Abstract:
In one aspect of the teachings herein, a controlling gateway and an associated radio access point are configured for operation in a radio access network and use a radio protocol stack that is split on the network side between the gateway and the access point, for conveying radio bearer traffic going between the radio access network and a wireless device. According to methods and apparatuses disclosed, the radio protocol entities affected by the stack split communicate using Internet Protocol, IP, sessions. Advantageously, the radio bearer traffic conveyed over the split stack maps to different IP sessions in dependence on any one or more of network capabilities, various isolation or privacy requirements associated with the device and/or traffic, the types of data being conveyed, the types of radio bearers involved, and the involved Radio Link Control, RLC, operating modes.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to wireless communication networks, and particularly relates to a radio node and a gateway node operating according to a split radio protocol stack. 
       BACKGROUND 
       [0002]    Increased network density and increased heterogeneity are among the key factors complicating the design and implementation of wireless communication networks. Network designers and operators must balance the necessity of having good coverage, at least in areas of high use, and having the right type of coverage, e.g., high-data rate coverage, against the enormous capital and operating expenditures needed to deploy and maintain the kind of equipment needed to ensure that those necessities are being met. 
         [0003]    In one approach to increasing network density, rather than simply adding more “macro” or large-cell base stations, network operators are deploying smaller, low-power base stations, or allowing third-parties, such as individual homeowners or other subscribers, to deploy such base stations. These base stations characteristically provide radio coverage in much smaller areas, e.g., only within the confines of a typical residence or office. Consequently, these coverage areas are often referred to as “small” cells. 
         [0004]    The base stations or access points, APs, that provide small-cell coverage may or may not use the same Radio Access Technology, RAT, in use in the macro-layer of the network, and varying degrees of integration are contemplated for APs with respect to the network at large. For example, the APs may or may not be part of overall coordinated interference reduction schemes that coordinate scheduling or other operational aspects of the network across and between cells. 
         [0005]    Merely by way of example, a network operator may lease or sell small, low-power APs that individual subscribers install in their homes or workplaces. These APs may provide better baseline coverage, or they may act as higher data-rate hotspots and, as such, they may have broadband connections back to the operator&#39;s network. In a particular approach, the APs couple to the operator&#39;s network through a controlling gateway. In such implementations, the AP has an air interface for connecting to devices and has one or more network connections, often “wired” connections, back to the controlling gateway, which in turn has some type of “backhaul” connection to the operator&#39;s core network. 
         [0006]    The gateway arrangement provides a number of advantages. For example, one gateway may support more than one AP. Consequently, at least some of the processing can be consolidated in the gateway. The centralization of certain Radio Access Network, RAN, processing functions is a topic of growing interest, and it is envisioned as a key aspect of future-generation network implementations. 
         [0007]    Broadly, the idea here involves dividing the overall air interface operations and management processing between the actual radio access points providing the radio bearers and centralized processing nodes that provide relatively cheap pools of processing resources that can be leveraged for potentially large numbers of radio access points, also referred to generically as “base stations”. The lower-level functions, such as radio resource allocations and dynamic user scheduling are performed at the radio access nodes, which provide the actual radio link(s), while at least some of the higher-layer processing is moved to a central location. 
         [0008]    This kind of disaggregation of the overall air interface processing protocols generally involves some “splitting” of the radio protocol stack between a radio access point and the centralized processing node. To better appreciate the split stack approach, consider the radio protocol stack used in Long Term Evolution or LTE. A wireless communication device and a network base station configured for operation in accordance with the LTE air interface each implements a version of the LTE protocol stack. 
         [0009]    Protocol entities in the device-side stack mirror and communicate with corresponding peer entities in the network-side stack. The LTE stack includes a physical or PHY layer, as its bottom-most layer, a Medium Access Control, MAC, layer above the physical layer, a Radio Link Control, RLC, layer above the MAC layer, a Packet Data Convergence Protocol, PDCP, layer above the RLC layer, and a Radio Resource Control, RRC, layer above the PDCP layer. For more details regarding these layers and their functions, the interested reader may refer to the following Third Generation Partnership Project, 3GPP, Technical Specifications: TS 36.201 for a discussion of the physical layer, TS 36.321 for a discussion of the MAC layer, TS 36.322 for a discussion of the RLC layer, TS 36.323 for a discussion of the PDCP layer, and TS 36.331 for a discussion of the RRC layer. 
         [0010]    In the context of the aforementioned gateway arrangement, a residential or other such radio access point implements a portion of the radio protocol stack on the network side, with the remaining portion of the stack implemented at the controlling gateway. This arrangement provides the twofold benefit of simplifying the radio access point and leveraging the gateway node for supporting more than one radio access point. However, the protocol endpoints or peers for the network-side radio protocol stack exist in the device-side protocol stack, and there are no standardized endpoints or mechanisms for the split-stack interface between the radio access point and the controlling gateway. 
         [0011]    It is recognized herein that the split should be transparent to the overall radio stack protocols and should be managed for link efficiencies and reliability. Further recognized herein are the dual needs for scalability and discoverability, e.g., so that individual connecting gateways can support tens, hundreds or even greater numbers of radio access points, and so that the involved inter-split connections can be easily configured between the involved controlling gateway and its supported radio access points. 
       SUMMARY 
       [0012]    In one aspect of the teachings herein, a controlling gateway and an associated radio access point are configured for operation in a radio access network and use a radio protocol stack that is split on the network side between the gateway and the access point, for conveying radio bearer traffic between the radio access network and a wireless communication device. According to methods and apparatuses disclosed, the radio protocol entities affected by the stack split communicate using Internet Protocol, IP, sessions. Advantageously, the radio bearer traffic conveyed over the split stack maps to different IP sessions in dependence on any one or more of network capabilities, various isolation or privacy requirements associated with the wireless communication device and/or traffic, the types of data being conveyed, the types of radio bearers involved, and the involved Radio Link Control, RLC, operating modes. 
         [0013]    In one embodiment, a method of operation in a gateway node that is coupled to a core network of a wireless communication network includes determining that data is available for sending to a wireless communication device—also referred to as a “wireless device” or simply “device”—that accesses the wireless communication network via a radio cell provided by a radio node that is coupled to a core network of the wireless communication network via the gateway node. The method includes generating service data units corresponding to the data, based on processing the data according to an upper portion of a radio protocol stack, where the radio protocol stack is split between the gateway node, which implements the upper portion of the radio protocol stack, and the radio node, which implements a remaining, lower portion of the radio protocol stack. Still further, the method includes establishing an IP session towards the radio node, via an intra-stack IP link communicatively coupling the upper portion of the radio protocol stack at the gateway node with the lower portion of the radio protocol stack at the radio node. 
         [0014]    The IP session is mapped to a radio bearer to be used for conveying the data to the wireless device via an air interface of the radio cell, and the method further includes encapsulating the service data units in one or more IP packets, according to IP session parameters associated with the IP session, and sending the IP packets to the radio node via the IP session, for de-encapsulation and recovery of the service data units, for subsequent processing by the radio node according to the remaining, lower portion of the radio protocol stack. Complementary processing and configurations also apply in the uplink direction, where data transmitted by the wireless device is received at the radio node and processed according to the portion of the protocol stack implemented at the radio node, and encapsulated for transfer across the intra-stack IP link. Note that the intra-stack IP link is transparent to the overall protocol flow going between the wireless network and the device. In other words, the intra-stack IP link merely provides a mechanism for conveying data between the protocol entities that would otherwise not be split if the radio protocol stack on the network side were consolidated in a single node. 
         [0015]    In another embodiment, a gateway node is configured for operation in a wireless communication network and includes a first communication interface that is configured for communicating with a radio node to be controlled by the gateway node. The gateway node further includes a second communication interface that is configured for communicating with one or more core network nodes in a core network of the wireless communication network. Still further, the gateway node includes processing circuitry that is operatively associated with the first and second communication interfaces. 
         [0016]    The processing circuitry is configured to determine that data is available for sending to a wireless device that accesses the wireless communication network via a radio cell provided by the radio node, where the radio node is coupled to the core network of the wireless communication network via the gateway node. The processing circuitry is further configured to generate service data units corresponding to the data, based on processing the data according to an upper portion of a radio protocol stack, where the radio protocol stack is split between the gateway node, which implements the upper portion of the radio protocol stack, and the radio node, which implements a remaining, lower portion of the radio protocol stack. The processing circuitry is further configured to establish an IP session towards the radio node, via an intra-stack IP link communicatively coupling the upper portion of the radio protocol stack at the gateway node with the lower portion of the radio protocol stack at the radio node. The IP session is mapped to a radio bearer to be used for conveying the data to the wireless device via an air interface of the radio cell and the processing circuitry is additionally configured to encapsulate the service data units in one or more IP packets, according to IP session parameters associated with the IP session, and send the IP packets to the radio node via the IP session, for de-encapsulation and recovery of the service data units, for subsequent processing by the radio node according to the remaining, lower portion of the radio protocol stack. Complementary processing and configurations also apply in the uplink direction, where data transmitted by the wireless device is received at the radio node and processed according to the portion of the protocol stack implemented at the radio node, and encapsulated for transfer across the intra-stack IP link. 
         [0017]    In yet another embodiment, a gateway node is configured for operation in a wireless communication network and includes a first communication interface that is configured for communicating with a radio node to be controlled by the gateway node, along with a second communication interface that is configured for communicating with one or more core network nodes in a core network of the wireless communication network. The gateway node further includes processing circuitry that is operatively associated with the first and second communication interfaces. 
         [0018]    The processing circuitry is configured to receive an IP packet from the radio node in an IP session on an intra-stack IP link that communicatively couples a lower portion of a radio protocol stack at the radio node to an upper portion of the radio protocol stack at the gateway node. The radio protocol stack at issue here a network-side radio protocol stack complementing a device-side radio protocol stack implemented at the wireless device that sent the uplink data encapsulated in the received IP packet. The processing circuitry is further configured to map the IP session to a radio bearer, according to session-to-bearer mapping known at the gateway node, and to de-encapsulate a service data unit contained in the IP packet. The processing circuitry is configured to input the service data unit into the upper portion of the radio protocol stack and to send data generated from processing the service data unit according to the upper portion of the radio protocol stack to a core network for higher-layer processing. 
         [0019]    In a related embodiment, a method of operation in a gateway node includes receiving an IP packet from a radio node in an IP session on an intra-stack IP link that communicatively couples a lower portion of a radio protocol stack at the radio node to an upper portion of the radio protocol stack at the gateway node. Here, the radio node is controlled by the gateway node and provides a cell for wirelessly connecting wireless devices to the network. The radio protocol stack in question is a network-side radio protocol stack complementing a device-side radio protocol stack implemented at the wireless device that sent uplink data encapsulated in the IP packet. 
         [0020]    The method further includes mapping the IP session to a radio bearer, according to session-to-bearer mapping known at the gateway node, de-encapsulating a service data unit contained in the IP packet, inputting the service data unit into the upper portion of the radio protocol stack, and sending the data generated from processing the service data unit according to the upper portion of the radio protocol stack to a core network for higher-layer processing. 
         [0021]    Of course, the present invention is not limited to the above features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a block diagram of one embodiment of a gateway node and a radio node controlled by the gateway node, where both the gateway node and the radio node are configured for operation in a wireless communication network. 
           [0023]      FIG. 2  is a diagram of a known radio protocol stack, such as may be advantageously split according to the teachings herein. 
           [0024]      FIG. 3  is a diagram of one embodiment of a split radio protocol stack as implemented in a split configuration, with an upper portion of the stack implemented in a gateway node and a lower portion of the stack implemented in a radio node controlled by the gateway node. 
           [0025]      FIG. 4  is a diagram of further example details for the split radio protocol stack of  FIG. 3 . 
           [0026]      FIG. 5  is a logic flow diagram of one embodiment of a method of processing at a gateway node controlling a radio node, wherein a network-side radio protocol stack is split between the gateway node and the radio node. 
           [0027]      FIG. 6  is a logic flow diagram of one embodiment of a method of processing at a radio node controlled by a gateway node, wherein a network-side radio protocol stack is split between the gateway node and the radio node. 
           [0028]      FIG. 7  is a logic flow diagram of another embodiment of a method of processing at a radio node controlled by a gateway node, wherein a network-side radio protocol stack is split between the gateway node and the radio node. 
           [0029]      FIG. 8  is a logic flow diagram of another embodiment of a method of processing at a gateway node controlling a radio node, wherein a network-side radio protocol stack is split between the gateway node and the radio node. 
           [0030]      FIG. 9  is a block diagram of one embodiment of a gateway node and a radio node controlled by the gateway node, where both the gateway node and the radio node are configured for operation in a Long Term Evolution, LTE, network. 
           [0031]      FIG. 10  is a diagram of the split radio protocol stack, shown in context with the additional supporting nodes seen in  FIG. 9 . 
           [0032]      FIG. 11  is a call flow diagram illustrating one embodiment of signaling between a radio node and customer premises equipment, CPE, used to couple the radio node to a controlling gateway node. 
           [0033]      FIG. 12  is a call flow diagram illustrating one embodiment of signaling between a radio node and a controlling gateway node, for establishing a secure connection between them. 
           [0034]      FIG. 13  is a call flow diagram illustrating one embodiment of signaling between a radio node and a controlling gateway node, for configuring the radio node and setting up an IP session between the controlling gateway node and the radio node, for coupling the radio protocol stack split between the gateway and radio nodes. 
           [0035]      FIG. 14  is a logic flow diagram illustrating one embodiment of downlink packet processing involving a wireless device, a radio node and a controlling gateway node, where the radio node and the controlling gateway node use a split radio protocol stack. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIG. 1  illustrates a wireless communication network  10  configured to provide communication services to any number of wireless communication devices  12 , where only two such devices  12 - 1  and  12 - 2  are shown by way of example. Unless suffixes are needed for clarity, the reference number “ 12 ” is used herein, for both singular and plural reference to any given device, or devices. The same usage applies with respect to any other “base” reference number where suffixing is used herein. 
         [0037]    The network  10  communicatively couples the individual devices  12  to one or more operator, OP, Internet Protocol, IP, services and/or external networks  14 , such as the Internet and may provide for inter-device communications within the network  10 . The network  10  includes a Radio Access Network, RAN  16 , and a Core Network, CN  18 . In this example, the RAN  16  includes a radio node  20  and a gateway node  22 . The gateway node  22  is configured to control the radio node  20  and to provide communicative coupling to the CN  18 . By way of example, the radio node  20  is a home base station or other small-cell device that provides radio coverage in a corresponding radio cell or cells  24 , which may have a limited coverage area, such as a low-power cell intended to encompass a single residence or other structure. 
         [0038]    While only one cell  24  is illustrated, it will be appreciated that the radio node  20  may provide more than one cell  24 , e.g., by using different carrier frequencies, using different frequency sub-bands, using Time Division Multiplexing, TDM, etc. Although only one radio node  20  and one gateway node  22  are illustrated, the network  10  may include any number of radio nodes  20 , e.g., each at different locations within a broader geographic area. Further, the network  10  may include a gateway node  22  for each such radio node  20 , or may have one gateway node  22  for subsets or groups of radio nodes  20 . In one or more embodiments, it is contemplated to control potentially large numbers of radio nodes  20  via one gateway node  22 . Additionally, the network  10  may include other entities not illustrated or described, as will be understood by those of ordinary skill in the wireless communication arts. For example, in one or more non-limiting embodiments, the network  10  comprises a Long Term Evolution, LTE, or LTE-Advanced network, configuring according to the applicable technical specifications promulgated by the Third Generation Partnership Project, 3GPP. Consequently, the network  10  includes a variety of nodes or other entities associated with such networks, including Mobility Management Entities or MMEs in the CN  18 , along with a Packet Data Gateway Nodes or PDGN, providing a packet data interface between the CN  18  and the external network(s)  14 . 
         [0039]    Regardless of whether the radio node  20  is implemented as a LTE Home eNB, HeNB, or as some other type of radio base station, it will be understood as comprising a mix of signal processing and control circuitry, along with supporting radio transceiver circuitry. In the example illustration, the radio node  20  includes first and second communication interfaces  30 - 1  and  30 - 2 —generally referred to as “communication interfaces  30 ”—along with processing circuitry  32  that is operatively associated with the communication interfaces  30 . 
         [0040]    The processing circuitry  32  comprises fixed circuitry, programmed circuitry, or a combination of fixed and programmed circuitry. In an example embodiment, the processing circuitry  32  is at least partly implemented using programmed circuitry and comprises, for example, one or more processors  34 , such as one or more microprocessors, Digital Signal Processors or DSPs, Application Specific Integrated Circuits or ASICs, Field Programmable Gate Arrays or FPGAs, or other digital processing circuitry. Correspondingly, the processing circuitry  32  includes or is associated with one or more types of computer-readable media—“STORAGE  36 ” in the figure—such as one or more types of memory circuits such as FLASH, EEPROM, SRAM, DRAM, etc. Additionally, or alternatively, the storage  36  comprises hard disk storage, Solid State Disk, SSD, storage, etc. 
         [0041]    In general, the storage  36  provides both working memory and longer-term storage. In at least one embodiment, the storage  36  provides non-transitory storage for a computer program  38  and one or more items of configuration data  40 . Here, non-transitory does not necessarily mean permanent or unchanging storage but does means storage of at least some persistence—i.e., holding information for subsequent retrieval. The computer program  38 , which may comprise a number of related or supporting programs, comprises program instructions that, when executed by the one or more processors  34  implement the processing circuitry  32  according to the configuration examples described herein. In other words, in some embodiments, one or more general-purpose processing circuits within the radio node  20  are specially adapted to carry out the teachings herein, based on their execution of the computer program instructions comprising the computer program  38 . 
         [0042]    However implemented, the radio node  20  is configured to provide radio coverage in one or more cells  24 , and the first communication interface  30 - 1  is configured for communicating with wireless devices  12  operating in any of the one or more cells  24 . For example, the communication interface  30 - 1  is configured for transmitting and receiving radiofrequency signals according to the air interface protocols and signal structure adopted for the air interface between the radio node  20  and the devices  12 . To that end, the communication interface  30 - 1  includes one or more radiofrequency transmitters and receivers, and associated protocol processing circuitry that is adapted to support the uplink and downlink air interfaces implemented within the network  10 . 
         [0043]    The radio node  20  further includes a second communication interface  30 - 2  configured to communicatively couple the radio node  20  to its controlling gateway node  22 , which in turn is coupled to the CN  18 . The second communication interface  30 - 2  may comprise a wired or wireless interface, e.g., a LAN or microwave-based interface, and shall be understood as providing physical-layer circuitry adapted for sending and receiving signals over the involved transmission medium, along with corresponding circuitry for protocol processing, as needed for communicating with the gateway node  22 . 
         [0044]    Similarly, the gateway node  22  will be understood as comprising a mix of signal processing and control circuitry, along with supporting communication interfaces—i.e., communication interface circuits. In the example illustration, the gateway node  22  includes first and second communication interfaces  50 - 1  and  50 - 2 —generally referred to as “communication interfaces  50 ”—along with processing circuitry  52  that is operatively associated with the communication interfaces  50 . 
         [0045]    The processing circuitry  52  comprises fixed circuitry, programmed circuitry, or a combination of fixed and programmed circuitry. In an example embodiment, the processing circuitry  52  is at least partly implemented using programmed circuitry and comprises, for example, one or more processors  54 , such as one or more microprocessors, Digital Signal Processors or DSPs, Application Specific Integrated Circuits or ASICs, Field Programmable Gate Arrays or FPGAs, or other digital processing circuitry. Correspondingly, the processing circuitry  52  includes or is associated with one or more types of computer-readable media—“STORAGE  56 ” in the figure—such as one or more types of memory circuits such as FLASH, EEPROM, SRAM, DRAM, etc. Additionally, or alternatively, the storage  56  comprises hard disk storage, Solid State Disk, SSD, storage, etc. 
         [0046]    In general, the storage  56  provides both working memory and longer-term storage. In at least one embodiment, the storage  56  provides non-transitory storage for a computer program  58  and one or more items of configuration data  60 . As before, the term non-transitory does not necessarily mean permanent or unchanging storage, but does means storage of at least some persistence. The computer program  58 , which may comprise a number of related or supporting programs, comprises program instructions that, when executed by the one or more processors  54  implement the processing circuitry  52  according to the configuration examples described herein. In other words, in some embodiments, one or more general-purpose processing circuits within the gateway node  22  are specially adapted to carry out the teachings herein, based on their execution of the computer program instructions comprising the computer program  58 . 
         [0047]    However implemented, the first communication interface  50 - 1  is configured for communicating with the radio node  20 , which is controlled by the gateway node  22 , and the second communication interface  50 - 2  is configured for communicating with one or more core network nodes—not individually depicted in  FIG. 1 —in the CN  18  of the network  10 . 
         [0048]    Now consider  FIG. 2 , which illustrates a known radio protocol stack used in LTE. It will be appreciated that a complementary or mirror copy of the illustrated stack is conventionally implemented in each of the involved protocol endpoints—e.g., in a wireless device and in its serving base station. In the context of these teachings, the “network side” radio protocol stack is split between the radio node  20  and its controlling gateway node  22 . 
         [0049]      FIG. 3  illustrates an example split-stack arrangement. In the diagram, a radio protocol stack  70  is split. The upper portion  72  of the radio protocol stack  70  resides in the gateway node  22  while a lower portion  74  of the radio protocol stack  70  resides in the radio node  22 . 
         [0050]    In this example, the upper portion  72  includes a Packet Data Convergence Protocol, PDCP, layer and a Radio Resource Control, RRC, layer. In the hierarchy of the overall radio protocol stack  70 , the PDCP layer is “below” the RRC layer. The lower portion  74  of the radio protocol stack  70  includes a Radio Link Control, RLC, layer, a Medium Access Control, MAC, protocol layer below the RLC protocol layer, and a Physical, PHY, protocol layer below the MAC protocol layer. 
         [0051]      FIG. 4  provides further example details. For example, one sees that a “PDCP stub” may be implemented in the lower portion  74  of the radio protocol stack  70 , to account for the fact that the illustrated split lies at the RLC-to-PDCP logical interface. The intra-stack IP link  26 /IP session(s)  28  communicatively couple the RRC and PDCP layers at the gateway node  22  to the RLC protocol layer at the radio node  20 . In particular, one or more IP sessions  28  are used to send SDUs from the RRC/PDCP layers RLC layer to the RLC layer over the intra-stack IP link  26  in the downlink direction and vice-versa in the uplink direction. 
         [0052]    Turning back to  FIG. 1 , the processing circuitry  52  of the gateway node  22  is operatively associated with the first and second communication interfaces  50  and is configured to determine that data is available for sending to a wireless device  12  that accesses the network  10  via a radio cell  24  provided by the radio node  20 , where the radio node  20  is coupled to the CN  18  of the network  10  via the gateway node  22 . The processing circuitry  52  is further configured to generate service data units corresponding to the data, based on processing the data according to an upper portion  72  of a radio protocol stack  70 . The radio protocol stack  70  is split between the gateway node  22 , which implements the upper portion  72  of the radio protocol stack  70 , and the radio node  20 , which implements the lower portion  74  of the radio protocol stack  70 . 
         [0053]    Here, it shall be understood that the radio protocol stack  70  is the network-side stack and that the wireless device  12  implements a complementary device-side radio protocol stack having peer entities corresponding to the protocol entities seen in the network-side stack  70 . Thus, what is at issue here is the split between portions of the network-side radio protocol stack  70  and the need for establishing a reliable, efficient, and scalable mechanism for intra-stack communications between the protocol entities within the network-side radio protocol stack  70  that are exposed to the split. 
         [0054]    To that end, the processing circuitry  52  of the gateway node  22  is configured to establish an IP session  28  towards the radio node  20 , via an intra-stack IP link  26  that communicatively couples the upper portion  72  of the radio protocol stack  70  at the gateway node  22  with the lower portion  74  of the radio protocol stack  70  at the radio node  20 . Notably, this IP session is distinct from and transparent to any IP sessions that may be running at the “applications” layer between the wireless device  12  and an application server in the OP services/external networks  14 . Indeed, according to the advantageous teachings herein, the IP session  28  is transparent to the end-to-end communications session(s) between the wireless device  12  and any end-point accesses via the network  10 , and is used purely to connect the upper portion  72  of the network-side radio protocol stack  70  at the gateway node  22  to the lower portion  74  of the network-side radio protocol stack  70  at the radio node  20 . 
         [0055]    Advantageously, the IP session  28  is mapped to a radio bearer to be used for conveying the data to the wireless device  12  via an air interface of the radio cell  24 , and the processing circuitry  52  is configured to encapsulate the service data units in one or more IP packets, according to IP session parameters associated with the IP session  28 , and send the IP packets to the radio node  20  via the IP session  28 , for de-encapsulation and recovery of the service data units, for subsequent processing by the radio node  20  according to the remaining, lower portion  74  of the radio protocol stack  70 . 
         [0056]    Complementary processing and functions at the gateway node  22  and at the radio node  20  provide for the transfer of uplink data and signaling from the wireless device over one or more IP sessions  28  on the intra-stack IP link  26 . That is, downlink data towards the wireless device  12  is processed at the gateway node  22  according to the protocol layers implemented in the upper portion  72  of the radio protocol stack  70 , and is encapsulated as IP traffic for conveyance over an IP session  28  supported via the intra-stack IP link  26 . The radio node  20  receives the encapsulated data and de-encapsulates it for processing according to the protocol layers implemented in the lower portion  74  of the radio protocol stack  70 . Conversely, uplink data—traffic or signaling—from the wireless device  12  is received by the radio node  20  and processed in the uplink direction according to the lower portion  74  of the radio protocol stack. The processed data is sent from the radio node  20  to the gateway node  22  as IP packets in an IP session  28  on the intra-stack IP link  26 . The gateway node  22  extracts the data encapsulated in the IP packets and continues processing that data in the uplink direction, according to the protocol layers implemented in the upper portion  72  of the radio protocol stack  70 . 
         [0057]    In at least some embodiments, the processing circuitry  52  is configured to establish the IP session  28  using a User Datagram Protocol, UDP, when the radio bearer is a data radio bearer, and the wireless device  12  is operating in a Radio Link Control, RLC, Unacknowledged Mode, UM. The processing circuitry  52  is further configured to establish the IP session  28  using a Transmission Control Protocol, TCP, when the radio bearer is a data radio bearer and the wireless device  12  is operating in a RLC Acknowledged Mode, AM, or in a RLC Transparent Mode, TM. Still further, the processing circuitry  52  is configured to establish the IP session  28  using a Transport Layer Security, TLS, protocol, when the radio bearer is a signaling radio bearer, for transmitting Broadcast Control Channel, BCCH, or Paging Control Channel, PCCH, signaling. TLS is also used for SRB 0  and SRB 1 , after AS. Further, in at least some embodiments, the IP session  28  is mapped uniquely for the radio bearer and the wireless device  12 , or is mapped according to a unique flow label assigned to the radio bearer, or is mapped to a unique flow label assigned to the wireless device  12 . 
         [0058]      FIG. 5  illustrates a method  500  of operation in a gateway node  22  that is coupled to a CN  18  of a network  10 . By way of example,  FIG. 5  focuses on downlink processing and the method  500  includes determining (Block  502 ) that data is available for sending to a wireless device  12  that accesses the wireless communication network  10  via a radio cell  24  provided by a radio node  20  that is coupled to the CN  18  of the wireless communication network  10  via the gateway node  22 . The method  500  further includes generating (Block  504 ) service data units corresponding to the data, based on processing the data according to an upper portion  72  of a radio protocol stack  70 , wherein the radio protocol stack  70  is split between the gateway node  22 , which implements the upper portion  72  of the radio protocol stack, and the radio node  20 , which implements a remaining, lower portion  74  of the radio protocol stack  70 . 
         [0059]    Still further, the method  500  includes establishing (Block  506 ) an IP session  28  towards the radio node  20 , via an intra-stack IP link  26  that communicatively couples the upper portion  72  of the radio protocol stack  70  at the gateway node  22  with the lower portion  74  of the radio protocol stack  70  at the radio node  20 . The IP session  28  is mapped to a radio bearer to be used for conveying the data to the wireless device  12  via an air interface of the radio cell  24 , and the method  500  includes encapsulating (Block  508 ) the service data units in one or more IP packets, according to IP session parameters associated with the IP session  28 , and sending (Block  510 ) the IP packets to the radio node  20  via the IP session  28 , for de-encapsulation and recovery of the service data units, for subsequent processing by the radio node  20  according to the remaining, lower portion  74  of the radio protocol stack  70 . 
         [0060]    The IP link  26  in one embodiment comprises an IP Version 6, IPv6, link. Of course, it is also contemplated that the IP link  26  be implemented as an IPv4 link and in operation, the gateway node  22  may support IP sessions  28  based on both IPv4 and IPv6. For example, a given radio node  20  may not support IPv6, while another radio node  20  does support IPv6. 
         [0061]      FIG. 6  illustrates a method  600  in a radio node  20 , corresponding to the gateway method  500 . The radio node  20  is configured for operation in the network  10  and is particularly configured for being controlled by the gateway node  22 . The method  600  includes establishing (Block  602 ) a radio bearer under control of a gateway node  22 , for communicating with a wireless device  12  and establishing (Block  604 ) an IP session  28  with the gateway node  22 , via an intra-stack IP link  26  between the radio node  20  and the controlling gateway node  22 . Again, this IP link  26  is for connecting the upper and lower portions  72  and  74  of the split radio protocol stack  70 , and should not be confused with end-to-end IP sessions/links between the wireless device  12  and any “application” layer servers or systems. 
         [0062]    The method  600  further includes receiving (Block  606 ) one or more IP packets via the IP session  28  and de-encapsulating the received IP packets to recover the data targeted to the wireless device  12 . More particularly, the de-encapsulation involves de-encapsulating the IP packets to recover the SDUs incoming from the protocol layer operating in the gateway node  22  at the point where the radio protocol stack  70  is split between the gateway node  22  and the radio node  20 . Correspondingly, the method  600  further includes inputting (Block  608 ) the de-encapsulated data into the remaining, lower-portion  74  of the radio protocol stack  70 , as implemented at the radio node  20 , for processing and sending to the wireless device  12  over the air interface. 
         [0063]      FIGS. 7 and 8  illustrate substantially similar processing as set forth in  FIGS. 5 and 6 , but are presented in the context of uplink processing. In particular, the method  700  of  FIG. 7  depicts radio node processing and includes receiving (Block  702 ) user traffic from a wireless device  12 . The method  700  further includes generating (Block  704 ) SDU(s) from the received user traffic, via the lower portion  74  of the radio protocol stack  70 , and mapping (Block  706 ) the radio bearer associated with the SDU(s) to an IP session  28  on the intra-stack IP link  26 . Processing continues with the radio node  20  encapsulating (Block  708 ) the SDU(s) into one or more IP packets, in accordance with the mapped/Identified IP session  28 , and sending (Block  710 ) the IP packet(s) towards the gateway node  22  over the intra-stack IP link  26 . 
         [0064]      FIG. 8  illustrates a corresponding method  800  as carried out by the gateway node  22 . The method  800  includes receiving (Block  802 ) an IP packet from the radio node  20  in an IP session  28  on the intra-stack IP link  26 , and mapping (Block  804 ) the IP session  28  to a radio bearer, according to session/bearer mapping known at the gateway node  22 , e.g., from connection setup/establishment processing. Processing continues with the gateway node  22  de-encapsulating (Block  806 ) the SDU(s) contained in the IP packet and inputting (Block  808 ) the SDU(s) into the upper portion  72  of the radio protocol stack. The method  800  continues with the gateway node  22  sending (Block  810 ) the data generated from processing the SDU(s) in the upper portion  72  of the radio protocol stack  70  on to the core network for higher-layer processing. 
         [0065]    Consequently, it will be appreciated that a SDU output from the “top” of the lower portion  74  of the radio protocol stack  70  is encapsulated in an IP packet for transport over the intra-stack IP link  26 , in the IP session  28  to which the involved radio bearer is mapped. At the gateway node  22 , the SDU is extracted from the IP packet and passed into the “bottom” of the upper portion  72  of the radio protocol stack  70 , for completion of the overall protocol processing associated with the radio protocol stack  70  in the uplink direction. The converse is true in the downlink direction, i.e., SDUs emerging from the bottom of the upper portion  72  of the radio protocol stack  70  are encapsulated as IP packets and transported in a mapped IP session  28  over the intra-stack IP link  26 . The radio node  20  de-encapsulates those IP packets to recover the SDUs, which are then input to the top of the lower portion  74  of the radio protocol stack  70 , for completion of the overall stack processing in the downlink direction. It will be appreciated that the “bottom” of the upper portion  72  is taken as the stack layer at the gateway node  22  that is exposed to the split. Likewise, the “top” of the lower portion  74  is taken as the stack layer at the radio node  20  that is exposed to the split. 
         [0066]      FIG. 9  illustrates an example embodiment in the context of a LTE network, wherein the CN  18  includes serving gateway, S-GW  80 , coupled to the gateway node  22  via a S1-UE interface, and a MME  82  coupled to the gateway node  22  via a S1-MME interface. The S-GW  80  and MME are communicatively coupled via a S11 interface, and the S-GW  80  is further communicatively coupled to a Packet Gateway, P-GW  84 , which provides the packet-routing interface, SGi, into and out of the network  10 . The MME  82  communicatively couples to a Home Subscriber Server, HSS  86 , via an S6a interface, and the HSS  86  couples to a Policy and Charging Rules Function, PCRF  88 , which is also coupled to the P-GW  84 . In the diagram, dashed connection lines are used to illustrate Control Plane, CP, signaling, while solid connection lines are used to illustrate User Plane, UP, signaling. 
         [0067]      FIG. 10  illustrates an example splitting of the radio protocol stack  70  between the radio node  20  and the gateway node  22 , in the context of the LTE network example of  FIG. 9 .  FIG. 10  illustrates the further supporting protocol stacks used at the various other CN nodes seen in  FIG. 9  and particularly highlights the IP link  26 /IP session  28  used to link the lower portion  74  of the split radio protocol stack  70 , as implemented in the radio node  20 , with the upper portion  72  of the stack  70 , as implemented in the gateway node  22 . It will be appreciated that there may be any number of split-stack “instances” implemented between the gateway node  22  and the radio node  20 , e.g., for simultaneously supporting multiple wireless devices  12 . 
         [0068]    With the above example implementation details in mind, it shall be appreciated that the mapping of radio bearer, RB, traffic, e.g., PDCP PDUs, to IP sessions  28  provides for flexible connectivity between a gateway node  22  and any number of controlled radio nodes  20 . The proposed RB-to-IP mapping schemes provide a scalable solution that supports potentially large numbers of radio nodes  20  with respect to a controlling gateway node  22 . 
         [0069]    Further, the mapping scheme(s) presented herein provide radio bearer traffic granularity and a sound, robust traffic isolation solution upon which various network use-cases become more easily deployable by the network operator. Example use cases include bearer-based or device-based routing policy deployment, for efficiently routing device traffic over the IP connection interconnecting the split stack  70 , e.g., using IPv6 flow labels. Another example is bearer-based and/or device-based access control security policy deployment, such as where firewalling parameters or policy settings are based on the identities of the wireless devices  12  being supported via the split-stack arrangement. Further examples include bearer-based and/or device-based Quality-of-Server, QoS, policy deployment, data packet inspection at the gateway node  22  on a per device  12  and a per radio node  20  basis, and lawful interception techniques, which typically requires per device discrimination. 
         [0070]    The teachings herein further provide for the use of IP service discovery for dynamic configuration of the radio node  20 , e.g. IPv6 address auto-configuration—stateless address auto configuration or SLAAC—as well as dynamic discovery of the gateway node  22  by each radio node  20  to be controlled by the gateway node  22 . The teachings herein further provide for the use of Transport Layer Security, TLS, encryption to secure BCCH, PCCH, SRB 0  and SRB 1  traffic, which is not PDCP-ciphered. Here, “SRB 0 ” and “SRB 1 ” denotes Signaling Radio Bearer  0  and Signaling Radio Bearer  1 , respectively. The SRB 0  and SRB 1  are used for the transfer of RRC and Non-Access Stratum signaling messages. RRC messages go between the wireless device  12  and the radio node  20  and NAS messages go between the wireless device  12  and the MME  82 . Still further, the teachings herein enable the use of TCP for window-based flow control of RLC traffic in the AM mode. 
         [0071]    In an example implementation, the radio node  20  provides the RLC/MAC/PHY layers of the radio protocol stack  70 , i.e., the lower portion  74  of the split stack  70  at the radio node  20  includes the RLC, MAC, and PHY layers. Correspondingly, the gateway node  22  provides centralized RRC and PDCP functions, which are managed by the involved network operator and are connected to any number of radio nodes  20 . Thus, the gateway node  22  provides centralized radio resource control for multiple radio nodes  20 . The gateway node  22  further provides the mapping between the GTP-U TEID-to-IP sessions for Data Radio Bearers, DRBs, as well as the mapping of RRC contexts-to-IP sessions for Signaling Radio Bearers, SRBs, based on the information supplied by each such radio node  20 . 
         [0072]    In the LTE context and with reference again to  FIG. 10 , the Uu and S1 interfaces are unchanged in one or more embodiments contemplated herein. The changes are limited to the newly proposed interface between the gateway node  22  and the radio node  20 , for communicatively coupling together the upper portion  72  of the split radio protocol stack  70  with the lower portion  74  of the split radio protocol stack  70 . This new interface, represented in  FIG. 10  as the IP link  26 /IP session(s)  28 , transports packets between the protocol entities that are exposed to the split. In LTE, the CP and UP traffic carried over this new interface, where RRC messages may be simply forwarded on a “pass-through” basis from RLC entities to PDCP entities and vice versa. BCCH, PCCH, SRB 0  and SRB 1  traffic are sent over the IP link  26  using TLS/TCP/IP. SRB 2  and DRBs are PDCP protected, i.e. encrypted, and, therefore, are sent over the IP link  26  using TCP or UDP. In one or more embodiments, Stream Control Transmission Protocol, SCTP, packets are avoided to prevent blocking issues that might otherwise arise with respect to CPE firewalling. 
         [0073]      FIG. 11  illustrates an example call flow diagram covering local network attachment operations, wherein the radio node  20  connects to the local network provided by CPE. The radio node  20  sends router solicitation signaling and receives a return router advertisement, performs SLAAC processing, and then sends a DHCPv6 information request. The radio node  20  receives a corresponding response from the CPE that includes the address of the gateway node  22  supporting the radio node  20  and coupling it to the CN  18 . Note that the router advertisement will contain a prefix to auto-configure an address, e.g., using SLAAC, and will have the Obit set to initiate stateless DHCPv6. It is also contemplated to use a Fully Qualified Domain Name, FQDN, if load balancing and/or failover of the gateway node  22  are required. 
         [0074]      FIG. 12  illustrates a call flow diagram covering a secure channel establishment between a radio node  20  and its supporting gateway node  22 . It is contemplated that in at least one embodiment of such signaling that a client certificate is used to authenticate the radio node  20  towards the network  10 . A TLS connection may be used for sending unencrypted control and data plane traffic over the IP link  26 /IP session  28 . 
         [0075]      FIG. 13  illustrates a call flow diagram covering processing that follows the establishment of a secure connection between a radio node  20  and its supporting gateway node  22 . After establishing a secure channel, the radio node  20  connects to the gateway node  22  to initiate configuration. The gateway node  22  will then provide the radio initialization parameters, such as radio frequency bands, bandwidth, access schemes, antenna technology, physical channel configurations, etc., for the radio node  20 . After receiving the radio parameters, the radio node  20  sends the set of mappings between each radio bearer and the IP address plus the port and/or IPv6 flow label combination that it will use for traffic on that specific bearer, with respect to the IP link  26 . 
         [0076]    Although it may be assumed that IPv6 links are used to transport data between the radio node  20  and the gateway node  22  for the IP link  26  supporting the stack split, the first mapping scheme presented below is also applicable to IPv4 links. It is assumed that there is a single PDU per IP packet, and all messages are sent in network byte order. All contemplated schemes consider UDP for bearers configured in RLC UM mode and TCP for RLC AM and TM. 
         [0077]    In a first mapping option contemplated herein, there is a unique IP session  28  per bearer and per wireless device  12 . That is, there is an IP session  28  on the IP link  26  for each bearer with respect to each wireless device  12  being supported by the radio node  20 . 
         [0078]    In a second mapping option contemplated herein, there is a unique IPv6 flow label per bearer type. As compared to the first mapping scheme, the difference is that flow isolation is achieved by using a different IPv6 flow label per radio bearer type. This second scheme allows for improved packet switching based on flow label or bearer type. 
         [0079]    In a third mapping option, there is a unique IPv6 flow label per wireless device  12 . As compared to the second mapping scheme, the difference with this third mapping scheme is that flow isolation is achieved by using a different IPv6 flow label per wireless device  12 , which is identified with a C-RNTI-like ID. If the flow labels are exchanged on demand, for example, upon initial attachment of a wireless device  12  to the radio node  20 , the IPv6 flow labels could embed the C-RNTI of the attaching wireless device  12 . 
         [0080]      FIG. 14  is a logic flow diagram illustrating another embodiment of a method  1400  of processing at a gateway node  22  that is configured for operation in a network  10 , and for controlling a radio node  20  that is configured to communicatively couple one or more wireless devices  12  to the network  10  via a cell  24  provided by the radio node  20 . The method  1400  focuses on a downlink example and begins with receiving a packet at the gateway node  22  for a given wireless device  12  (Block  1402 ). Processing continues with identifying the radio bearer or radio bearer type to be used for conveying the received packet (Block  1404 ). If the received packet is user traffic, it is associated with a DRB and processing continues in Block  1406 , with performing Robust Header Compression, ROHC, and ciphering at the PDCP layer of the radio protocol stack  70 . Here, the PDCP layer resides in the gateway node  22 . 
         [0081]    The involved DRB is mapped to an IP session  28  (Block  1408 ) that provides the intra-stack connection between the split entities of radio protocol stack  70 , and the RLC mode is determined (Block  1410 ). For AM mode operation, the method  1400  includes checking whether a connection to the wireless device  12  has been established (Block  1412 ) and performing connection setup (Block  1414 ) if not. Once the connection has been setup, or if the RLC mode is UM, processing continues with encapsulating (Block  1416 ) the received user-traffic packet in an IP packet for conveyance (Block  1418 ) to the radio node  20  via the IP session  28  supported by the IP link  26  that interconnects the lower portion  74  of the split radio protocol stack  70  in the radio node  20  with the upper portion  72  of the split radio protocol stack  70  in the gateway node  22 . 
         [0082]    That is, the encapsulation occurs here for purposes of conveying the packet between the split entities of the radio protocol stack  70 , as split between the gateway node  22  and the radio node  20 , and is unrelated to any IP running at protocol layers above the split radio protocol stack  70 . It will also be appreciated that a corresponding de-encapsulation, therefore, occurs within the lower portion  74  of the radio protocol stack  70  at the radio node  20 . Thus, this usage of IP conveyance is transparent to higher-layer protocol endpoints running at the wireless device  12  and, e.g., at the P-GW  84  or at some server external to the network  10 , and is operative only with respect to interconnecting the entities within the radio protocol stack  70  that are exposed to the split between the radio node  20  and the gateway node  22 . 
         [0083]    On the other hand, with reference again to Block  1404 , if the received packet is BCCH, PCCH, or otherwise associated with SRB 0 , SRB 1  or SRB 2  control signaling, RRC processing is performed at Block  1420  and, for SRB 1  signaling, processing includes determining whether AS Security—a LTE security protocol associated with RRC signaling—is active (Block  1422 ). If AS Security is not active, it is contemplated herein to advantageously apply TLS, and processing in this case thus continues with RB-to-IP-Session mapping (Block  1428 ), for the IP link  26 , and TLS encryption of the received packet (Block  1430 ). TLS could be used for the duration of the SRB 1  traffic, but switching after AS is another option. For SRB 2  signaling, or in the case where AS Security is active, the PDCP layer processing includes encryption of the packet, and thus processing can continue from Block  1420  or Block  1422  with PDCP processing (Block  1424 ) and RB-to-IP-Session mapping for the IP link  26  (Block  1426 ). 
         [0084]    From Block  1426 , processing continues with determining whether a connection to the wireless device  12  has been established (Block  1432 ) and, if so, performing IP encapsulation of the packet for conveyance over the IP link  26  in the mapped IP session  28  (Blocks  1434  and  1436 ). If the connection has not already been setup, the connection is setup at Block  1438  (NO from Block  1432 ), and then the encapsulation and conveyance operations in Blocks  1434  and  1436  are carried out. 
         [0085]    Notably, modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.