Patent Publication Number: US-9907099-B2

Title: Relay node, a donor radio base station and methods therein

Description:
This application is a divisional application of pending U.S. application Ser. No. 13/132,576, filed 2 Jun. 2011, which claims priority from International Application PCT/SE2011/050457 (filed 14 Apr. 2011), which in turn claims priority to U.S. Provisional Application No. 61/373,328 (filed 13 Aug. 2010) and is a continuation of International Application PCT/SE2010/040687 (filed 18 Jun. 2010). The disclosures of each of these applications are incorporated in their entireties by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a relay node, a donor radio base station and methods therein. Furthermore, embodiments herein relate to acquire information or inform about a type of a radio network connection between the donor radio base station and a radio base station. 
     BACKGROUND 
     In today&#39;s radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. A radio communications network comprises radio base stations providing radio coverage over at least one respective geographical area forming a cell. The cell definition may also incorporate frequency bands used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. User equipments (UE) are served in the cells by the respective radio base station and are communicating with respective radio base station. The user equipments transmit data over an air or radio interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data over an air or radio interface to the user equipments in downlink (DL) transmissions. 
     One important aspect with radio communications networks also referred to as wireless networks is to ensure that the radio communications network is simple to deploy and cost efficient to operate. The vision is that the radio communications network shall be self-organizing in as many aspects as possible. Furthermore, good coverage is important when aiming at a mobile broadband experience, both outdoors and indoors. Typically, this coverage is provided via radio base stations covering larger cells, also referred to as macro base stations, with dedicated transport connections, but it is also possible to consider self-backhauling radio base stations also referred to as Relay Nodes (RN) where the same technology is used both for user data between a user equipment and the RN and for the transport connection between the RN and a radio base station with a dedicated transport connection. Self-backhauled here means that the RN is acting as a relay node to the donor radio base station. 
     The architecture of the 3G Long Term Evolution (LTE) system may thus include Relay Nodes (RN) also called relay base stations. Furthermore, the LTE architecture discloses logical interfaces between radio base stations (eNBs) called X2 interfaces, and between radio base station and Mobility Management Entity (MME) or Serving Gateway (S-GW), called S1 or S11 interfaces. The radio base station serving the RN acts as an X2 and S1 proxy, terminating and forwarding the X2 communication between the RN and another radio base station, and the S1 communication between the RN and the MME. The radio base station serving the RN may be referred to as a donor radio base station (DeNB). 
     RNs that are self-backhauling are further considered for LTE Advanced. LTE-Advanced extends LTE Release 8 with support for relaying as a tool to improve e.g. the radio coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide radio coverage in new areas. 
     RNs are wirelessly connected to a respective donor cell of a donor radio base station (donor eNB) via a radio interface denoted a Un interface, and user equipments are connected to respective RN via a radio interface denoted a Uu interface. The donor radio base station further connects the respective RN to the core network, e.g. the Evolved Packet Core (EPC) in LTE. The Uu interface is the radio interface between the user equipment and the RN. The Un interface is the radio interface between the RN and the donor radio base station. 
     The Un interface connection may be a “Type 1” connection, which means that the connection is an in-band connection, in which case the eNB-to-RN connections or links share the same frequency band with direct eNB-to-UE connections or links within the donor cell. The Un interface connection may furthermore be a “Type 2” connection, which means that the connection is an out-band connection, in which case the eNB-to-RN connection does not operate in the same band as direct eNB-to-UE connections within the donor cell. 
     At least “Type 1” RNs are supported by LTE-Advanced. A “Type 1” RN is an in-band RN that controls cells, each of which appears to a user equipment as a separate cell distinct from the donor cell. The cells have their own Physical Cell ID (PCI), which is a fingerprint used by a user equipment to identify the cell, and transmit their own synchronization channels and reference symbols. In the context of single-cell operation, the user equipment receives scheduling information and data transmission feedback directly from the in-band RN and sends its control information to the in-band RN. The in-band RN appears as a radio base station to a legacy user equipment, i.e. the in-band RN is backwards compatible. The in-band RN may be nomadic meaning that it may change donor eNBs over time, via disruptive events such as physical relocations or the relay node associated with the disconnection of the radio interface. The in-band RN may further be inactive at times for example to save energy. 
     To a large extent, the RNs may be perceived as any radio base station in the radio communications network. For example, the connections X2 and S1 between RN and other radio base stations are established, partly over Un. But also, the RN is handled to a large extent as any user equipment served by the serving radio base station. For example, when the RN is installed, it attaches to the radio communications network via the UE attach procedure, which is a procedure used to attach a user equipment to the network, and first when Radio Resource Control (RRC) connectivity is established, the serving radio base station is informed by the core network that the user equipment is in fact a RN. 
     From the perspective of the RN it is not possible to disclose whether a certain type of radio network connection is established between the donor radio base station and a neighboring radio base station. Since the RN may need to select between different types of radio network connections e.g. X2 connectivity and S1 connectivity, when for example performing handover, the performance of the radio communications network will be reduced if the wrong type of radio network connection is selected. 
     SUMMARY 
     An object of some embodiments herein is to provide a mechanism to improve the performance in a radio communications network. 
     According to an aspect of embodiments herein the object is achieved by a method in a relay node for acquiring information about a type of a radio network connection between a donor radio base station and a radio base station. The relay node and donor radio base station are comprised in a radio communications network. The donor radio base station is serving the relay node. The relay node receives a message from the donor radio base station, which message is indicating a type of radio network application protocol. The type of radio network application protocol is related to a type of a radio network connection between the donor radio base station and the radio base station. The relay node determines the type of the radio network connection based on the type of radio network application protocol indicated in the message. The relay node further stores the type of radio network connection in relation to the radio base station. This stored information may be used for selecting the type of radio network connection when later communicating with the radio base station. 
     In order to perform the method a relay node for acquiring information about the type of the radio network connection between the donor radio base station and the radio base station. The relay node is arranged to be comprised in a radio communications network and is arranged to be served by the donor radio base station. The relay node comprises a receiver configured to receive a message from the donor radio base station. The message is indicating a type of radio network application protocol, which type of radio network application protocol is related to a type of a radio network connection between the donor radio base station and the radio base station. The relay node further comprises a determining circuit configured to determine the type of the radio network connection based on the type of radio network application protocol indicated in the message. Additionally, the relay node comprises a memory circuit configured to store the type of radio network connection in relation to the radio base station to be used when selecting the type of radio network connection when later communicating with the radio base station. 
     According to an aspect of embodiments herein the object is achieved by a method in a donor radio base station for informing a relay node about a type of a radio network connection between the donor radio base station and a radio base station. The relay node and the donor radio base station are comprised in a radio communications network. The donor radio base station serves the relay node. The donor radio base station receives a protocol message of a first type of a radio network application protocol, from the relay node or from the radio base station. The donor radio base station furthermore transmits a message to the relay node, which message is indicating the first type or a second type of a radio network application protocol. Each type of a radio network application protocol is related to a type of the radio network connection and thereby the relay node is informed of the type of the radio network connection. 
     Embodiments herein describe means to enable the relay node to know whether a certain type of the radio network connection, such as X2 connection, is established between its serving donor radio base station and other radio base stations, or not in an efficient manner. Thereby the signaling procedure is facilitated and the performance is improved as the stored information in the relay node is used to communicate, e.g. during a handover procedure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described in more detail in relation to the enclosed drawings, in which: 
         FIG. 1  is a schematic overview of a radio communications network, 
         FIG. 2  is a schematic overview of a radio communications network, 
         FIG. 3  is a schematic signalling scheme in a radio communications network, 
         FIG. 4  is a schematic signalling scheme in a radio communications network, 
         FIG. 5  is a schematic flow chart of a method in a radio communications network disclosing X2 connectivity support learning procedure, 
         FIG. 6  is a schematic X2 probing signalling scheme in a radio communications network, 
         FIG. 7  is a schematic X2 probing signalling scheme in a radio communications network, 
         FIG. 8  is a schematic X2 probing signalling scheme in a radio communications network, 
         FIG. 9  is a schematic overview of a radio communications network, 
         FIG. 10  is a schematic signalling scheme in a radio communications network, 
         FIG. 11  is a schematic signalling scheme in a radio communications network, 
         FIG. 12  is a schematic signalling scheme in a radio communications network, 
         FIG. 13  is a schematic signalling scheme in a radio communications network, 
         FIG. 14  is a schematic signalling scheme in a radio communications network, 
         FIG. 15  is a schematic flow chart of a method in a relay node in a radio communications network, 
         FIG. 16  is a block diagram of a relay node, 
         FIG. 17  is a schematic flow chart of a method in a donor radio base station in a radio communications network, and 
         FIG. 18  is a block diagram of a donor radio base station. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic overview of a radio communications network. Embodiments herein are discussed based on an Evolved Universal Terrestrial Radio Access (E-UTRA) system, which is also commonly referred to as the Long-Term Evolution (LTE) of the widely deployed WCDMA systems but may be implemented in any radio communications network that uses inter radio access network interfaces and intra radio access network interfaces between radio network entities. Inter radio access network interfaces may also be referred to as peer to peer interfaces and intra radio access network interfaces may also be referred to as interfaces terminated in a core network of the radio communications network. However, the figures will relate to the LTE and especially the LTE Advance network architecture. In the example of LTE, X2 is the peer to peer interface between radio base stations with signalling defined by the X2 Application Protocol, and S1 or S11 is the interface terminated in the core network between a radio base station and a core network with signalling defined by the S1 Application Protocol. The radio communication network may use a radio technology, such as Long Term Evolution (LTE), LTE-Advanced, 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. 
     In order to improve coverage of the radio communications network a relay node  10  is provided covering, for example, a radio coverage hole or similar in the radio communications network. The relay node  10  provides radio coverage over a geographical area forming a relay cell  11 . Thereby, the relay node  10  provides improved radio coverage within the radio communications network. The radio communications network further comprises a first radio base station  12  and a second radio base station  14  each providing radio coverage over at least one respective geographical area forming a respective cell, a first cell  13  and a second cell  15 . The relay node  10  is served by the first radio base station  12 , which is referred to as the donor radio base station  12 . 
     The donor radio base station  12  may be connected to the second radio base station  14  over a type of radio network connection e.g. over a peer to peer connection such as an X2 connection. The donor radio base station  12  may be a member of a Mobility Management Entity (MME) pool comprising a first MME  16 . The second radio base station  14  may be a member of a Mobility Management Entity (MME) pool comprising a second MME  17 . Thus, the donor radio base station  12  is controlled by the first MME  16  and the second radio base station  14  is controlled by the second MME  17 . The donor radio base station  12  may additionally or alternatively be connected to the second radio base station  14  through an interface terminated in the core network over a type of radio network connection, such as a S1 or S11 connection, via the first MME  16  or the second MME  17 . User equipments (UE) are served in cells by respective radio base station  12 , 14  and are communicating with respective radio base station  12 , 14 . The user equipments transmit data over a radio interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data to the user equipments in downlink (DL) transmissions. A user equipment  18  has poor channel conditions to the radio base station  12  at a certain geographic location but is served by the relay node  10 . 
     It should be understood by the skilled in the art that “user equipment” is a non-limiting term which means any wireless terminal, device or node e.g. personal digital assistant (PDA), laptop, mobile, sensor, relay, or even a small base station communicating within respective cell. 
     The respective radio base station  12 , 14  may also be referred to as e.g. a NodeB, an evolved Node B (eNB, eNode B), a base transceiver station, Access Point Base Station, base station router, or any other network unit capable to communicate with a user equipment within the cells  13 , 15  served by the respective radio base station  12 , 14  depending e.g. of the radio access technology and terminology used. 
     Embodiments herein concentrate on a situation where the relay node  10  is unaware of the connectivity between the donor radio base station  12  and the second radio base station  14 , also referred to as the radio base station  14 . 
     Especially, embodiments herein disclose ways for the relay node  10  to acquire information about the type of connectivity, also referred to as type of radio network connection. The relay node  10  receives a message from the donor radio base station  12 , which message indicates a type of radio network application protocol. The type of radio network application protocol is related to the type of the radio network connection. The relay node  10  then determines the type of the radio network connection between the donor radio base station  12  and the second radio base station  14  based on the type of radio network application protocol indicated in the message. The relay node  10  stores the type of radio network connection in relation to the second radio base station  14  within the relay node  10 . The relay node  10  may then select the type of radio network connection when later communicating with the second radio base station  14 . For example, when the relay node  10  later performs a handover process of the user equipment  18  to the second radio base station  14  the relay node  10  uses the acquired information and sends a handover request of an application protocol related to the stored type of radio network connection. 
     According to some embodiments herein the donor radio base station  12  may inform the relay node  10  about type of radio network connection e.g. X2 support to the second radio base station  14  in a new explicit message or a new Information Element (IE) in an existing message. This may require that a new message and Information Element (IE) are defined only for this specific case. 
     According to some embodiments, the donor radio base station  12  may implicitly inform the relay node  10  of the type of the radio network connection to the second radio base station  14 . For example, the relay node  10  detects a presence of the second radio base station  14  and sends an address recovery message to the donor radio base station  12 . The donor radio base station  12  may know that an X2 connection is already set up to the second radio base station  14  and compiles an X2 setup request message to the relay node  10  on behalf of the second radio base station  14 . The donor radio base station  12  may alternatively setup an X2 connection to the second radio base station  14 . The relay node  10  then receives the X2 setup request message and based on the type of the message, being an X2 message, the relay node  10  determines that an X2 connection is present to the second radio base station  14 . 
     According to some embodiments the relay node  10  may be informed by receiving an X2 handover request from the second radio base station  14  and based on that determine that an X2 connection is setup between the donor radio base station  12  and the second radio base station  14 . 
     According to some embodiments the relay node  10  may be informed by sending an X2 handover request to the second radio base station  14  and receiving either an X2 handover acknowledgement or a S1AP handover command via the donor radio base station  12  from the second radio base station  14 . The relay node  10  may alternatively send a S1AP Handover Required to the donor radio base station  12  and based on the type of the application protocol in the response received, store the type of radio network connection in relation to the second radio base station  14  for future knowledge. 
     Thus, in some embodiments the knowledge of X2 connectivity is acquired by the relay node  10  from the donor radio base station  12  when the relay node  10  tries to use X2 or S1 as the signaling means to the second radio base station  14 . From the type of the application protocol of the response received the relay node  10  may determine if X2 is established. In this way the signaling is facilitated and requires no new IEs or messages. 
       FIG. 2  is a block diagram depicting interfaces in the radio communications network. The relay node  10  is wirelessly connected to the donor cell  13  of the donor radio base station  12  via a Un interface, and the user equipment  18  is connected to the relay cell  11  of the relay node  10  via a Uu interface. The donor radio base station  12  further connects the relay node  10  to the core network, e.g. the evolved packet core (EPC). The Uu interface is the radio interface between the user equipment  18  and the relay node  10 . The Un interface is the radio interface between the relay node  10  and the donor radio base station  12 . 
     The Un interface connection may be an in-band connection. In-band connection means that ‘radio base station-to-relay node’ connection share the same frequency band with a direct ‘radio base station-to-UE’ connection within the donor cell  13 . The Un interface connection may alternatively be an out-band connection. Out-band connection means that the ‘radio base station-to-relay node’ connection does not operate in the same frequency band as the direct ‘radio base station-to-UE’ connection. 
     As stated above, the relay node  10  may be perceived as any radio base station. For example, the connections X2 and S1 between the relay node  10  and other radio base stations may be established, partly over Un. But also, the relay node  10  may be handled to a large extent as any user equipment served by the serving donor radio base station  12 . For example, when the relay node  10  is installed, it attaches to the network via a UE attach procedure. First when Radio Resource Control (RRC) connectivity is established, the donor radio base station  12  is informed by the core network that the ‘user equipment’ is in fact the Relay Node (RN)  10 . 
     As mentioned above, the relay node  10  acquires information whether the radio network connection type between the donor radio base station  12  and the second radio base station  14  is a peer to peer interface, also called X2 interface, or an interface terminated in the core network, also referred to as a S1 interface. The type of the radio network connection is then stored in relation to the second radio base station  14  at the relay node  10  for being used when selecting the type when later communicating with the radio base station  14 . This is performed according to some embodiments described below. 
       FIG. 3  is a schematic signaling scheme of some embodiments of a method in the radio communications network, exemplified as an LTE network. In this example, the relay node  10  may be informed of type of radio network connection between the donor radio station  12  and the second radio base station  14  by sending a handover request of a certain type to the second radio base station  14 . In some embodiments, the relay node  10  attempts to use X2 handover preparation signaling to the second radio base station  14  assuming that X2 interface is established between donor radio base station  12  and the second radio base station  14 . X2 handover preparation may be used since an X2 handover procedure is more efficient than the S1 handover procedure. 
     Step  301 . The relay node  10  sends an X2 Application Protocol (AP) Handover (HO) Request to the donor radio base station  12  of e.g. the user equipment  18  served in the relay cell  11 . This is an example of step  1501  in  FIG. 15 . 
     Step  302 . If X2 is established, then the handover process proceeds and the donor radio base station  12  forwards the X2AP Handover Request to the second radio base station  14 . 
     Step  303 . The second radio base station  14  accepts the handover of the user equipment  18  and sends an X2AP Handover Request Acknowledgement (ACK) to the donor radio base station  12 . 
     Step  304 . The donor radio base station  12  then forwards the X2AP Handover Request ACK to the relay node  10 . This is an example of step  1705  in  FIG. 17 . Thus, the relay node  10  receives eventually a response of X2AP, acknowledging the handover preparations, and indicating that X2 is established. This means that the relay node  10  may learn the existence of X2 connectivity, that is, the type of the radio network connection, from the type of the response from the donor radio base station  12 , and stores this connectivity information for future or later use. 
       FIG. 4  shows a signaling scheme of some embodiments of a method in the radio communications network. Also in this example, the relay node  10  may be informed of the type of radio network connection between the donor radio base station  12  and the second radio base station  12  by sending a handover request of a certain type to the second radio base station  14 .  FIG. 4  shows a converted X2 handover preparation into S1 handover signalling. An S1 response message may include information related to the UE context or the original X2 message so that the relay node  10  may link the X2 procedure and the S1 procedure together, i.e. so it knows that the S1 message is a response to the X2 message. The information may comprise a temporal context or transaction ID, or some other information related to the user equipment  18 . 
     Step  401 . The relay node  10  sends an X2AP Handover (HO) Request to the donor radio base station  12  of e.g. the user equipment  18  served in the relay cell  11 . This is an example of step  1501  in  FIG. 15 . 
     Step  402 . If X2 is not established, the donor radio base station  12  converts the X2 message to a corresponding S1 message, a so called S1AP Handover Required, which is sent to the first MME  16 . 
     Step  403 . The first MME  16  sends an S1AP Handover Request to the second radio base station  14 . 
     Step  404 . The second radio base station  14  accepts the handover of the user equipment  18  and sends a S1AP Handover Request ACK to the first MME  16 . 
     Step  405 . The first MME  16  may respond with the result of the handover attempt in an S1 message, a so called S1AP Handover Command, to the donor radio base station  12 . 
     Step  406 . The donor radio base station  12  forwards the S1AP Handover Command to the relay node  10 . This is an example of step  1705  in  FIG. 17 . Since the response is a type defined as an S1AP type, the relay node  10  learns that X2 connectivity is not available and stores this information for later or future use. 
     This means that the relay node  10  will gradually over time learn and store the existence of X2 connectivity to neighboring radio base stations. 
     An overview of some embodiments of a total learning procedure using handover messages is illustrated in  FIG. 5 . 
     Step  501 . The relay node  10  may receive a measurement report of received signal strength from the user equipment  18  indicating a handover to the second cell  15  of the second radio base station  14 . The measurement report may be represented by a RRC-UE Measurement report. 
     Step  502 . The relay node  10  may: know that the second radio base station  14  has an X2 connectivity to the donor radio base station  12 ; know that the second radio base station  14  doesn&#39;t have an X2 connectivity to the donor radio base station  12 ; or don&#39;t know the radio network connection type between the second radio base station  14  and the donor radio base station  12 . 
     Step  503 . When the relay node  10  knows that the second radio base station  14  doesn&#39;t have an X2 connectivity to the donor radio base station  12 , the relay node  10  may send a S1AP Handover Required to the second MME  17  via the donor radio base station  12 . 
     Step  504 . After step  503 , the S1 handover procedure may continue in a normal manner. Thus, normal S1 handover takes places. 
     Step  505 . When the relay node  10  knows that the second radio base station  14  has an X2 connectivity to the donor radio base station  12 , the relay node  10  sends an X2AP Handover Request of the user equipment  18  to the donor radio base station  12 . 
     Step  506 . After step  505 , the X2 handover procedure may continue in a normal manner. Thus, normal X2 handover takes places. 
     Step  507 . When the relay node  10  doesn&#39;t know whether that the second radio base station  14  has an X2 connectivity or not to the donor radio base station  12 , the relay node  10  may send, according to embodiments herein, an X2AP handover request of the user equipment  18  to the donor radio base station  12 . This is an example of step  1501  in  FIG. 15 . 
     Step  508 . The donor radio base station  12  determines whether an X2 connectivity between the second radio base station  14  and the donor radio base station  12  exists or not based on previous knowledge, stored information, of the type of radio network connection between the second radio base station  14  and the donor radio base station  12 . 
     Step  509 . When the donor radio base station  12  has an X2 connectivity to the second radio base station  14 , may also referred to as the target radio base station  14 , normal X2 handover procedure will take place. 
     Step  510 . After the step  509 , the relay node  10  updates its X2 connectivity information by storing that X2 to the second radio base station  14  is present. This is an example of step  1504  in  FIG. 15 . 
     Step  511 . When the donor radio base station  12  doesn&#39;t have an X2 connectivity to the second radio base station  14 , the donor radio base station  12  sends a S1AP Handover Required for the user equipment  18  to the first MME  16 . 
     Step  512 . The relay node  10  eventually receives an S1AP Handover Command from the first MME  16  via the donor radio base station  12 . This is an example of step  1502  in  FIG. 15 . 
     Step  513 . After step  512 , then normal S1 handover takes place. 
     Step  514 . As the type of received application protocol was an S1AP type, the relay node  10  then updates its X2 connectivity information by storing that X2 is not present to the second radio base station  14 . The second radio base station may also be referred to as target radio base station. This is an example of step  1504  in  FIG. 15 . 
     Thus, the relay node  10  learns and stores the radio network connection type and thereby improves the performance in future or later use. 
     In some embodiments, the relay node  10  may signal any relevant X2 message to each neighboring radio base station  14  with unknown X2 connectivity. If X2 is established, the relay node  10  will receive the expected X2 response. However, if X2 is not established, then the donor radio base station  12  responds with a failure or reject cause to the relay node  10 , indicating that the X2 connectivity is missing. These procedures are exemplified in  FIG. 6  and  FIG. 7  considering the X2 message being an eNB configuration update message, but other X2 messages may be used in a similar fashion. 
       FIG. 6  is disclosing an X2 probing method according to some embodiments wherein X2AP is used. 
     Step  601 . The relay node  10  sends an X2AP eNB configuration update message to the donor radio base station  12  targetting the second radio base station  14  for which the X2 connectivity is probed. This is an example of step  1501  in  FIG. 15 . 
     Step  602 . The second radio base station  14  sends an X2AP eNB configuration update ACK message. This is a case in which X2 is established between donor radio base station  12  and the other, second, radio base station  14 . This interface connection to the second radio base station  14  is then stored in the relay node  10 . 
       FIG. 7  is disclosing an X2 probing method according to some embodiments wherein X2AP is used. 
     Step  701 . The relay node  10  sends or transmits an eNB configuration update message to the donor radio base station  12  targetting the second radio base station  14  for which the X2 connectivity is probed. This is an example of step  1501  in  FIG. 15 . 
     Step  702 . The donor radio base station  12  sends an eNB configuration update failure message to the relay node  10 . This is the case in which X2 is not established between donor radio base station  12  and the second radio base station  14 , and the fact that X2 is missing between donor radio base station  12  and the second radio base station  14  may be encoded in a dedicated failure cause, e.g. “X2 connectivity is missing”. This radio network connection, determined to be a S1 connection, is then stored in the relay node  10  in relation to the second radio base station  14 . 
       FIG. 8  shows a similar but yet alternative embodiments, where the relay node  10  attempts to use S1 for handover signaling and learns about X2 support from the response of the donor radio base station  12 . In some embodiments where X2 is established, the donor radio base station  12  may convert the S1 message to a corresponding initial handover X2 message, and the relay node  10  may learn the X2 support from the X2 response from the donor radio base station  12 . The X2 response message may include information related to the UE context or the original S1 message so that the relay node  10  may link the S1 procedure and the X2 procedure together, i.e. so it knows that the X2 message is a response to the S1 message. The information may include a temporal context or transaction ID, or some other information related to the user equipment  18 . 
       FIG. 8  shows a S1 handover preparation into X2 handover signaling, in case X2 is established, but where the relay node  10  initiated the handover procedure using S1AP. 
     Step  801 . The relay node  10  sends a S1AP handover required to the donor radio base station  12 . This is an example of step  1501  in  FIG. 15 . 
     Step  802 . The donor radio base station  12  converts the S1 message to an X2 message and sends an X2AP handover request to the second radio base station  14 . 
     Step  803 . The second radio base station  14  sends a X2AP handover request ACK to the donor radio base station  12  acknowledging the handover request. 
     Step  804 . The donor radio base station  12  then forwards the X2AP handover request ACK to the relay node  10 . This is an example of step  1705  in  FIG. 17 . 
     The relay node  10  then stores that X2 is present to the second radio base station  14  based on the received X2 message. 
       FIG. 9  shows a schematic overview of a radio communications network. The radio communications network comprises the user equipment  18  served by the relay node  10 . The relay node  10  is connected to the donor radio base station  12  in an X2 connection and an S1 connection. The donor radio base station  12  is connected to the second radio base station  14  with an X2 connection and is also neighboring a third radio base station  19 . However, there exists no X2 connection to the third radio base station  19 . Each radio base station  12 , 14 , 19  is connected to the first MME  16  over a respective S1 connection. 
     LTE may feature an Automatic Neighbour Relations (ANR) function, where the user equipment  18  may detect and report a unique cell identity such as Physical Cell ID (PCI), E-UTRAN Cell Global Identifier (ECGI), Tracking Area (TA) of discovered cells to its serving radio base station, in the illustrated example the relay node  10 . This function is referred to as UE ANR in the sequel. When the donor radio base station  12  is notified by the served user equipment  18  about a discovered neighbouring radio base station, e.g. the second radio base station  14 , it may initiate an X2 connection establishment using X2AP and S1AP. The donor radio base station  12  needs the Transport Network Layer (TNL) Internet Protocol (IP) address, TNL address for short, of the discovered neighbouring radio base stations to set up a connection. The TNL address may be recovered using ‘Configuration Transfer’ messages to the neighbouring radio base stations via the first MME  16  and back. These ‘Configuration Transfer’ messages may comprise a Self Organising Network (SON) Information Transfer Information Element (IE). The SON Information Transfer IE may comprise the radio base station ID of both radio base stations on the way to the neighbouring radio base station, e.g. the second radio base station  14 . The SON Information Transfer IE may additionally or alternatively comprise the TNL address on the way back to the originating donor radio base station  12 . With the TNL address of the second radio base station  14 , the donor radio base station  12  may establish an X2 connection, and with this connection in place, the donor radio base station  12  and the neighbouring second radio base station  14  may exchange information about radio base station IDs and served cells. 
     The ANR function for the relay node  10  is facilitated if the relay node  10  broadcast cell identities that include the eNB ID of its serving donor radio base station  12 . This means that when neighbouring second radio base station  14  discover the relay node  10 , the TNL address recovery procedure will return the TNL address of the donor radio base station  12  of the relay node  10 , and X2 will be established between the neighbouring second radio base station  14  and the donor radio base station  12 . 
     According to some embodiments herein four cases are considered:
     1 The relay node  10  discovers a neighboring radio base station, e.g. the second radio base station  14  or the third radio base station  19 , via UE ANR
       a. X2 is established between neighboring radio base station, the second radio base station  14 , and the donor radio base station  12 ,   b. X2 is not established between neighboring radio base station, the third radio base station  19 , and the donor radio base station  12 .   
       2 The neighboring radio base station  14 , 19  discovers the relay node  10  via UE ANR
       a. X2 is established between neighboring radio base station, the second radio base station  14 , and the donor radio base station  12 ,   b. X2 is not established between neighboring radio base station, the third radio base station  19 , and the donor radio base station  12 .   
       

     These cases are illustrated in  FIG. 9 , where X2 is established between the donor radio base station  12  and the second radio base station  14  but not between the donor radio base station  12  and the third radio base station  19 . The relay node  10  has no neighbor relations with cells served by neither the second radio base station  14  nor the third radio base station  19 . Furthermore, it is assumed that a radio base station ID of the relay node  10  is the radio base station ID of the donor radio base station  12 . Radio base station ID may be referred to as eNB ID. It will be exemplified below how the relay node  10  may acquire the type of the radio network connection to the respective neighboring radio base station  14 , 19  for the different cases. 
       FIG. 10  is a schematic combined flowchart and signaling scheme of case  1   a ) above wherein X2 is established between the neighboring second radio base station  14  and the donor radio base station  12 . 
     Step  1001 . The relay node  10  may discover a cell served by the second radio base station  14  by receiving an eNB ID from the user equipment  18 . The UE ANR function of the user equipment  18  finds the eNB ID of the second radio base station  14  (eNB_ID_eNB14) and provides the eNB ID to the relay node  10  that initiates TNL address recovery. 
     Step  1002 . The relay node  10  may then send an S1AP eNB configuration transfer message comprising a SON information transfer IE to the donor radio base station  12 . The received eNB ID is used in the SON information transfer IE from the relay node  10 , intended to be forwarded to the first MME  16  and further on to the second radio base station  14  to recover its TNL address. This step is an example of step  1501  in  FIG. 15 . 
     Step  1003 . However, the donor radio base station  12  may conclude that the TNL address recovery procedure may be terminated since X2 is established to the second radio base station  14 . Instead the donor radio base station  12  compiles an X2AP X2 Setup Request message on behalf of the second radio base station  14 , comprising all details of the second radio base station  14 . Seemingly, the X2AP X2 Setup Request message could have originated from the second radio base station  14  itself, and a Global eNB ID is the eNB ID of the second radio base station  14 . Note that the X2 connection between the donor radio base station  12  and the relay node  10  is not affected. The donor radio base station  12  then signals an X2AP X2 Setup Request on behalf of the second radio base station  14 , indicating the Global eNB ID of the second radio base station  14 , and is only a means to exchange information using the existing X2 connection between donor radio base station  12  and the relay node  10 . 
     Alternatively, the donor radio base station  12  may compile an X2AP eNB configuration update message to the relay node  10  on behalf of the second radio base station  14 . However, this is less intuitive, since the relay node  10  has to disclose the message origin in terms of the eNB ID from the ECGIs in a Served Cell Information IE. These X2AP eNB configuration update messages may also be compiled if X2 is established at a later stage. 
     These embodiments may use existing signaling, with the additions of the following two embodiments: 
     The donor radio base station  12  may terminate an initiated TNL address recovery over S1AP indicating the eNB ID of the second radio base station  14  by the relay node  10  if X2 is available between the donor radio base station  12  and the second radio base station  14 . The donor radio base station  12  may alternatively or additionally store information about a TNL address recovery to the second radio base station  14  initiated by the relay node  10 . Furthermore, the donor radio base station  12  may compile an X2AP X2 setup request or X2AP eNB configuration update to the relay node  10  on behalf of the second radio base station  14 , including all details about the second radio base station  14 , if X2 is, or when it becomes, available between the donor radio base station  12  and the second radio base station  14 . 
     The relay node  10  discloses X2 availability between donor radio base station  12  and the second radio base station  14  upon reception of an X2 message sent by the donor radio base station  12  on behalf of the second radio base station  14 . 
     In some embodiments, donor radio base station  12  may compile a SON Information Transfer IE in a MME configuration transfer message to the relay node  10 , including the TNL address of the second radio base station  14 . This step is an example of step  1705  in  FIG. 17 . 
     Step  1004 . The relay node  10  responds to the received X2 setup by sending a X2AP X2 setup response to the donor radio base station  12 . 
     The relay node  10  thus acquires the type of the radio connection, in the example an X2 connection is setup, between the donor radio base station  12  and the second radio base station  14 , based on the type of application protocol received. The relay node  10  stores this information to select X2 based communication when later communicating with the second radio base station  14 . 
     Thus, in some embodiments the knowledge of X2 connectivity is acquired by the relay node  10  from the donor radio base station  12  by X2 messages sent on behalf of the second radio base station  14 . This means that X2 messages are compiled by the donor radio base station  12  but includes information from the second radio base station  14  such that the X2 message seems to originate from the second radio base station  14 . 
       FIG. 11  is a schematic combined flowchart and signaling scheme of case  1   b ) above wherein X2 is not established between the third radio base station  19  and the donor radio base station  12 . 
     Step  1101 . The UE ANR function may provide the eNB ID of the third radio base station  19  (eNB_ID_eNB19) as mentioned in step  1001  in  FIG. 10 . 
     Step  1102 . The relay node  10  may then send an S1AP eNB configuration transfer message comprising a SON information transfer IE to the donor radio base station  12 . The received eNB ID is used in the SON information transfer IE from the relay node  10  intended to be forwarded to the first MME  16  and further on to the third radio base station  19  to recover its TNL address. This step is an example of step  1501  in  FIG. 15 . 
     Step  1103 . The donor radio base station  12  may then forward the S1AP eNB configuration transfer message to the first MME  16 . 
     Step  1104 . The first MME  16  may then transmit a S1AP MME configuration transfer message to the third radio base station  19  to recover the TNL address of the third radio base station  19 . An indicated source radio base station is already the eNB ID of the donor radio base station  12  since it is equal to the eNB ID of the relay node  10 . 
     Step  1105 . The third radio base station  19  may respond with its TNL address in an S1AP eNB configuration transfer message to the first MME  16 . 
     Step  1106 . The first MME  16  then sends a S1AP MME configuration transfer message to the donor radio base station  12 . 
     Step  1107 . The donor radio base station  12  and the third radio base station  19  may then initiate an X2 TNL establishment. 
     Step  1108 . If The X2 TNL establishment is successful, the donor radio base station  12  and the neighboring third radio base station  19  exchange information using X2AP X2 Setup Request/Response. First the donor radio base station  12  sends a X2AP X2 setup request to the third radio base station  19 . 
     Step  1109 . Then the third radio base station  19  may respond to the request by sending an X2AP X2 setup response. 
     Step  1110 . In direct communication over X2 between the third radio base station  19  and the donor radio base station  12 , the sending radio base station, e.g. the third radio base station  19 , encloses its Global eNB ID in the message for identification. In this step, the donor radio base station  12  may compile an X2AP X2 Setup Request message on behalf of the third radio base station  19 , which means that the donor radio base station  12  encloses the Global eNB ID of the third base station  19  and sends this to the relay node  10 . The message comprises information as if it would have been originating from the third base station  19 . The message may further comprise Tracking Area Codes (TAC) and transmission parameters, neighbour information, and Globally Unique (GU) Group ID. Seemingly, the X2AP X2 Setup Request message could have originated from the third radio base station  19  itself. This is used by the relay node  10  to disclose X2 availability to the third radio base station  19 . 
     An alternative is that the donor radio base station  12  forwards the X2AP X2 Setup Response from the third radio base station  19  to the relay node  10  to inform about X2 availability. However, this is less consistent with how these procedures are used between macro radio base stations. 
     This step is an example of step  1705  in  FIG. 17 . 
     Step  1111 . The relay node  10  sends an X2AP X2 setup response to the donor radio base station  12 . The relay node  10  also stores the information that an X2 is setup between the donor radio base station  12  and the third radio base station  19 . 
     Thus, the relay node  10  uses S1 to signal to the third radio base station  19  while awaiting X2 TNL establishment or if the X2 TNL establishment fails. This alternative may be solved using existing signalling, wherein the donor radio base station  12  stores information about a TNL address recovery to a neighboring radio base station, such as the second or third radio base station, initiated by the relay node  10 . The donor radio base station  12  then compiles an X2AP X2 Setup Request or X2AP eNB configuration update message to the relay node  10  on behalf of the neighboring radio base station, including all details about the neighboring radio base station, if X2 is, or when it becomes, available between donor radio base station  12  and neighboring radio base station. 
     The relay node  10  thus discloses X2 availability between the donor radio base station  12  and the neighboring radio base station upon reception of an X2 message sent by the donor radio base station on behalf of the neighboring radio base station. 
     In some embodiments, the donor radio base station  12  may forward the MME configuration transfer message to the relay node  10 , including the TNL address of the neighboring radio base station. This can be seen by the relay node  10  as another means of confirmation that X2 is established between the donor radio base station  12  and the third radio base station  19 . It can also be seen by the relay node  10  as a confirmation that the TNL address recovery was successful. The MME configuration transfer message may be used to transfer information from the third radio base station  19 , e.g. Source eNB-ID, X2 TNL configuration info, to the donor radio base station  12  via S1, i.e. traditionally through the first MME  16 . The relay node  10  may use this information to learn about information of its cells. This is a way to send neighbor information over S1. 
       FIG. 12  is a schematic overview of a method wherein the knowledge of X2 connectivity is acquired via incoming handover requests that originate from the second radio base station  14 , as stated in case  2   a , and are forwarded to the relay node  10  by the donor radio base station  12 . 
     Step  1201 . The neighbor radio base station, e.g. the second radio base station  14  may discover the relay node  10  via UE ANR. For example, another user equipment served by the second radio base station  14  reports signal strength measurement of the relay cell  11 . 
     Step  1202 . X2 is established between the second radio base station  14  and the donor radio base station  12  and in this case, the donor radio base station  12  has already informed the second radio base station  14  about the relay node  10  and its served cells either at startup of the relay node  10 , via X2AP eNB configuration update message, or when X2 was established, via X2AP X2 setup request. Therefore, when the second radio base station  14  discovers the relay cell  11  served by the relay node  10 , it may directly initiate handover preparations by sending X2AP handover request to the donor radio base station  12 . 
     Step  1203 . The X2AP handover request may comprise target cell ECGI, and from that the donor radio base station  12  may conclude that the discovered cell is served by the relay node  10  and forwards the X2AP handover request to the relay node  10 . This is an example of the step  1705  in  FIG. 17 . 
     According to embodiments herein, the relay node  10  is made aware of the second radio base station  14  and also, based on the type of the Handover Request, the type of the radio network connection e.g. X2 availability. The relay node  10  additionally stores this information in relation to the second radio base station  14 . 
     Step  1204 . The relay node  10  may then transmit a X2AP Handover Request ACK to the donor radio base station  12 . 
     Step  1205 . The donor radio base station  12  then forwards the X2AP Handover Request ACK to the second radio base station  14 . 
     This alternative may be handled by existing signaling and node behavior. 
       FIG. 13  is a schematic overview of some embodiments where X2 is not established between a neighbor radio base station, e.g. the third radio base station  19 , and the donor radio base station  12 , as stated in case  2   b.    
     This case is essentially analogous to the case when X2 has been established, except for including the X2 establishment steps. 
     Step  1301 . The neighbor radio base station, e.g. the third radio base station  19  discovers the relay node  10  via UE ANR. For example, another user equipment served by the third radio base station  19  reports signal strength measurement of the relay cell  11 . 
     Step  1302 . Since X2 is not established, the third radio base station  19  initiates TNL address recovery via S1 towards the donor radio base station  12  as the eNB ID of the relay node  10  is the same as eNB ID for donor radio base station  12 . Thus, the third radio base station  19  sends an S1 eNB Configuration Transfer message to the first MME  16 . 
     Step  1303 . The first MME  16  sends an S1AP MME Configuration Transfer message to the donor radio base station  12 . 
     Step  1304 . The donor radio base station  12  sends an S1AP eNB Configuration Transfer message to the first MME  16 . 
     Step  1305 . The first MME  16  sends an S1 MME Configuration Transfer message to the third radio base station  19 . 
     Step  1306 . The donor radio base station  12  and the third radio base station  19  then initiates and performs a TNL establishment process. 
     Step  1307 . Finally, when X2 TNL establishment, between the third radio base station  19  and the donor radio base station  12  is completed, served cell information is shared between the radio base stations  19 , 12  using X2AP, X2 Setup Request/Response. Thus, the third radio base station  19  sends an X2 setup request to the donor radio base station  12 . 
     Step  1308 . The donor radio base station  12  responds by sending an X2 setup response to the third radio base station  19 . 
     Step  1309 . Similar to the case when X2 was already established, the relay node  10  is not informed about the X2 availability until third radio base station  19  initiates handover preparations via X2AP. The third radio base station  19  thus sends an X2 handover request to the donor radio base station  12 . 
     Step  1310 . The donor radio base station  12  then forwards the X2AP handover request to the relay node  10 . This is an example of the step  1705  in  FIG. 17 . 
     The relay node  10  then discloses the radio network connection type based on the received message and stores the type in relation to the identity of the third radio base station  19 . 
     Step  1311 . The relay node  10  sends an X2AP handover request ACK to the donor radio base station  12 . 
     Step  1312 . The donor radio base station  12  then forwards the X2AP handover request ACK to the third radio base station  19 . 
     If the X2 establishment is prohibited or fails, then S1 signaling is used instead. This alternative may thus also be handled by existing signaling and behavior. Thus, the relay node  10  may disclose X2 availability from an incoming X2 Handover Request forwarded by the donor radio base station. 
       FIG. 14  schematically shows an embodiment where X2 is disconnected between donor radio base station and a neighbouring eNB, such as the second radio base station  14 , either controlled or due to failures. 
     Step  1401 . The X2 connection between the donor radio base station  12  and the second radio base station  14  is disconnected. 
     Step  1402 . The relay node  10  may need to be informed by the donor radio base station  12  about the disconnection. One example is for the donor radio base station  12  to compile a X2AP Reset message and send the X2AP reset request message to the relay node  10  on behalf of the second radio base station  14 . This step is an example of step  1705  in  FIG. 17 . 
     Thus, the relay node  10  is informed about the type of the application protocol and consequently of the type of radio network connection. The relay node  10  stores that no X2 exists anymore to the second radio base station  14 . This may be used by the relay node  10  to disclose X2 unavailability to a neighboring radio base station. 
     Step  1403 . The relay node  10  may send an X2AP reset response to the second radio base station  14 . 
     The method steps in the relay node  10  for acquiring information about a type of a radio network connection between a donor radio base station  12  and a radio base station  14 , referred to as the second radio base station  14  above, according to some general embodiments will now be described with reference to a flowchart depicted in  FIG. 15 . The steps do not have to be taken in the order stated below, but may be taken in any suitable order. The relay node  10  and the donor radio base station  12  are comprised in a radio communications network and the donor radio base station  12  is serving the relay node  10 . 
     Step  1501 . In some embodiments as indicated by the dashed line, the relay node  10  may initiate a radio access network communication to the radio base station  14  by transmitting a communication message of a first type of a radio network application protocol to the radio base station  14  over the donor radio base station  12 . The received message, i.e. the response, is indicating the first type, e.g. X2AP, or a second type, e.g. S1AP, of a radio network application protocol. 
     In some embodiments, the communication message may comprise information, for address recovery of a detected cell served by the radio base station  14 , such as a S1 Configuration ANR message. In some embodiments, a measurement report is received from a user equipment  18  in a cell of the radio communications network controlled by the relay node  10 . The measurement report may indicate a cell identity of the detected cell of the radio base station  14 . For example, the user equipment  18  may comprise an ANR functionality that detects the detected cell e.g. a cell identity detected in a broadcast channel. 
     In some embodiments, the communication message may comprise a handover request message of a first type of a radio network application protocol to a detected cell of the radio base station  14 , e.g. an X2 or S1 HO request. 
     Step  1502 . The relay node  10  receives a message from the donor radio base station  12 . The message is indicating a type of radio network application protocol, e.g. the first type or the second type, which type is related to a type of the radio network connection between the donor radio base station  12  and the radio base station  14 . 
     In some embodiments wherein the communication message may comprise information for address recovery, the received message may comprise a setup request of the first type or the second type of a radio network application protocol, e.g. X2 Setup or S1 setup. 
     In some embodiments wherein the HO request is sent, the received message comprises a handover confirmation indicating the first type or the second type of a radio network application protocol, e.g. X2 or S1 command or confirmed. 
     In some embodiment, the received message may comprise a handover request indicating the type of radio network application protocol, e.g. S1 or X2 HO request. 
     In some embodiments, the received message explicitly states the type of the radio network connection between the donor radio base station  12  and the radio base station  14 , 19 . For example, the donor radio base station  12  may inform the relay node  10  about X2 support to the radio base station  14  in a new explicit message or a new Information Elements (IE) in an existing message. 
     In some embodiments, the received message may be represented by an application protocol message indicating a peer to peer connection in a radio access network of the radio communications network. The received message may alternatively be represented by an application protocol message indicating a connection terminated in a core network of the radio communications network. 
     Step  1503 . The relay node  10  determines the type of the radio network connection based on the type of radio network application protocol indicated in the message. 
     In some embodiments, wherein the received message comprises a handover request, the relay node  10  determines the type of the radio network connection based on the type indicated in the handover request. 
     Step  1504 . The relay node  10  stores the type of radio network connection in relation to the radio base station  14  for selecting the type of radio network connection when later communicating with the radio base station  14 . 
     In some embodiments, the type of a radio network application protocol indicated in the received message is an X2 application protocol message or an S1 application protocol message, and the determined type of the radio network connection is an X2 application protocol connection or an S1 application protocol connection. 
     It should be understood that some embodiments herein disclose ways to acquire information whether the donor radio base station  12  has X2 connectivity to a neighbor radio base station. X2 support between the donor radio base station  12  and another radio base station may, in some embodiments, be disclosed by the relay node  10  without defining new dedicated signalling and new dedicated information elements. The donor radio base station  12  may compile X2 messages sent to the relay node  10  on behalf of a neighbouring radio base station means little modifications to the behaviour of the relay node  10  compared to the behaviour of an ordinary radio base station. 
     In some alternative embodiments the relay node  10  may acquire information about which radio base stations the donor radio base station  12  has X2 connectivity in the X2 setup procedure. In this procedure each radio base station should in the X2 SETUP REQUEST message or X2 SETUP RESPONSE message provide information about which cells are being served by each radio base station, Served Cell Information. In case of relay nodes and donor radio base stations it would be possible for the donor radio base station  12  to not only provide information about which cells is served by the donor radio base station  12  in this IE but also provide information about all cells being served by radio base stations that the donor radio base station  12  has X2 connectivity to. The relay node  10  could then use this information to determine which radio base stations and cells the relay node  10  can use the X2 procedure to. 
     In case more X2 connectivity neighbors are added or removed to the donor radio base station  12  at a later time the donor radio base station  12  may use the eNB configuration updated to the relay node  10  and add or remove the corresponding cells on the cells served indicated by a donor radio base station list. 
     In some embodiments above it is possible for the relay node  10  to initiate the X2 setup procedure or possible an eNB configuration update procedure in order to try to establish X2 connectivity for cells that the donor radio base station  12  is not X2 connected to. One possible trigger for this setup would be in the case the relay node  10  detects a new neighboring cell which the donor radio base station  12  currently does not have an X2 connection with. The X2 SETUP REQUEST may in this case be addressed to the second radio base station  14  serving the “new cell” but may still be intercepted by the donor radio base station  12  making it possible for the donor radio base station  12  to initiate X2 setup to the second radio base station  14  which it does not have an X2 connection to. Once the donor radio base station  12  have completed the X2 setup, the relay node  10  may be informed about the new X2 connection using any of the means outlined herein. 
     Another variant of the solution above is that the donor radio base station  12  based on learning that the relay node  10  is trying to contact another radio base station via X2 signaling, decides to try to establish an X2 connection to the second radio base station  14  in question. The X2 connection could be established fast enough to handle the X2 signaling from the relay node  10  directly or it may be established for future use. 
     Thus, X2 support between donor radio base station  12  and another radio base station, such as the second radio base station  14  may be disclosed by the relay node  10  without defining new dedicated signaling and new dedicated information elements. This facilitates the handover procedure. 
     As stated above, herein it is also disclosed a method in a relay node  10  initiating signaling between the relay node  10  and the second radio base station  14  via the donor radio base station  12  serving the relay node  10 . The relay node  10  receives a response from the donor radio base station  12  based on the X2 establishment information in donor radio base station  12 , disclosing whether X2 is established or not. The initiating signaling may include X2 signaling from the relay node  10  to the donor radio base station  12  or S1 signaling from the relay node  10  to the donor radio base station  12 . 
     The received response from donor radio base station  12  to relay node  10  may be via X2, if X2 is established between donor radio base station  12  and the other radio base stations such as the second radio base station  14 . The received response from the donor radio base station  12  to the relay node  10  may be via X2 if X2 is not established between donor radio base station  12  and the other radio base stations such as the second radio base station  14 , and the X2 message may then include a reject or failure cause informing that X2 is not established between donor radio base station  12  and the other radio base stations such as the second radio base station  14 . 
     The received response from the donor radio base station  12  to the relay node  10  may be via S1 if X2 is not established. The received response may then comprise explicit information in the cells served by eNB IE if X2 connectivity exists or not to a specific cell. 
     In the donor radio base station  12  an X2 message may be converted to the corresponding S1 message, which is sent to the second radio base station  14 . 
     In order to perform the steps above a relay node  10  is provided.  FIG. 16  is a block diagram depicting the relay node  10  for acquiring information about a type of a radio network connection between a donor radio base station  12  and a radio base station  14 . The relay node  10  is arranged to be comprised in a radio communications network and is arranged to be served by the donor radio base station  12 . 
     The relay node  10  comprises a receiver (RX)  1620  configured to receive a message from the donor radio base station  12 , which message is indicating a type of radio network application protocol. The type of radio network application protocol is related to a type of the radio network connection between the donor radio base station  12  and the radio base station  14 . The received message may comprise a handover request indicating the type of radio network application protocol. The received message may explicitly state the type of the radio network connection between the donor radio base station  12  and the radio base station  14 , 19 . The received message may be represented by an application protocol message indicating a peer to peer connection in a radio access network of the radio communications network. The received message may alternatively be represented by an application protocol message indicating a connection terminated in a core network of the radio communications network. 
     The relay node further comprises a determining circuit  1630  configured to determine the type of the radio network connection based on the type of radio network application protocol indicated in the message. In some embodiments, wherein the received message comprises a handover request, the determining circuit may be configured to determine the type of the radio network connection based on the type indicated in the handover request. 
     Furthermore, the relay node  10  comprises a memory circuit  1640  configured to store the type of radio network connection in relation to the radio base station  14  to be used when selecting the type of radio network connection when later communicating with the radio base station  14 . The memory circuit may further be used to store Cell IDs, connectivities, mobility parameters, and/or application to perform the methods herein when being executed on the relay node  10 . 
     The embodiments herein for acquiring information about a type of a radio network connection between the donor radio base station  12  and the radio base station  14  may be implemented through one or more processors, such as a processing circuit  1650  in the relay node  10  depicted in  FIG. 16 , together with computer program code for performing the functions and/or method steps of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the present solution when being loaded into the relay node  10 . One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the relay node  10 . 
     The processing circuit  1650  may further be configured to initiate a radio access network communication to the radio base station  14  by transmitting, via a transmitter (TX)  1660 , a communication message of a first type of a radio network application protocol to the radio base station  14  over the donor radio base station  12 . The received message is indicating the first type or a second type of a radio network application protocol. 
     In some embodiments, the communication message may comprise information for address recovery of a detected cell served by the radio base station  14 , and the received message may then comprise a setup request of the first type or the second type of a radio network application protocol. 
     In some embodiments, the communication message may comprise a handover request message of a first type of a radio network application protocol to a detected cell of the radio base station  14 . The received message may then comprise a handover confirmation indicating the first type or the second type of a radio network application protocol, e.g. X2 or S1 command or confirmed. 
     In some embodiments, a measurement report is received over a receiving circuit  1670  from a user equipment  18  in a cell of the radio communications network controlled by the relay node  10 . The measurement report may indicate a cell identity of the detected cell of the radio base station  14 . 
     In some embodiments, the type of a radio network application protocol indicated in the received message is an X2 application protocol message or an S1 application protocol message, and the determined type of the radio network connection is an X2 application protocol connection or an S1 application protocol connection. 
     The method steps in the donor radio base station  12  for informing the relay node  10  about the type of the radio network connection between the donor radio base station  12  and the radio base station  14  according to some general embodiments will now be described with reference to a flowchart depicted in  FIG. 17 . The steps do not have to be taken in the order stated below, but may be taken in any suitable order. The relay node  10  and the donor radio base station  12  are comprised in the radio communications network, and the donor radio base station  12  serves the relay node  10 . 
     Step  1701 . The donor radio base station  12  receives a protocol message of a first type of a radio network application protocol, from the relay node ( 10 ), e.g. an X2AP HO request or a S1 eNB Configuration Transfer message; or from the radio base station ( 14 ), e.g. X2AP HO request or S1AP MME Configuration Transfer message. 
     Step  1702 . In some embodiments as indicated by the dashed line, the donor radio base station  12  may determine whether a Peer to Peer (P2P) connection in a radio access network of the radio communications network is set up between the donor radio base station  12  and the radio base station  14 . 
     Step  1703 . In some embodiments as indicated by the dashed line, the donor radio base station  12 , when such a peer to peer connection is setup, may perform a handover procedure over the peer to peer connection. The donor radio base station  12  may then transmit in the step below the handover confirmation to the relay node  10 . The handover confirmation indicates a type of a peer to peer application protocol. 
     Step  1704 . In some embodiments as indicated by the dashed line, the donor radio base station  12 , when no such a peer to peer connection is setup, may initiate a handover procedure over a connection terminated in a core network of the radio communications network. The donor radio base station may then transmit in the step below a handover command as the handover confirmation. The handover confirmation indicates a type of an application protocol of a connection terminated in the core network. 
     Alternatively, when no such a peer to peer connection exists, the donor radio base station  12  may initiate a setup of a peer to peer connection to the radio base station  14  via a connection terminated in a core network of the radio communications network to a mobility management entity  16 . The donor radio base station  12  may then transmit a setup message to the relay node  10  in the step below. The setup message is indicating the first type or the second type to be a peer to peer connection. 
     Step  1705 . The donor radio base station  12  transmits a message to the relay node  10 . The message is indicating the first type or a second type of a radio network application protocol. Each type of a radio network application protocol is related to a type of a radio network connection and thereby the relay node  10  is informed of the type of the radio network connection. 
     In some embodiments, when a peer to peer connection exists, the donor radio base station  12  may transmit a setup message to the relay node  10 . The setup message is indicating the first type or the second type to be a peer to peer connection. That is, if the received first type of radio network application protocol is of an application protocol of a connection terminated in a core network, the setup message indicating the second type to be an application protocol of a peer to peer connection. 
     In some embodiments, the donor radio base station  12  may compile the setup message to be on behalf of the radio base station  14 . 
     In some embodiments, the received protocol message may comprise a handover request of a user equipment  18  to a cell of the radio base station  14  or to a cell of the relay station  10 . The transmitted message may then comprise a handover confirmation or a handover request, forwarded. 
     The handover request may represented by a handover message of the first type. The first type may indicate a peer to peer connection in a radio access network of the radio communications network, or may indicate a connection terminated in a core network of the radio communications network. 
     In some embodiments, the received protocol message may comprise information for address retrieval of a detected cell of the radio base station  14 , which received protocol message is sent from the relay node  10 . Then, the transmitted message may comprise a connection setup request to the relay node  10  of the first type. 
     In some embodiments, the first type of a radio network application protocol may be an X2 application protocol or an S1 application protocol and the second type of a radio communications network may be an S1 application protocol or an X2 application protocol. 
     In order to perform the method steps in the donor radio base station  12  for informing the relay node  10  about the type of the radio network connection between the donor radio base station  12  and the radio base station  14 , a donor radio base station is provided.  FIG. 18  is a block diagram depicting the donor radio base station  12 . The donor radio base station  12  serves the relay node  10 . 
     The donor radio base station  12  comprises a receiving circuit  1801  configured to receive a protocol message of a first type of a radio network application protocol, from the relay node  10  or from the radio base station  14 . 
     In some embodiments, the donor radio base station  12  may comprise a determining circuit  1802  configured to determine whether a peer to peer connection in a radio access network of the radio communications network is set up between the donor radio base station  12  and the radio base station  14 . The determining circuit  1802  may, when such a peer to peer connection is setup, further be configured to perform a handover procedure over the peer to peer connection. 
     The donor radio base station  12  further comprises a transmitting circuit  1803  configured to transmit a message to the relay node  10 . The message is indicating the first type or a second type of a radio network application protocol, and wherein each type of a radio network application protocol is related to a type of the radio network connection. Thereby, the relay node  10  is informed of the type of the radio network connection. 
     The transmitting circuit  1803  may be configured to transmit the handover confirmation to the relay node  10 . The handover confirmation indicates a type of a peer to peer application protocol. 
     The determining circuit  1802  may, when no such a peer to peer connection is setup, initiate a handover procedure over a connection terminated in a core network of the radio communications network. The transmitting circuit  1803  may then transmit a handover command as the handover confirmation. The handover confirmation indicates a type of an application protocol of a connection terminated in the core network. 
     Alternatively, when no such a peer to peer connection exists, the determining circuit  1802  may initiate a setup of a peer to peer connection to the radio base station  14  via a connection terminated in a core network of the radio communications network to a mobility management entity  16 . The transmitting circuit  1803  may then transmit a setup message to the relay node  10 . The setup message is indicating the first type or the second type to be a peer to peer connection. 
     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.