WO2013167160A1

WO2013167160A1 - Speeding up user equipment reachability after network element restart

Info

Publication number: WO2013167160A1
Application number: PCT/EP2012/058327
Authority: WO
Inventors: Giorgi Gulbani; Vesa Pauli Hellgren
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-05-07
Filing date: 2012-05-07
Publication date: 2013-11-14

Abstract

There are provided measures for speeding up UE reachability after network element restart. Such measures exemplarily comprise starting a timer when a network element is restarted, receiving a first packet, forming a second packet upon receipt of said first packet, if said timer is not expired, and transmitting the second packet, wherein said second packed comprises a predetermined mark.

Description

Title

Speeding up user equipment reachability after network element restart

Field

The present invention relates to speeding up user equipment (UE) reachability after restart of a network element, e.g. a packet data network gateway (P-GW, PDN-GW) or a gateway general packet radio service support node (GGSN). More specifically, the present invention exemplarily relates to measures (including methods, apparatuses, systems and computer program products) for realizing speeding up UE reachability after network element restart.

Background

The present specification generally relates to situations where a (controlling) network element, e.g. a P-GW (PDN-GW) or a GGSN, respectively, is restarted during normal operation.

In such situations, UEs assigned to the restarted network element but presently in idle state will experience, among others, following problems related to Mobile Terminated (MT) internet protocol multimedia subsystem (IMS) services, like voice over long term evolution (Voice over LTE, VoLTE). Those UEs become unreachable (from the internet), since their existence is not known anymore to the restarted network element. In case of a P-GW, or a GGSN, which connect the respective UEs via the involved universal terrestrial radio access network (UTRAN) and the core network (CN) to the internet, incoming connections from the internet can not be forwarded to the intended recipient. Since the restart of the (controlling) network element is not known to the UE itself, it assumes that it is still pageable and thus reachable. However, hundreds of thousands of UEs in idle state become unreachable for a very long time, unless for example the user of a UE brings the UE into connected state by chance, or if the periodic tracking area update (TAU) timer expires and network brings UEs into connected state.

If P-GW restarts and receives a downlink session initiation protocol (SIP) message for an UE in idle state earlier connected to the P-GW, while the packet data network (PDN) connection for the UE is not restored for example by the mobility management entity (MME) and the serving gateway (S-GW) of the considered network, the P-GW discards the incoming SIP message. As stated above, restoring the PDN connections may take quite long time (for example by chance or by TAU timer) and therefore the impacted UEs are unreachable for a quite long period of time, i.e. incoming SIP messages are discarded for a long period. The following approach, when restart of a P-GW occurred, is known according to 3GPP TS 23.007 (3^rd Generation Partnership Project, 3GPP):

When an S-GW detects that a peer P-GW has restarted (see clause 18 "GTP-C based restart procedures") it shall delete all PDN connection table data/mobility management (MM) bearer contexts associated with the peer node that restarted, as well as freeing any internal S-GW resources associated with those PDN connections. In addition, if the optional feature P-GW Restart Notification is supported by the S-GW and MME/S4-SGSN (serving GPRS support node) as specified in clause 8.83 in 3GPP TS 29.274, the S-GW shall initiate the cleanup of the hanging PDN connections associated with the S-GW and the restarted P-GW at the corresponding MMEs/S4-SGSNs by sending GPRS tunneling protocol version 2 (GTPv2) message(s) P-GW Restart Notification, with the control plane IP address of the restarted P-GW and the control plane IP address of the S-GW on the S1 1/S4 interface included. The S-GW may optionally perform other implementation specific actions such as messages to clear other external resources (e.g. policy control and charging (PCC) messages).

Upon receipt of this message comprising the control plane IP address of the restarted P- GW and the control plane IP address of the S-GW on the S1 1/S4 interface by the MME/S4-SGSN, the MME/S4 SGSN should delete all PDN connection table data/MM bearer contexts associated with the S-GW and the restarted P-GW as well as freeing any internal MME resources associated with those PDN connections. The MME may optionally perform other implementation specific actions such as to clear external resources (e.g. S1-MME messages to clear evolved node B (eNodeB, eNB) resources) or more advanced forms of restoration.

On the one hand, it is relied on the support of an optional feature, when S-GW sends a GTPv2 "PGW Restart Notification" message to MME/S4-SGSN and the MME/S4-SGSN sends a NAS message to the impacted UEs that the reactivation is required. On the other hand, these reactivations, however, may take an unacceptably long time, for the UEs, which may be intended to get IMS requests (e.g. SIP-lnvite messages from remote SIP peers) during that time.

Hence, according to the known behaviour, S-GW (as well as MME/S4-SGSN) deletes all contexts impacted by the restart of the P-GW (or GGSN).

However, even with the optional feature of a P-GW Restart Notification procedure, both S- GW and MME are deleting hundreds of thousands of contexts and MME would need to send hundreds of thousands of S1-MME or non-access stratum (NAS) messages. In order to avoid network failure, MME would need to restrain the amount of these messages per second, which in turn would result in quite a long time for informing all UEs assigned to the certain, failed and restarted, P-GW.

3GPP TR 23.857 specifies two alternative solutions for the P-GW restart: (1 ) When the MME/S4-SGSN itself detects the P-GW has restarted, the MME should release the PDN connections. If the UE has multiple PDN connections, the MME/S4- SGSN may send the release cause "reactivation required" to the UE. If the UE has only one PDN connections, the MME/S4-SGSN may send the release cause "explicit detach with re-attach required" to the UE. This alternative, however, is technically incomplete, because there is no standard way for MME/S4-SGSN to detect the P-GW restart and proprietary solutions are out of 3GPP scope.

(2) If the optional feature P-GW Restart Notification is supported by the S-GW and MME/S4-SGSN, the S-GW may also send a P-GW Restart Notification message to the MME or S4-SGSN if the S-GW detects that a peer P-GW has failed and not restarted. Also this alternative is technically incomplete, because for some reason it does not address P-GW restart case. As already mentioned above, even if this solution is extended to cover also -P-GW restart, it cannot resolve the above problem. Hence, the problem arises that an UE in idle mode is unreachable though assuming to be reachable. This state does not change before the UE is actively brought into connected state, for example by chance or if a TAU timer expires. Since at the time the P-GW restarts many UEs may be in idle state, many UEs may be unknowingly unreachable for a long period of time.

In particular, the problem arises for the MT-IMS services, like VoLTE. Since Restoring the PDN connections (by chance or expired timers) may take quite long time (more than 15- 30 minutes), the impacted UEs are unreachable for an unacceptably long period of time. Hence, there is a need to provide for speeding up UE reachability after a (controlling) network element (e.g. P-GW/GGSN) restart.

Summary Various exemplary embodiments of the present invention aim at addressing at least part of the above issues and/or problems and drawbacks.

Various aspects of exemplary embodiments of the present invention are set out in the appended claims.

According to an exemplary aspect of the present invention, there is provided a method comprising starting a timer when a network element is restarted, receiving a first packet, forming a second packet upon receipt of said first packet, if said timer is not expired, and transmitting the second packet, wherein said second packed comprises a predetermined mark.

According to variations of said exemplary aspect of the present invention said first packet comprises at least a first address information indicating an intended recipient, said method further comprising checking for connection information corresponding to said first address information, and said forming said second packet comprises adding said predetermined mark to said first packet, if said connection information is not available.

According to variations of said exemplary aspect of the present invention said first packet comprises a create session request or a create packet data protocol context request of a requesting terminal, said method further comprising allocating second address information to said requesting terminal, and said forming said second packet comprises generating said second packet comprising at least said second address information, if said timer is not expired, and adding said predetermined mark to said second packet, if said timer is not expired.

According to variations of said exemplary aspect of the present invention said first address information is an Internet Protocol address, and/or said second address information is an Internet Protocol address, and/or said second packet is a general packet radio service tunneling protocol data unit or a generic route encapsulation packet, and/or said predetermined mark is a tunnel endpoint identifier and/or generic route encapsulation key value set to 0, and/or said terminal is a user equipment, and/or said network element is a packet data network gateway or a gateway general packet radio service support node, and/or the method is performed on the packet data network gateway or gateway general packet radio service support node, and said timer is started when said packet data network gateway or gateway general packet radio service support node is restarted.

According to a further exemplary aspect of the present invention, there is provided a method comprising starting a timer when an information indicative of an executed restart of a network element is received, preserving binding information regarding one or more registered terminals, receiving a packet comprising address information, said packet being provided with a predetermined mark, searching for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and transmitting a re-attachment demand message comprising said address information, if said entry is found in said searching step.

According to variations of said exemplary aspect of the present invention said reattachment demand message further comprises information indicative of a re-attachment requirement. According to variations of said exemplary aspect of the present invention said preserving binding information is performed when said information indicative of said executed restart of the network element is received. According to variations of said exemplary aspect of the present invention said method further comprising transmitting a predetermined message indicative of said executed restart of said network element if said timer is expired.

According to variations of said exemplary aspect of the present invention said method further comprising prohibiting transmitting said predetermined message if said timer is not expired.

According to variations of said exemplary aspect of the present invention said method further comprising deleting said preserved binding information, if said timer is expired.

According to variations of said exemplary aspect of the present invention said preserving comprises copying at least one binding information per registered terminal, wherein said at least one binding information comprises at least one of a bearer identifier of a default bearer used by said terminal, a third address information assigned to said terminal, and an identifier of a control entity assigned to said terminal, and storing said at least one binding information per registered terminal.

According to variations of said exemplary aspect of the present invention said preserving comprises deleting all binding information except for at least one binding information of a predetermined bearer per registered terminal.

According to variations of said exemplary aspect of the present invention said information indicative of an executed restart of a network element is an incremented Restart Counter, and/or said network element is a serving gateway or a serving general packet radio service support node, and/or said re-attachment demand message is a Downlink Data

Notification message, and/or said predetermined message indicative of said executed restart is a packet data network gateway Restart Notification or a gateway general packet radio service support node restart notification, and/or said bearer identifier is an Evolved Packet System bearer Identifier of the default bearer for Internet Protocol Multimedia System signaling Access Point Name, and/or said third address information is an Internet Protocol address, and/or said Identifier of a control entity is a Fully Qualified Tunnel Endpoint Identifier for Control plane value, and/or said re-attachment demand message is a delete bearer request message, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

According to a further exemplary aspect of the present invention, there is provided a method comprising receiving a re-attachment demand message comprising address information and information indicative of a re-attachment requirement, transmitting a paging message using said address information, and transmitting a re-attachment force request using said address information.

According to variations of said exemplary aspect of the present invention said re- attachment demand message is a Downlink Data Notification message, and/or said address information is an Internet Protocol address, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

According to a further exemplary aspect of the present invention, there is provided an apparatus comprising a control module configured to start a timer when the apparatus is restarted, a connection controller configured to receive a first packet, to form a second packet upon receipt of said first packet, if said timer is not expired, and to transmit the second packet, wherein said second packed comprises a predetermined mark.

According to variations of said exemplary aspect of the present invention said first packet comprises at least a first address information indicating an intended recipient, said apparatus further comprising a checking module configured to check for connection information corresponding to said first address information, and related to said forming said second packet, said connection controller is further configured to add said predetermined mark to said first packet, if said connection information is not available.

According to variations of said exemplary aspect of the present invention said first packet comprises a create session request or a create packet data control context request of a requesting terminal, and said connection controller is further configured to allocate second address information to said requesting terminal, and related to said forming said second packet, said connection controller is further configured to generate said second packet comprising at least said second address information, if said timer is not expired, and to add said predetermined mark to said second packet, if said timer is not expired.

According to variations of said exemplary aspect of the present invention said first address information is an Internet Protocol address, and/or said second address information is an Internet Protocol address, and/or said second packet is a general packet radio service tunneling protocol data unit or a generic route encapsulation packet, and/or said predetermined mark is a tunnel endpoint identifier and/or generic route encapsulation key value set to 0, and/or said terminal is a user equipment, and/or said network element is a packet data network gateway or a gateway general packet radio service support node, and/or said apparatus is the packet data network gateway or gateway general packet radio service support node, and said timer is started when said packet data network gateway or gateway general packet radio service support node is restarted.

According to a further exemplary aspect of the present invention, there is provided an apparatus comprising a control module configured to start a timer when an information indicative of an executed restart of a network element is received, and to preserve binding information regarding one or more registered terminals, and a connection controller configured to receive a packet comprising address information, said packet being provided with a predetermined mark, wherein said control module is further configured to search for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and said connection controller is further configured to transmit a re-attachment demand message comprising said address information, if said entry is found.

According to variations of said exemplary aspect of the present invention said re- attachment demand message further comprises information indicative of a re-attachment requirement.

According to variations of said exemplary aspect of the present invention said control module is configured to preserve said binding information when said information indicative of said executed restart of the network element is received. According to variations of said exemplary aspect of the present invention the connection controller is further configured to transmit a predetermined message indicative of said executed restart of said network element if said timer is expired.

According to variations of said exemplary aspect of the present invention said connection controller is further configured to prohibit transmitting said predetermined message if said timer is not expired. According to variations of said exemplary aspect of the present invention said control module is further configured to delete said preserved binding information, if said timer is expired.

According to variations of said exemplary aspect of the present invention in relation to said preserving, said control module is configured to copy at least one binding information per registered terminal, wherein said at least one binding information comprises at least one of a bearer identifier of a default bearer used by said terminal, a third address information assigned to said terminal, and an identifier of a control entity assigned to said terminal, and to store said at least one binding information per registered terminal.

According to variations of said exemplary aspect of the present invention in relation to said preserving, said control module is configured to delete all binding information except for at least one binding information of a predetermined bearer per registered terminal. According to variations of said exemplary aspect of the present invention said information indicative of an executed restart of a network element is an incremented Restart Counter, and/or said network element is a serving gateway or a serving general packet radio service support node, and/or said re-attachment demand message is a Downlink Data Notification message, and/or said predetermined message indicative of said executed restart is a packet data network gateway Restart Notification or a gateway general packet radio service support node restart notification, and/or said bearer identifier is an Evolved Packet System bearer Identifier of the default bearer for Internet Protocol Multimedia System signaling Access Point Name, and/or said third address information is an Internet Protocol address, and/or said Identifier of a control entity is a Fully Qualified Tunnel Endpoint Identifier for Control plane value, and/or said re-attachment demand message is a delete bearer request message, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

According to a further exemplary aspect of the present invention, there is provided an apparatus comprising a connection controller configured to receive a re-attachment demand message comprising address information and information indicative of a reattachment requirement, to transmit a paging message using said address information, and to transmit a re-attachment force request using said address information.

According to variations of said exemplary aspect of the present invention said reattachment demand message is a Downlink Data Notification message, and/or said address information is an Internet Protocol address, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

According to a further exemplary aspect of the present invention, there is provided a system, comprising an apparatus according to the fourth aspect of the present invention, an apparatus according to the fifth aspect of the present invention, and an apparatus according to the sixth aspect of the present invention.

According to a further exemplary aspect of the present invention, there is provided a computer program product comprising computer-executable computer program code which, when the program is run on a computer, is configured to cause the computer to carry out the method according to any one of the method related aspects of the present invention. According to variations of said exemplary aspect of the present invention the computer program product comprises a computer-readable medium on which the computer- executable computer program code is stored, and/or wherein the program is directly loadable into an internal memory of the processor. According to a further exemplary aspect of the present invention, there is provided an apparatus comprising at least one processor and at least one memory comprising computer program code, wherein said at least one processor with the at least one memory and the computer program code is configured to cause the apparatus to perform starting a timer when a network element is restarted, receiving a first packet, forming a second packet upon receipt of said first packet, if said timer is not expired, and transmitting the second packet, wherein said second packed comprises a predetermined mark.

According to a further exemplary aspect of the present invention, there is provided an apparatus comprising at least one processor and at least one memory comprising computer program code, wherein said at least one processor with the at least one memory and the computer program code is configured to cause the apparatus to perform starting a timer when an information indicative of an executed restart of a network element is received, preserving binding information regarding one or more registered terminals, receiving a packet comprising address information, said packet being provided with a predetermined mark, searching for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and transmitting a re-attachment demand message comprising said address information, if said entry is found in said searching step.

According to a further exemplary aspect of the present invention, there is provided an apparatus comprising at least one processor and at least one memory comprising computer program code, wherein said at least one processor with the at least one memory and the computer program code is configured to cause the apparatus to perform receiving a re-attachment demand message comprising address information and information indicative of a re-attachment requirement, transmitting a paging message using said address information, and transmitting a re-attachment force request using said address information.

Any one of the above aspects enables an efficient restoring of reachability of UEs in case of restart of a (controlling) network element, like for example a P-GW or GGSN.

By way of exemplary embodiments of the present invention, there is provided speeding up UE reachability after P-GW/GGSN restart. More specifically, by way of exemplary embodiments of the present invention, there are provided measures and mechanisms for realizing speeding up UE reachability after P-GW/GGSN restart. It is shown that certain serious misoperations can occur upon P-GW failure with the procedures currently specified in 3GPP, e.g. a subscriber may not be able to receive any downlink data packets until other procedure (such as Service Request) makes the U E re- attach to the network.

The solution according to exemplary embodiments of the present invention may enable the UE to initiate the PDN Connection establishment or PDP Context Activation procedure with same Access Point Name (APN).

Thus, improvement is achieved by methods, apparatuses and computer program products enabling/realizing speeding up UE reachability after (controlling) network element (e.g. P- GW/GGSN) restart. In particular the improvement according to exemplary embodiments of the present invention may speed up UE reachability for those UEs, for which the restarted controlling network element (e.g. P-GW/GGSN) has received a SI P request.

Brief description of the drawings

In the following, the present invention will be described in greater detail by way of non- limiting examples with reference to the accompanying drawings, in which

Figure 1 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention,

Figure 2 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention, Figure 3 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention,

Figure 4 is a schematic diagram of a procedure according to exemplary embodiments of the present invention, Figure 5 is a schematic diagram of a procedure according to exemplary embodiments of the present invention,

Figure 6 is a schematic diagram of a procedure according to exemplary embodiments of the present invention,

Figure 7 is a block diagram alternatively illustrating exemplary apparatuses according to exemplary embodiments of the present invention, and Figure 8 shows a schematic diagram of an exemplary system environment comprising of exemplary apparatuses according to exemplary embodiments of the present invention.

Detailed description of drawings and embodiments of the present invention The present invention is described herein with reference to particular non-limiting examples and to what are presently considered to be conceivable embodiments of the present invention. A person skilled in the art will appreciate that the invention is by no means limited to these examples, and may be more broadly applied. It is to be noted that the following description of the present invention and its embodiments mainly refers to specifications being used as non-limiting examples for certain exemplary network configurations and deployments. Namely, the present invention and its embodiments are mainly described in relation to 3GPP specifications being used as non- limiting examples for certain exemplary network configurations and deployments. In particular, IMS communication is used as a non-limiting example for the applicability of thus described exemplary embodiments. As such, the description of exemplary embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way. Rather, any other communication or communication related system deployment, etc. may also be utilized as long as compliant with the features described herein.

By way of exemplary embodiments according to the present invention, speeding up reactivation of PDN connections, specifically for those UEs for which the restarted P-GW receives a SIP request message, can be achieved. If a UE had a PDN connection to a P- GW, which has restarted, and a remote device is after that trying to call this UE by sending SIP-lnvite, then the P-GW should inform S-GW and MME about the incoming SIP message for the given IP address of the UE. S-GW and MME can subsequently reactivate the PDN connection with the sought UE.

By means of exemplary embodiments of the present invention, the overall time for the considered UE to become reachable is reduced to a few minutes. This time is the sum of the following time intervals (as an overview):

- after the P-GW receives a SIP-lnvite (after restart of the P-GW) for a certain UE, the P-GW informs all concerned S-GWs about this,

- the S-GW assigned to the UE sends a Downlink Data Notification message to the respective MME/S4-SGSN,

- the MME/S4-SGSN pages the UE, and

- the UE re-attaches and establishes default bearer for SIP signalling.

After such procedure, the UE is ready, and the next SIP-lnvite can reach the UE.

Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are described using several variants and/or alternatives. It is generally noted that, according to certain needs and constraints, all of the described variants and/or alternatives may be provided alone or in any conceivable combination (also including combinations of individual features of the various variants and/or alternatives).

According to exemplary embodiments of the present invention, in general terms, there are provided measures and mechanisms for (enabling/realizing) speeding up UE reachability after network element restart.

The functionality described in the following may be implemented in P-GW or local mobility anchor (LMA), in S-GW or mobile access gateway (MAG), and in MME or any other (controlling) network element. However, the proposed functionality of the P-GW may also be implemented in a GGSN, and the proposed functionality of the S-GW and the MME may also be implemented in a Gn/Gp SGSN.

Figure 1 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention. As shown in Figure 1 , according to exemplary embodiments of the present invention, the apparatus is a network node 10 comprising a connection controller 1 1 and a control module 12. The control module 12 starts a timer when a network element is restarted. The timer may be common for the whole network node 10, that is, the timer may be a P-GW- wide global timer. The timer is started once the network node 10, i.e. the P-GW has restarted. During the period after restart defined by the timer, special behavior of the P- GW according to exemplary embodiments of the present invention is performed. Once this timer expires, the P-GW may stop executing below specified functionality, and returns to usual processing.

The connection controller 1 1 receives a first packet. Upon receiving said first packet and if the first timer is not expired, the connection controller 1 1 forms a second packet and transmits said second packet. That is, said forming and transmitting said second packet is triggered by the received first packet and takes place only if the first timer is not expired. The second packet is marked with a predetermined mark.

According to exemplary embodiments of the present invention, the first packet received by the connection controller comprises at least a first address information, that is, P-GW receives a downlink (DL) IP packet across SGi interface (between the P-GW and the internet) with a destination IP address (which is the UE's IP-address), e.g. 'A' which matches IMS APN.

The network node 10 may further comprise a checking module (not shown), which checks, when the timer is not expired, for connection information corresponding to the first address information. That is, it is searched for bearer context matching with the destination IP address.

If no connection information is available, i.e. if no matching bearer context is found, which may indicate that the PDN connection is not restored for this UE/IP address and the DL data belongs to the UE that may still be in idle state, the message may be forwarded to all S-GWs as for example an ordinary G-PDU (type value 255) with Tunnel End Point Identifier (TEID) value in the header set to 0, or an ordinary Generic Route Encapsulation (GRE) packet with GRE key value in the header set to 0. That is, in such case the connection controller may add a predetermined mark (TEID/GRE key value 0 in the header) to said first packet, if said connection information is not available and if said timer is not expired to thereby form the second packet. As a consequence, said second packet provided with said predetermined mark may be transmitted to the involved S-GWs. According to exemplary embodiments of the present invention, the message may be only forwarded if the destination IP address belongs to the IMS APN subnets, which are managed by the P-GW. Further, such message may be not forwarded if a message with the same destination IP address has already been forwarded previously. According to further exemplary embodiments of the present invention, the connection controller may transmit information indicative of an executed restart. That is, all involved S-GWs/MAGs may be informed about the executed restart once the restart is done by sending an incremented Restart Counter with respective GTP/proxy mobile internet protocol (PMIP) messages.

According to further exemplary embodiments of the present invention, if connection information is available, i.e. if matching bearer context is found, which may indicate that the PDN connection is already restored for this UE/IP address, the DL packet may be forwarded to the intended recipient via this new PDN connection, as usual. Hence, the connection controller may transmit, said downlink packet based on connection information, if said connection information are available and thus found by the checking module. In other words, If P-GW receives a downlink packet after a new PDN connection was already created in P-GW for this UE, and the restarted P-GW has already allocated IP address, e.g. 'A' (i.e. P-GW received Create Session Request from S-GW for IMS APN and have allocated this IP address 'A' to some UE), then the DL packet may be forwarded via this new PDN connection, as usual. Matching bearer context may be found, if the following happened.

In addition, if P-GW receives some request message from S-GW for IMS APN, which does not require allocating an IP address to the UE, then this indicates that the UE is in connected state, but does not know that the P-GW has restarted. In this case P-GW sends back a response message with GTPv2 Cause value 64 "Context not found". S-GW will handle this as usual and reject the respective request from MME/S4-SGSN. MME/S4- SGSN also will notify the UE that the PDN connection is not available anymore. Consequently, the UE will try to re-attach. According to still further exemplary embodiments of the present invention, the connection controller may receive a create session request or a create packet data control context request of a requesting terminal. That is, a Create Session Request (or create packet data control context request) is received from an involved S-GW for IMS APN, which in turn means that the respective UE may be changed into connection state and which requests IP address allocation for the UE. In such case, the connection controller may allocate a second address information to said requesting terminal (UE). However this second address may be similar to an address allocated to a UE connected to the network node 10 before it restarted, which may lead to an address conflict. Thus, if said timer is not expired, the connection controller may for forming the second packet generate a packet comprising at least said second address information and add said predetermined mark to said generated packet, if said timer is not expired. As a consequence, said generated packet provided with said predetermined mark is transmitted as said second packet, if said timer is not expired. Said generated packet may be then used to check if a potential address conflict exists and initiate counter measures if needed. In other words, an IP address (e.g. TV) may be allocated to some UE (and a ordinary Create Session Response may be transmitted), an empty G-PDU/GRE packet containing IP header with destination address 'A' may be created as T-PDU and the packet may be sent it to all other S-GWs with TEID/GRE key value in the header set to 0.

According to exemplary embodiments of the present invention, the apparatus 10 as shown in Figure 1 is operable as or at a network node, in particular as or at a P-GW or as or at a GGSN.

Figure 2 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention.

As shown in Figure 2, according to exemplary embodiments of the present invention, the apparatus is a network node 20 comprising a connection controller 21 and a control module 22. The control module 22 starts a timer when an information indicative of an executed restart of a network element is received. The timer may be common for the whole network node 20, that is, the timer may be a S-GW-wide global timer. The timer is started once a restart of a connected network node is detected, i.e. the connected P-GW has restarted. During the period after detection defined by the timer, special behavior of the S-GW according to exemplary embodiments of the present invention is performed. Once this timer expires, the S-GW may stop executing below specified functionality, and returns to usual processing. The control module further preserves binding information regarding registered terminals. Preferably, both is performed upon detection of a restart of a connected network node, e.g. a P-GW. In other words, once the network node 20, e.g. S-GW, detects the P-GW restart, the S-GW may preserve binding information, e.g. for only one bearer per impacted UE which is connected to IMS APN, from all impacted bearer contexts. After such preserving, the network node 20, i.e. the S-GW, may delete all impacted contexts. After this deletion, S-GW may have binding info for only one bearer per UE, which is connected to IMS APN. That is, S-GW may delete all info about other bearers.

The connection controller further receives a packet comprising address information. Said packet may be a downlink packet and may be provided with a predetermined mark. In other words, a G-PDU packet with type value 255 and TEID value set to 0 (predetermined mark) or a GRE packet with GRE key value set to 0 (predetermined mark) in the header may be received which may comprise an IP address of a sought UE.

In case the received packet is a packet transmitted e.g. from a P-GW according to exemplary embodiments as described above and is formed by said P-GW by adding a predetermined mark to a first packet comprising at least a first address information indicating an intended recipient, the address information comprised in said received packet may indicate a intended recipient. If the S-GW timer is not expired, the control module 22, upon receiving such packet with

TEID/GRE key value set to 0 in the header, may search for an entry in the preserved binding information corresponding to said address information. In other words, the control module may look up UEs IP address in the preserved database. Before looking up, the control module may initially perform usual error handling on the received, special (marked) G-PDU packet.

If the lookup is successful, that is if such entry is found, the connection controller 21 may transmit a re-attachment demand message comprising the address information. The reattachment demand message may further comprise information indicative of a re- attachment requirement. In other words, if a match is found in the preserved database, ordinary Downlink Data Notification message may be sent to the MME/S4-SGSN with a new Cause value, which may indicate that UE shall re-attach, e.g. "UE re-attach is required". The message may need to contain only EBI and the new Cause. According to exemplary embodiments of the present invention, the connection controller 22 may receive information indicative of an executed restart. Such information may be a received incremented Restart Counter transmitted by, e.g. a restarted P-GW, packed in a respective GTP/PMIP message, and may be indicated to the control module 22. As shown above, the control module starts the S-GW timer, upon receiving of said information indicative of said executed restart.

According to exemplary embodiments of the present invention, if the timer is expired, the connection controller 21 may transmit a predetermined message indicative of said executed restart of a connected network node, i.e. the P-GW. As a result, S-GW may inform MME/S4-SGSN about the executed restart of the P-GW by sending an optional P- GW Restart Notification message to clean up the hanging contexts in MME/S4-SGSN. In order to make this step transparent to MME/S4-SGSN, the optional PGW Restart Notification message may be not sent to MME/S4-SGSN while S-GW timer is running. So, MME/S4-SGSN will keep all bearers for all idle state UEs, but may delete them once S- GW timer expires, i.e. once the P-GW Restart Notification message is transmitted.

Such transmission may be prohibited as long as the timer is not expired.

According to further exemplary embodiments of the present invention, the control module 22 may delete the preserved binding information upon expiration of the timer, i.e. of the S-

GW timer.

According to still further exemplary embodiments of the present invention, the connection controller 21 may transmit a create session request comprising an identifier indicative of a requesting terminal. That is, a Create Session Request may be transmitted to the P-GW for IMS APN, which in turn means that the respective UE corresponding to the identifier changed into connection state.

According to still further exemplary embodiments of the present invention, when preserving, the control module 22 may copy at least one binding information per registered terminal, wherein said binding information may comprise a bearer ID of a default bearer used by said terminal, a third address information assigned to said terminal, and an ID of a control entity assigned to said terminal, and may store said one binding information per registered terminal. In other words, the following binding information for e.g. only one bearer per UE, which is connected to IMS APN may be copied and stored:

(a) EBI of the default bearer for IMS signalling APN;

(b) UEs IP address; and

(c) MME/SGSNs F-TEID-C value, which is used for this UE (IP address). Alternatively, when preserving, the control module 22 may delete all binding information except for at least one binding information of a predetermined bearer per registered terminal. In other words, the S-GW may preserve one bearer context, which is suitable for IMS signalling. The criteria for determining such context is operator specific (e.g. operator may specify that a bearers with quality of service class identifier (QoS class identifier, QCI)=5 shall be preserved.

According to exemplary embodiments of the present invention, the re-attachment demand message may be or may contain a Delete Bearer Request and/or a newly defined request suitable to trigger the re-attachment of the UE.

Figure 3 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention.

As shown in Figure 3, according to exemplary embodiments of the present invention, the apparatus is a network node 30 comprising a connection controller 31 . The connection controller may receive a re-attachment demand message comprising address information and information indicative of a re-attachment requirement. In other words, an ordinary Downlink Data Notification message may be received from an involved S-GW with a new Cause value, which may indicate that a UE (identified by for example the comprised address information) may re-attach, e.g. "UE re-attach is required". Preferably, the message may contain only EBI and the new Cause. Hence, the network node 30, which may be a MME/S4-SGSN, is able to comprehend the new Cause value (which indicates that the UE shall re-attach) in Downlink Data Notification message. In case such re-attachment demand message is received, the connection controller 31 may transmit a paging message using the address information, and may transmit a reattachment force request using said address information. In other words, in such case the UE may be paged as usual but also forced to re-attach.

Subsequently, the UE may re-attach to the network and may become thus reachable from the internet again.

In the following, either the previously attached MME/S4-SGSN (re-attach to the same node) or the newly attached MME/S4-SGSN (attach to a new node) may send a Delete Session Request to the S-GW. Further, according to present functionality the receiving S- GW may forward the message to other, healthy (not restarted) P-GWs, if UE had multiple PDN connections. According to exemplary embodiments of the present invention, the re-attachment demand message may be or may contain a Delete Bearer Request and/or a newly defined request suitable to trigger the re-attachment of the UE.

Further, the connection controller 31 may receive a predetermined message indicative of an executed restart. Such predetermined message may be a P-GW Restart Notification received from a connected S-GW and indicating that an involved P-GW is restarted.

In such case, the connection controller 31 may delete binding information regarding registered terminals, i.e. hanging contexts are cleaned up in such network node 30, e.g. MME/S4-SGSN. If the UE has multiple PDN connections, the MME/S4-SGSN may send the release Cause "reactivation required" to the UE. If the UE has only one PDN connection, the MME/S4-SGSN may send the release Cause "explicit detach with reattach required" to the UE. Figure 4 is a schematic diagram of a procedure according to exemplary embodiments of the present invention.

As shown in Figure 4, a procedure according to exemplary embodiments of the present invention may comprise an operation of starting (S41 ) a timer when a network element is restarted, an operation of receiving (S42) a first packet, an operation of forming (S43) a second packet, and an operation of transmitting (S44) said second packet, wherein said second packet comprises a predetermined mark.

According to a variation of the procedure shown in Figure 4, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention further comprises an operation of transmitting information indicative of an executed restart. According to a variation of the procedure shown in Figure 4, exemplary additional operations and modifications are given, which are inherently independent from each other as such. According to such variation, said first packet may comprise a first address information indicating an intended recipient. In addition, an exemplary method according to exemplary embodiments of the present invention further comprises an operation of checking for connection information corresponding to said first address information. Further, according to such variation, a modification of said forming operation may comprise an operation of adding said predetermined mark to said first packet, if said connection information is not available. According to a variation of the procedure shown in Figure 4, exemplary additional operations and modifications are given, which are inherently independent from each other as such. According to such variation, said first packet comprises a create session request or a create packet data protocol context request of a requesting terminal. In addition, an exemplary method according to exemplary embodiments of the present invention further comprises an operation of allocating second address information to said requesting terminal, . Further, according to such variation, a modification of said forming operation may comprise an operation of generating said second packet comprising at least said second address information, if said timer is not expired and an operation of adding said predetermined mark to said second packet, if said timer is not expired.

According to a variation of the procedure shown in Figure 4, said first address information is an Internet Protocol (I P) address, said second address information is an Internet Protocol (I P) address, said second packet is a general packet radio service tunneling protocol data unit (G-PDU) or a generic route encapsulation (GRE) packet, said predetermined mark is a tunnel endpoint identifier (TEI D) and/or generic route encapsulation (GRE) key value set to 0, said terminal is a user equipment (UE), or said network element is a packet data network gateway (P-GW) or a gateway general packet radio service support node (GGSN), the method is performed on the packet data network gateway (P-GW) or gateway general packet radio service support node (GGSN), and said timer is started when said packet data network gateway (P-GW) or gateway general packet radio service support node (GGSN) is restarted.

Figure 5 is a schematic diagram of a procedure according to exemplary embodiments of the present invention.

As shown in Figure 5, a procedure according to exemplary embodiments of the present invention comprises an operation of starting (S51 ) a timer when an information indicative of an executed restart of a network element is received, an operation of preserving (S52) binding information regarding one or more registered terminals, an operation of receiving (S53) a packet comprising address information, said packet being provided with a predetermined mark, an operation of searching (S54) for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and an operation of transmitting (S55) a re-attachment demand message comprising said address information, if said entry is found in said searching operation.

In some cases, said address information comprised in said packet received in step S53 may indicate an intended recipient.

According to a variation of the procedure shown in Figure 5, exemplary modifications are given, which are inherently independent from each other as such. According to such variation, said re-attachment demand message may further comprise information indicative of a re-attachment requirement.

According to a further variation, said preserving binding information is performed when said information indicative of said executed restart of the network element is received.

According to a variation of the procedure shown in Figure 5, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention may further comprise an operation of transmitting a predetermined message indicative of said executed restart of said network element if said timer is expired.

According to a variation of the procedure shown in Figure 5, exemplary details of the preserving operation are given, which are inherently independent from each other as such.

Such exemplary preserving operation according to exemplary embodiments of the present invention comprises an operation of copying at least one binding information per registered terminal, wherein said binding information comprises at least one of a bearer identifier (ID) of a default bearer used by said terminal, a third address information assigned to said terminal, and an identifier (ID) of a control entity assigned to said terminal, and an operation of storing said one binding information per registered terminal. Alternatively, such exemplary preserving operation according to exemplary embodiments of the present invention may comprise an operation of deleting all binding information except for at least one binding information of a predetermined bearer per registered terminal. According to a variation of the procedure shown in Figure 5, said information indicative of an executed restart of a network element is an incremented Restart Counter, said network element is a serving gateway (S-GW) or a serving general packet radio service support node (SGSN), said re-attachment demand message is a Downlink Data Notification message, said predetermined message indicative of said executed restart is a packet data network gateway (P-GW) Restart Notification or a gateway general packet radio service support node (GGSN) restart notification, said bearer identifier is an Evolved Packet System bearer Identifier (EBI) of the default bearer for Internet Protocol Multimedia System (IMS) signaling Access Point Name (APN), said third address information is an Internet Protocol (IP) address, said Identifier of a control entity is a Fully Qualified Tunnel Endpoint Identifier for Control plane (F-TEID-C) value, said re-attachment demand message is a delete bearer request message, said information indicative of a reattachment requirement is a general packet radio service tunneling protocol version 2 (GTPv2) cause value indicating that a user equipment (UE) re-attach is required, or said terminal is a user equipment (UE). Figure 6 is a schematic diagram of a procedure according to exemplary embodiments of the present invention.

As shown in Figure 6, a procedure according to exemplary embodiments of the present invention comprises an operation of receiving (61 ) a re-attachment demand message comprising address information and information indicative of a re-attachment requirement, an operation of transmitting (62) a paging message using said address information, and an operation of transmitting (63) a re-attachment force request using said address information.

According to a variation of the procedure shown in Figure 6, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention further comprises an operation of receiving a predetermined message indicative of an executed restart, and an operation of deleting binding information regarding registered terminals.

According to a variation of the procedure shown in Figure 5, said re-attachment demand message is a Downlink Data Notification message, said address information is an Internet Protocol (IP) address, said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 (GTPv2) cause value indicating that a user equipment (UE) re-attach is required, or said terminal is a user equipment (UE). Figure 8 shows a schematic diagram of an exemplary system environment comprising of exemplary apparatuses according to exemplary embodiments of the present invention.

A system according to exemplary embodiments comprises a network node 10, a network node 20 and a network node 30. More specifically, a system according to exemplary embodiments comprises a P-GW, a S-GW and a MME.

A system according to further exemplary embodiments (not shown) comprises a GGSN and a SGSN, wherein the SGSN combines the functionality of network node 20 and network node 30. In such system, corresponding functionality as above described by means of a P-GW, an S-GW and a MME may be implemented by the network elements GGSN and SGSN. In the following, an overview of such implementation is given: If GGSN has restarted, the GGSN may start a new (GGSN-) timer, which is common for the whole GGSN. During running of such timer, special behavior of the GGSN according to exemplary embodiments of the present invention is performed. Once this timer expires, the GGSN may stop executing below specified functionality, and returns to usual processing.

GGSN may inform all Gn/Gp SGSNs about its restart by sending incremented Restart Counter with respective GTP/PMIP messages.

In the usual behaviour, once a Gn/Gp SGSN detects the GGSN restart, the Gn/Gp SGSN deletes all impacted contexts. According to exemplary embodiments of the present invention, the Gn/Gp SGSN may preserve at least some contexts and starts a new (SGSN-) timer, which is common for the whole Gn/Gp SGSN. During running of such timer, special behavior of the Gn/Gp SGSN according to exemplary embodiments of the present invention is performed. Once this timer expires, the Gn/Gp SGSN may delete all preserved contexts, stops executing below specified functionality, and returns to usual processing.

If the (GGSN-) timer is still running, then the following events may take place for the GGSN:

- if GGSN receives a downlink (DL) IP packet across Gi interface with a destination

IP address (this is UE's IP address), e.g. TV, which matches IMS APN and if GGSN cannot find matching bearer context, then this indicates that the PDN/PDP connection was not restored for this UE/IP address and the DL data belongs to the UE that is still in idle state. In this case, GGSN shall forward the message to all Gn/Gp SGSNs as an ordinary G-PDU (type value 255), but with TEID key value in the header set to 0;

- if GGSN receives Create PDP Context Request from Gn/Gp SGSN for IMS APN, which requests IP address allocation for the UE (i.e. the message shall contain End User Address IE), then GGSN allocates an IP address, e.g. 'A' to the UE and sends back an ordinary Create PDP Context Response, and, according to exemplary embodiments of the present invention, additionally creates an empty G- PDU packet containing IP header with destination address 'A' as T-PDU and sends it to all other Gn/Gp SGSNs with TEID key value in the header set to 0; if GGSN receives some request message from Gn/Gp SGSN for IMS APN, which does not require allocating an IP address to the UE, then this indicates that the UE is in connected state, but does not know that the GGSN has restarted. In this case GGSN sends back a response message with GTPvl Cause value 210 "Context not found". SGSN will handle this as usual and will notify the UE that the PDP connection is not available anymore;

- if GGSN receives a downlink packet after a new PDN/PDP connection was already created in GGSN for this UE IP address 'A' (i.e. GGSN received Create PDP Context Request from Gn/Gp SGSN for IMS APN and have allocated this IP address 'A' to some UE), then the DL packet is forwarded via this new PDN/PDP connection, as usual.

If, in Gn/Gp SGSN, the (SGSN-) timer is still running and the received G-PDU packet contains TEID key value in the header set to 0, then, according to exemplary embodiments of the present invention:

- the GTP-U function in Gn/Gp SGSN may perform usual error handling for such special G-PDU packet;

- the GTP-U function in Gn/Gp SGSN may inform the GTP-C function that a special G-PDU packet was received from GGSN;

- the Gn/Gp SGSN (GTP-C function) may lookup UE's IP address in the preserved database;

- if Gn/Gp SGSN finds a match in the preserved database, the MME/S4-SGSN may page the UE, as usual, but forces it to re-attach (see TS 24.008 and TS 24.301 ).

Consequently, the UE re-attaches and becomes reachable. Thereby, either the old SGSN (re-attach to the same node) or the new SGSN (attach to a new node) will send Delete PDP Context Request to the GGSN.

In an exemplary network compound implementing LTE technology, a system according to exemplary embodiments of the present invention is arranged in an evolved packet core (EPC). A P-GW may connect the system with the IP internet. S-GW and MME may connect the system with a terminal like a UE 100 via an evolved node B (eNB) 200, which may be arranged in an evolved universal terrestrial radio access network (eUTRAN).

In a system according to exemplary embodiments of the present invention, the network node 10 is connected to the network node 20, and the network node 20 is connected to the network node 30.

The above-described procedures and functions may be implemented by respective functional elements, processors, or the like, as described below.

In the foregoing exemplary description of the network entity, only the units that are relevant for understanding the principles of the invention have been described using functional blocks. The network entity may comprise further units that are necessary for its respective operation. However, a description of these units is omitted in this specification. The arrangement of the functional blocks of the devices is not construed to limit the invention, and the functions may be performed by one block or further split into sub- blocks.

When in the foregoing description it is stated that the apparatus, i.e. network entity (or some other means) is configured to perform some function, this is to be construed to be equivalent to a description stating that a (i.e. at least one) processor or corresponding circuitry, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be equivalently implementable by specifically configured circuitry or means for performing the respective function (i.e. the expression "unit configured to" is construed to be equivalent to an expression such as "means for").

Figure 7 is a block diagram alternatively illustrating exemplary apparatuses according to exemplary embodiments of the present invention.

In Figure 7, an alternative illustration of apparatuses according to exemplary embodiments of the present invention is depicted. As indicated in Figure 7, according to exemplary embodiments of the present invention, the network node (P-GW) 10' comprises a processor 15, a memory 16 and an interface 17, which are connected by a bus 18 or the like. The processor 15, and/or the interface 17 respectively may also comprise a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 17 may comprise a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device(s), respectively. The interface 17 is generally configured to communicate with at least one other apparatus, i.e. the interface thereof.

The memory 16 may store respective programs assumed to comprise program instructions or computer program code that, when executed by the respective processor, enables the respective electronic device or apparatus to operate in accordance with the exemplary embodiments of the present invention.

Further, the network node (S-GW) 20' comprises a processor 25, a memory 26 and an interface 27, which are connected by a bus 28 or the like.

The processor 25 and/or the interface 27 may also comprise a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 27 may comprise a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device(s), respectively. The interface 27 may be generally configured to communicate with at least one other apparatus, i.e. the interface thereof.

The memory 26 may store respective programs assumed to comprise program instructions or computer program code that, when executed by the respective processor, enables the respective electronic device or apparatus to operate in accordance with the exemplary embodiments of the present invention.

Further, the network node (MME) 30' comprises a processor 35, a memory 36 and an interface 37, which are connected by a bus 38 or the like.

The processor 35 and/or the interface 37 may also comprise a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 37 may comprise a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device(s), respectively. The interface 37 may be generally configured to communicate with at least one other apparatus, i.e. the interface thereof. The memory 36 may store respective programs assumed to comprise program instructions or computer program code that, when executed by the respective processor, enables the respective electronic device or apparatus to operate in accordance with the exemplary embodiments of the present invention.

The apparatuses 10', 20' and 30' may, in a system according to exemplary embodiments of the present invention, be connected via links 40 and 41 , respectively. In general terms, the respective devices/apparatuses (and/or parts thereof) may represent means for performing respective operations and/or exhibiting respective functionalities, and/or the respective devices (and/or parts thereof) may have functions for performing respective operations and/or exhibiting respective functionalities. When in the subsequent description it is stated that the processor (or some other means) is configured to perform some function, this is to be construed to be equivalent to a description stating that at least one processor, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be equivalently implementable by specifically configured means for performing the respective function (i.e. the expression "processor configured to [cause the apparatus to] perform xxx-ing" is construed to be equivalent to an expression such as "means for xxx-ing"). According to exemplary embodiments of the present invention, an apparatus representing the network node (P-GW) 10' comprises at least one processor 15, at least one memory 16 comprising computer program code, and at least one interface 17 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 15, with the at least one memory 16 and the computer program code) may be configured to cause the apparatus to perform starting a timer (thus the apparatus comprising corresponding means for starting), to perform receiving a first packet (thus the apparatus comprising corresponding means for receiving), to perform forming a second packet (thus the apparatus comprising corresponding means for forming), and to perform transmitting said second packet, wherein said second packet comprises a predetermined mark (thus the apparatus comprising corresponding means for transmitting). According to exemplary embodiments of the present invention, an apparatus representing the network node (S-GW) 20' comprises at least one processor 25, at least one memory 26 comprising computer program code, and at least one interface 27 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 25, with the at least one memory 26 and the computer program code) may be configured to cause the apparatus to perform starting a timer (thus the apparatus comprising corresponding means for starting), to perform preserving binding information regarding registered terminals (thus the apparatus comprising corresponding means for preserving), to perform receiving a packet comprising address information indicating an intended recipient, said downlink packet being provided with a predetermined mark (thus the apparatus comprising corresponding means for receiving), to perform searching for an entry in said preserved binding information corresponding to said address information, if said timer is not expired (thus the apparatus comprising corresponding means for searching), and to perform transmitting a re-attachment demand message comprising said address information, if said entry is found in said searching (thus the apparatus comprising corresponding means for transmitting).

According to exemplary embodiments of the present invention, an apparatus representing the network node (MME) 30' comprises at least one processor 35, at least one memory 36 comprising computer program code, and at least one interface 37 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 35, with the at least one memory 36 and the computer program code) may be configured to cause the apparatus to perform receiving a re-attachment demand message comprising address information and information indicative of a re-attachment requirement (thus the apparatus comprising corresponding means for receiving), to perform transmitting a paging message using said address information (thus the apparatus comprising corresponding means for transmitting), and to perform transmitting a reattachment force request using said address information. For further details regarding the operability/functionality of the individual apparatuses 10

(10'), 20 (20') and 30 (30'), reference is made to the above description in connection with any one of Figures 1 to 6, respectively.

For the purpose of the present invention as described herein above, it should be noted that - method steps likely to be implemented as software code portions and being run using a processor at a network server or network entity (as examples of devices, apparatuses and/or modules thereof, or as examples of entities comprising apparatuses and/or modules therefore), are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

- generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the embodiments and its modification in terms of the functionality implemented;

- method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module(s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field- programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

- devices, units or means (e.g. the above-defined network entity or network register, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus like the user equipment and the network entity /network register may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example. In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person.

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or code means/portions or embodied in a signal or in a chip, potentially during processing thereof.

The present invention also covers any conceivable combination of method steps and operations described above, and any conceivable combination of nodes, apparatuses, modules or elements described above, as long as the above-described concepts of methodology and structural arrangement are applicable.

In view of the above, there are provided measures for speeding up UE reachability after network element restart. Such measures exemplarily comprise starting a timer when a network element is restarted, receiving a first packet, forming a second packet upon receipt of said first packet, if said timer is not expired, and transmitting the second packet, wherein said second packed comprises a predetermined mark.

Even though the invention is described above with reference to the examples according to the accompanying drawings, it is to be understood that the invention is not restricted thereto. Rather, it is apparent to those skilled in the art that the present invention can be modified in many ways without departing from the scope of the inventive idea as disclosed herein.

List of acronyms and abbreviations

3GPP 3^rd Generation Partnership Project

APN Access Point Name

CN core network

DL downlink

EBI EPS bearer ID, Evolved Packet System bearer Identifier

eNB eNodeB, evolved node B

EPC evolved packet core

eUTRAN evolved universal terrestrial radio access network

F-TEID-C Fully Qualified Tunnel Endpoint Identifier for Control plane

GGSN gateway GPRS support node, gateway general packet radio service

support node

G-PDU GPRS tunneling protocol data unit, general packet radio service tunneling protocol data unit

GRE Generic Route Encapsulation

GTPv2 GPRS tunneling protocol version 1

GTPv2 GPRS tunneling protocol version 2

IMS internet protocol multimedia subsystem

IP internet protocol

LMA local mobility anchor

MAG mobile access gateway

MM mobility management

MME mobility management entity

MT Mobile Terminated NAS non-access stratum

PCC policy control and charging

PDN packet data network

PDU Protocol Data Unit

P-GW PDN-GW, packet data network gateway

PMIP proxy mobile internet protocol

QCI QoS class identifier, quality of service class identifier

SGSN serving GPRS support node

S-GW serving gateway

SIP session initiation protocol

TAU tracking area update

TEID Tunnel Endpoint Identifier

UE user equipments

UTRAN universal terrestrial radio access network

VoLTE Voice over LTE, voice over long term evolution

Claims

1. A method comprising starting a timer when a network element is restarted, receiving a first packet, forming a second packet upon receipt of said first packet, if said timer is not expired, and transmitting the second packet, wherein said second packed comprises a predetermined mark.

2. The method according to claim 1 , wherein said first packet comprises at least a first address information indicating an intended recipient, said method further comprising checking for connection information corresponding to said first address information, and said forming said second packet comprises adding said predetermined mark to said first packet, if said connection information is not available.

3. The method according to claim 1 , wherein said first packet comprises a create session request or a create packet data protocol context request of a requesting terminal, said method further comprising allocating second address information to said requesting terminal, and said forming said second packet comprises generating said second packet comprising at least said second address information, if said timer is not expired, and adding said predetermined mark to said second packet, if said timer is not expired.

4. The method according to any of claims 1 to 3, wherein said first address information is an Internet Protocol address, and/or said second address information is an Internet Protocol address, and/or said second packet is a general packet radio service tunneling protocol data unit or a generic route encapsulation packet, and/or said predetermined mark is a tunnel endpoint identifier and/or generic route encapsulation key value set to 0, and/or said terminal is a user equipment, and/or said network element is a packet data network gateway or a gateway general packet radio service support node, and/or the method is performed on the packet data network gateway or gateway general packet radio service support node, and said timer is started when said packet data network gateway or gateway general packet radio service support node is restarted.

5. A method comprising starting a timer when an information indicative of an executed restart of a network element is received, preserving binding information regarding one or more registered terminals, receiving a packet comprising address information, said packet being provided with a predetermined mark, searching for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and transmitting a re-attachment demand message comprising said address information, if said entry is found in said searching step.

6. The method according to claim 5, wherein said re-attachment demand message further comprises information indicative of a re-attachment requirement.

7. The method according to claim 5 or 6, wherein said preserving binding information is performed when said information indicative of said executed restart of the network element is received.

8. The method according to any of claims 5 to 7, further comprising transmitting a predetermined message indicative of said executed restart of said network element if said timer is expired.

9. The method according to claim 8, further comprising prohibiting transmitting said predetermined message if said timer is not expired.

10. The method according to any of claims 5 to 9, further comprising deleting said preserved binding information, if said timer is expired.

1 1 . The method according to any of claims 5 to 10, wherein said preserving comprises copying at least one binding information per registered terminal, wherein said at least one binding information comprises at least one of a bearer identifier of a default bearer used by said terminal, a third address information assigned to said terminal, and an identifier of a control entity assigned to said terminal, and storing said at least one binding information per registered terminal.

12. The method according to any of claims 5 to 10, wherein said preserving comprises deleting all binding information except for at least one binding information of a predetermined bearer per registered terminal.

13. The method according to any of claims 5 to 12, wherein said information indicative of an executed restart of a network element is an incremented Restart Counter, and/or said network element is a serving gateway or a serving general packet radio service support node, and/or said re-attachment demand message is a Downlink Data Notification message, and/or said predetermined message indicative of said executed restart is a packet data network gateway Restart Notification or a gateway general packet radio service support node restart notification, and/or said bearer identifier is an Evolved Packet System bearer Identifier of the default bearer for Internet Protocol Multimedia System signaling Access Point Name, and/or said third address information is an Internet Protocol address, and/or said Identifier of a control entity is a Fully Qualified Tunnel Endpoint Identifier for Control plane value, and/or said re-attachment demand message is a delete bearer request message, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

14. A method comprising receiving a re-attachment demand message comprising address information and information indicative of a re-attachment requirement, transmitting a paging message using said address information, and transmitting a re-attachment force request using said address information.

15. The method according to claim 14, wherein said re-attachment demand message is a Downlink Data Notification message, and/or said address information is an Internet Protocol address, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment reattach is required, and/or said terminal is a user equipment.

16. An apparatus comprising a control module configured to start a timer when the apparatus is restarted, a connection controller configured to receive a first packet, to form a second packet upon receipt of said first packet, if said timer is not expired, and to transmit the second packet, wherein said second packed comprises a predetermined mark.

17. The apparatus according to claim 16, wherein said first packet comprises at least a first address information indicating an intended recipient, said apparatus further comprising a checking module configured to check for connection information corresponding to said first address information, and related to said forming said second packet, said connection controller is further configured to add said predetermined mark to said first packet, if said connection information is not available.

18. The apparatus according to claim 16, wherein said first packet comprises a create session request or a create packet data control context request of a requesting terminal, and said connection controller is further configured to allocate second address information to said requesting terminal, and related to said forming said second packet, said connection controller is further configured to generate said second packet comprising at least said second address information, if said timer is not expired, and to add said predetermined mark to said second packet, if said timer is not expired.

19. The apparatus according to any of claims 16 to 18, wherein said first address information is an Internet Protocol address, and/or said second address information is an Internet Protocol address, and/or said second packet is a general packet radio service tunneling protocol data unit or a generic route encapsulation packet, and/or said predetermined mark is a tunnel endpoint identifier and/or generic route encapsulation key value set to 0, and/or said terminal is a user equipment, and/or said network element is a packet data network gateway or a gateway general packet radio service support node, and/or said apparatus is the packet data network gateway or gateway general packet radio service support node, and said timer is started when said packet data network gateway or gateway general packet radio service support node is restarted.

20. An apparatus comprising a control module configured to start a timer when an information indicative of an executed restart of a network element is received, and to preserve binding information regarding one or more registered terminals, and a connection controller configured to receive a packet comprising address information, said packet being provided with a predetermined mark, wherein said control module is further configured to search for an entry in said preserved binding information corresponding to said address information, if said timer is not expired, and said connection controller is further configured to transmit a re-attachment demand message comprising said address information, if said entry is found.

21 . The apparatus according to claim 20, wherein said re-attachment demand message further comprises information indicative of a re-attachment requirement.

22. The apparatus according to claim 20 or 21 , wherein said control module is configured to preserve said binding information when said information indicative of said executed restart of the network element is received.

23. The apparatus according to any of claims 20 to 22, wherein the connection controller is further configured to transmit a predetermined message indicative of said executed restart of said network element if said timer is expired.

24. The apparatus according to claim 23, wherein said connection controller is further configured to prohibit transmitting said predetermined message if said timer is not expired.

25. The method according to any of claims 20 to 24, wherein said control module is further configured to delete said preserved binding information, if said timer is expired.

26. The apparatus according to any of claims 20 to 25, wherein in relation to said preserving, said control module is configured to copy at least one binding information per registered terminal, wherein said at least one binding information comprises at least one of a bearer identifier of a default bearer used by said terminal, a third address information assigned to said terminal, and an identifier of a control entity assigned to said terminal, and to store said at least one binding information per registered terminal.

27. The apparatus according to any of claims 20 to 25, wherein in relation to said preserving, said control module is configured to delete all binding information except for at least one binding information of a predetermined bearer per registered terminal.

28. The apparatus according to any of claims 20 to 27, wherein said information indicative of an executed restart of a network element is an incremented Restart Counter, and/or said network element is a serving gateway or a serving general packet radio service support node, and/or said re-attachment demand message is a Downlink Data Notification message, and/or said predetermined message indicative of said executed restart is a packet data network gateway Restart Notification or a gateway general packet radio service support node restart notification, and/or said bearer identifier is an Evolved Packet System bearer Identifier of the default bearer for Internet Protocol Multimedia System signaling Access Point Name, and/or said third address information is an Internet Protocol address, and/or said Identifier of a control entity is a Fully Qualified Tunnel Endpoint Identifier for Control plane value, and/or said re-attachment demand message is a delete bearer request message, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment re-attach is required, and/or said terminal is a user equipment.

29. An apparatus comprising a connection controller configured to receive a re-attachment demand message comprising address information and information indicative of a re-attachment requirement, to transmit a paging message using said address information, and to transmit a re-attachment force request using said address information.

30. The apparatus according to claim 29, wherein said re-attachment demand message is a Downlink Data Notification message, and/or said address information is an Internet Protocol address, and/or said information indicative of a re-attachment requirement is a general packet radio service tunneling protocol version 2 cause value indicating that a user equipment reattach is required, and/or said terminal is a user equipment.

31 . A system, comprising an apparatus according to any of claims 16 to 19 an apparatus according to any of claims 20 to 28, and an apparatus according to any of claims 29 to 30.

32. A computer program product comprising computer-executable computer program code which, when the program is run on a computer, is configured to cause the computer to carry out the method according to any one of claims 1 to 4, 5 to 13 or 14 to 15.

33. The computer program product according to claim 32, wherein the computer program product comprises a computer-readable medium on which the computer-executable computer program code is stored, and/or wherein the program is directly loadable into an internal memory of the processor.