GB2493346A

GB2493346A - Mobile communications terminal for communicating short message data packets in a context-less manner without a communications bearer being established

Info

Publication number: GB2493346A
Application number: GB1113144.8A
Authority: GB
Inventors: Stephen Barrett
Original assignee: SCA IPLA Holdings Inc
Current assignee: SCA IPLA Holdings Inc
Priority date: 2011-07-29
Filing date: 2011-07-29
Publication date: 2013-02-06
Anticipated expiration: 2031-07-29
Also published as: GB2493346B; GB201113144D0

Abstract

A communications terminal communicates data packets to or from a mobile communications network via a radio access interface. The mobile communications network comprises a radio network part including a plurality of base stations for communicating data packets to or from the mobile communications terminals via the radio access interface, and a core network part which is configured to communicate the data packets to destination addresses from the radio network part or to communicate the data packets to the radio network part from source addresses. The mobile communications network being configured to establish one or more communications bearers for communicating the data packets to or from the communications terminal via the radio network part and the core network part, each of the one or more communications bearers being established using context information associated with one or more connections from the communications terminal to the destination addresses, or to the communications terminal from source addresses. The communications terminal is configured to attach to one of the base stations of the mobile communications network, and when in an idle state, to communicate a short message data packet to the base station of the radio network part as a signalling message, the short message data packet including an indication of context information for use by the mobile communications network for communicating the short message data packet. A short message data packet can therefore be communicated (e.g. from a machine type communications (MTC) terminal) in a context-less or quasi-context-less manner without a communications bearer being established thereby reducing an amount of signalling overhead required, which can be an efficient way of communicating relatively small amounts of data.

Description

COMMUNICATIONS TERMINAL AND METHOD

Field of the Invention

The present invention relates to communications terminals for communicating data packets to or from a mobile communications network via a radio access interface.

Background of the luventioD

Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined TJMTS and Long Term Evolution (LTE) architecture are able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems.

For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed tine data connection. Ihe demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks. i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.

The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of terminals and applications which, rather than taking advantage of the high data rates available, in stcad take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, which are typified by semi-autonomous or autonomous wireless communication terminals (i.e. MTC tenninals) communicating small amounts of data on a relatively infrequent basis. Thus the use of an MTC tenninal may differ from the conventional "always-on" use ease for conventional LTE terminals. Examples of MTC terminals include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MTC server data relating to the customers consumption of a utility such as gas, water, electricity and so on. In the example of a smart nieler, Lhe meter may both receive small dala Lransniissions (e.g. new price plans) and send small data transmissions (e.g. new reading) where thcse data transmissions are generally infrequent and delay-tolerant transmissions. Characteristics of MTC terminals may include for example one or more of: low mobility; time controlled; time tolerant; packet switched (PS) only; small data transmissions; mobile originated only; infrequent mobile tenninated; MTC monitoring; priority alarm; secure connection; location specific trigger; network provided destination fr uplinic data; infrequent transmission; and group based MTC features (for example: group based policing and group based addressing). Other examples of MTC terminals may include vending machines. "sat nay" terminals, and security cameras or sensors, etc. Mobile networks developed recently are generally well adapted to high-rate and high reliability services and may not always be well suited to MTC services.

Summary of the invention

According to the present invention there is provided a communications terminal for communicating data packets to or from a mobile communications network via a radio access interface. The mobile communications network comprises a radio network part including a plurality of base stations for communicating data packets to or from the mobile communications terminals via the radio access interface, and a core network part which is configured to communicate the data packets to destination addresses from the radio network part or to communaeatc the data packets to the radio network part from source addresses. The mobile conrniunieations network being configured to establish one or more communications bearers for communicating the data packets to or from the communications terminal via the radio network part and the core network part, each of the one or more communications bearers being established using contcxt information associated with one or more connections from the communications terminal to the destination addresses, or to the communications tenninal from source addresses. The communications terminal is configured to attach to one of the base stations of the mobile communications network, and when in an idle state, to communicate a short message data packet to the base station of the radio network part as a signalling message, the short message data packet including an indication of context information for use by the mobile communications network for communicating the short message data packet.

Embodiments of the present invention can provide an arrangement for communicating a data packet in a context-less or quasi-context-less manner without a communications bearer being established or established only temporarily between the communications terminal and the base station and from the base station to a mobility manager as a signalling message, thereby reducing an amount of signalling overhead required, which can be an efficient way of communicating relatively small amounts of data. Embodiments of the present invention one example can be used for communicating small amounts of data from more simple devices such as those deployed for MIC types applications.

There are a variety of system architedture options for the delivery of small MIC messages. One option is to establish an internet protocol UP) connection between the communications terminal and an MTC server. The provision of a conventional IP stack at a mobile communications terminal may he attractive from an application development point of view. However, the overhead associated with connection oriented signalling which is required to establish user plane hearers and to manage the core network tunnels during mobility may be excessive when potentially only a few bytes of application data need to be transferred. Another option, and one that is utilised by many existing (3SMAIMIS wide area cellular MTC applications, is to make use of the short message service. With SMS, messages are carried over the control plane and a signalling overhead associated with establishing user plane connections and their associated tunnels can be avoided. An advantage of SMS is the provision of store and forward fimctionality in the SMS Service Centre (SMS-SC), which means that if a communications tenninal is out of coverage or has run out of power then the message will be buffered awaiting the time whcn the terminal comcs back into covel-age or re-attaches. In 3GPP LIE Release 1 0, SMS over LIE is facilitated eithcr through interconnection between the MME and a legacy 20/30 core network (so-called SMS over SOs) or by inter-connection between a communications tenninal and a legacy SMS-GMSC/SMS-IWMSC using 1MS eolrnectivity supported over an IP PDN connection.

Embodiments of the present invention can provide methods of enhancing SMS which reduce signalling overhead by avoiding establishment of access sttatum (AS) security and instead relying on security provided by the non access stratum (NAS). Likewise, alternatives to network controlled handover based mobility management may also he appropriate when only small amounts of traffic are being conveyed.

In some examples the context information provided in the short message packet includes an identifier of the mobile communications terminal, the identifier having been provided to the mobile communications termina] by the mobile communications network, when the mobile communications terminal attached to thc base station of the mobile communications network. Therefore by arranging for the communications terminal to including the identifier in the short message data packet, the base station can recognise that there is no context available for communicating thc short message data packet and use a default context or communications bearer for communicating the data packet. If the base station also treats the short message data packet as a sigualling message then the base station can establish a context for communicating the short message data packet to a mobility manager. In one example, the identifier of the mobile communications terminal is a temporary international mobile subscriber identity number or a representation thereof. In another example the short message data packets includes a field identiing the short message data packet to the base station, which therefore recognises that the short message should be communicated to the mobility manager.

In some embodiments the base station establishes temporarily a radio hearer for eontnunicating the short message data packet between the communications terminal and the base station, the radio bearer being removed after the short message data packet has been received by the base station. The radio bearer may be a default radio bearer or may be established after an exchange of messages between the communications terminal and the base station.

Various ifirther aspects and features of the present invention are defined in the appended claims and include a base station, a mobile communications terminal and methods.

Brief Description of the Drawings

Example embodiments of the present invention will now be described with reference to the accompanying drawings in which like parts have the same designated references and in which: Figure 1 is a schematic block diagram of a mobile communications network according to the LYE standard; Figure 2 illustrates an example of a path followed by a message sent by a terminal in a conventional network; Figure 3 is an illustration of transitions between EMM arid ECM states in a conventional LTE network; Figure 4 is an illustration of a possible call flow con-esponding to Figure 2; Figure 5 is a schematic illustration of Figure 4; Figures 6 to 10 are schematic illustrations of a call flows associatcd with the communication of a short messagc; Figure 11 is an illustration of a possible path for sending a short message; Figure 12 is another illustration of a possible path for sending a short message; Figure 13 is an illustration of a possible protocol stack for sending short messages; Figure 14 is an illustration of another possible protocol stack for sending short messages; Figure 15 is a schematic block diagram of a parts of a mobile communications network according to the LTE standard shown in Figures 1 and 2 illustrating a change of affiliation of a mobile communications tem,inal from one base station to another; Figure 16 is schematic block diagram oF a mobility manager shown in Figure 15; Figure 17 is an illustrative representation of a call flow process for delivering a down link data packet according to one example of the present technique; Figure 1 8 is an illustrative representation of a call flow process for delivering a down link data packet according to another example of the present technique; Figure 19 is an illustrative representation of a call flow process for delivering a down link data packet according to a further example of the present technique; Figures 20 to 23 provide illustrative arrangements of states which a mobile communications terminal can adopt when operating in accordance with the present technique; Figure 24 is a schematic illustration of a path of packets through elements of the mobile communications network for both a conventional RRC connected state and an RRC messaging connected state in accordance with the present technique; and Figure 25 is a table illustrating a relationship between the RRC messaging connected leashed/unleashed states and the ECM Idle, ECM messaging connected and the ECM connected states.

Description of Example Embodiments

The example embodiments will be generally described in the context of a 3GPP LTE architecture. However, the invention is not limited to an implementation in a 3GPP LTE architecture. Conversely, any suitable mobile architecture is considered to be relevant.

Conventional Network Figure 1 provides a schematic diagram illustrating the basic flinctionality of a conventional mobile telecommunications network. The network includes one or more base stations 102 (one base station represented) connected to a serving gateway (S-OW) 1 03 for traffic in the user plane and to a Mobility Management Entity (MME) for signalling in the control plane. In LYE, the base stations are called e-NodcB, which are referred to in the following description as eNl3. Each base station provides a coverage area 103 within which data can be communicated to and from mobile terminals 101. Data is transmitted from a base station 102 to a mobile terminal 101 within a coverage area via a radio downlink. Data is transmitted from a mobile teniiina] 101 to a base station 102 via a radio uplink. The core network, comprising the MME 105, the S-OW 103 and the PDN-Oateway (P-GW) 104, routes data to and from the mobile terminals 101 and provides functions such as authentication, mobility management, charging and so on. The P-OW is connected to one or S more other networks, which may for example include the internet, an IMS core network, etc. In the illustration of Figure 1, connections on the user plane have been represented with a plain line while connections on the control plane have been represented with a dashed line.

Figure 2 illustrates an example of a path followed by a message 130 communicated by a mobile terniinal 101. in that example an MTC terminal 101, wishes to send the message 130 to a destination 120, the destination being reachable via the internet. In this example, a destination device is represented as a computer. However the destination 120 could be an element of any suitable type where the clement can be addressed by the mobile terminal 101.

For example, the destination device 120 may be another terminal, a personal computer, a server, a proxy, or an intermediary element (to a final destination).

The following description provides a summary explanation of an example of operation in which a mobile terminal communicates the message 130 via an LTB network, which is helpifil in appreciating some aspects and advantages of the present technique.

In order for the mobile terminal 1 01 to send data to a destination, an BPS bearer between the terminal 101 and the PGW 104 is set up, the BPS hearer being partially carried over a OTP tunnel between the eNB 102 and the SOW and another (iTP tunnel between SOW and POW 104, as illustrated in Figure 2. As the message 130 is carried to the destination device, it is sent from the terminal 101, at a first end of an BPS bearer to the cNB 102 (step 1), then to the S-OW 103 (step 2) and then to the P-OW 104 (step 3), at the other end of the BPS bearer. The P-OW 104 then forwards the message 130 to the destination 120 (step 4).

Figure 3 illustrates the various transitions between the four possible combinations of BCM states (connected or idle) and BMM states (registered or unregistered) as defined in the LTE standards for a terminal with a view to illustrating how terminals' connections are managed. The acronym ECM stands for "BPS Connection Management" and the ECM state generally indicates whether the terminal has a Non-Access Stratum (NAS) connection set up with the MIMB. In LTE, as the terminal connects to the MME and switches to ECM connected, it also sets up an BPS bearer, that is, a data connection to the P-OW via the S-OW. Also, as the terminal switches from BCM connected to ECM idle, the BPS hearer is torn down, and all SI and RRC connections are released. The acronym BMM stands for "BPS Mobility Management" and the EMM state generally indicates whether a terminal is attached to the network. When the terminal is in EMMunregistered, it may for example be turned oft out of coverage or connected to a different network. In contrast, when a terminal is in EMM_registered. it is attached to the network and, as such, it has an IP address and a S NAS security context in the MME. It may or may not have an BPS bearer set up, but in any ease, it has some context associated with it in the MME (e.g. NAS security context) and in the P-GW (e.g. the IP address). In addition the MIIvIE will know in which tracking areas the UE is located. The four ECM/EMM states and the transitions between them is described next.

The mobile terminal 101 is assumed to start from a state 153 in which the mobile terminal 101 is not connected to the network. In the state 153, the terminal is in EMM unregistered and ECM_idle states. From this stale, the terminal can attach to the network to be in BMM_registered and ECM connected states. However, in order to attach, the terminal cannot switch to BMM_registered if it has not switched to ECM connected first.

In other words, starting from state 153, the terminal cannot go to states 152 or 151 and it has to go to state 154 first. Therefore, as illustrated by arrow 161, a terminal in state 153 can attach to the network by first switching to ECM connected and then to EMM registered. As a terminal starts an attaclunent procedure from state 153, the terminal moves from a state 153 where it does not have any connection to a state 151 where it has a NAS connection to the MME. an IP address allocated by the P-OW, and a EPS bearer to the P-OW via the c-NB and the S-GW.

Transitions between states 151 and 152 occur when a data connection (BPS bearer) is set up (164) or when all data connections have been released (165). Generally, transition 165 occurs when the user had an EPS bearer active and has not been using the bearer for a certain time. The network can then decide that the terminal no longer needs an EPS bearer and thus release all the corresponding resources and switch the terminal to ECM idle. Transition 1 64 generally occurs when the terminal has not been using any BPS bearer (see for example the discussion on transition 164) and now has data to send or receive. An EPS bearer is then set up for this terminal and it is switched to ECM connected. Whenever the terminal is EMM registered, regardless of the ECM states, the terminal will have an IP address that can be used to reach the terminal, in other words an II' context remains active even if no actual BPS bearer is currently active (e.g. state 152).

If the terminal detaches from the network, for example because it is turned off, moving to a different network, or for any other reason, it will switch from any state it is into state 1 53. releasing any outstanding EPS bearer or contexi that was previously maintained for the terminal, via transitions 162 or 163.

As can be understood, the state 154 where the terminal is in ECM_eonnected and in EMM unregistered is a transient state and the terminal does not generally remain in that particular state. A terminal in that state is either a terminal switching from state 153 (detached and inactive) to state 151 (attached and active) or a terminal switching from state 151 to state 153.

RRC states are also provided to reflect the status of the RRC connection between the terminal arid the eNB (RRC_connected and RRC die). Under conventional operation conditions, the RRC states colTespond to the ECM states: if the terminal is in ECM connected, it should also be in RRC connected and if it is in ECM idle, it should also be in RRC_idle. Discrepancies between ECM and RRC states may occur for a short period of time as a connection is being set-up or torn-down.

Figure 4 illustrates an example oIthe messages exchanged for setting up a connection from the terminal 101 to the destination 120, for using the connection to communicate data and for releasing the connection after the communications between the terminal 101 and the destination 120 have been bompleted. The call flow of Figure 4 can be schematically divided into four steps A-D. Beibre step A starts, the terminal 101 is in the ECM idle state which means that the tenninal 101 is not currently communicating. At step A (messages 1-3) an RRC connection is set up between the terminal 101 and the eNB 102 for controlling communications between the tennirial 101 and the eNB 102. Once this RRC connection has been successfully established, at step B (messages 3-12), the terminal 101 can establish a NAS connection with the MME 105. Following this NAS connection request from the terminal 101 to the MME 105, the MME scts up a connection (e.g. EPS bearer) bctwccn the terminal 101 and the P-OW 104, via the S-OW 103 and the eNB i02, and controls this connection. Although they have not been represented here, messages may also be sent to the P-OW 104, for example from the S-OW 103, for setting up the connection (e.g. EPS bearer) at the P-OW 104, for example the EIIP tunnel and EPS hearer. At the end of step B, the terminal 101 has an EPS bearer set-up and available to send and receive messages and is therefore in the ECM-connected state. The call flow of Figure 4 is an illustration and some of the messages may vary, for example depending on the BIvIM state before step A. For example, the terminal may be in EMM unregistered state and switch to Elvllvf_registered during step B, or may already he in EMM_registered before step A starts.

Once this connection (e.g. BPS bearer) has been set up, the terminal 101 can use the connection to send the message 130 to the destination 120 (step C). In the example illustrated in Figure 4, the message 130 sent via messages 13-16 and is followed by an acknowledgement message to confirm that the message 130 has been received by the destination 120 and/or its fmal destination. In other example, messages 13-16 may not he followed by any acknowledgement messages as this is likely to depend on the protocol used for sending the message 130. The scenario shown in Figure 4 may be applicable where an application layer protocol running over UDP requires an acknowledgement to he sent..

At a point in time after completion of step C, the resources are released (step D). Step D could happen at any time after step C, for example just after message 20, or at a later point in time, for example after the terminal 101 stopped communicating for a predetermined time.

The aim of step D is to release all unused connections, that is, to release the NAS connection between the MME 105 and the tenninal 101 (also leading to the release of resources such as the GTP tunnel between S-OW and eNB and the EPS bearer), and to release the RRC connection betweeii the terminal 101 and the eNB 102. Again, depending on whether the terminal 101 should remain in EMM_registered after step D or should switch to EIvIIVI_unregistered, the call flow for step D is likely to be affected. For example, the terminal 101 may remain in EMMjegistered if the terminal simply releases the RRC connection, NAS connection and BPS bearer because it has been inactive for too long, or the terminai 101 may de-attach from the network and switch to EMMuuregistered (for example following a handover to a GSM network).

In the event that the terminal 101 has to send and/or receive large amount of data, this connection method can be efficient in setting up a high-thioughput connection to the P-OW for transmitting such data. it is however based on the exchange of a large number of signalling messages between different parties and the setup of a large number of advanced connections (RRC. NAS, EPS, ete), which may render the system inefficient if the terminal's transmission is actually a brief and small transmission, which is likely to be the ease for an MTC type applications. Furthennore, MTC type applications are likely to require reduced thnctionality in comparison to conventional mobile terminals, in order to reduce the cost of producing such devices. This is because it is envisaged that MTC devices will be more ubiquitous and utilitarian then conventional mobile terminals and therefore should be less expensive to produce in order to be attractive to use mobile communications networks to transmit and receive data. Accordingly, the present technique aims to provide an advantage of adapting conventional mobile communications techniques, particularly in respect of data communications in order to reduce a complexity and therefore a cost of implementing mobile tenninals which use the techniques as provided by an adapted mobile communications network. This is because recent networks, including LTE networks, have been designed for high-capabilities and high-mobility terminals and, as a result, they usually provide for the setup of a high-speed high-reliability connection with an advanced mobility management with a view to supporting terminals potentially transmitting large amount of data while moving.

1-lowever, in the case of a terminal that is not moving as much as a personal phone and/or transmits only small amount of data on a relatively infrequent basis, the amount of signalling and of mobility tracking required for the terminal to communicate may be excessive. In particular, it may be excessive compared to the sometimes low level of service that may be acceptable for this type of terminals. For example MTC terminals are more delay-tolerant than a human-to-human terminal, are less likely to move and/or to change cell during transmissions and usually send or receive small amount of data.

It may therefore be desirable to provide ways to improve an efficiency of the network for transmitting small messages and/or MTC communications. The Following sections provide different example techniques which fonii aspects and features of the present technique.

Transmission of Short Messages in LIE, SMS can currently be supported in two ways. In the first method the short message is conveyed via an Application Server (AS), called an IF Short Message Gateway (IF-SM-OW), in the IMS core which provides an inter-working function into the legacy SMS network. For example, when the terminal wishes to send a SMS in LTE, it will then set-up an BPS bearer as discussed above and will send the SMS through the BPS bearer and to the IMS core's ll'-SM-GW. Likewise, if the terminal is to receive a SMS, the network will trigger an EPS bearer set-up and the IMS core's IP-SM-GW will then forward the SMS to the terminal through the EPS bearer. As discussed above, a large number of messages have to be exchanged for setting up and tearing down at least the RRC connection, the NAS connection and the BPS bearer which makes the sending and receiving of infrequent short messages very inefficient. Of course, in the case of a personal phone, the user is likely to take hill advantage of the "always-on" approach and the user may have most of the time an BPS bearer already set-up for other services as well (e.g. emails, web browsing, etc.). However, MTC terminals may have to send only one short message and this may be the only data sent or received for a long period of time. In that case, selling-up an RRC connection, a NAS connection and an BPS bearer for sending a short message to the IMS core is very inefficient when using SMS over IMS.

In case the mobile network is not connected to an [MS core or the UE does not have S 1MS functionality, a transition solution has been proposed under the name "SMS over SOs" for transferring a SMS message to the legacy and circuit-switched (CS) core via a SOs interface between the MME and an MSC. Short messages are conveyed between the MFv[B and the UP using control plane protocols including RRC and NAS. Because Packet Switched-only mobile networks have been designed for high-capacity and high-usage tenninals, it is therefore assumed that if a terminal sends a service request, a high capacity data path (e.g. an BPS bearer) will be setup for the terminal's use, not necessarily limited to the usc of thc service that triggered the service request. This path may he thus used by the terminal for accessing one or more services (e.g. web browsing, emails, etc.) so that the terminal is in "always-on" mode and does not need to set up a new bearer for every new service. Therefore, as the terminal informs the network of its wish to use the mobile network to communicate (for example sending an SMS message) or as the network detects that it has data to communicate with the tenninal (for example an SMS message), a data path is set up first before the terminal can start communicating using the mobile network. As a result, according to SMS over SOs, a terminal sending a SMS should first perform a full attachment to the network, including the setup of an RRC connection. NAS connection and an BPS bearer before it sends a SMS to the legacy SMSC in the 20/30 network, via the MIV[E. This failback solution uses a new interface SOs between a MMB and a MSC. As for SMS over IMS, the terminal should first set up all connections, including RRC, NAS and BPS before it can send or rcceive a SMS.

In other words, because of the way that recent networks have been designed, any time that a terminal has data to send or receive, a full PS data path (for example an EPS bearer) is set up before everything, which include setting up other connections as well (e.g. RRC and NAS) and only then data can be communicated. Such an approach may be appropriate for high-throughput and high-usage terminals but is less suitable for MIC terminals. For example, the amount of signalling compared to the amount of data to be transmitted is disproportionate. Also, the various elements involved all have to maintain connection information called "context" which relate to information that may not be needed in the specific case of MTC terminals having only brief communications. For example, the advanced mobility services provided by the network involve a significant amount of signalling and context which could be reduced with less advanced and more tailored mobility.

Accordingly, an alternative solution for sending short messages is proposed so as to improve the efficiency of the sending of short messages.

S it is proposed that short messages he sent without setting up the full RRC and NAS connections and he sent in a signalling packet on the control plane rather than on the User plane. The amount of signalling, context and mobility management can thus be reduced, thereby improving the efficiency of the network for MIC terminals.

Connection and Context for Sending Short Messages In order to better illustrate the simplification for the connections and contexts, the call flow of Figure 4 can be schematically represented as in Figure 5. At first, a RRC connection is setup between the terminal 101 and the eNB 102. Once this RRC connection has been set up, at time t1, the eNB maintains an RRC context, referred to as Cont RRC, for the duration of the RRC connection. In other words, until the RRC is released, the eNB will maintain this ContRRC. Such a context may for example include a terminal identifier (e.g. C-RNTI), power control settings, mobility settings, security settings, other radio settings or any other information. There will also be a corresponding context in the UE storing similar information pertaining to the operation of the radio layers, however, this is not shown in the diagram.

Once the RRC connection has been set up, a NAS connection is set up between the tenninal 101 and the MME 105. Once this NAS connection has been set up, at time t, the MME 105 maintains a context for this NAS connection to the terminal 101, referred to as C0ntNAS, for the duration of the NAS connection. Such a NAS context may for example include a terminal identifier, a terminal's if address, a current eNB, mobility settings, security settings, QoS settings, or any other information. As explained above, when the terminal 101 attaches/sets up a data connection via the mobile network, an EPS bearer is set up in the user plane between the terminal and the P-ow 104, the bearer being controlled in the control plane by the MME 105. There will also be a context in the UE storing L'E related information pertaining to the NAS protocol. Note that the context Cont NAS shown in the diagram as being stored at the MME, may include more information than just that used by or transferred in EPC NAS signalling procedures, it may also contain information pertaining to the session which has been gathered by the MME from for example, an 1-155.

Once the RRC connection, the NAS connection and the EPS bearer have been set up, the terminal can send uplink data through the BPS bearer and to the destination. Even though in the example of Figure 5. the terminal 1011 sends uplink data, the same connection setup would occur for a downlink or for an uplink and downlink transmission. Likewise the path of an acknowledgement message has been illustrated in the example of Figure 5 even though there may not be any acknowledgement message in other examples. As discussed earlier, this may for example he dependent upon the type of protocol(s) used for transmitting the data.

As can be seen in Figure 5, Cant RRC and Cont NAS are maintained for the duration of the RRC and NAS connection (ic. until they are expressly released with a connection release message exchange) and, as a result, the RRC context is used for every packet that eNB 101 receives from or sends to the terminal 101. Once the BPS hearer can be released, the NAS connection between the terminal 101 and the MME 105 is released at the same time. As a result, at the time t3 where the NAS comiection is released, the context Cont NAS is also released. I he tearing down of the NAS connection is followed by a tearing down of the corresponding RRC connection at time t4. Again, as thc RRC connection is released, the context Cont RRC is also relcased Generally according to embodiments of the present technique the short messages are sent in a context-less or quasi-context-less maimer. In one example, the tenninal may send a message prior to the establishment of any NAS connection between the terminal and the MME, thereby reducing the signalling hut also the level of service for the terminal, hi another example, the terminal may send a message prior to the establishment of any RRC connection between the terminal and the eNB. thereby also reducing the signalling but also the level of service for the terminal. In firrther examples, the terminal may send a message after a temporary RRC and/or NAS connection has been set-up, with for cxample limited features, where the connection is only set up for a predetermined number of messages or for no more than a predetermined number of mcssages, the number being any number greater than or equal to one. In one example, it may be set up for one message only, in another example it may be set up for the duration of a two-mcssage exchange. It is intended that any suitable combination of the establishment of a partial connection and of the absence of connection establishment for the RRC connection and the NAS connection be considered under the present disclosure. Various combinations are considered below.

The illustration of Figure 6 shows an example where the terminal 101 sends the message when a temporary and reduced RRC connection is set up for a one-message conversation and where no NAS connection is pre-established In the example of Figure 6, a temporary RRC connection is setup at t1, where the RIRC connection is not a conventional full RRC connection but is a connection that is (I) limited to a one-message conversation and (2) only configures the power settings. For example, Access Stratum (AS) security and mobility settings may not be configured even though it would normally be configured for a conventional transmission. As a result, the context to be maintained at the eNB can be reduced to contain only a reduced amount of information. For example, it may only comprise a terminal identifier and power settings. The RRC connection setup could rely on a new type of RRC message or on i-c-using existing RRC messages. For example, the terminal 101 could use an existing message and use a flag, field or indicator in the message to indicate that the RRC setup is not a conventional and complete RRC setup hut is only a limited and/or temporary RRC setup. Alternatively, conventional RRC messages may be used at all stages where for example only the power settings parameters have been indicated in the messages.

The terminal then sends a NAS packet, i.e. a signalling packet, comprising upliuk data for the destination 120, and sends this NAS packet to the MME 105, via a message to the eNB 102. In the example of Figure 6, the NAS packet is can-ied in a RRC message, for example in a "RRC Uplink Information Transfer" message, however in other examples it may be carried in another type of RRC message or in a message for a different protocol. As the packet goes through the cNB 1 02, the eNB can release the REf context at t2 as this context was only setup for a one message conversation with the terminal 101. Afler receiving the message, the cNl3 102 forwards the NAS packet to the MME 105 at t3. In the illustration of Figure 6, t3 has been represented as being after t2. However, the skilled person will understand that t3 could also he before t2 or at the same time as t2. For example, the cNB 102 may first forward the NAS packet to the MME 105 first and then only release the RRC context. Even though this has not been illustrated in the Figures, the NAS packet sent by the eNB 102 to the MME 105 is generally sent in a Sl-AP message. However, any other suitable protocol may be used for sending the NAS packet to the MME 105.

As the MME 105 receives the NAS packet, it will detect that it does not have any NAS context already set up with the terminal 101 and can then set up a temporary context ContNAS-temp. In the example of Figure 6, the temporary context is set up for a two packet conversation with the terminal 101. The MME 105 then sends the uplink data to the destination 120. As the context Cont_NAS-temp has been set up for a two packet conversation, the MME 1 05 niaintains the context even after the upliuk data has been sent.

In the example of Figure 6, a successful transmission of the uplink data triggers an acknowledgement message in response. As generally the acknowledgement ("ack") message comes back via the same path as the uplink data, this ack message comes back to the MME 105. The MME then recogniscs that this message is associated with the terminal 101 and with the context Cont_NAS-temp and sends the aek p aelcet to the terminal 101 via the eNB 102 using the context. After the MMF. 105 has sent the ack message, for example in a NAS packet, to the eNB 102 at time t4, the MME 105 can delete the context Cont NAS-temp as two packets have been exchanged and the context was setup for a two-packet conversation.

In this example, the MlvIE 1 05 sets up a temporary context for a two message conversation when it receives the NAS packet comprising the data for the destination 120. For the MME to know that it should set up a two-packet conversation context, as opposed to for example no context, a one-packet conversation context, etc., various solutions may he uscd.

In one example, the MME 105 can always set up a two-packet conversation context, i.e. the IvvIE may not have any decision making capabilities in respect of the context. This may, fin example, be well suited to an environment where only MIC short messages arrive at the MME 105 without any prior NAS connection setup and where it is known in advance that such messages are sent in a two-message conversation (e.g. message and acknowledgement).

In another example, the MME may have some higher-layer(s) capabilities and may for example be arranged to identt1' the protocol above the NAS layer (or the relevant layer for terminal-MME direct communications), and/or to recognise some information in this higher layer protocol. For example, the MME may be able to detect whether the content of the NAS packet is transported in a short message protoco', and to detect whether the content of the NAS packet relates to a short message (e.g. first part of the conversation) or to an acknowledgement (e.g. second part of the conversation). In anoth.er example, the NAS packet may include a flag or an indication obtained from higher layer(s) (e.g. from a short messaging protocol layer) which indicates if and how a context should be set up. For example, to achieve the two-packet conversation contexL of Figure 6, the NAS packet might include an indicator set to the value two to indicate that the MME 105 should expect a two packet NAS conversation.

As the NAS packet arrives from the MME 105 to the eNB 102, the eNB can then detect that it is not associated with any RRC connection or context for the tenninal 101 and, at time t5, it sets up a limitedltemporary RRC connection for sending a message comprising the NAS packet, i.e. for a one-message conversion. In the example of Figure 6, t4 has been shown as being before t5, however, in some examples, t5 could in fact be before t4. Once the temporary RRC context has been set up, the cNB 1 02 forwards the NAS packet comprising the ack message to the terminal 101. For example the NAS packet may be carried by a RRC message, or by a message of any other protocol lower than NAS.

Once the RRC message has been sent to the terminal 101, the eNB can then discard the temporary context at a time t6 as the one message conversation has been completed.

In the example of Figure 6, the terminal does not have to set up a data path in the user plane for sending its message. Therefore a sitificant amount of signalling and set up can thereby be avoided. Also, the terminal can send the message before any conventional connection or context is set up at the eNB 102 and MME 105. in this particular example, the MME 105 does not have any context or connection set up for terminal 101 when it receives the message.

Therefore the amount of signalling arid of context can be reduced by being set-up as the message arrives, rather than prior to sending any message.

In the example of Figure 6 where radio layer context information is stored in the eNB during a temporary radio connection, radio layer information may also be stored in the UB, this is not shown in the diagram. The UF may also store infonnation of relevance to the NAS protocol such as security algorithm related infontiation, this information may be stored during and between short message transfers, if any such information is required to be shared with the MME NAS protocol then this can be conveyed by the communications terminal to the MME along with the message carrying the application packet. Infonnation stored in the MME context Cont_NAS-temp may also include information gathered from other sources than the communications terminal via the NAS protocol, for example it could includc routing or security information gathered from the HSS.

As a result the complexity of sending a short message for an MTC terminal can be reduced and the efficiency of sending short messages can also therefore be improved. For example, the terminal can send a message according to Figure 6 (or Figures 7-10) while it remains in the ECM idle state, and the terminal can then communicate a short message to a remote destination even though a conventional tenninal would have to set up RRC, NAS and EPS connections first and therefore would have to be in ECM_connected to send a message.

Typically the terminal would have perfonned an ATTACH to the network and be in EMM Registered state prior to conveying any short messages. which would avoid the necessity for an authentication process and NAS security establishment process with every packet transfer. However, the possibility that the terminal is also in EMM_unregistered state when sending a short message would also be a possibility, particularly where the frequency of short message exchange is very low or where simplified NAS security management processes are utilised. However, as the skilled person will recognise, some conventional mobile network features may be lost in sending a short message in this manner. For example, if the RRC connection comprises only power control and ARQ related contexts but does not include any mobility or AS security parameters or settings, the mobile network may be unable to provide any AS security or any mobility services to terminal 101. In that case, if the terminal 101 loses connectivity with eNB 102 ([or example moves out of range of eNB 102), then no mechanism will be in place for the terminal 1 01 to handover to another base station while maintaining a continuity of services during and after the handover. As a result, the terminal 101 may not receive the ack message from the destination and it then cannot know whether the destination has received the short message. This may have to be managed by upper layer protocols (for example a messaging protocol) which may for example detect that the message should be re-sent because the terminal has not received any ack message in response to the first transmission. Therefore while such an approach may be well suited to MTC communications, it may be less suited to conventional mobile transmissions from a convention terminal.

Another example is illustrated in Figure 7. In this example, the MME 105 sets up a one-packet conversation context ContNAS-temp at time t3, i.e. when it receives a NAS message from a terminal 101 and when this message is not associated with any pre-existing context at the MME 105-This behaviour from the MME 105 may for example be a default behaviour which may for example always be used, or may be used unless it is overwritten by a specific behaviour. For example a system niay be configured to have the example of Figure 7 as a default configuration and may use the example of Figure 6 when the NAS message comprises an indicator that a two-packet conversation context should be set up.

At time t4, i.e. when or after the uplink data has been transmitted to its destination, the MME discards the context Cont_NAS-teinp as the packet of the one-packet conversation has already been received from the terminal 101 (via the eNB 102) and processed.

Likewise, as the ack message arrives at the MME 105 from the destination 120 at time t5, the MME 105 sets us a further temporary context Cont NAS-temp' for sending the NAS packet comprising the ack message to the terminal 101 via the cNI3 102 As this packet is sent to the eNB 102 for transmission to the terminal 101, the MME 105 can discard the context ContNAS-temp' at time t6.

Then, as the eNB 102 receives the NAS packet, it sets up a temporary RRC connection with the terminal 101 for the purposes of sending the ack message, for example in an RItC message. This temporary RRC connection is also associated with the setup of a temporary RRCT context at the eNB 102, which is therefore set up at t7 and discarded at ts. An example of where contextual information Cont NAS-temp may be stored for a short period in the MME as shown in Figure 7 might be where the MME needs to access infonnation from another entity, such as accessing routing or security infornrntion storcd in an 1-1SS.A further example is illustrated in Figure 8, In this example, the eNB sets tip a temporary RRC context for a two-message conversation, but the cNB 102 sets up this context as the RRC message arrives, rather than after a temporary RRC connection set up as in Figures 6 and 7. To elaborate further, the temporary connection setup of Figure 7 might include a period whereby charnel soundings and channel souiiding measurements arc exchanged so that message transmissions can be madc at the appropriate power settings and in the optimum time/frequency resources. In the ease of figure 8 transmissions might be made using common channels, where there is no prior train up of power control loops and exchange of channel soundings. In the case of Figure 7 the temporary connection release at the radio layer may be implicit, for example the temporary connection being released immediately that the radio layer ARQ ACK has been received. Also, in the example of Figure 8, the MME does not set up any context and simply forwards the message to the destination. Likewise, as the ack message arrives back from the destination 120, the MML 105 simply forwards the aek message to the terminal 101 via the eNB 102. This can be achieved, for example, with a message that includes information that may usually be found in the context. For example any routing information that may be required for routing the ack message back to the terminal 101 may be included in the first message sent by the terminal, so that the destination can then send a message that is routablc by the MME. One example is that the terminal may include its S TMSI identifier in the message sent to the destination 120, the message might also include the address of the cell wider which the UE is camped and the address of the destination. The destination 120 can then include some or all of this information in the aelc message such that, as this ack message arrives at the MME 105, the MME is able to identify that this message is for the terminal 101 and can then route this ack message to the appropriate eNB and then the eNB is able to route the packet to the appropriate terminal 101 in the appropriate cell. 101.

Because in this example the RRC temporary context is a two-message conversation context, as the ack message is sent by the eNB to the terminal 101 at time t2. the eNB 102 can Ihen delete the temporary context.

In a conventional syctem during the ATTACH procedure the MME could be loaded up with useful NAS security information. The NAS information could be stored thr a predetennined time in the MMF between ATTACH and DETTAC1-1. As illustrated in Figure 9 the NAS information could be established once the mobile terminal is switched on. which includes authentication and security which could be maintained indefinitely. In some examples, when communicating an RRC message 140, the communications terminal could establish a temporary context or context update for the communication of the RRC message 140. In Figure 9, an example is provided in which the communications terminal 101 sets up a NAS connectJon with the MME 105. At time tl,the temporary NAS connection is set up and the MME creates a context Cont_NAS-temp including, for example, the NAS security parameters, which cou]d be after the communications terminal is switched on. Tn that example, the context is set up 1 hr a two-packet conversation. F owever the context might be set up for a conversation of any number of messages of one or more.

Then the terminal 101 sends the RRC message 140 to the eNB. The eNB detects that the content of the RRC message should be forwarded to the MME 105. For example, the eNB 102 can identi' that the RRC message is not associated with any existing connection with the terminal 101 and/or with any context for this terminal. In another example, the eND 102 could be arranged to identi' that the message 140 is not associated with any connection or context and to detect a flag or indicator 142 in the RRC message and would then set up a temporary context. In that particular example, the flag or indicator 142 could be used as a check for the eNB 102 to ensure that the message 140 is intended for the MME 105. In one example, the eNB 102 could then for example reject an incoming message 140 if it is not associated with any context and if it does not include the flag or indicator 142. The message of course also includes data 144 which is being communicated to the destination device and may also include an indication of the TTMSI 146.

The eNB 102 then forwards the NAS packet to the MME, which then recognises that this NAS packet is associated with the context ContNAS-temp. The MME. 105 then forwards the message to the destination 120.

As the MME 105 receives the aek message back from the destination 120, confirming that the destination has received the short message. The MME 105 recognises that the ack message is for the terminal 101 and is therefore associated with the context Cont_NAS-temp.

It sends the aek message to the terminal 101 in a NAS, which may itself be in a SI -AP message for sending it to the eNB 102. The eNB 102 then transfers the ack message to the terminal 101 in a measage 140.

At time t2, after the two-packet conversation between the MME 105 and the terminal 101 has been completed, the connection can he released and the temporary context Cont_NAS-temp can be discarded.

In In the example of Figure 10, the terminal 101 sends the short message while no context exists for this message in the eNB 102 or in the MME 105. Also the eNB 102 and the MME 1 05 do not set up any context, temporary or not, and they forward the message to the next node in a context-less maimer. The ack message received in return is sent to the terminal 101 in a similar manner. In that particular example, the amount of signalling and of context to be maintained can be significantly reduced compared to sending a message in a conventional manner Of course, some features or services may be lost in doing so, such as some secur-ity, mobiliz or session management features. Even though the loss of these features is likely to he considered as unacceptable for a conventional terminal, they may be acceptable for an MTC terminal at least because the transmissions are shorter, MTC terminals may be less likely to move andlor to change cell during a (brief) transmission andlor because MTC terminals are more delay-tolerant than other terminals (e.g. human-to-human communications terminals) andlor because a higher layer protocol such as that running between destination and UE may be able to re-instantiate or recover from failed short message transfers.

In the example of Figures 10, as the RRC messages are sent when the eNB does not have any existing context for them, some features provided by a RRC connection establishment may not be provided. For example, the terminal 101 may not have any C-RNTJ allocated as this identifier is generally allocated during a RRC connection establishment.

Thus, the terminal may use and be addressed using the S-TMSI as the identifier. Other identifiers may also he used, for example the 1MST or MSISDN. Therefore for the example shown in Figure 10, the allocation message used to specify the resources on which the RRC message can be transferred may include the S-TMSI or a proxy therefor.

In general, in Figure 6-10, a situation has been illustrated where the temporary contexts (RRC or NAS) are discarded after a certain number of messages or packets of a conversation have been received and/or processed. The eNB 102 and M]\{E 105 may also have timers for discarding the context. For example, in the example of Figure 6, the MME might have a timer TCOUtNAS for maintaining the temporary context Cont_NAS-temp. For example, it may be desirable to discard the context at the timer's expiry even if the ack message has not been received. This may For instance be preferable in the event that the ack message is lost between the destination 120 and the MME 1 OS and Ihus never reaches the MME 105 or if the nature of operation of any destination server is such that the delay in receipt of the higher layer ACK by the MMF may he long, If for example an ack message is generally received within 0.5s. one might consider that if the ack message has not been received after 3s, it has very probably been lost and is therefore unlikely to arrive at the MME at all. In that case, one bound for the setting of the TcontNAS timer might be 3s.

Alternatively, if the context includes routing information about the last known location of the UE then the timer might be set according to expectations about for how long the routing information is likely to be valid (and whether routing subsequent messages using that information is likely to be successful). This example and the values used in it is purely illustrative, the timer might have any value that is considered to be suitable to a particular 1 5 situation and/or environment.

Examnic of Short Messa2es Infrastructure In order to forward the message to the destination 120, adaptations to the infrastructure and/or protocols may be provided.

Figure 11 is a schematic illustration of a mobile terminal, in that example MTC terminal 101, sending a message 130 to the destination 120 via the MME 105. At first (step 1). the message is sent by the terminal 101 to the eNB 102, the message being carried in a signalling message (e.g. NAS message encapsulated in an RRC message). Sending this message does not require or trigger the set-up of a data path as would normally be expected in PS networks when sending user data, and (step 2) the eNB, upon reception and identification of the signalling message, forwards the message 130 to the MME 105 in a signalling message.

The MI4E 105 then sends the message 130 to the destination 120 at step 3. This illustration is a schematic illustration of a mobile-originated sending of a short message, it does not for example illustrate the specific connection between the MME 105 and the destination 120.

This connection may for example be a direct connection or indirect, going via the Internet or via another route.

Figure 12 is an illustration where the connection is indirect and is via a messaging server 106. For the purposes of illustration, the messaging server will be called "MTC-SC" for "MTC Service Centre". As illustrated in Figure 12, the MME 105 detects that the signalling packet carrying the message 130 is a short message to he forwarded to MTC-SC 106. This detection could be earned out in different ways, for example and as discussed above, the MMIE 105 could detect the type of message carried in the NAS packet, or the NAS packet may comprise an indicator that this NAS packet actually carries a short message for forwarding to MTC-SC 106. Finally, MTC-SC lOG can transmit the message 130 to its destination 120. This transmission can also be perfbrmed in any other appropriate manner.

For example, it can be transmitted directly to the destination, or via a further messaging server and/or a router.

Although this MTC-SC 106 has been represented in Figure 12 as separate from the MME. the skilled person would understand that the separation in the illustration is only logical and for the ease of representation and understanding, and that the MTC-SC may for example physically form part of the MME. In another example, the MTC-SC may be a separate server, for example a standalone server.

Advantageously, this MTC-SC 106 can be used for advanced functionalities such as store and forward. For example, the server can store an incoming mobile terminated message if the terminal 101 is not attached to the network yet and sends this message as soon as it attaches to the network. Likewise, if the terminal 101 sends a message to another party that cmmot be reached, the messaging server MTC-SC 106 can store the message and forward it when this other party becomes available.

Figures 13 and 14 illustrate two possible protocol stacks an-angement that may be suitable for an arrangement according to for exaxnplc Figure 11 or Figure 12. In Figure 13, the MME can act as a relay for messages between the terminal (or liE) and the MTC-SC and, in this example, the short messages are carried by a protocol called "Protocol for short messaging" (PSM). This name does not refer to any particular specific protocol and is used for illustrative purposes: PSM may be any existing, modified or new protocol suitable for sending the message to the MTC-SC. In Figure 13, protocols from LTE have been used for illustrative purposes and the skilled person will understand that the invention could also be earned with a different set of protocols. Because in LTE the terminal communicates directly with the MME using a "NAS" protocol, the short message may be carried by a NAS packet so that the short message can be sent to the destination 120 and/or MTC-SC 106 via the MME (via the eNB 102). The MME can then forward the upper layer (relative to the NAS layer) information to the MTC-SC. In the example of Figure 13, the protocols used between the MME and the MTC-SC have not been specified and have simply been referred to as P1 -P6. In effect any suitable protocol and suitable number of protocols (it could for example be more or less than six protocols) for an interface between the tvth'IE and the MTC-SC may be used. For example, the stack may include five main layers such as Ethernet; MAC; IPsec; SCTP; and MTC-AP where MTC-AP is a protocol for MTC applications (standing for example for "MIC Application Protocol").

With such a protocol stack, a short message 130 can he sent by the terminal 101 in a PSM message, the message itself being sent in a NAS packet, and the packet being sent in a RRC message to the eNB 102. The eNB 102 then forwards the NAS packet in a Sl-AP message to the MME 105. After receiving the NAS packet, the MME 105 can then forward the PSM message comprising (the short message 130) to the MTC-SC for transmission to the destination 120. Tn the event that the terminal receives a short message and has to return an ack message to confirm that the short message was successffilly received, the ack message can follow the same path as the mobile-originated short message 130 discussed above.

Any PSM message for the terminal 101 (mobile-terminated message) may follow the same path in the other direction as a mobile originated short message. Such a mobile terminated mecsage may for example be a mobile-terminated short message (e.g. the terminal 101 receives a short message) or an ack message in response to a mobile-originated short message.

The example of Figure 14 illustrates another protocol stack arrangement which may be suitable for an MME that includes short messaging capabilities. In that case, the MNTE may for example process the actual short message 1 30. It may also not actually process the short message 130 but may for example have PSM-relay capabilities that require that the MME implements some PSM ffinctionalities.

Some might consider that including PSM capabilities in the MME 105 may not be preferable as the MME was originally designed to perform only as a signalling node, while other might consider that it might simplify the global architecture to have PSM capabilities in the MME 105. The skilled person will be able to identify which arrangement would be preferred in a specific situation, depending on its specific requirements.

Reduced Mobility Management for MTC Terminals According to an aspect of the present invention a mobile communications network is configured to provide a reduced mobility fimctionality to reflect a reduction in a capability of a niobile terminal which might for example be used for MTC type applications. The following description and figures provides an explanation of the reduced mobility functionality in accordance with the present technique.

Embodiments of the present technique can provide a reduced mobility functionality to some mobile terminals, such as those which might be operating as MTC type terminals.

Examples illustrating the reduced mobility ffinctionality are explained as fellows with reference to Figures 15 to 25.

Figure 15 provides a schematic block diaam of parts of a mobile communications network which are provided to illustrate the reduced mobility functionality in accordance with the present technique. The parts of the mobile communications network are illustrative of an example of an LTE network as for example illustrated in Figures 1 and 2. In Figure 15 a mobile terminal 201 communicates a message datagram to or -from a source or an anchor base station (cNB) 202. The anchor eNB 202 fonns part of a cluster of eNB's 204, 206 which serve to provide a facility for communicating data to or from mobile terminals 201 via a wireless access interface provided by each of the eNB's 202, 204, 206. In accordance with a conventional operation the eNB's 202, 204, 206 are connected to a serving gateway (SG) 208 as for example shown in Figure 1. Also connected to the eNB's 202, 204. 206 is a mobility management entity (MME) 210. Of particular relevance to thc present explanation is a message server 212 which is connected to the MME 210. In one example the message server 212 is an MTC-SC referred to in the above explanations.

According to the present technique and in relation to the context-less communication explained above, the MIME 210 is arranged to provide a reduced mobility ifinction in connection with the communication of messages to or from the mobile terminal 201. To this end, the MME 210 is arranged to store a current location of a mobile terminal 201 until either all outstanding message transfers have occurred or an "routing information freshness timer" has expired. If either of these conditions is met then the routing contexts for the mobile terniinal in the MME are removed, According to one aspect the mobility management functionality for MTC terminals will then have to establish a location of the communications terminal when this has changed attachment from one base station to a second base station.

Thus the mobility management solution as proposed in accordance with the present technique can he applied to one or both of the following messaging scenarios: NAS signalling message exchange in whic], most NAS messaging exchanges consist of multiple messages exchange between a mobile terminal and an MME 210. These message exchanges should typically be completed in a short period of time.

Short message exchange, short messages are transferred in a NAS container in which the short message exchanges are expected to consist of two steps that is a transfer of the message from the originator entity (eg MTC-SC) followed by an acknowledgement from the recipient entity, for example the mobile communication terminal 201.

As an illustration of a reduced mobility management functionality, Figure 15 illustrates that the mobile terminal 201 which is currently attached to an eNB 202 changes affiliation to a second eNB 206. in the following description the first eNB 202 will he referred to as the anchor eNB whereas the second eNB 206 will be referred to as the second eNB or the target eNB. The present technique therefore addresses a technical problem of how to deliver a message to the mobile terminal 201 when the mobile terminal 201 has changed affiliation from one base station to another.

Conventionally, the communication of data messages or datagrams to or from a mobile terminal which changes its affiliation from one base station to another is handled using handover procedures in which the network directs the mobile terminal to change affiliation in response to link quality measurements reported by the mobile terminal. The mobile communications network then arranges to communicate data from a new target base station or eNB 706 and stops communicating from the source or first base station 202. Flowever the present technique provides a simplification for mobility management which does not include a full liandover procedure which typically requires a significant amount of signalling to configure measurements, send measurement reports. prepare target base station, command handover, reconfigure tunnels and release resources from the source base station. As explained above, if the amount of data communicated to or from the mobile terminal 201 is relatively small then the amount of signalling overhead required to deliver this message would represent a very inefficient usc of radio eornniunications resources According to the present technique therefore it is envisaged that a mobile communication tenninal which for example may be operating as an MTC type terminal is provided with a reduced mobility functionality which may be reflected in a new connection state which will bc explained below. However the following paragraphs serve to provide an illustration of an example of the present technique in providing a reduced mobility management function.

Figure 16 provides a more detailed view of the MME 210. In Figure 16 a processor 220 is arranged to control the operation of the MIME arid includes a data store 222. The processor also receives an input from a clock 224. The processor is connected to a eomnmnications protocol stack 226 which serves to implement the various levels of the communications protocol stack which are performed by the MME 210.

In accordance with the present technique the MME 210 is arranged to store a current location of each of the mobile terminals for which it is responsible within a tracking area sen'ed by the MME. However the location of each of the mobile terminals in respect of a base station (eND) to which they are currently attached is stored in the data store 222 by the processor 220 only for a predetermined period. The eNB to which the mobile terminal is attached is maintained until all outstanding message Iransfers to a mobile terminal have been completed or until a "routing information freshness timer" as determined by the clock 224 has expired. At this time the eND location of the mobile terminal is deleted from the data store 222. Thus as shown in Figure 16 a list 230 ol mobile terminals within a tracking area served by the MME is stored in a table with the mobile temunal's STMSI and an identifier of the base station eND-A to which the mobile terminal is attached. In addition a clock value indicating a time at which the location of the mobilc terminal was registered 232 is provided within the table. Thus as mentioned above once the mobile terminal has been attached to an eNB forn predetermined amount of time then the entry in the data store of the current location of the mobile communication terminal is cancelled. In figure 16 this is illustrated with respect to the mobile terminal identified as UE3, According to the present technique there is provided a reduced mobility functionality to a mobile terminal which might find application in particular with MTC type mobile terminals which are simplified with respect to conventional mobile terminals. Accordingly with the present technique full handover may not be supported. Thus if a mobile terminal wishes to transfer a message to a destination via the mobile communications network or receive a message from the mobile communications network as for example a NAS signalling message or a short message exchange, then handover is not supported. To this cnd, the mobile terminal may include a further coimnunications state referred to in the description below as a "radio resource communication (RRC) messaging connected" state. In this state the mobile communications network does not support frill handover and therefore does not direct the mobile terminal to reattach to a new base station for continuing a commwucations session. Accordingly if the mobile terminal detaches from a first or source base station and attaches to a second or target base station then in accordance with the present technique the message which is to be communicated to the mobile terminal is simply lost. Higher layer protocols can then arrange fur the message to be resent to the mobile terminal. To this end, the mobile terminal determines that it should reselect to a target base station and reselects to that base station. The network may be adapted to determine a location of the mobile terminal in order to communicate the message. Examples of detecting that the mobile terminal has reselected to a new target base station and determining an identification of the target base station will be explained in the following paragraphs.

In Figure 17 a message flow diagram is presented for operalion of an TYIME 210 in arranging for a messagc to be communicated to a mobile tenninal 201 when the terminal 201 has moved on from a source base station 202 and reselected to a target base station 206.

As shown in Figure 17 and reflecting the situation shown in Figure 15, after the mobile terminal 201 has detached from the first or source base station 202 and reselected the second or target base station 206 the mobile terminal 201 sends a first message Ml to provide a cell update to thc source base station 202 to indicate that it will be changing affiliation to thc target base station 206. The MME 210 has previously communicated a message N from the mobile terminal 201 to the destination and therethrc assumes that the mobile terminal 201 is still attached to the source base station. Accordingly the MME 210 has in its data store a loaatinn of the mobile terminal 201 which is that of the source base station 202. Accordingly when the MME 210 has a message N±x to communicate to the mobile terminal 201 the MME 210 communicates using a message M2 the data packet for communication to the mobile communication terminal 201. However as illustrated in Figure 17 the MME 210 communicates the data packet to the source base station or eNB 202.

In message M3 when the source base station 202 attempts to communicate the packet to the mobile terminal 201, that conununication fails. However since in message Ml the mobile terminal 201 communicated the cell update to the source base station 202 indicating that it had reselected to the target base station 206, the source base station 202 in message M3.2 communicates the data packet to the target base station 206. Accordingly the target base station 206 communicates the data packet to the mobile terminal in message M4.

in Figure 18 a similar arrangement is shown to that rcprcsented in Figure 17 except that the mobile terminal communicates its cell update through the target eNB 206. Thus as shown in Figure 18 a mobile terminal 201 sends a message MlO.1 which includes a cell update to the target base station 206 which advises the target eNB that the mobile terminal is currently attached to the target base station 206. The target base station 206 sends a message Ml 0.2 to inform the source base station 202 of an update of the mobile terminals' location by informing the source station 202 that the mobile communication terminal 201 is attached to the target base station 206. In message M12 the MME communicates a data packet N+x to the source base station 202 because, as with the case shown in Figure 17, the MME last communicated a message N from the source base station 202 to the destination and therefore assumes that the mobile terminal is attached to the source base station. However since the source base station 202 has been informed by the target base station 206 that the mobile terminal is attached to the target base station 206 the source base station 202 forwards the data packet to the target base station 206. Accordingly the target base station 206 then communicates the data packet as the message N+X in a message M14 to the mobile terminal.

In accordance with a rther aspect of the present technique the MME may have the previous location of the mobile terminal as attached to the anchor base station 202.

Accordingly with a message M3 1 the MME communicates a data packet providing a message N+x to the anchor base station or eND 202 for communication to the mobile tenninal. As shown in message M32 the anchor base station 202 attempts to communicate the message to the mobile terminal 201. However the message delivery fails. This is because the mobile terminal has now reselected itself onto the target or second base station 206. Accordingly, the anchor base station triggers paging messages to be transmitted to its neighbouring base stations 204, 206 in order to page the mobile terminal. The base stations which are paged are provided from the anchor base station 202 in a list which is to be used in case that the message M32 cannot be delivered to mobile tenninal in winch case it is assumed that the mobile terminal has changed its location. This list may contain the same set of cells/eNDs as are in the neighbour list which an eNodeB may anyway store for the purposes of handover control or improving cell reselection performance. Accordingly, as shown in messages M33 the source or anchor eNB 202 communicates a message to the neighbouring base stations 204, 206 to trigger a paging message to be transmitted from thoe base stations. Since the mobile terminal 201 is attached to the second base station 206, the second base station 206 detects that the mobile terminal 201 is currently attached to it and responds to the paging trigger message M33 with a message M34 informing the anchor eNB 201 that the mobile terminai is currently attached to it. The anchor base station 202 therefore transfers the packet in a transfer message M35 to the second base station 206 which the second base station 206 then communicates to the mobile terminal 201 in a transfer message M36. Accordingly the data packet providing message NH-X is communicated to a mobile terminal from the second base station 206.

In another example the mobility manager 210 is configured to request from at least one of the mobile communications terminal or the eNB 206 information providing an update of the second base station which the mobile communications terminal has reselected. The information could be provided by the communications terminal in an RRC message, which is communicated by the communications terminal via the eNB as a a non access stratum message. Thus in one example, thc cell update information is provided in a way which is substantially transparent to the eNB. If the e.NR does not know the content of the NAS message is, it just forwards it to the M1VIE.

The alternative is that the aommunieations terminal can provide a cell update to the eNB (which may then use the information) as per for example Figures 17 or 18), hut in which case additionally the eNB also forwards the cell update to the MME.

In another example the first base station may send the paging message to one or more base stations in a list of neighbouring base stations, which may be provided to base stations in a neighbour list'. The neighbour list' may be OMC configured or an eNB learnt list of surrounding base stations which communications terminals may hand over or hand off to.

This list is conventionally already available in base stations and is conventionally used for configuring handover rneasuremcnt reporting. identifying local cells to aid cell reselection.

New RRC Messaging Connected State As mentioned above, in accordance with the present technique the mobile terminal 201 and the base station to which the mobile terminal is attached 206 can form a new state referred to as an RRC messaging connected state which is shown in Figure 20. Tn Figure 20 an RRC messaging connected state 280 is shown to be one of three statcs which include an RRC idle state 282 and an RRC connected state 284. The RRC idle state 282 and the RRC coimected state 284 are conventional states of the mobile tenninal and the base stations which fransition between these states in response to whether the mobile terminal is currently provided with a communications hearer For communicating data or not. Thus when in the idle state 282 the communication to or from the mobile tenninal is not possible and the eNB is unaware that the UE is camped on it. However in the RRC connected state 284 the mobile tennina I is attached to the mobile communications network and is provided with radio communications resources for communicating data.

According to the present technique the mobile terminal 201 and the base station 206 to which it is attached fonn a new RRC messaging connected state in which only messaging is supported and no user plane can be provided, reduced radio frmnctionality sufficient and optimised for a messaging only application is provided for communication to/from the mobile terminal. Furthermore within the RRC messaging connected state 280 there are two sub states referred to as the RRC messaging connected unleashed state and the RRC messaging connected leashed state 286, 288 which are showing in Figure 21. In the leashed state the mobile terminal is required to update the RAN about changes in the location of the terminal so that the RAN can route downlink packets to the correct base station to which the terminal is attached. In contrast in the unleashed state the mobile terminal and the base station are not required to update the RAN about changes in the location of the mobile terminal. The leashed state may he supported using conventional network controlled handover. Alternatively the state may be supported using UE controlled cell reselection, which may he augmented with other mobility techniques as have already been described such as UF provided cell update to source or target eNB or anchor eNB triggered paging to fmd the UEs new location.

The states of the state diagram of the mobile terminal shown in Figure 21 are summarised as follows:

State descriptions:

RRC idle a mobile terminal is unknown to the RAN. No contexts associated with that mobile terminal exist in the RAN o No data transfer or signalling transfer is possible in idle mode (except as part of transitioning to another state) RRcConnecled e mobile terminal is known to RAN. contexts exist within the RAN for that mobile terminal * Access Stratum security is set up * SRB1, SRB2 and DRB available * C-RNllassigned * IIandovcr based mobility management o Transfei of ally NAB signalling, short mcssagcs or data over an IP connection is possible in this state RRCMassuging_Connected_Unleathed * Transfer of short messages and optionally NAS signalling possible a No SRB2,DRB or AS security is available a Preferentially, contexts will be established/deleted in the RAN implicitly as part of the message transfer transaction (not using separate a priori, a posteriori RRC signalling) * Unleashed: cell reselection mobility provided, IJE does not provide notification to network of cell change. This may imply reliance on higher layers such as NAS or PSM to recover from any packet loss that occurs as a result.

* No signalling based SI tunnel re-arrangement.

S Optionally mobile terminal listens to and utilises RAN stack optimised for messaging and/or MTC, which may include simplified P1W, MAC, RLC.

RRC Messaging Connected Leashed * Only transfer of short messages and optionally NAS signalling possible * Leashed: mobile terminal/cNB required to update RAN about changes in mobile terminal location, so that RAN can route downlink packets to the correct eNB.

* May use network controlled handover based mobility management: o This means that mobile terminal location is tracked as the mobile terminal moves from cell to cell, handover measurements will be configured, packet forwarding on handovcr may be supported. cNB may notify MM2 of cell IS change..

a Instead of handovc.r source eND may act as an anchor and cithcr the. lIE dircctly or indirectly provides the anchor eNB with information about cell change or the anchor eND pages local cells to discover the lIE's new location.

a No DRB or AS security is available Optionally mobile tenninal listens to and utilises RAN stack optimised for messaging and/or MTC Transitions: RRC Idle to RRQMessagingConnected_Unleashed * Trigger: Short message (or possibly NAS signalling) to he sent either on uplink or doi1ink Realiwd by Signalling prior to dat-a ti-aiisfcr or prcfcrcntially implicitly as part of packet transmission RRQMessaging_Connected_ Unleashed to RRG_Idle * Trigger: One way short message transfer is completed or multi-step message conversation is completed or inactivity timer expires * Realized by: Signalling or implicitly by removal of contexts after message transfer(s) are completed or afler inactivity timer expires RRC Messaging_Connected_Unleashed to RRG_Messaging_Connecled_L cashed Trigger: Frequency of messaging exceeds threshold and/or number of cell changes per unit time exceeds threshold Realized by: Signalling RRC Messaging Connected Leashed to RRC Messaging Connected h ileashed SLIppOIL Rn this transition is not critical and is shown as not supported in the diagram.

If activity in RRC Messaging Connected_Leashed drops below a threshold then a transition to RRC Idle should be enacted. However, optionally the transition could he supported if frequency of messaging drops below a threshold and/or number of cell changes per unit time drops below a threshold.

RRC Messaging_Connected_Unleashed to RRQConnected Trigger: This transition could be triggered by the need to set up an IP pipe or possibly by a need to transfer NAS signalling Realized by. Signalling RRC Connected to RRC Messaging Connected_Unleashed Support for this LEUHSJ Lion is not cr heal and is shown as not supported in the diagram.

If a mobile terminal is currently cngaged in an SMS transfer or a NAS signalling exchange then the system should remain in IUtC_Connectcd state. If the system is in RRC Connected and all data transfers have ceased and/or there has been a period of inactivity then a transition to RRC_Idle is expected instead.

RRCMessaging_Connected_Leashed to RR C_Idle o Trigger: Inactivity tinter expires or all outstanding message transfer conversations have completed o Realized by: Signalling RRC Idle to RRCMessaging_Connected_Leashed ° It would not be essential to supporL Ibis transiliou (hence dotted line).

o Trigger: The transition might be triggered if an application was started for which it was a priori known that only a messaging bearer would be iuitially requiued and if it were additionally known that the frequency of messaging, frequency of cell change or link reliability requirement would be such that a leashed mobility management approach (handover or cell reselection with cell update) should be supported.

* Realized by: Signalling RRCMessaging_ConnectedjLeashed to RRC_Connected Trigger: This transition could be triggered by the need to set up an IP pipe or possibly by a need to transfer NAS signaling o Realized by: Signalling RRCconnecteci to REC Messaging Connected_ Leasltcd o Trigger: Support for this transition is non-essential. Whether or not the transition should be supported would depcl]d on whether there are efficiencies to be gained by working in RRMessaging_Connected_LeaShed mode (for example through use of MTC/messaging optimised PHY/MAC/RLC/PDCP).

o Realized by: Signalling RRC Connected to RRC Idle * Trigger: Inactivity timer expires o Realized by: Signalling RRC Idle to RRC Connected o Trigger: mobile terminal requires EPS bear-er (II' pipe) to be established or possibly required for the transfer of NAS signalling o Realized by: Signalling Note that transition between from/to eel) reselcetion and handover based mobility management within the RRC Messaging_Connected_Leashed state may be triggered when frequency of messaging exceeds/reduces below threshold and/or number of cell changes per unit time exceeds/reduces below a threshold An alternative arrangement for including the REf message in connected unleashed and leashed states is shown in Figure 22. Accordingly a transition between the states and sub states is performed internally within the RRC messaging connected state 280.

According to the present technique the mobile terminal and the base station to which it is attached may transition between the various states shown in Figures 20 dependent on the need to support functionality and whether for example only messaging needs to he supported or whether an I? pipe is required. Within the messaging connected state 280 and depending upon a relative numbcr of packets generated andlor the frequency of cell change, the mobile terminal and the base station may transition between the unleashed and leashed states, the leashed state being used for more frequently generated data packets or higher frequency of cell change than is the case for the unleashed state. Of course where no data is to be sent then the:mobile terminal transitions to the RRC idle state 282.

in a more simplified arrangement a mobile terminal and base station could form the messaging state shown in Figure 23 in which the terminal can only transition to the RRC messaging connected state 280 or the idle state 282 thus providing an even more simplified tepresentation of possible states.

An illustration of a difference between the communication of data packets which is supported for the RRC_MessagingConnected state and the RRC Connected slate is illustrated in Figure 24. As shown in Figure 24, for the RRCjdessaging_Connected state, application packets are communicated to/from thc mobile terminal 2200 via an eNB 2202 and MME 2210 fromlto the MTC-SC 2204, whereas for the RRc_Connectcd state data packets are communicated 2212 to/from the mobile terminal either via the eNB 2202, PDN_GW 2216 and SOW 2212 to/from IP PDN 2214 and/or via the control plane 2200 to/from the MTC-en A schematic block diagram summarising the relative states explained above with reference to Figures 20 to 24 is shown in Figure 25 in association with states corresponding to NAS signalling connections providing communications between the mobile terminal and the MME. In particular, a new ECM Messaging state is introduced; properties of the state include the following: Only transfer of SMS or NAS messages over the control plane is supported, no user plane is supported.

o The last known eNB address of the LB may be storcd and made available for routing of packets which arrive later on during the period while the MME is in this stale.

No SI bearer or tunnels are configured * An RRC Connection may not exist and any radio funclionality that does exist may be limited (eg no AS security, no handover configured) c Period in this state may be very short * State change from tOM_idle to tOM_Messaging_Connected at the MME may be triggered: Tniplicitly by the arrival of a packet within a message transfer transa.tion * State change from ECM_Messaging to ECM Idle may be triggered by: o Age of last update of eNB <> MM1i routing information exceeding some period o Completion of single message transfer, completion of outstanding message transfers within a message conversation and/or completion of all outstanding message conversations o Inactivity timer s The MME may need to page to find the UE's location if no sufficiently recent routing iiifomjation exists, or if a network initiated message transaction is new.

The DE may optionally be leashed' to the MME, specifically the UE could be configured via signalling to provide the MIIVITE with cell updates when the UE changes cell. The decision to invoke this signalling may be triggered by the quantity of paging messages per unit time exceeding some quantity and/or if the frequency of short message conversations becomes high.

o Stored knowledge of UE location may he inaccurate or more specifically out of date.

This may he dealt with by requinng that higher layers sucFi as NAS or PSM recover from any packet loss which results from the MME forwarding a packet to an eND under which the TIE is no longer camped. Alternatively the RAN could provide a mobility management solution to prevent packet loss if the MME uses its last lcnown cNB address for routing purposes, for example according to the methods described cat-her.

As indicated by the dotted lines in Figure 25, whilst the MME NAS is in ECM Messaging_Connected state the RRC state can be variously in RRC Idle or an RRC_Messaging_Connected state dependent on the radio solution adopted, arid as described previously. The ECM_Connected stale is most commonly associated with the RRC Connected state Routing information in the MME concerning which eNS the UE is camped under may be updated by a number of means: * Response to paging performed by the MME o Inclusion of routing information in any mobile originated packet/messsage that transits the MME * Through configuring the liE to send a cell update to the MME every time a cell change occurs By the eNB notifying the MME if a cell change occurs which may be possible if the RAN is in an RRC Messaging_Conneeted_Leashcd state.

Conclusion

Generally, the invention has been described in an LTF environment as the invention can be advantageously implemented in this environment, however the invention is not limited to zm LIE environment and may be implemented in any other suitable environment.

Various modifications can be made to examples of the present invention.

Embodiments of the present invention have been defined largely in terms of reduced capability terminals, however, it will be understood that any suitable terminal can transmit and receive short messages according to the present disclosure, including conventional terminals such as a personal phone.

Also, for the ease of illustration and in the interest of intelligibility, only one node for each element of the network has been represented and discussed. However, the skilled person Will understand that there may he more than one of each node. For example, the mobile network may comprise a plurality of eKE, of MME, of S-OW and/or of P-OW.

Various further acpeets and features of the present invention are defined in the appended claims. Various modifications may bc made to the embodiments described above without departing from the scope of the present invention. For example, embodiment of the present invention finds application with other types of mobile communications networks and is not limited to LTE.

Claims

<claim-text>CLAIMS1. A communications tenninal for communicating data packets to or from a mobile conununications network via a radio access interface, the mobile communications S network comprising a radio network part including a plurality of base stations for communicating data packets to or from the mobile communications tenninals via the radio access interface, and a core network part which is configured to communicate the data packets to destination addresses from the radio network part or to communicate the data packets to the radio network part front source addresses, the mobile communications network being conflgurcd to establish one or more communications bearers for communicating the data packets to or from the communications terminal via the radio network part and the core network part, each of the one or more communications hearers being established using context inFormation associated with one or more connections from the communications terminal to the destination addresses, or to the communications terminal from source addresses, wherein one of the communications terminal is configured to attach to one of the base stations of the mobile communications network, and when in an idle state, to communicate a short message data packet to the base station of the radio network part as a signalling message, the short message data packet including an indication of context information for use by the mobile communications network for communicating the short message data packet.</claim-text> <claim-text>2. A communications terminal as claimed in Claim 1, wherein the context information provided in the short message packet includes an identifier of the communications terminal, which was provided to the communications teniiinal by the mobile corn_municalions network, when [he mobile eoIJHhlwlieatious Lenuinal attached to [he base station of the mobile communications network.</claim-text> <claim-text>3. A communications terminal as claimed in Claim 1, wherein the identifier of the mobile communications terminal is a temporary international mobile subscriber identity number.</claim-text> <claim-text>4. A communications terminal as claimed in any preceding Claim, wherein the short message data packets includes a field identi'ing the short message data packet to the base station.</claim-text> <claim-text>5. A communications terminal as claimed in any of Claims 1 to 4, wherein tile communications terminal is configured to establish a radio bearer for communicating the short message data packet between the communications terminal and the base station, the radio bearer being removed after the short message data packet has been received by the base station.</claim-text> <claim-text>6. A communications terminal as claimed in Claim 5, wherein the radio bearer is established using prcdetennined context information, which includes at least one of power control level, modulation and encoding of the short message data packet for communicating the short message data packet from the communications terminal to the base station.</claim-text> <claim-text>7. A communications terminal as claimed in Claim 6, wherein the context information is predetermined for establishing the radio bearer between the communications terminal and the base station for communicating the short message data packet.</claim-text> <claim-text>8. A communications terminal as claimed in any preceding Claim, wherein the context information is sufficient to communicate the short message data packet from the base station to a mobihty manager of the core network part.</claim-text> <claim-text>9. A method of communicating a short message data packet from a communications terminal via a mobile communications network, the mobile communications network comprising a radio network part including a plurality of base stations for communicating data packets to or from the mobile communications terminals via a radio access interface, and a core network part which is configured to communicate the data packets to destination addresses from the radio network part or to communicate the data packets to the radio network part from source addresses, the method comprising establishing one or more communications bearers for communicating the data packets to or from the communications terminal via the radio network part and the core network part, each of the one or more conuinunications bearers being established using context information associated with one or more connections from the commurications terminal to the destination addresses, or to the conmiunications terminal from source addresses, wherein the establishing includes arranging for the communications terminal to attach to one of the base stations, S establishing a radio communications bearer for communicating the short message data packet from the communications terminal to the base station, and when in an idle state, communicating the short message data packet to the base station as a signalling message, the short message data packet including an indication of context infonnation for use by the mobile communications network for communicating the short message data packet via the core network.</claim-text> <claim-text>10. A signal representing a short message data packet including an indication of context information for use by a mobile communications network for communicating the short message data packet from a base station when received from a communications terminal in an idle mode as a signalling message.</claim-text> <claim-text>11. A communications terminal substantially as hereinbefore described with reference to the accompanying drawings.</claim-text> <claim-text>12. A method of communicating substantially as hereinbefore described with refrence to the accompanying drawings.</claim-text>