Abstract:
A method and system for reducing latency by anticipating responsive data communications is described. When the user of a first mobile station receives a message sent from a second mobile station, the user of the first mobile station may responsively reply. If, before the reply is sent, the second mobile station releases its network radio link and goes dormant, the reply may be delayed as the radio link is set up again after the reply is sent. To reduce this latency, the first mobile station may monitor its user&#39;s actions and, upon an indication that the user intends to soon reply to the earlier received message, the first mobile station may send a signal into the network which causes the second mobile station to maintain its radio link or to set up a new radio link if it has gone dormant.

Description:
BACKGROUND 
     In wireless communication systems, particularly cellular radio communication systems, mobile stations operating on a network may communicate via an air interface with a base transceiver station (BTS) and in turn with a base station controller (BSC). The BSC may also be coupled with a mobile switching center (MSC). Further, the BSC may be coupled with packet data serving element (PDSN) or other gateway, which may provide connectivity with an IP network, such as the public Internet or a private intranet (e.g., a wireless carrier&#39;s core IP network). The mobile station may thus communicate with entities on the IP network via a communication path comprising the air interface, the BTS, the BSC and the PDSN. 
     A properly equipped mobile station can initiate packet-data communication by sending a packet-data origination request message over an air interface access channel, and via the BSC, to the MSC. Applying industry standards, the origination request message may include a “packet data” service option code that characterizes the requested communication as packet-data communication, as compared with traditional voice communication. When the MSC receives the origination request, it may then detect the “packet data” service option code and responsively send the message back to the BSC for handling. (Note that, commonly, the MSC and BSC may be physically co-located and perhaps integrated in a common entity, sometimes referred to as an MSC/BSC or simply “switch.”) 
     In turn, when the BSC receives an origination request, the BSC may establish a radio link layer connection with the mobile station by assigning the mobile station to operate on a particular traffic channel over the air interface (e.g., a fundamental traffic channel, and perhaps one or more supplemental channels). In addition, the BSC may pass the origination request to the PDSN. The PDSN and mobile station may then negotiate with each other to establish a data-link layer connection, typically a point-to-point protocol (PPP) session over which packet data can be communicated between the mobile station and the PDSN. As part of this process, the mobile station may obtain an IP address, to facilitate packet communications. For instance, the PDSN may assign an IP address to the mobile station, or the PDSN may communicate with a mobile-IP “home agent” to obtain an IP address for mobile station. (Note that it may also be possible for a mobile station to engage more directly in packet-switched communications, rather than communicating packet data through a channelized PPP connection. For instance, the BSC itself might sit as a element on an IP network, and the mobile station might send and receive individual packets via the BSC.) 
     In most wireless communication systems like this, the radio-link layer connection with a mobile station may time-out after a predefined period of inactivity. For instance, after 10 seconds in which no data is communicated to or from the mobile station over the air interface, the BSC or the mobile station may “tear-down” the radio-link layer connection by releasing the traffic channel that had been assigned to the mobile station. At the same time, however, the data-link layer (e.g., PPP) connection with the mobile station might remain. 
     Once the radio-link layer connection with a mobile station has timed out, the mobile station will be considered “dormant.” However, if its data-link layer connection still exists, the mobile station may still seek to send packet data to other entities, and other entities may seek to send packet data to the mobile station. When another entity seeks to send packet data to the mobile station, the BSC may page the mobile station over an air interface paging channel. When a dormant mobile station receives a page indicative of an incoming data communication, or if the dormant mobile station seeks to send data, the radio link layer connection with the mobile station will need to be reestablished. To do so, the mobile station may send a message to the BSC over the access channel, requesting radio-link resources, and the BSC may then assign a traffic channel. The mobile station may then send or receive packet data over that traffic channel. 
     Some mobile stations may be equipped to automatically enter into an “always-on” data session upon power up, so as to provide IP network connectivity similar to that available through today&#39;s broadband landline modems. In particular, such a mobile station may be programmed to automatically send a “packet data” origination request upon power up and to then negotiate with the PDSN to establish a PPP session. After an initial period of inactivity, the radio-link layer connection with the mobile station may time-out. But, as indicated above, the mobile station may then acquire a radio-link connection when desired. 
     A mobile station that lacks both a radio-link and a data-link is considered to be in an “idle” state, contrasted with a “dormant” state. In the idle state, in order for the mobile station to engage in packet-data communication, it may conventionally send a packet data origination request in the manner described above. 
     Using packet-based communications, a mobile station may participate in data communications with other mobile stations operating on the wireless communication network via a variety of communication options and protocols. For examples, a mobile station may send and receive short messaging service (SMS) messages. As defined by TIA/EIA 637-A and/or other industry standards, a short messaging service center (SMSC) may operate on the wireless communication system network to receive, store and forward short messaging service messages to SMS-capable mobile stations. Additional communications options and protocols are possible as well, such as multimedia messaging service (MMS) messages, Real Time Protocol (RTP) communications, and e-mail messaging. 
     OVERVIEW 
     It is not uncommon for users of mobile stations on a wireless network to have responsive data communications with each other. For example, one user may use a mobile station to send a communication, such as an SMS message, to another user&#39;s mobile station and that other user may then responsively reply to the SMS message (and this cycle may continue repeatedly). This messaging cycle may occur quite rapidly and preferably with low latency. However, if the responding user delays in sending a reply message beyond the radio link timeout limit of the original sender&#39;s mobile station, the original sender&#39;s mobile station may go dormant in the intervening time. The acquisition of a radio link for a dormant mobile station takes time to complete and conventionally occurs only after data is being sent to the mobile station. In the context of a responsive SMS message exchange, that means that the targeted, but dormant, mobile station will begin reacquiring a radio link only after a responsive SMS message has reached the targeted mobile station&#39;s BSC or MSC and the BSC subsequently notifies the mobile station. Consequently, there is an increase in communication latency as the targeted mobile station goes through a wake-up period in which it reestablishes a communication link with the BSC, such as a radio link layer connection, in order to receive the responsive SMS message. A period of several seconds can pass until the responsive communication is ultimately received and displayed to the user. 
     An exemplary embodiment of the present invention provides a mechanism for reducing latency for responsive data communications between mobile stations. The invention provides a means of predictively reserving a radio link for the mobile station that is being responded to, thereby either preventing the mobile station from going dormant or allowing the mobile station to begin waking up before a user actually sends a responsive communication to the mobile station. 
     From this point forward, for the sake of convention, a mobile station that has received a message and is being used to prepare a responsive message will be referred to as the first mobile station. The corresponding user of the mobile station will be referred to as the first user. A mobile station that is both the sender of the original message and the intended target of the responsive message will be referred to as the second mobile station, and the corresponding user will be the second user. Also, although SMS messaging is used as a primary example, the invention applies with equal effect to other responsive communication schemes such as MMS, RTP, and e-mail exchanges. 
     In an exemplary embodiment of the invention, the first mobile station may predict when its user is going to send a responsive user-generated message and then, prior to the user sending the responsive message, the first mobile station may send a signal into the wireless communication network to notify the network to wake up the second mobile station and/or to cause the second mobile station to not go dormant. To predict a responsive message, the first mobile station may monitor user activity on the first mobile station for an indication that the first user is likely to soon instruct the mobile station to send a responsive message to the second mobile station. For example, if the first mobile station employs an SMS software application in which a user would conventionally press a “REPLY” button to begin composing a response to a previously received SMS message, the first mobile station may monitor the SMS software for the “REPLY” button-press action. Once the button-press has occurred, but before the user directs the first mobile station to send the responsive message, the first mobile station may send a reservation message to a communication server in the wireless communication network. The communication server may be a BSC, an MSC, a switch, an SMSC, or some other network element or combination of elements communicatively coupled to the wireless communication network. Transmission of the reservation message would preferably be invisible to the user of the first mobile station—i.e., a conventional user would not be aware that the reservation message had been sent—and the transmission would not interrupt the user&#39;s continued composition of the responsive message. 
     Upon receiving the reservation message, the communication server may then responsively send a message to the second mobile station or to a switch serving the second mobile station, which will ultimately cause the second mobile station to acquire a radio link and, if the mobile is in an idle state, to acquire a data link. The radio link may then be maintained for some set period of time. 
     This process can conveniently rely on existing technology, according to which a dormant second mobile station will be awakened when its serving switch has packet data to deliver to the mobile. For instance, according to an exemplary embodiment of the invention, the communication server, in response to receipt of a reservation message from a first mobile station, may cause an industry standard PING or other generic data to be sent to the second mobile station. For example, the communication server may instruct the terminating switch (i.e., the switch through which the second mobile station would normally establish a radio link) to page the second mobile station and the second mobile station would responsively request and acquire a radio link. 
     Alternatively, the process can involve more advanced signaling and intelligence. For example, in response to receipt of a reservation message, the communication server could send an SMS message to the second mobile station, and the SMS message could cause the second mobile station to acquire a radio link. For example, this could be a WAP Push type message. The SMS message would preferably be invisible to the user of the second mobile station; i.e., a conventional user would not be aware that the SMS message had been received. This process could also cause a second mobile station that is in an idle state, and not just dormant, to acquire a radio link and data link. Further, the SMS message could alternatively or additionally cause the second mobile station to not go dormant and to instead maintain any current and active packet-data connection. Additionally, the SMS message could instruct the second mobile station to maintain the radio link for at least a fixed period of time. 
     As another example, the first mobile station can be programmed so that, in response to detecting that the first user is likely to soon instruct the first mobile station to send a user-generated reply to the to the second mobile station, the first mobile station sends a signal to the second mobile station, causing the second mobile station to acquire or maintain a radio link to the wireless communication network. For example, on an SMS-enabled first mobile station, once a “REPLY” button-press trigger event has occurred but before the user sends a responsive message, the first mobile station may send a reservation message to the second mobile station through the wireless communication network. The reservation message could be a SMS message to the second mobile station, and the message could cause the second mobile station to originate a packet-data connection (i.e., to acquire a radio link). The SMS message would preferably be invisible to the users of both the first mobile station and the second mobile station. This process could also cause a second mobile station that is in an idle state, and not just dormant, to acquire a radio link and data link. Further, the SMS message could alternatively or additionally cause the second mobile station to not go dormant and to instead maintain any current and active packet-data connection. Additionally, the SMS message could instruct the second mobile station to maintain the radio link for at least a fixed period of time. Alternatively or additionally, the first mobile station could send an industry standard PING to the second mobile station, as described above. 
     As another example, in response to receipt of a reservation message from a first mobile station, the communication server could cause a specially-coded voice-call initiation message to be sent to the terminating switch (i.e., the switch through which the second mobile station would normally establish a radio link). The terminating switch may respond to the specially coded voice-call initiation message by paging the second mobile station with a coded page message that causes the second mobile station to originate a packet-data connection or to not go dormant. For instance, the terminating switch can respond to the specially coded voice-call initiation message as it would respond to a packet data communication that has arrived from the network for transmission over a radio link to the second mobile station. Namely, the terminating switch could responsively alert (e.g., page) the second mobile station to cause the second mobile station to acquire a radio link over which it could receive packet data. 
     Advantageously, in all cases, by sending a signal from the first mobile station that causes the second mobile station to initiate or maintain a radio link in response to an indication of an anticipated responsive message from the first mobile station, rather than waiting until the first mobile station actually sends the responsive message, the communication delay resulting from dormancy of the second mobile station can be greatly reduced or avoided. Preferably, the second mobile station will be fully awakened (or will at least have begun the process of acquiring a radio link) by the time the responsive message arrives at the terminating switch, so there would be no need to then begin awakening the second mobile station in order to send the responsive message from the terminating switch to the second mobile station. 
     These and other aspects, advantages, and alternatives of the exemplary embodiment will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention are described herein with reference to the drawings, in which: 
         FIG. 1  is a block diagram illustrating a system in which exemplary embodiments can be implemented; 
         FIG. 2  is a flowchart illustrating a process carried out in accordance with an exemplary embodiment; 
         FIG. 3  is a flowchart illustrating a process carried out in accordance with an exemplary embodiment; 
         FIG. 4  is an exemplary message flow diagram illustrating an embodiment of the invention; 
         FIG. 5  is a block diagram depicting an exemplary mobile station; and 
         FIG. 6  is a block diagram depicting an exemplary communication server. 
     
    
    
     DETAILED DESCRIPTION 
     1. Communication System 
     Referring to the drawings,  FIG. 1  depicts an example communication system in which an exemplary embodiment of the present invention may be employed. It should be understood, however, that this and other arrangements and processes described herein are set forth for purposes of example only, and other arrangements and elements (e.g., machines, interfaces, functions, orders of elements, etc.) can be added or used instead, some elements may be omitted altogether, and some functions may occur across multiple elements. Further, as in most telecommunications applications, those skilled in the art will appreciate that many of the elements described herein are functional entities that may be implemented as discrete components or in conjunction with other components, in any suitable combination and location. 
     Still further, various functions described herein as being performed by one or more entities may be carried out by a processor executing an appropriate set of machine language instructions stored in memory. Provided with the present disclosure, those skilled in the art can readily prepare appropriate computer instructions to perform such functions. 
     As depicted in  FIG. 1 , the exemplary system may include a plurality of mobile stations, such as mobile stations  100  and  110 , for example. (Note that the term “mobile station” is used here by convention to refer to a wireless communication terminal. In practice, the wireless communication terminal could actually be mobile, such as a traditional cellular phone, or it could be a fixed wireless terminal, such as a wirelessly connected pay phone for instance.) 
     Each mobile station (MS) can be linked with a packet network (e.g., an IP network)  120  through a radio access network. As shown by way of example, MS  100  is linked with packet network  120  through a first radio access network  132 . Likewise, MS  110  is linked with packet network  120  through a second radio access network  134 . In an alternative network arrangement, both MS  100  and MS  110  can be linked to packet network  120  by a common radio access network, or networks  132  and  134  might be subparts of a common wireless carrier&#39;s network. Other alternative arrangements are possible as well. 
     Each radio access network  132  and  134  provides wireless connectivity with packet network  120  and can take any of a variety of forms. By way of example, radio access network  132  may include a BTS  104  that radiates to define an air interface  102  through which MS  100  can communicate. BTS  104  may then be coupled with a BSC/MSC  106 , which may in turn be coupled through a PDSN  108  or another gateway to packet network  120 . Conventionally, MS  100  can acquire a radio link over air interface  102  to communicate with BSC/MSC  106  and in turn with other entities via packet network  120 . Further, as shown, BSC/MSC  106  may have a more direct connection to packet network  120 , so that BSC/MSC  106  can itself engage in packet data communications over the packet network, and/or so that BSC/MSC  106  can facilitate more end-to-end packet-data communications with MS  100 . 
     Similarly, radio access network  134  may include a BTS  114  that radiates to define an air interface  112  through which MS  110  can communicate. BTS  114  may then be coupled with a BSC/MSC  116 , which may in turn be coupled through a PDSN  118  or another gateway to packet network  120 . Conventionally, MS  110  can acquire a radio link over air interface  112  to communicate with BSC/MSC  116  and in turn with other entities via packet network  120 . Further, as shown, BSC/MSC  116  may have a more direct connection to packet network  120 , so that BSC/MSC  116  can itself engage in packet data communications over the packet network, and/or so that BSC/MSC  116  can facilitate more end-to-end packet-data communications with MS  110 . 
     In exemplary operation, each MS in  FIG. 1  can engage in packet-data communication over packet network  120  after acquiring a radio link over an air interface and a data link with a PDSN or other gateway. As described generally above, for instance, an MS such as MS  100  may send an origination message to a base station such as BTS  104 , asking for a radio link for packet-data communication, and BSC/MSC  106  may responsively instruct MS  100  to operate on a given traffic channel over air interface  102 . Through that traffic channel, MS  100  may then negotiate with a gateway such as PDSN  108  to establish a data link such as a PPP session. Further, the gateway and/or some other entity such as a mobile-IP home agent or AAA server (not shown) could assign an IP address to MS  100  for use in communicating over packet network  120 . More specifics of this conventional operation are described, by way of example, in 3GPP2 and later specifications with which those of ordinary skill in the art are familiar. 
     In each of these exemplary radio access networks, the functional elements sometimes referred to as BSC and MSC are shown combined into a single entity, referred to as BSC/MSC. It should be understood that these respective functional elements could instead reside as discrete entities in their respective radio access networks. Those of ordinary skill in the art are well aware of the arrangement and operation of typical BSC and MSC functions. Additionally, other entities, not shown, might reside on or be accessible via the packet network  120  as well. Further, depending on the air interface protocol and other factors, network elements of different names and different functions could be implemented instead. 
     A communication server  122  that directs, controls, and/or facilitates communications between mobile stations may reside on the packet network  120 . The communication server  122  may comprise or be directly coupled with BSC/MSC  106 , BSC/MSC  116 , PDSN  108 , and/or PDSN  118 , or it may be a discrete element on the network  120 . If the communication server  122  comprises a BSC/MSC, such as BSC/MSC  106 , then other communication servers (not shown) may respectively comprise other BSC/MSCs, such as BSC/MSC  116 . Alternatively or additionally, the communication server  122  may comprise a short messaging service center (SMSC). As defined by TIA/EIA 637-A and/or other industry standards, the SMSC can receive, store and forward short messaging service (SMS) messages to short messaging entities, such as an SMS-capable mobile station for instance. MS  100  and MS  110 , in the exemplary arrangement, can be SMS-capable mobile stations. 
     Referring next to  FIG. 2 , a flow chart  200  is provided to generally illustrate functions that can be involved in carrying out an exemplary embodiment. At block  202 , a first mobile station, such as MS  100  in  FIG. 1 , may receive a message from a second mobile station, such as MS  110 . The message may contain content which is displayed to the user of MS  100 . For example, the message may be an SMS message generated by the user of MS  110 . At block  204 , MS  100  may monitor user interaction with MS  100  in order to detect an activity that indicates that the user of the first mobile station is likely to soon instruct the first mobile station to send a user-generated reply to the previously received message. For example, after receiving the message at the first mobile station, the user of MS  100  may read the message on a display interface of MS  100  and decide to reply to the message. To begin composing a reply message, the user of MS  100  may need to take an affirmative action, such as pressing a “REPLY” button on a user interface or using a voice command to instruct MS  100  to activate a user-input mode that allows the user to begin composing the reply message. Alternatively, on some SMS message handler programs, the user of MS  100  may, upon viewing the received SMS message, immediately begin typing the reply. Other examples are possible as well. At block  204 , MS  100  may detect this affirmative action (e.g., pressing “REPLY,” sending the relevant voice command, typing a reply directly) of the user acting to reply to the message from MS  110 . 
     At block  206 , in response to detecting the affirmative action, MS  100  may then send through the network a reservation message to MS  110  so as to ultimately (with or without intervening operations in the network) cause MS  110 , at block  208 , to either maintain an active radio connection to the network or to begin waking up if it has gone dormant. For example, the reservation message may be a SMS message that causes MS  110  to originate or accept a new radio link to the network, or to maintain an existing radio link to the network. Preferably, MS  100  would send the reservation message silently, so that the reservation message would be invisible to the users of both MS  100  and MS  110 ; i.e., conventional users would not be aware that a reservation message had been sent or received. Alternatively, the reservation message could be a ping request, which would also preferably be invisible to the users of both MS  100  and MS  110 . 
     Additionally, the reservation message may cause the second radio link to the second mobile station to be maintained for a fixed period of time, or for at least a fixed period of time. For example, the reservation message may contain data instructing the second mobile station to maintain its radio link for at least a fixed period of time, e.g., 45 seconds. Alternatively, the reservation message may contain data instructing a network entity through which the message travels, such as an MSC or BSC, to maintain the radio link for at a fixed period of time. 
       FIG. 3  shows a flow chart  300  that also generally illustrates functions that can be involved in carrying out an exemplary embodiment. At block  302 , a first mobile station, such as MS  100  in  FIG. 1 , may receive a message from a second mobile station, such as MS  110 . The message may contain content which is displayed to the user of MS  100 . For example, the message may be an SMS message generated by the user of MS  110 . At block  304 , MS  100  may monitor user interaction with MS  100  in order to detect an activity that indicates that the user of the first mobile station is likely to soon instruct the first mobile station to send a user-generated reply to the previously received message. For example, after receiving the message at the first mobile station, the user of MS  100  may read the message on a display interface of MS  100  and decide to reply to the message. To begin composing a reply message, the user of MS  100  may need to take an affirmative action, such as pressing a “REPLY” button on a user interface or using a voice command to instruct MS  100  to activate a user-input mode that allows the user to begin composing the reply message. Alternatively, on some SMS message handler programs, the user of MS  100  may, upon viewing the received SMS message, immediately begin typing the reply. Other examples are possible as well. At block  304 , MS  100  may detect this affirmative action (e.g., pressing “REPLY,” sending the relevant voice command, typing a reply directly) of the user acting to reply to the message from MS  110 . 
     At block  306 , MS  100  may then, in response to detecting the affirmative action, send through the network a reservation message to a communication server that is communicatively coupled to MS  100 , such as communication server  122 . The reservation message would preferably contain identification information, such as an identifier of MS  110 , an identifier of a user of MS  110 , or some other information that could ultimately be used to contact MS  110 . For example, the identifier may be a mobile identification number (MIN), a mobile directory number (MDN), or a network access identifier (NAI). 
     At block  308 , the communication server  122  may, alone or in conjunction with other elements on the network, reserve a radio link for MS  110 , in anticipation of future data communications from MS  100  to MS  110  through the network. For example, if MS  110  is dormant, the communication server  122  may send generic data, like an industry standard ping request, over packet network  120  to MS  110 . To facilitate sending the ping request to MS  110 , BSC/MSC  116  may then conventionally page MS  110  and thereby cause MS  110  to request a radio link over which to receive the data. 
     Alternatively or additionally, if MS  110  currently has an active radio link with the network, the communication server  122  may deny, or cause to be denied, future tear-down requests in which the MS  110  or another network entity attempts to disable the current active radio link. For example, communication server  122  may instruct and/or cause BSC/MSC  116  to keep a traffic channel assigned to MS  110 , regardless of any conventional requests to release the traffic channel. Preferably, if the communication server  122  denies tear-down requests, or causes them to be denied, it would only be for a limited period of time, so as to eventually allow the active radio link to be released at some future time. For example, if communication server  122  is distinct from the BSC/MSC  116  serving MS  110 , then communication server  122  could instruct BSC/MSC  116  to ignore and not issue for a fixed period of time any release orders regarding the traffic channel on which MS  110  may be operating. 
     As still another example, if communication server  122  is distinct from BSC/MSC  116 , communication server  122  could send a specially-coded voice-call setup message, such as an ISDN User Part (ISUP) Initial Address Message (IAM) to BSC/MSC  116 . Normally, an IAM would be used to set up a voice call. However, in accordance with the exemplary embodiment, the IAM could include a special code that BSC/MSC  116  may be programmed to detect and respond to in a new way. In particular, BSC/MSC  116  may respond to the special code in the IAM by treating the IAM as though it were an incoming data communication for MS  110 . Thus, the BSC/MSC  116  could responsively page MS  110  and cause MS  110  to request and acquire a radio link, optimally without causing MS  110  to ring, as would normally occur with voice call setup. 
     As yet another example, communication server  122  could send, or cause to be sent, an SMS message to MS  110 . For example, this could be a WAP Push type message. The SMS message may cause MS  110  to originate, accept, or maintain an existing radio link to the network. Preferably, MS  110  would receive the SMS message silently, so that the SMS message would be invisible to the user of MS  110 ; i.e., a conventional user would not be aware that the SMS message had been received. 
       FIG. 4  depicts a representative message flow diagram that illustrates functions that can be involved in carrying out an exemplary embodiment using SMS messaging as an example. In  FIG. 4 , MS  402  may be considered the second mobile station according to previous nomenclature, i.e., the mobile station that sends the original message to which the first mobile station, or MS  414 , responds. Also, some messages and actions that would conventionally occur in a messaging scenario as described in relation to  FIG. 4  are not illustrated in the figure. For example, certain acknowledgement and confirmatory response messages, such as data burst acknowledgement messages, may occur in response to received messages, but are not shown in  FIG. 4 . The specifics of such messages in relation to SMS messaging operations are known to those of ordinary skill in the art and do not need to be detailed in  FIG. 4  in order understand the embodiment. Further, one or more BSCs are not specifically shown in  FIG. 4 , but any of BTS  404 , MSC  406 , MSC  410 , and/or BTS  412  may include or be coupled with a BSC. 
     In the SMS messaging embodiment illustrated in  FIG. 4 , the user of MS  402  may send an SMS message to MS  414 . When that occurs, MS  402  may send an origination message  416  to the BTS  404  that radiates the air interface under which MS  402  is operating. In response to the origination message  416 , MS  402  and MSC  406  may work cooperatively, as shown by block  418 , to set up a radio link layer connection by assigning MS  402  to operate on a particular traffic channel over the air interface of BTS  404 . Other network elements may also participate in the traffic channel setup; for example, a PDSN (not shown) may be consulted to assign an IP address to MS  402 . 
     After the radio link is set up, MS  402  may then send an SMS message in a data burst message  420 , which may be forwarded as an SMS origination message  422  to SMS Server  408 . SMS Server  408  may then send an SMS delivery message  424  based on the SMS origination message  422  to MSC  410 , which controls BTS  412 , which in turn radiates the air interface under which MS  414  operates. MSC  410  may then page MS  414  via the BTS  412 , by means of page messages  426  and  428 . Once MS  414  responds to page message  428  with page response  440 , MS  414  and MSC  410  may work cooperatively to set up a radio link connection by assigning MS  414  to operate on a particular traffic channel over the air interface of BTS  412 . Other network elements may also participate in the traffic channel setup; for example, a PDSN (not shown) may be consulted to assign an IP address to MS  414 . Once the traffic channel is set up, MSC  410  may then deliver the SMS message to MS  414  via BTS  412 , by means of SMS delivery message  444  and data burst message  446 . 
     Before, during, or after final delivery of the SMS message to MS  414 , MS  402  and the radio network under which it operates may disconnect their active radio link connection in order to conserve network and/or mobile station resources. For example, after a certain time-out period has elapsed without further communication from MS  402 , MSC  406  may send a release order to MS  402  via BTS  404  and by means of release order messages  448  and  450 . MS  402  may then acknowledge the release order by sending a release acknowledgement back to the MSC by means of messages  452  and  454 . At that point, the traffic channel would be torn down, as shown by block  456 . Alternatively, and not shown, MS  402  may initiate the tear down by sending a release order message to MSC  406  and MSC  406  may respond with an acknowledgement and a subsequent tear down of the traffic channel connection. 
     Returning now to events at MS  414 , MS  414  may monitor user interaction with MS  414  in order to detect an intent by the user of MS  414  to reply to the SMS message previously received via data burst message  446 , as shown by block  458 . For example, after receipt of the SMS message, the user of MS  414  may read the SMS message on a display interface of MS  414  and decide to reply to the SMS message. To begin composing the reply SMS message, the user of MS  414  will have to take an affirmative action, such as pressing a “REPLY” button on a user interface of an SMS message handler program present on MS  414  or by using a voice command to instruct MS  414  to activate a user-input mode in the SMS message handler program, either of which may allow the user to begin composing the reply message. Alternatively, on some SMS message handler programs, the user of MS  414  may, upon viewing the received SMS message, immediately begin typing the reply directly. Other examples are possible as well. 
     MS  414  may then detect the affirmative action (e.g., pressing “REPLY,” sending the relevant voice command, typing a reply directly, etc.) of the user acting to reply to the message received from MS  402 . For example, MS  414  may be programmed to monitor the button-press event in the SMS message handler program and, upon capturing a button-press event, to then take actions as described below. 
     Once MS  414  detects its user&#39;s intent to reply, MS  414  may send a reservation message in order to predictively reserve a radio link for MS  402 . MS  414  may send the reservation message  460  to BTS  412 , which may then forward the message as reservation message  462  to MSC  410 . In the embodiment illustrated by  FIG. 4 , MSC  410  could serve the role of a communication server  122 . MSC  410 , alone or in conjunction with other network elements not shown, may determine that MSC  406  controls BTS  404  through which MS  402  operates and therefore MSC  410  may forward the reservation message as reservation message  464  to MSC  406 . Assuming, in this example, that MS  402  has gone dormant (i.e., its traffic channel connection has been torn down, as shown by block  456 ), MSC  406  may then page MS  402  in order to restore an active radio link. MSC  406  may send a page message  466  to BTS  404 , which will actively page MS  402  with page message  468 . Once MS  414  responds with page response  470 , MS  402  and MSC  406  may work cooperatively, as shown by block  472 , to re-set up a radio link layer connection by assigning MS  402  to operate on a particular traffic channel over the air interface of BTS  404 . Other network elements (not shown) may also participate in the traffic channel setup. 
     At the same time or after MS  402  is paged and its traffic channel is set up, the user of MS  414  may be composing the SMS reply message, as represented by block  474 . Once the user has finished composing the reply message, the user may affirmatively act to send the reply message to MS  402  (e.g., the user may press a “SEND” button). MS  414  may then send a data burst message  478  containing the SMS reply message to BTS  412 , which may then forward the SMS replay message to SMS server  408  in SMS origination message  480 . SMS Server may then deliver the SMS reply message to MS  402  via MSC  406  and BTS  404  by means of SMS delivery messages  482  and  484  and data burst message  486 . Because an active radio link has already been set up with MS  402 , as shown at block  472 , the SMS reply message should be delivered with very low latency as compared to conventional operation in which the traffic channel was previously torn down and MS  402  would have been dormant when the SMS reply message came in. 
     2. Exemplary Mobile Stations 
     The mobile stations described herein may be data-capable terminals of any suitable form, and may be the same as or different than each other. To help illustrate,  FIG. 5  is a simplified block diagram depicting an exemplary MS  500 . As shown in  FIG. 5 , the exemplary MS  500  includes a processor (i.e., one or more processors)  504 , data storage  508 , a user interface  506 , and a wireless communication interface  502 , all of which may be coupled together by a system bus, network, or other connection mechanism  512 . 
     Each component of the exemplary MS  500  can take various forms. For instance, processor  504  may be an Intel® x86 standard or mobile class processor, or a digital signal processor (which may integrate part or all of data storage  508 ). Data storage  508  may be flash memory and/or a storage drive. 
     User interface  506  may provide means for interaction with a user. As such, the user interface may include touch and voice input and media output mechanisms. The user interface may include a display, speaker or other mechanism (not shown) for presenting information to a user, as well as an input mechanism (e.g., keyboard, keypad, microphone, mouse, and/or touch-sensitive display overlay) (not shown) for receiving input from a user. 
     Wireless communication interface  502  may facilitate communication over an air interface with a respective base station. As such, the wireless communication interface  502  may include an antenna for sending and receiving radio-frequency signals over the air interface. Wireless communication interface  502  may also include a protocol-dependent chipset (not shown), which may facilitate encoding, transmission and decoding of communication signals according to a wireless protocol used by the mobile station. The chipset may also enable the mobile station to enter into idle, dormant, and active wireless communication states. 
     The manner in which MS  500  establishes and carries out data communication might vary depending on the protocol used for communication over the air interface. In the exemplary embodiment, for instance, the air interface could be a code division multiple access (CDMA) air interface, as set forth in an industry standard such as EIA/TIA/IS-2000a (“IS-2000”) and revisions thereof. It should be understood, however, the air interface could take other forms as well, including CDMA (e.g., 1xRTT, 1xEV-DO), iDEN, WiMAX (e.g., IEEE 802.16), LTE, TDMA, AMPS, GSM, UMTS, or EDGE, Wi-Fi (e.g., IEEE 802.11), or BLUETOOTH, as is well know in the art. 
     Data storage  508  may hold a set of program logic  510  (e.g., machine language instructions and reference data) applicable by processor  504  to carry out various functions described herein. Alternatively, various functions could be carried out by additional hardware and/or firmware not shown. The logic  510  may cause processor  504  to carry out certain functions automatically (for example, to establish a radio link and/or a data link upon mobile station power up) without any signaling input from a user, and to carry out the same or other functions in response to user requests, network messages, or other triggering events. According to the logic  510 , the processor  504  may receive user input from user interface  506  and respond accordingly. For examples, in response to user actuation of a “REPLY” button (or another input mechanism designated to indicate a responsive user message is likely to soon be sent), the processor may cause the wireless communication interface  502  to send a reservation message or other signal into the network, as described above in various embodiments. 
     In accordance with an embodiment, the logic  510  in data storage  508  may also define a message-handler application executable by the processor  504  to recognize reservation messages and to responsively maintain a current radio link with the network or to set up a new radio link, such as by sending an origination message as described above. This way, MS  500  could receive a reservation message sent from a remote MS or from a remote BSC/MSC and MS  500  could begin waking up. The logic  510  may also contain an application executable by the processor  504  to invisibly receive and send reservation messages, particularly SMS reservation messages. In this way, MS  500  could use conventional SMS signaling, but special codes within the SMS messages could be used to define the messages as invisible to the user. 
     2. Exemplary Communication Server 
       FIG. 6  is a simplified block diagram depicting an example BSC/MSC suitable for use in accordance with the exemplary embodiment. As shown in  FIG. 5 , the exemplary BSC/MSC includes a processor (i.e., one or more processors)  604 , data storage  608 , and a network communication interface  602 , all of which may be coupled together by a system bus, network or other connection mechanism  612 . 
     Each component of the exemplary communication server  600  can take various forms. For instance, processor  604  may be an Intel® x86 class processor or a digital signal processor (which may integrate part or all of data storage  608 ). Data storage  608  may be flash memory and/or a storage drive. 
     Network communication interface  602  may facilitate communication over a variety of interfaces, depending on the location and additional functionality of the communication server  600 . For example, if the communication server  600  comprises a BSC/MSC, the interface  602  may include air and landline communication functionality. It may also include a protocol-dependent chipset (not shown), which may facilitate encoding, transmission and decoding of communication signals according to wireless protocols used by mobile stations served by the BSC/MSC. The interface  602  may also include functionality to enable communications over a packet-network and communications with a PDSN, as well as communications with other elements in the network. 
     Data storage  608  may hold a set of program logic  610  (e.g., machine language instructions and reference data) applicable by processor  604  to carry out various functions described herein. Alternatively, various functions could be carried out by additional hardware and/or firmware not shown. The logic  610  may cause processor  604  to carry out certain functions automatically or in response to network messages or other triggering events. For example, and in accordance with an embodiment, the logic  610  may define a message-handler application executable by the processor  604  to recognize reservation messages and to responsively set up or maintain, or cause other network elements to set up or maintain, communication links with mobile stations identified by the reservation messages. 
     Exemplary embodiments have been shown and described herein. Those of ordinary skill in the art will appreciate that numerous modifications from the embodiments described are possible, while remaining within the scope of the claims.