurs. In the present
 invention, however, the HLR transmits a route request message 218
 containing the voice mailbox number to the adjunct mobile switching center
 (MSC-A), which is this example is also located in Dallas. The MSC-A
 allocates a TLDN for the call redirection and returns a route request
 response message 220 containing the TLDN to the HLR. The HLR relays the
 allocated TLDN to the MSC-O in a transfer number request response message
 222. The MSC-O then employs the TLDN to establish a connection 224 to the
 MSC-A via a land-line network. Upon receiving the call at the allocated
 TLDN, the MSC-A employs the voice mailbox number previously received to
 establish a connection 226 to the voice mail system and relay the call to
 the appropriate voice mailbox.
 With reference now to FIG. 3, a high level flowchart for a process of
 redirecting a wireless call to a subscriber's voice mailbox at an
 originating mobile switching center utilizing a TLDN allocated for the
 wireless call at the adjunct mobile switching center in accordance with a
 preferred embodiment of the present invention. The process begins at step
 302, which depicts a REDREQ message for a wireless call being received by
 an originating mobile switching center from a serving mobile switching
 center. The process then passes to step 304, which illustrates
 transmitting a TRANUMREQ message from the originating mobile switching
 center to the called mobile's home location register.
 The process next passes to step 306, which depicts transmitting a ROUTREQ
 message with the VoiceMailboxNumber from the home mobile switching center
 home location register to the adjunct mobile switching center hosting the
 called subscriber's voice mailbox. The process then passes to step 308,
 which depicts allocating a temporary local directory number at the adjunct
 mobile switching center for the wireless call being redirected to voice
 mail, and returning the allocated temporary local directory number to the
 home mobile switching center home location register in a ROUTREQ return
 response message.
 The process passes next to step 310, which illustrates returning the
 allocated temporary local directory number from the home mobile switching
 center home location register to the originating mobile switching center
 in a TRANUMREQ return response message, and routing the wireless call at
 the originating mobile switching center via a land-line network utilizing
 the allocated temporary local directory number. The process then passes to
 step 312, which depicts retranslating on the VoiceMailboxNumber at the
 adjunct mobile switching center upon receiving the wireless call at the
 allocated temporary local directory number, and routing the call to the
 appropriate voice mailbox. The process finally passes to step 314, which
 illustrates the process becoming idle until another mobile-to-mobile
 wireless call is to be redirected to the called subscriber's voice mail.
 The present invention allows an originating wireless call to connect to the
 called subscriber's voice mailbox from any originating network node rather
 than requiring the redirection of the wireless call to voice mail to be
 performed by the home mobile switching center.
 It is important to note that while the present invention has been described
 in the context of a fully functional communications system, those skilled
 in the art will appreciate that the mechanism of the present invention is
 capable of being distributed in the form of a computer readable medium of
 instructions in a variety of forms, and that the present invention applies
 equally regardless of the particular type of signal bearing media used to
 actually carry out the distribution. Examples of computer readable media
 include: nonvolatile, hard-coded type media such as read only memories
 (ROMs) or erasable, electrically programmable read only memories
 (EEPROMs), recordable type media such as floppy disks, hard disk drives
 and CD-ROMs, and transmission type media such as digital and analog
 communication links.
 The description of the preferred embodiment of the present invention has
 been presented for purposes of illustration and description, but is not
 intended to be exhaustive or limit the invention in the form disclosed.
 Many modifications and variations will be apparent to those of ordinary
 skill in the art. The embodiment was chosen and described in order to best
 explain the principles of the invention and the practical application to
 enable others of ordinary skill in the art to understand the invention for
 various embodiments with various modifications as are suited to the
 particular use contemplated.