WO2015021597A1

WO2015021597A1 - Traffic offload in small cell systems

Info

Publication number: WO2015021597A1
Application number: PCT/CN2013/081375
Authority: WO
Inventors: Xiang Xu; Yixue Lei; Tsunehiko Chiba
Original assignee: Nokia Siemens Networks Oy
Priority date: 2013-08-13
Filing date: 2013-08-13
Publication date: 2015-02-19

Abstract

There are provided measures for traffic offload in small cell systems in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network. Such measures exemplarily comprise, in said first gateway, providing functionality for at least communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting a create session request message comprising said correlation identifier. Such measures further exemplarily comprise, in said second gateway, providing functionality for at least communication with said local network, and receiving a create session request message including a correlation identifier.

Description

TRAFFIC OFFLOAD IN SMALL CELL SYSTEMS

Field

The present invention relates to traffic offload in small cell systems. More specifically, the present invention exemplarily relates to measures (including methods, apparatuses and computer program products) for realizing traffic offload in small cell systems.

Background

The present specification generally relates to small cell system for Long Term Evolution (LTE) and beyond systems. In more detail, methods and apparatuses (measures) to support offload for LTE small cell is proposed. Traffic offload provides multiple advantages to wireless communication system operators as well as to users of such systems. Namely, in view of increasing mobile traffic, offloading may reduce operating costs e.g. by saving additional hardware, and may improve user experiences by increasing throughput.

Selected Internet Protocol (IP) traffic offload (SIPTO) is a method to offload traffic from a wireless communication system operator's core network (CN) to a defined IP network that is close to a point of attachment to the access point of a wireless transmit receive unit (WTRU).

Small cell is being discussed in 3GPP RAN for Rel-12 (3GPP TR 36.932 Scenarios and Requirements of LTE Small Cell Enhancements). During discussion on different backhaul alternatives in RAN2 paper R2-131907, small cell dual connectivity architecture is addressed.

Currently in radio access network group 2 (RAN2) discussions, local breakout for small cells is identified as one important issue because for radio access network (RAN) split option, traffic load over the S1 interface between master evolved NodeB (Master eNB, MeNB) and CN is regarded as a concern. Local breakout is expected as one potential solution to address such concern. Meanwhile, in enterprise or residential environment, local breakout can bring considerable offloading benefits. However, current dual connectivity architecture (RAN split) does not support local breakout using local IP access (LIPA) or SIPTO with the local gateway (L-GW) located in local area. Note that current SIPTO at local network (SIPTO@LN) can not work well in case L-GW is in local area because for secondary eNB (SeNB) there are no direct S1/S5 interfaces to serving gateway (S-GW).

Hence, the problem arises that local breakout (in particular with dual connectivity enabled small cell architecture), i.e., SIPTO@LN with L-GW located in local area network, is not supported.

Hence, there is a need to provide for traffic offload in small cell systems.

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 in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing functionality for at least communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting a create session request message comprising said correlation identifier. According to an exemplary aspect of the present invention, there is provided a method in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said second gateway providing functionality for at least communication with said local network, and receiving a create session request message including a correlation identifier.

According to an exemplary aspect of the present invention, there is provided an apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing means configured to provide functionality for at least communication with said core network, allocating means configured to allocate a correlation identifier to a communication endpoint, and communication means configured to transmit a create session request message comprising said correlation identifier.

According to an exemplary aspect of the present invention, there is provided an apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said second gateway providing means configured to provide functionality for at least communication with said local network, and communication means configured to receive a create session request message including a correlation identifier.

According to an exemplary aspect of the present invention, there is provided a system in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising an apparatus according to any one of the aforementioned apparatus-related exemplary aspects of the present invention as said first gateway, and an apparatus according to the other aforementioned apparatus-related exemplary aspect of the present invention as said second gateway. According to an exemplary aspect of the present invention, there is provided a method in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing functionality for at least communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting, to said second gateway, a create session request message comprising said correlation identifier, and in relation to said second gateway, said method further comprises providing functionality for at least communication with said local network, and receiving, from said first gateway, a create session request message including a correlation identifier.

According to an 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 (e.g. a computer of an apparatus according to any one of the aforementioned apparatus-related exemplary aspects of the present invention), is configured to cause the computer to carry out the method according to any one of the aforementioned method-related exemplary aspects of the present invention.

Such computer program product may comprise (or be embodied) a (tangible) computer-readable (storage) medium or the like on which the computer-executable computer program code is stored, and/or the program may be directly loadable into an internal memory of the computer or a processor thereof.

Any one of the above aspects enables an efficient local breakout, i.e. Selected IP Traffic Offload at Local Network (SIPTO@LN) with local-gateway (L-GW) located in local area network working with dual connectivity enabled small cell architecture to thereby solve at least part of the problems and drawbacks identified in relation to the prior art.

By way of exemplary embodiments of the present invention, there is provided traffic offload in small cell systems. More specifically, by way of exemplary embodiments of the present invention, there are provided measures and mechanisms for realizing traffic offload in small cell systems. Thus, improvement is achieved by methods, apparatuses and computer program products enabling/realizing traffic offload in small cell systems.

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 schematic diagram of a procedure 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 shows a schematic diagram of an example of a system environment with signaling variants/interfaces,

Figure 6 shows a schematic diagram of an example of a system environment with signaling variants/interfaces,

Figure 7 shows a schematic diagram of an example of a system environment with signaling variants/interfaces, Figure 8 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention,

Figure 9 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention,

Figure 10 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention,

Figure 1 1 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention,

Figure 12 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention,

Figure 13 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention,

Figure 14 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention,

Figure 15 is a block diagram alternatively illustrating 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 3^rd Generation Partnership Project (3GPP) specifications being used as non-limiting examples for certain exemplary network configurations and deployments. 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.

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) traffic offload in small cell systems.

SeNBs may be installed in the local networks, e.g. in corporate intranets, enterprise networks, campus networks etc., when local IP breakout could be considered in addition to provide a backhaul off-loading option with direct user access to local networks from the small cell eNBs. Then, on demand, some user traffic can optionally be offloaded by SeNB directly without user plane traversing via the mobile operator's transport network at all.

The main drawback of some backhaul alternatives may be the potential increase in backhaul capacity requirements between the MeNB and the first intermediate router towards the S-GW. In order to address that aspect, local IP breakout could be considered in addition (actually to any alternative) to provide a backhaul off-loading option. As shown in Figure 5 (illustrating a local IP breakout as an add-on feature in small cell eNBs), some traffic can optionally be offloaded by SeNB directly without user plane traversing via the mobile operator's transport network at all. In this alternative, added functionality is needed for local IP breakout bearer management. This requires specifying some additional functions in MeNB, SeNB and UEs.

Current LIPA and SIPTO@LN services are based on using a L-GW as a breakout point that may be co-located in (H)eNB (i.e. eNB or home eNB), or a stand-alone S-GW/L-GW placed near RAN-nodes.

An L-GW is actually an evolved packet core (EPC) node, i.e., a simplified PDN gateway (P-GW) that is controlled via the mobility management entity (MME) and S-GW by using the S5 interface. From the user equipment (UE) perspective, LIPA and SIPTO@LN operates by using a secondary packet data network (PDN) connection via an L-GW; and the "primary" PDN connection for the default evolved packet system (EPS) bearer services UE is using simultaneously a P-GW located in the EPC.

It should be noted that LIPA is allowed only for UEs that are members of a closed subscriber group (CSG) the serving cell is advertising. It has been agreed that the small cells shall not follow the CSG concept with closed access mode, which means that the current LIPA feature cannot be applied, i.e., that only SIPTO@LN is relevant in conjunction with small cell architecture.

SA2 has already agreed that SIPTO@LN can be applied both with the HeNBs and with the ordinary (pico, macro) eNBs. Applicability of SIPTO@LN can be divided into at least two cases:

Case 1 - SIPTO@LN using L-GW collocated in the (H)eNB: One possibility is shown in Figure 6 (illustrating SIPTO@LN with co-located L-GW for small cells). The co-located L-GW is placed in the serving MeNB, i.e., the local breakout point is at the master eNB site. When the SeNB is deployed in local network, the offloaded traffic has to be sent back and forth between the local network (SeNB), and master eNB, e.g. the uplink traffic is first sent from local network (i.e. SeNB) to MeNB, then from L-GW to local network. This adds more transmission delay and poses higher bandwidth requirement on the backhaul between the local network and MeNB.

Another possibility is that the collocated L-GW is placed in the SeNBs in order to access local network directly from the SeNB/L-GWs. In that case, current SIPTO@LN does not work. A serving (H)eNB has one to one mapping with its co-located L-GW, which means that it can advertise only one L-GW to the EPC, resulting in that multitude of SeNB/L-GWs cannot be supported via single S1-MME terminating in the MeNB.

Also each SeNB co-located L-GW would require termination of the S5 interface from the EPC, which results in that numerous SeNB/L-GWs become exposed to the EPC even if there is a single S1-MME in the MeNB.

Case 2: SIPTO@LN using stand-alone S-GW/L-GW

One possibility is shown in Figure 7 (illustrating SIPTO@LN with stand-alone L-GW for small cell). For similar reasons as mentioned above, it is not advantageous to have the

S-GW/L-GW placed near the MeNB site in the operator domain.

Another possibility is to place the standalone S-GW/L-GW with SeNBs. However, the SIPTO@LN feature is not viable when a stand-alone S-GW/L-GW is placed in the same local network with the SeNBs in order to access this local network directly, or route traffic to internet without traffic traversing via the operator's network. A UE can have just one serving S-GW at the time, which results in that initiation of a SIPTO@LN service necessitates relocating the serving S-GW to a stand-alone S-GW/L-GW located in the local network. This means that all the ongoing bearer services for the UE must be routed there, i.e., the ongoing non SIPTO@LN bearers served via the MeNB would suffer from non-optimal routing of S1-u via the S-GW in a local network and further up using the S5 to the P-GW located in the EPC.

To sum up, current SIPTO@LN cannot support the offload when the L-GW is placed close to the SeNB or local network.

Hence, according to exemplary embodiments of the present invention, an architecture/solution is provided to enable local breakout in small cell environment. Exemplary embodiments of the present invention may impact 3GPP stage 2 architecture (TS 36.300) and RAN protocols (new specifications for Xn and S5'). According to exemplary embodiments of the present invention, traffic offloading at SeNB is enabled while exposing SeNB to the CN is avoided (i.e. introducing direct interfaces between SeNB and the CN is avoided).

In particular, according to exemplary embodiments of the present invention there are provided methods and apparatuses (i.e. measures) that support offload in small cell system.

Those measures according to exemplary embodiments of the present invention, in general, comprise an architecture with distributed local gateway functionalities in MeNB and SeNB consisting of L-GW functionality collocated in SeNB responsible for offload user data (i.e. breakout to local network) and L-GW functionality collocated in MeNB responsible for communicating with core network.

The L-GW functionality collocated in MeNB appears as SGW to L-GW functionality collocated in SeNB, and appears as P-GW to the S-GW functionality in the core network. In operation, in principle the SeNB informs the MeNB about the information of L-GW collocated in the SeNB. Further, the L-GW functionality in MeNB allocates a tunnel endpoint identifier (TEID, or GRE key) to be used as Correlation ID on behalf L-GW functionality in SeNB.

In addition, L-GW functionality in MeNB determines the target L-GW collocated in SeNB based on the correlation ID received from the core network, the information of target SeNB, and the information of the L-GW collocated in the target SeNB.

Moreover, L-GW functionality in MeNB informing the L-GW functionality in SeNB about the TEID or GRE key to be used to receive the offloaded uplink (UL) data transmitted from SeNB.

Besides, L-GW functionality in SeNB forward the downlink (DL) packet to L-GW functionality in MeNB to trigger the network initiated service request for an IDLE UE.

Figure 1 is a block diagram illustrating an apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network according to exemplary embodiments of the present invention. In relation to the first gateway, the apparatus may be an access node 10 such as a base station (in particular a master eNB) comprising a providing means 1 1 , an allocating means 12 and a communication means 13. The providing means 1 1 provides functionality for at least communication with a core network for both control plane and user plane. Further, the allocating means 12 allocates an endpoint identifier for uplink tunnel to a communication endpoint. In addition, the communication means 13 transmits a create session request message comprising said endpoint identifier, and receiving a downlink packet. Figure 3 is a schematic diagram of a procedure according to exemplary embodiments of the present invention. The apparatus according to Figure 1 may perform the method of Figure 3 but is not limited to this method. The method of Figure 3 may be performed by the apparatus of

Figure 1 but is not limited to being performed by this apparatus. As shown in Figure 3, a procedure according to exemplary embodiments of the present invention comprises an operation of providing (S31 ) functionality for at least communication with a core network for both control plane and user plane, an operation of allocating (S32) an endpoint identifier for uplink tunnel to a communication endpoint, and an operation of transmitting (S33) (to said second gateway) a create session request message comprising said identifier, and an operation of receiving (S34) a downlink packet from another communication endpoint (from said second gateway).

According to a variation of the procedure shown in Figure 3, 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 comprise an operation of receiving (from said second gateway) a create session response message including a first endpoint identifier generated using said endpoint identifier.

According to a variation of the procedure shown in Figure 3, 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 comprise an operation of receiving (from said eNB collocated with the second gateway) a setup request message including accessibility information of functionality (i.e., of said second gateway) for at least communication with a local network.

According to a variation of the procedure shown in Figure 3, 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 comprise an operation of generating a second endpoint identifier using said correlation identifier, and an operation of transmitting (to said core network) a create session response message including said second endpoint identifier.

According to a variation of the procedure shown in Figure 3, 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 comprise an operation of receiving (from said core network) bearer setup request message including said correlation identifier, an operation of assigning said bearer setup request message based on said correlation identifier, and an operation of forwarding (to said eNB collocated with the second gateway) said bearer setup request message based on said assigning.

According to a variation of the procedure shown in Figure 3, 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 comprise an operation of receiving (from said second gateway) a first packet of a sequence of downlink data, and an operation of forwarding said first packet to said core network.

According to further exemplary embodiments of the present invention, said method may be utilized in data traffic offload scenario, said correlation identifier may be a tunnel endpoint identifier TEID, or generic routing encapsulation GRE key, said first and second endpoint identifier may be a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, said accessibility information may be an internet protocol address, and/or said bearer setup request message may be an evolved radio access bearer E-RAB setup request message, or Initial Context Setup message.

Figure 2 is a block diagram illustrating an apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network according to exemplary embodiments of the present invention. In relation to the second gateway, the apparatus may be an access node 20 such as a base station (in particular a secondary eNB) comprising a providing means 21 and a communication means 22. The providing means 21 provides functionality for at least communication with a local network. Further, the communication means 22 receives a create session request message including a correlation identifier, and forwards the downlink packet. Figure 4 is a schematic diagram of a procedure according to exemplary embodiments of the present invention. The apparatus according to Figure 2 may perform the method of Figure 4 but is not limited to this method. The method of Figure 4 may be performed by the apparatus of Figure 2 but is not limited to being performed by this apparatus. As shown in Figure 4, a procedure according to exemplary embodiments of the present invention comprises an operation providing (S41 ) functionality for at least communication with a local network, an operation of receiving (S42) (from said first gateway) a create session request message including a correlation identifier, and an operation of transmitting (S43) (to said first gateway) the received downlink packet.

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 may comprise an operation of generating a first endpoint identifier using said correlation identifier, and an operation of transmitting (to said first gateway) a create session response message including said first endpoint identifier.

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 may comprise an operation of transmitting (to said eNB collocated with the first gateway) a setup request message comprising accessibility information to said provided functionality.

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 may comprise an operation of receiving (from said eNB collocated with the first gateway) a bearer setup request message comprising said correlation identifier.

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 may comprise an operation of receiving (from a terminal) uplink data, and an operation of forwarding said uplink data to said local network or Internet. Additionally or alternatively, according to such variation, an exemplary method according to exemplary embodiments of the present invention may comprise an operation of receiving downlink data from said local network or Internet, and an operation of forwarding (to said terminal) said downlink data.

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 may comprise an operation of receiving a first packet of a sequence of downlink data from said local network without active data connection for an addressee of said first packet, and forwarding (to said first gateway) said first packet to functionality for at least communication with a core network.

According to further exemplary embodiments of the present invention, said method may be utilized in data traffic offload scenario, said correlation identifier may be a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, said first endpoint identifier may be a tunnel endpoint identifier TEID, or generic routing encapsulation GRE key, said accessibility information may be an internet protocol address, and/or said bearer setup request message may be an evolved radio access bearer E-RAB setup request message, or Initial Context Setup Request message.

Exemplary embodiments of the present invention are described in the following in more detail.

Figure 8 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention. In particular, an exemplary architecture for offload in small cell according to embodiments of the present invention is illustrated.

As is can be seen on Figure 8, the SL-GW, which is the local gateway functionality collocated with SeNB comprises the SGi interface (to the PDN, i.e., the local network, or internet). The offloaded UL IP traffic is sent from SL-GW to external public or private packet data network via such SGI interface. The DL IP traffic is received by the SL-GW and sent directly to SeNB, except for the first DL packet to an UE in idle mode (IDLE UE). In that case, the first DL packet is forwarded to ML-GW to trigger a network initiated service request procedure.

Further, ML-GW, which is the L-GW functionality collocated with MeNB comprises the S5 interface to SGW. The ML-GW appears to SGW as a PGW, and appears to SL-GW as a SGW.

According to exemplary embodiments of the present invention, a S5' interface is provided and used between SL-GW and ML-GW. The S5' interface may be based on GTP, or PMIP. It is also possible to implement such S5' functions as a subset of Xn control plane (CP) functions.

Figure 9 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention. In particular, exemplary signaling sequences according to embodiments of the present invention regarding offload packet data network (PDN) connection establishment for single-radio UE are illustrated.

As can be seen in Figure 9, such exemplary signaling sequence can be divided in multiple steps which are described in the following. The following steps assume G5-based S5/S5' interface (GTP) is used. In case of PMIP-based S5/S5', GRE key is used instead of TEID.

Step 0 in Figure 9 illustrates that, during the Xn setup procedure, SeNB informs MeNB about the IP address of SL-GW. MeNB maintains the information {SeNB's ID, IP adr of

SeNB, IP adr of SL-GW} for each SeNB.

In Step 1 of Figure 9, a UE initiates PDN connection request. Note, in this example, it is assumed that radio resource control (RRC) terminates at SeNB in single radio mode operation. However, if RRC terminates at MeNB using SeNB as a relay node, this message will be terminated in MeNB and following step 2 may be saved. In Step 2 according to Figure 9, the SeNB sends Xn Initial UE Message to MeNB.

In Step 3 of Figure 9, MeNB sends S1 Initial UE Message including the IP address of ML-GW, i.e. "adr2".

In Step 4 of Figure 9 is shown how MME initiates a create session request (Create Session Req) procedure.

In Step 5 of Figure 9, UE's SGW sends Create Session Request message to ML-GW.

In Step 6 of Figure 9, ML-GW allocates an unused tunnel endpoint identifier, e.g. TEID#1 , and includes this TEID in Create Session Rsp (response) message to SGW. ML-GW does not initiate the Create Session procedure to SL-GW until it knows the target SL-GW (see Step 8)

In Step 7 of Figure 9, UE's SGW sends Create Session Rsp (response) to MME.

In Step 8 of Figure 9, MME sends evolved radio access bearer (E-RAB) Setup Req (request) message, or Initial Context Setup Request message to eNB. The message includes the correlation ID setting to TEID#1. Upon the reception of E-RAB Setup Req message, or Initial Context Setup Request message including a correlation ID set to a previously allocated TEID (Step 6), MeNB knows that this is related to the offload PDN connection setup. The ML-GW then initiates Create Session procedure to SL-GW. The target SL-GW is determined based on the ID or IP address of target SeNB and the information received in Step 0 (i.e. "adrl ").

In Step 9 of Figure 9, the MeNB initiates the Create Session Req message including TEID#1. Upon the reception of Create Session Req message, SL-GW uses the received TEID#1 for UL TEID which is used later to receive the offloaded UL data transmitted from the SeNB.

In Step 10 of Figure 9, the SL-GW sends Create Session Response to ML-GW.

In Steps 1 1 -15 of Figure 9 is illustrated how MeNB sends Xn E-RAB Setup Req message, or Initial Context Setup Request message including the correlation ID set to TEID#1 to SeNB, and how SeNB initiates RRC reconfiguration.

In Steps 16-18 of Figure 9, it is shown that UE sends direct transfer including non-access stratum (NAS) PDN connectivity complete message to SeNB, which is subsequently forwarded to MME.

In Steps 19-20 of Figure 9, the MME then initiates a bearer modify procedure

In Step 21 of Figure 9, the offloaded UL data is sent directly from SL-GW to external packet data network.

In Step 22 of Figure 9, the offloaded DL data is sent directly from SL-GW to UE via SeNB.

Figure 10 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention. In particular, exemplary signaling sequences according to embodiments of the present invention regarding offload PDN connection establishment for dual-radio UE are illustrated.

The main difference between the signaling sequences of offload PDN connection establishment for single-radio UE (according to Figure 9) and the signaling sequences of offload PDN connection establishment for dual-radio UE (according to Figure 10) is that UE sends the RRC message to MeNB no matter whether single RRC or dual RRC option is adopted.

Figure 1 1 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention. In particular, an exemplary offloaded user-plane path for single-radio UE according to embodiments of the present invention is illustrated.

Figure 12 shows a schematic diagram of an example of a system environment with signaling variants/interfaces according to exemplary embodiments of the present invention. In particular, an exemplary offloaded user-plane path for dual-radio UE according to embodiments of the present invention is illustrated.

In Figures 1 1 and 12, the difference between the cases "single-radio UE" and "dual-radio UE" in relation to the user-plane path is shown. In particular, while in single-radio case only a user-plane path between the UE and the SeNB exists, in dual-radio case there is also a user-plane path between the UE and the MeNB.

Figure 13 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention. In particular, exemplary signaling sequences according to embodiments of the present invention regarding network triggered service request for single-radio UE are illustrated (IDLE UE).

As can be seen in Figure 13, such exemplary signaling sequence can be divided in multiple steps which are described in the following.

According to Step 1 of Figure 13, first of all, the SL-GW receives a DL IP packet.

In Step 2 of Figure 13 it is shown how the ML-GW appears to SL-GW as SGW, such that SL-GW forwards the first DL packet to ML-GW. In Step 3 of Figure 13, the ML-GW forwards the first DL packet to SGW.

In Steps 4-18 of Figure 13, SGW sends downlink data notification to MME to trigger network initiated service request.

Finally, in Steps 19-21 of Figure 13, after the UE is connected, SGW forwards the first IP packet to MeNB, which is then sent to SeNB.

According to Step 22 of Figure 13, other DL packets are subsequently sent directly from SL-GW to SeNB.

Figure 14 shows a schematic diagram of signaling sequences according to exemplary embodiments of the present invention. In particular, exemplary signaling sequences according to embodiments of the present invention regarding network triggered service request for dual-radio UE are illustrated.

The main difference between the signaling sequences of network triggered service request for single-radio UE (according to Figure 13) and the signaling sequences of network triggered service request for dual-radio UE (according to Figure 14) is that that RRC message is sent from MeNB to UE no matter whether single RRC or dual RRC option is adopted.

It is noted that the solutions according to exemplary embodiments of the present invention, as provided above, require less changes to the small cell system. Further, no impact to CN is necessary. According to exemplary embodiments of the present invention, the small cell and the offload are kept invisible to CN, and existing 3GPP procedures are mostly reused. 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").

In Figure 15, an alternative illustration of apparatuses according to exemplary embodiments of the present invention is depicted. As indicated in Figure 15, according to exemplary embodiments of the present invention, the apparatus (network node, access node) 10' (corresponding to the network node, access node 10) comprises a processor

151 , a memory 152 and an interface 153, which are connected by a bus 154 or the like. Further, according to exemplary embodiments of the present invention, the apparatus (network node, access node) 20' (corresponding to the network node, access node 20) comprises a processor 155, a memory 156 and an interface 157, which are connected by a bus 158 or the like., and the apparatuses may be connected via link 159, respectively.

The processor 151/155 and/or the interface 153/157 may also include a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 153/157 may include 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 153/157 is generally configured to communicate with at least one other apparatus, i.e. the interface thereof.

The memory 152/156 may store respective programs assumed to include 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.

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 access node 10 comprises at least one processor 151 , at least one memory 152 including computer program code, and at least one interface 153 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 151 , with the at least one memory 152 and the computer program code) is configured to perform providing functionality for at least control communication with a core network (thus the apparatus comprising corresponding means for providing), to perform allocating a correlation identifier to a communication endpoint (thus the apparatus comprising corresponding means for allocating), and to perform transmitting a create session request message comprising said correlation identifier (thus the apparatus comprising corresponding means for transmitting). Further, according to exemplary embodiments of the present invention, an apparatus representing the access node 20 comprises at least one processor 155, at least one memory 156 including computer program code, and at least one interface 157 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 155, with the at least one memory 156 and the computer program code) is configured to perform providing functionality for at least data communication with a local network (thus the apparatus comprising corresponding means for providing), and to perform receiving a create session request message including a correlation identifier (thus the apparatus comprising corresponding means for receiving).

For further details regarding the operability/functionality of the individual apparatuses, reference is made to the above description in connection with any one of Figures 1 to 14, 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 including 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 traffic offload in small cell systems in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network. Such measures exemplarily comprise, in said first gateway, providing functionality for at least control communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting a create session request message comprising said correlation identifier. Such measures further exemplarily comprise, in said second gateway, providing functionality for at least communication with said local network, and receiving a create session request message including a correlation identifier.

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

CN core network

CP control plane

CSG closed subscriber group

DL downlink

eNB evolved NodeB

EPC evolved packet core

EPS evolved packet system

E-RAB evolved radio access bearer F-TEIDfully qualified tunnel endpoint identifier

GRE Key Generic Routing Encapsulation Key

GTP GPRS Tunneling Protocol

HeNB home eNB, home evolved NodeB

IP Internet Protocol

L-GW local gateway

LIPA local IP access

LTE Long Term Evolution

MeNB Master eNB, Master evolved NodeB

ML-GW MeNB local gateway

MME mobility management entity

NAS non-access stratum

PDN packet data network

PMIP Proxy Mobile IP

P-GW PDN gateway

RAN radio access network RAN2 radio access network group 2

RRC radio resource control

SeNB secondary eNB, secondary evolved NodeB

S-GW serving gateway

SL-GW SeNB local gateway

SIPTO Selected Internet Protocol traffic offload SIPTO@LN SIPTO at local network

TEID tunnel endpoint identifier

UE user equipment

UL uplink

Uu interface between UE and eNB

WTRU wireless transmit receive unit

Claims

WHAT IS CLAIMED IS:

1 . A method in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing functionality for at least communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting a create session request message comprising said correlation identifier.

2. The method according to claim 1 , further comprising receiving a create session response message including a first endpoint identifier generated using said correlation identifier.

3. The method according to claim 1 or 2, further comprising receiving a setup request message including accessibility information of functionality for at least communication with said local network.

4. The method according to any of claims 1 to 3, further comprising generating a second endpoint identifier using said correlation identifier, and transmitting a create session response message including said second endpoint identifier.

5. The method according to any of claims 1 to 4, further comprising receiving bearer setup request message including said correlation identifier, assigning said bearer setup request message based on said correlation identifier, and forwarding said bearer setup request message based on said assigning.

6. The method according to any of claims 2 to 5, further comprising receiving a first packet of a sequence of downlink data, and forwarding said first packet to said core network.

7. The method according to any of claims 1 to 6, wherein said method is utilized in data traffic offload scenario, and/or said correlation identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said first and second endpoint identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said accessibility information is an internet protocol address, and/or said bearer setup request message is an evolved radio access bearer E-RAB setup request message or Initial Context setup request message.

8. A method in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said second gateway providing functionality for at least communication with said local network, and receiving a create session request message including a correlation identifier.

9. The method according to claim 8, further comprising generating a first endpoint identifier using said correlation identifier, and transmitting a create session response message including said first endpoint identifier.

10. The method according to claim 8 or 9, further comprising transmitting a setup request message comprising accessibility information to said provided functionality.

1 1. The method according to any of claims 8 to 10, further comprising receiving a bearer setup request message comprising said correlation identifier.

12. The method according to any of claims 9 to 1 1 , further comprising receiving uplink data, and forwarding said uplink data to said local network, and/or said method further comprising receiving downlink data from said local network, and forwarding said downlink data.

13. The method according to any of claims 9 to 12, further comprising receiving a first packet of a sequence of downlink data from said local network without active data connection for an addressee of said first packet, and forwarding said first packet to functionality for at least communication with said core network.

14. The method according to any of claims 8 to 13, wherein said method is utilized in data traffic offload scenario, and/or said correlation identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said first endpoint identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said accessibility information is an internet protocol address, and/or said bearer setup request message is an evolved radio access bearer E-RAB setup request message or Initial context setup request message.

15. An apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing means configured to provide functionality for at least communication with said core network, allocating means configured to allocate a correlation identifier to a communication endpoint, and communication means configured to transmit a create session request message comprising said correlation identifier.

16. The apparatus according to claim 15, wherein said communication means is further configured to receive a create session response message including a first endpoint identifier generated using said correlation identifier.

17. The apparatus according to claim 15 or 16, wherein said communication means is further configured to receive a setup request message including accessibility information of functionality for at least communication with said local network.

18. The apparatus according to any of claims 15 to 17, further comprising generating means configured to generate a second endpoint identifier using said correlation identifier, and wherein said communication means is further configured to transmit a create session response message including said second endpoint identifier.

19. The apparatus according to any of claims 15 to 18, wherein said communication means is further configured to receive bearer setup request message including said correlation identifier, and said apparatus further comprising assigning means configured to assign said bearer setup request message based on said correlation identifier, and wherein said communication means is further configured to forward said bearer setup request message based on said assigning.

20. The apparatus according to any of claims 16 to 19, wherein said communication means is further configured to receive a first packet of a sequence of downlink data, and to forward said first packet to said core network.

21. The apparatus according to any of claims 15 to 20, wherein the apparatus is operable as or at a base station or access node of a cellular system, and/or the apparatus is operable in at least one of a LTE and a LTE-A cellular system, and/or the apparatus is operable in data traffic offload scenario, and/or said correlation identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said first and second endpoint identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said accessibility information is an internet protocol address, and/or said bearer setup request message is an evolved radio access bearer E-RAB setup request message or Initial Context Setup Request message.

22. An apparatus in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said second gateway providing means configured to provide functionality for at least communication with said local network, and communication means configured to receive a create session request message including a correlation identifier.

23. The apparatus according to claim 22, further comprising generating means configured to generate a first endpoint identifier using said correlation identifier, and wherein said communication means is further configured to transmit a create session response message including said first endpoint identifier.

24. The apparatus according to claim 22 or 23, wherein said communication means is further configured to transmit a setup request message comprising accessibility information to said provided functionality.

25. The apparatus according to any of claims 22 to 24, wherein said communication means is further configured to receive a bearer setup request message comprising said correlation identifier.

26. The apparatus according to any of claims 23 to 25, wherein said communication means is further configured to receive uplink data, and to forward said uplink data to said local network, and/or said communication means is further configured to receive downlink data from said local network, and to forward said downlink data.

27. The apparatus according to any of claims 23 to 26, wherein said communication means is further configured to receive a first packet of a sequence of downlink data from said local network without active data connection for an addressee of said first packet, and to forward said first packet to functionality for at least communication with said core network.

28. The apparatus according to any of claims 22 to 27, wherein the apparatus is operable as or at a base station or access node of a cellular system, and/or the apparatus is operable in at least one of a LTE and a LTE-A cellular system, and/or the apparatus is operable in data traffic offload scenario, and/or said correlation identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said first endpoint identifier is a tunnel endpoint identifier TEID or generic routing encapsulation GRE key, and/or said accessibility information is an internet protocol address, and/or said bearer setup request message is an evolved radio access bearer E-RAB setup request message or Initial Context Setup request message.

29. A system in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising an apparatus according to any of claims 15 to 21 as said first gateway, and an apparatus according to any of claims 22 to 28 as said second gateway.

30. A method in a distributed gateway disposal of a first gateway associated with a first base station in contact with a core network and a second gateway associated with a second base station in contact with a local network, comprising in relation to said first gateway providing functionality for at least communication with said core network, allocating a correlation identifier to a communication endpoint, and transmitting, to said second gateway, a create session request message comprising said correlation identifier, and in relation to said second gateway, said method further comprises providing functionality for at least communication with said local network, and receiving, from said first gateway, a create session request message including a correlation identifier.

31. 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 7 or 8 to 14.

32. The computer program product according to claim 31 , 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.