A method of associating call back data with an emergency call to a call center

<u>BACKGROUND OF THE INVENTION</u>

<u>I. FIELD OF THE INVENTION</u>

The present invention relates to telecommunications, and more particularly, to wireless communications.

<u>II. DESCRIPTION OF THE RELATED ART</u>

Emergency service calls in North America are originated by dialing "9-1-1." Other parts of the world may use some other abbreviated string of dialable digits, such as "6-1-1" in Mexico, for example. These abbreviated string of digits share the intent of simplify calling for help with an easy to remember number. These calls are routed to a local Public Service Answering Point Call Center ("PSAP-CC") to enable the initiation of an emergency response (e.g., police, fire department, road repair, and/or ambulance) while the caller is kept on the phone. If, however, the call is somehow disconnected or dropped before the emergency is completely reported or the responder arrives, the PSAP-CC may be required to call back the originator.

It should be noted that the record for a "9-1-1" call originated through a wired network may include Automatic Line Identification ("ALI") or the telephone number of the access line from which the call originated. The directory number ("DN") or telephone number of a wireless subscriber may not, however, be associated with a physical line or wireless unit. Instead, calls to a roaming wireless subscriber are routed to the wireless unit by way of the mobile station identification ("MSID"), as opposed to the mobile DN ("MDN"). Accordingly, performing an emergency call back to a wireless unit poses hurdles not encountered with landline devices, for example.

Typically, the MSID may be characterized as either a 10-digit mobile identification number ("MIN") or a 15-digit International Mobile Subscriber Identifier ("IMSI"). The IMSI may be programmed into a wireless unit or a Subscriber Identity Module ("SIM") card by the service provider with whom the wireless unit user has entered into a service agreement. Accordingly, the MSID may not necessarily be a dialable number.

The DN of a wireless unit is a dialable number. The DN is dialed by a caller and used to route a call through the network to the wireless subscriber's home system. At the subscriber's home system, the home location register ("HLR") contains the MSID associated with the subscriber's DN. The MSID, as opposed to the DN, may then be used to route the call through the network to the serving wireless system and page the subscriber. The subscriber's DN may be provided to the serving system from the SIM card through the wireless unit or by the home system to the serving system in a separate data file called the subscriber profile.

The rollout of systems employing a separate number for DN and MSID is a relatively recent occurrence for some wireless systems. Others have used this technique since their inception. Historically, the mobile identification number of a wireless unit was the same as the DN for some systems, particularly in systems supportive of TIA/EIA-41 standards, prior to implementing wireless number portability ("WNP") or thousands block number pooling ("TBNP") based on the Local Routing Number ("LRN") method and international roaming ("IR"). However, with WNP and TBNP, the MDN became "portable" or "poolable" from one service provider to another service provider. Since MSID may not be portable or poolable, the recipient service provider may assign a new MSID for a subscriber with a ported-in or pooled MDN.

International roaming has also forced the separation of MSID and MDN. While the MIN is a 10-digit number modeled after the North American Numbering Plan's 10-digit MDN, other nation's carriers using a different directory numbering plan may not allow their subscriber's DN to be equivalent to the internationally recognized MIN format. Another standard MSID is the IMSI. It may be used in TIA/EIA-41 and GSM systems around the world. IMSI is a 15-digit non-dialable number based on ITU-T Recommendation E.212, and therefore, may not serve as a 10-digit MDN.

Historically, when the MDN was the same as the MIN, the MIN would be delivered to a PSAP-CC and would be used as a call back number. With the separation of MIN and MDN as described above, it became necessary to deliver the MDN as a separate call back number to the PSAP-CC, as well as the caller's MSID. There are certain problems, however, associated with implementing this solution. One issue is that the serving system may not have the caller's MDN, only the MSID, to present to the PSAP-CC with the call. Some of the reasons for this relate to the way MSID-MDN separation has been implemented according to standards. Another reason is that the network interface used to deliver the call to the PSAP-CC may not have the capacity to signal both the DN and MSID or, in some cases, even a full DN.

An old serving TIA/EIA-41 system may not support WNP, TBNP or IR. This means that the older serving system may be expecting the MIN and the MDN to be the same. The older system would not even know to look for a separate MDN in the subscriber's service profile (e.g., keyed on MIN, not MDN). With this limitation, these subscribers may not be allowed to use basic services, but they must be allowed to call for emergency services. As a result, a roamer who dials "9-1-1" while on an old system will have his or her call delivered to the PSAP-CC with an MSID but no MDN. Accordingly, no call back is possible.

A newer serving system that is WNP and IR capable may not be able to deliver MDN to the PSAP-CC. This could happen if the calling wireless unit is not registered with any service provider (e.g., there are mobile phones used for emergency calls only). These wireless units may be referred to as non-subscriber initialized ("NSI") phones. It is also possible for a subscriber to place an emergency call before the HLR has responded to the serving system with the subscriber's service profile containing the DN. Even if the PSAP-CC has been provided with a working DN for callback, the callback to the DN will not go through if the subscriber has call forwarding ser vice inbound calls or if the subscriber has a limited, pre-paid service and there is no remaining balance available to pay for the inbound callback from the PSAP-CC. Further, if the callback number is to a visiting international roamer, the PSAP-CC may need to place an international call. Some PSAP-CC may not have the ability to callback an international number. There is also the risk of network congestion or delay in completing an international call which would be detrimental to handling an emergency in a timely manner. Some PSAP-CCs may not even be equipped to place any outbound calls through separate, outbound administrative lines.

The call back DN for an international roamer would require the PSAP-CC to place an international call to reach a subscriber in their local Emergency Service Zone ("ESZ"). This is not a practical, timely or sufficiently reliable solution for a PSAP-CC that normally does not place international calls and for applications that may require immediate call back information for emergency purposes. In addition, the entire international MDN (up to 15 digits including a country code) may not be presented to the PSAP-CC for call back if the PSAP-CC only supports 10 digits.

It is also possible that the calling wireless unit is not registered with any service provider. As a result, there may be no DN associated with the wireless unit or no permanent MSID encoded in the wireless unit - such wireless units are referred to as NSI mobile phones, for example. This could be because (a) the NSI phone was never intended to be registered (there are such phones to use for emergency calls only), (b) the phone is new and has not yet been initialized by a service provider, (c) the subscription has expired and the NSI phone is no longer registered with a service provider or (d) the SIM card is lost, stolen, or simply never been inserted or been removed either advertently or inadvertently.

Some wireless units also support a removable User Identity Module ("R-UIM") or Subscriber Identity Module ("SIM") that may contain the MSID and the DN. If the R-UIM or SIM are not in the phone, then it can still be used to place an emergency call. However, there is no DN or MSID known to the phone or the serving system to provide the PSAP-CC as a call back number.

Every MS contains a unique mobile equipment identification number ("MEIN") encoded in the phone by the manufacturer. The MEIN may be, for example, an electronic serial number ("ESN"), as used in ANSI/TIA/EIA-41 systems or an International Mobile Equipment Identity ("IMEI") used in GSM systems. The MEIN is independent of the MSID and DN. The MEIN is signaled over the air between the wireless unit and the base station of a wireless system with a call origination attempt or soon thereafter. For example, if not supplied with the call origination attempt, the MEIN may be requested by the serving system.

Current standards for wireless emergency services call for delivering "9-1-1 + the last seven digits of the MEIN" to the PSAP-CC as the form call back number when the directory number assigned to the wireless subscriber is not available. While this may serve to notify the PSAP-CC that no working callback number is available with the call, this "9-1-1 + the last seven digits of the MEIN (MEIN7)" does not uniquely identify the call (i.e., many emergency calls may be identified by the same "9-1-1+MEIN7) and is not routable through the network. This is attributable because to the "9-1-1 + the last seven digits of the MEID" does not contain a complete MEID, and therefore is not unique.

While the hereinabove approach provides the PSAP-CC some measure for performing an emergency call back of a wireless unit, several hurdles still exist. For example, the callback number for a wireless unit in certain circumstances may be nothing more than a dummy number with user location data. Consequently, a need exists for a method and system architecture for ensuring the PSAP-CC receives a real call back number for a wireless unit originating a "9-1-1" call. The doucment <patcit id="pcit0001" dnum="US6038437A"><text>US 6,038,437</text></patcit> discloses a method of call back following an emergency call from a cellular radiotelephone.

<u>SUMMARY OF THE INVENTION</u>

The present invention provides for a method for ensuring a real callback number may be provided for a wireless unit originating a "9-1-1" call as defined by independent method claim 1. More particularly, the present invention enables a call center, such as a local Public Service Answering Point Call Center ("PSAP-CC"), to initiate a callback, irrespective of whether the originating "9-1-1" caller was placed over wireless or wireline communications infrastructure, based on at least one tag identifier. For the purposes of the present disclosure, a tag identifier may correspond with a name or label to uniquely associate signaling from different sources such as, for example, the association of a voice with associated data transmitted over a different channel or in a separate message. Consequently, the tag identifier may include one or more reference keys to a database, such as an emergency call register or an emergency service message entity, for example. The tag identifier(s), therefore, may correspond with an emergency service routing key, a local public safety number, a paging identity and/or a mobile equipment identification number, for example.

In one embodiment of the present invention, a method of communication is provided to at least one wireless unit originating an emergency call. The method includes the step of receiving at least one tag identifier in response to the emergency call originating from the at least one wireless unit. Once the tag identifier is received, a wireless call back number corresponding with the at least one tag identifier may be transmitted. It should be noted that a public service answering point emergency call register may receive the tag identifier(s) and transmits the wireless call back number over a D interface.

In another embodiment of the present invention, a method is provided for establishing an emergency call originated by at least one wireless unit within a communication system having an emergency call register. The method may include transmitting at least one tag identifier from a mobile switching center associated with the at least one wireless unit over an E<i>_x</i> interface, for example, in response to the emergency call from the at least one wireless unit. As in the previously detailed embodiment, the tag identifier(s) may include a reference key to the emergency call register. Moreover, the tag identifier(s) may correspond with at least one of an emergency service routing key, a local public safety number, a paging identity and a mobile equipment identification number. Thereafter, the transmitted tag identifier(s) may be entered into the emergency call register (e.g., a serving system emergency call register or a public service answering point emergency call register).

In yet another embodiment of the present invention, a method is provided for establishing an emergency callback originated by at least one wireless unit within a communication system having an emergency call register. The method may include transmitting at least one tag identifier from the emergency call register over a B<i>_e</i> interface. The tag identifier may then be received and entered into a database, such as an emergency service message entity. Thereafter, the emergency callback corresponding with the entered tag identifier may be requested.

In still another embodiment of the present invention, a method is provided for establishing an emergency callback originated by at least one wireless unit within a communication system having an emergency service message entity. The method may include receiving at least one tag identifier from an emergency call register over a B<i>_e</i> interface and entering the tag identifier(s) into the emergency service message entity. Subsequently, the emergency callback corresponding with the entered at least one entered tag identifier may be requested.

In still another embodiment of the present invention, a method is provided for establishing an emergency call originated by at least one wireless unit associated with a mobile switching center. The method includes transmitting at least one tag identifier from the mobile switching center associated with the wireless unit(s) to an emergency service entity in response to the emergency call from the at least one wireless unit. The method may include transmitting callback and location information associated with the wireless unit(s) from the emergency service message entity over a D interface, wherein the callback and location information correspond with the at least one tag identifier.

These and other embodiments will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001"><b>FIGS. 1</b></figref> and <figref idref="f0002"><b>2</b></figref> depicts an architecture and flow chart of one embodiment of the present invention; and</li><li><figref idref="f0003"><b>FIGS. 3</b></figref> and <figref idref="f0004"><b>4</b></figref> depicts an architecture and flow chart of another embodiment of the present invention.</li></ul>

It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations, and thus are not intended to portray the specific dimensions of the invention, which may be determined by skilled artisans through examination of the disclosure herein.

<u>DETAILED DESCRIPTION</u>

The present invention provides for a method and system architecture for ensuring a real callback number may be provided for a wireless unit originating a "9-1-1" call. More particularly, the present invention enables a call center, such as a local Public Service Answering Point Call Center ("PSAP-CC"), to initiate a callback, irrespective of whether the originating "9-1-1" caller was placed over wireless or wireline communications infrastructure, based on at least one tag identifier. For the purposes of the present disclosure, a tag identifier may correspond with a name or label to uniquely associate signaling from different sources such as, for example, the association of a voice. Consequently, the tag identifier may include one or more reference keys to a database, such as an emergency call register or an emergency service message entity, for example. The tag identifier(s), therefore, may correspond with an emergency service routing key, a local public safety number, a paging identity and/or a mobile equipment identification number, for example.

Referring to <figref idref="f0001"><b>FIGS. 1</b></figref> and <figref idref="f0002"><b>2</b></figref><b>,</b> a set of embodiments of the present invention is illustrated. With respect to <figref idref="f0001"><b>FIG. 1</b></figref><b>,</b> an architecture <b>10</b> of a network reference model ("NRM") supporting mobile emergency service is shown, while <figref idref="f0002"><b>FIG. 2</b></figref> illustrates a message flow diagram <b>100</b> corresponding with the NRM of <figref idref="f0001"><b>FIG. 1</b></figref><b>.</b> More particularly, the embodiments of <figref idref="f0001"><b>FIGS. 1</b></figref> and <figref idref="f0002"><b>2</b></figref> may be associated with a non-call associated signaling ("NCAS") technique for delivering a call to a call center over a designated interface without the data that may be necessary to handle the particular call over this designated interface.

As shown in <figref idref="f0001"><b>FIG. 1</b></figref><b>,</b> a wireless unit <b>20</b> is shown for communicating a "9-1-1" call to architecture <b>10.</b> For the purposes of the present disclosure, a "9-1-1" call corresponds with an emergency call and/or a request for an emergency service(s) (e.g., police, fire department, road repair, and/or ambulance). The communication, as originated by wireless unit <b>20,</b> is conveyed to a mobile switching center <b>40</b> ("MSC") through a base station <b>30</b> over an air interface, U<i>_m</i>. This step of communicating a "9-1-1" call to architecture <b>10</b> corresponds with message flow <b>110</b> in diagram <b>100</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

Once the "9-1-1" call is received by MSC <b>40,</b> identification information associated with wireless unit <b>20</b> may be communicated to an emergency call register at a serving system <b>50</b> ("ECR-SS"). This step of communicating information to ECR-SS <b>50</b> corresponds with the message flow <b>120</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b> More particularly, the information associated with wireless unit 20 includes, for example, a mobile equipment identification number ("MEIN"). The transfer of the MEIN to ECR-SS <b>50</b> is performed by MSC <b>40</b> over a first NRM interface, E<i>_x</i>. It should be noted that the MEIN, as transferred to ECR-SS <b>50</b>, might be realized by an International Mobile Equipment Identity ("IMEI"), electronic serial number ("ESN"), pseudo ESN ("pESN") and/or mobile equipment identity ("MEID").

Along with transferring the MEIN, MSC <b>40</b> may also communicate a paging identity ("PGID") to ECR-SS <b>50</b> as part of message flow <b>120.</b> In the event that the "9-1-1" call from wireless unit <b>20</b> is dropped or disconnected from base station <b>30</b> and MSC <b>40,</b> the PGID may be used to page wireless unit <b>20.</b> To page wireless unit <b>20</b> in the circumstance of a call drop or disconnect, a local public safety number ("LPN") of MSC <b>40</b> may be needed to uniquely identify the switch serving "9-1-1" caller (e.g., wireless unit <b>20</b>). The LPN may be a realized by a dialable number from a native or non-portable number block assigned to MSC <b>40.</b> The LPN may assist in identifying ECR-SS <b>50</b> and for originating a call back to the "9-1-1" caller in the event of a call drop or disconnect within architecture <b>10.</b>

In addition to the LPN, an Emergency Service Routing Key ("ESRK") may also be employed for uniquely identifying the "9-1-1" caller as part of message flow <b>120</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b> The ESRK may support the communication of location information of wireless unit <b>20,</b> as associated with the "9-1-1" call. The network elements and interfaces involved in providing an ESRK may be realized, in one embodiment, using existing communication standards.

From the hereinabove, the PGID may be one of a number of communication standards-based identifiers supporting paging wireless unit <b>20</b> to deliver an inbound call if the "9-1-1" call is dropped or disconnected. With respect to a GSM-based system, wireless unit <b>20</b> may be paged via an international mobile station identity ("IMSI") provided by wireless unit <b>20,</b> a temporary mobile station identity ("TMSI") associated with the IMSI and/or an IMEI from wireless unit <b>20.</b> In a CDMA2000 system, this paging step may be realized using a mobile identification number ("MIN"), an IMSI, a default mobile station identity ("dMSID") from a non-subscriber initiated ("NSI") wireless unit(s), an ESN from wireless unit <b>20</b> and/or a pESN generated from an MEID within wireless unit <b>20.</b>

With identification information associated with wireless unit <b>20</b> received from MSC <b>40,</b> SS-ECR <b>50</b> may then redirect this information over a network interface, E<i>_y</i>, to another emergency call register ("ECR") associated with a public service answering point <b>70</b> ("PSAP"). This activity corresponds with message flow <b>130</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b> Consequently, the MEIN, LPN, dMSID and/or ESRK may be re-transmitted from SS-ECR <b>50</b> to ECR-PSAP <b>70.</b> It should be noted that a PSAP-ECR database is shown as associated with an emergency service message entity <b>80</b> ("ESME"). Other associated databases in ESME <b>80,</b> however, may be keyed on the ESRK, the MEIN, the mobile station identity (e.g., MIN or IMSI) and/or the directory number of the caller.

Thereafter, the ESRK may be signaled with the "9-1-1" call from MSC 40 to an emergency service network element <b>60</b> ("ESNE"). This transmission is performed over another network interface, A<i>_ix</i>. This activity corresponds with message flow <b>140</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

Once delivered to ESNE <b>60,</b> the ESRK is then re-transmitted to a public safety access point call center <b>90</b> ("PSAP-CC"). This further transmission of the ESRK may be performed over another network interface, C. This activity corresponds with message flow <b>150</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

Subsequently, PSAP-CC <b>90</b> may use the ESRK to query ESME <b>80</b> about wireless unit <b>20</b> from which the "9-1-1" call originated. It should be noted that ESME <b>80</b> now should include the information previously redirected from interface E<i>_y</i> to ECR-PSAP <b>70.</b> This query of ESME <b>80</b> may be performed over another network interface, D. This activity corresponds with message flow <b>160</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

In response to the query from PSAP-CC <b>90,</b> ESME <b>80</b> may provide a callback number ("CBN"), as well as the cell site location and/or the wireless unit location, the LPN of the serving system and the MEIN of wireless unit <b>20</b> to PSAP-CC <b>90.</b> This information may be directed to PSAP-CC <b>90</b> over the D interface. This activity corresponds with message flow <b>170</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b> It should be noted that the CBN directed to PSAP-CC <b>90,</b> in one embodiment of the present invention, may not be the directory number of the wire less unit or a non-dialable number as prescribed by exiting standards for NSI phones. In contrast, here, the callback number may consist of the LPN of MSC <b>40</b> serving wireless unit <b>20</b> and the MEIN of wireless unit <b>20.</b>

With the CBN at its disposal, PSAP-CC <b>90</b> may further signal the PSAP-ECR <b>70</b> and ESME <b>80</b> over the D interface using the ESRK as a database key. This signaling step may be performed to request a callback through MSC <b>40</b> should the "9-1-1" originating call be dropped or disconnected. Callback through MSC <b>40</b> allows any PSAP-CC without the ability to immediately place an outbound call to use the D interface as an alternative to signal the PSAP-CC within the ESME to request MSC <b>40</b> to originate a new 9-1-1 call between the mobile phone and the PSAP-CC. Here, the request for a callback may be relayed through PSAP-ECR <b>70</b> to SS-ECR <b>50</b> over the E<i>_y</i> interface. Thereafter, SS-ECR <b>50</b> may then request a callback through MSC <b>40</b> over the E<i>_x</i> interface. This activity corresponds with message flows <b>180</b> through 200 of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

In alternative embodiment, an attendant in PSAP-CC <b>90</b> could use the LPN and/or MEIN to originate a callback directly to MSC <b>40</b> serving wireless unit <b>20</b> if PSAP-CC <b>90</b> were equipped with the appropriately lines and equipment. Here, the MEIN may be inserted in an ISDN user part ("ISUP") relating to global address parameter ("GAP"). It should be noted that PSAP-CC <b>90</b> might also use the ESRK to send a request ESME <b>80</b> over the D interface to demand ESNE <b>60.</b> This demand may be intended to initiate a callback from PSAP-CC <b>90</b> to MSC <b>40</b> using the LPN and the MEIN. This activity corresponds with message flows <b>210</b> through <b>220</b> of <figref idref="f0002"><b>FIG. 2</b></figref><b>.</b>

It should be noted that the MEIN might identify wireless unit <b>20</b> for paging by MSC <b>40</b> to complete the callback. The directory number of PSAP-CC <b>90</b> may be contained in the calling party field of the call origination message. This number may be known by MSC <b>40</b> and checked in the calling party field to insure the caller may be authorized for emergency callback service.

Referring to <figref idref="f0003"><b>FIGS. 3</b></figref> and <figref idref="f0004"><b>4</b></figref><b>,</b> a set of another embodiments of the present invention is illustrated. With respect to <figref idref="f0003"><b>FIG. 3</b></figref><b>,</b> an architecture <b>300</b> of a network reference model ("NRM") supporting mobile emergency service is shown, while <figref idref="f0004"><b>FIG. 4</b></figref> illustrates a message flow diagram <b>400</b> corresponding with the NRM of <figref idref="f0003"><b>FIG. 3</b></figref><b>.</b> More particularly, the embodiment of <figref idref="f0003"><b>FIGS. 3</b></figref> and <figref idref="f0004"><b>4</b></figref> may be associated with an alternative technique for establishing a call by a call center.

As shown in <figref idref="f0003"><b>FIG. 3</b></figref><b>,</b> a wireless unit <b>320</b> is shown for communicating a "9-1-1" call to architecture <b>300.</b> The communication, as originated by wireless unit <b>320,</b> is conveyed to an MSC <b>340</b> through a base station <b>330</b> over an air interface, U<i>_m</i>. This step of communicating a "9-1-1" call to architecture <b>300</b> corresponds with message flow <b>410</b> in diagram <b>400</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b>

Once the "9-1-1" call is received by MSC <b>340,</b> identification information associated with wireless unit <b>320</b> may be communicated to an ECR-SS <b>350.</b> This step of communicating information to ECR-SS <b>350</b> corresponds with the message flow <b>420</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> More particularly, the information associated with wireless unit <b>320</b> includes, for example, a MEIN. The transfer of the MEIN to ECR-SS <b>350</b> is performed by MSC <b>340</b> over a first NRM interface, E<i>_x</i>. It should be noted that the MEIN, as transferred to ECR-SS <b>350,</b> might be realized by an IMEI, ESN, pESN and/or MEID.

Along with transferring the MEIN, MSC <b>340</b> may also communicate a PGID to ECR-SS <b>350</b> as part of message flow <b>420.</b> In the event that the "9-1-1" call from wireless unit <b>320</b> is dropped or disconnected from base station <b>330</b> and MSC <b>340,</b> the PGID may be used to page wireless unit <b>320.</b> To call wireless unit <b>320</b> in the circumstance of a call drop or disconnect, an LPN of MSC <b>340</b> may be needed to uniquely identify the particular switch or end office serving the "9-1-1" caller (e.g., wireless unit <b>320</b>). The LPN may be a realized by a dialable number from a native or non-portable number block assigned to MSC <b>340.</b> The LPN may assist in identifying ECR-SS <b>350</b> and for originating a call back to the "9-1-1" caller in the event of a call drop or disconnect within architecture <b>300</b>.

In addition to the LPN, an ESRK may also be employed for uniquely identifying the "9-1-1" caller (e.g., wireless unit <b>320</b>) as part of message flow <b>420</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> The ESRK may support the communication of location information of wireless unit <b>320,</b> as associated with the "9-1-1" call. The network elements and interfaces involved in providing an ESRK may be realized, in one embodiment, using existing communication standards.

From the hereinabove, the PGID may be one of a number of communication standards-based identifiers supporting paging wireless unit <b>320</b> if the "9-1-1" call is dropped or disconnected. With respect to a GSM-based system, wireless unit <b>320</b> may be paged via an IMSI provided by wireless unit <b>320,</b> a TMSI associated with the IMSI and/or an IMEI from wireless unit <b>320.</b> In a CDMA2000 system, this paging step may be realized using a MIN, an IMSI, a dMSID from a NSI wireless unit(s), an ESN from wireless unit <b>320</b> and/or a pESN generated from an MEID within wireless unit <b>320.</b>

In contrast with approach of the embodiments of <figref idref="f0001"><b>FIGS. 1</b></figref> and <figref idref="f0002"><b>2</b></figref><b>,</b> architecture <b>300</b> and message flow diagram <b>400</b> depict a combination of call associated signaling ("CAS") and non-call associated signaling ("NCAS"). More particularly, the CAS technique may be associated with ESNE <b>360,</b> while the NCAS method is associated with a PSAP-CC <b>390</b> based on separating a PSAP-ECR 370 from an ESME 380. Consequently, this technique may be termed a Hybrid CAS and NCAS for mobile emergency service.

Achitecture <b>300</b> employs a network interface E<i>_y</i> between an SS-ECR <b>350</b> and PSAP-ECR <b>370.</b> Furthermore, besides the addition of a network interface, E, between MSC <b>340</b> and ESME <b>380,</b> network interface, B, may now be positioned between ESNE <b>360</b> and ESME <b>380</b> without PSAP-ECR <b>370.</b> Consequently, a direct interface between ESNE <b>360</b> and PSAP-ECR <b>370</b> is not shown. Moreover, an additional network interface, B<i>_e</i>, has also been included between PSAP-ECR <b>370</b> and ESME <b>380.</b> Network Interface D may now be positioned between ESME <b>380</b> and PSAP-CC <b>390.</b> Finally, a separate additional network interface, De, has been incorporated between PSAP-ECR <b>370</b> and PSAP-CC <b>390.</b>

With identification information associated with wireless unit <b>320</b> received from MSC <b>340,</b> unlike the embodiments of <figref idref="f0001"><b>FIGS. 1</b></figref> and <figref idref="f0002"><b>2</b></figref><b>,</b> SS-ECR <b>350</b> may communicate this information about the new emergency call over the Ey interface to PSAP-ECR 370. This activity corresponds with message flow <b>430</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> It should be noted that PSAP-ECR <b>370</b> is logically separated from ESME <b>380.</b> Consequently, the LPN, MEIN and ESRK may also be communicated over the B<i>_e</i> interface from PSAP-ECR 370 to ESME <b>380.</b>

Thereafter, the ESRK may be communicated with the call (e.g., as call associated signaling) by MSC <b>340</b> over the A<i>_ix</i> interface with the LPN and MEIN to ENSE <b>360.</b> This activity corresponds with message flow <b>440</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> It should be noted that the ESRK may be sent over the C interface to the PSAP-CC <b>390</b> from ESNE <b>360,</b> while the LPN and MEIN may be sent from ESNE <b>360</b> to ESME <b>380</b> over the B interface corresponding with message flow <b>450.</b>

Once the ESRK has been communicated with the call and transmitted over the C interface, PSAP-CC <b>390</b> may use the ESRK to query ESME <b>380.</b> This query is intended to provide PSAP-CC <b>390</b> with the callback number (i.e., the LPN and MEIN) associated with wireless unit <b>320.</b> This activity corresponds with message flow <b>460</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b>

Subsequently, ESME <b>380</b> may responds to PSAP-CC <b>390.</b> More particularly, ESME <b>380</b> may provide the callback number, wireless unit location and other pertinent information needed to PSAP-CC <b>390</b> for handling the emergency call. This activity corresponds with message flow <b>470</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b>

If the "9-1-1" call is dropped or disconnected, PSAP-CC <b>390</b> may use the ESRK to signal ESME <b>380</b> over the D interface. In so doing, a callback may be requested through MSC <b>340.</b> This activity corresponds with message flow <b>480</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> Thereafter, ESME <b>380</b> may use the MEIN associated with the ESRK in its database to request a callback through MSC <b>340</b> from PSAP-ECR <b>370</b> corresponding with message flow <b>490.</b> Alternatively, PSAP-ECR 370 may use the MEIN to signal PSAP-CC <b>390</b> may use the MEIN to signal PSAP-ECR <b>370</b> directly over the D<i>_e</i> interface to request a callback through MSC <b>340</b> corresponding with message flow <b>495.</b>

Subsequently, PSAP-ECR <b>370</b> may use the MEIN to request callback through MSC service. Here, the callback is made by MSC <b>340</b> with the request from PSAP-ECR <b>370</b> sent through the SS-ECR <b>350.</b> This activity corresponds with message flow <b>500</b> of <figref idref="f0004"><b>FIG. 4</b></figref><b>.</b> Finally, SS-ECR <b>350</b> may provide MSC <b>340</b> with the PGID and request a callback through MSC <b>340</b> to wireless unit <b>320</b> and to PSAP-CC <b>390.</b>