EP2832139A1

EP2832139A1 - Network load control

Info

Publication number: EP2832139A1
Application number: EP13708442.2A
Authority: EP
Inventors: Simon WÅHLÉN; Lasse Olsson
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2012-03-28
Filing date: 2013-03-11
Publication date: 2015-02-04
Also published as: WO2013143831A1

Abstract

The embodiments herein relate to a method in a mobility management entity, MME (203), for handling signaling overload in a communications network (200). The MME (203) is connected to a plurality of radio base stations (205). The MME (203) comprises at least a connection to a first radio base station (205a) and a connection to a second radio base station (205b). The first radio base station (205a) and second radio base station (205b) are comprised in the plurality of radio base stations (205). The MME (203) obtains(301, 701) priority information associated with the first radio base station (205a) and the second radio base station (205b) indicating whether the first radio base station (205a) and the second radio base station (205b) can be disconnected from the MME (203) to reduce signaling load in case of a signaling overload.

Description

NETWORK LOAD CONTROL

TECHNICAL FIELD Embodiments herein relate generally to Mobility Management Entity (MME), a method in the MME, a network node and a method in the network node. More particularly the embodiments herein relate to network load control and protection.

BACKGROUND

In a typical cellular network, also referred to as a wireless communication system, User Equipments (UEs), communicate via a Radio Access Network (RAN) to one or more Core Networks (CNs).

A user equipment is a mobile terminal by which a subscriber may access services offered by an operator's core network and services outside operator's network to which the operator's RAN and CN provide access. The user equipments may be for example communication devices such as mobile telephones, cellular telephones, smart phones, tablet computers or laptops with wireless capability. The user equipments may be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server. User equipments are enabled to communicate wirelessly in the cellular network. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between the user equipment and a server via the radio access network and possibly one or more core networks, comprised within the cellular network.

The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a Radio Base Station (RBS), which in some radio access networks is also called eNodeB (eNB), NodeB, B node or base station. In the following, the term radio base station will be used. The radio base station is referred to as RBS in some of the figures. A cell is a geographical area where radio coverage is provided by the radio base station at a radio base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The radio base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the radio base stations.

Voice over IP (VoIP) relates to delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. In future mobile telephony, VoIP will use Voice over LTE (VoLTE). Therefore, the need for load control and protection between RAN and Packet Core (PC) network mobility node arises. This is needed to be able to discard/shed the correct messages. A mobility node may be for example the MME or a Serving General packet radio service (GPRS) Support Node (SGSN). The MME is responsible for the Non-Access Startum (NAS) connection with the UE. The MME is also responsible for paging subscribers and is concerned with tracking area list management. When necessary, a relocation of gateways will be triggered and controlled by the MME. The MME manages handovers by selecting a new/target MME or Service General Packet Radio Service (GPRS) Support Node (SGSN) for handovers to Second Generation (2G) or Third Generation (3G) Third Generation Partnership Protect (3GPP) access networks. The MME is also responsible for roaming management and authentication of subscribers, i.e. user equipments. The MME also sets up, modifies, and releases default and dedicated bearers. This function is commonly known as the bearer management function. The MME allows lawful interception of signaling traffic and transfer of warning messages to inform people about upcoming natural disasters like storms, bush fires or tsunamis. The SGSN, as mentioned above, is a network node which mediates access to network resources on behalf of user equipments, it implements packet scheduling policy between different Quality of Service (QoS) classes and it is responsible for establishment of a Packet Data Protocol (PDP) context with a Gateway GPRS Support Node (GGSN) when activated.

In 3GPP, there are procedures for handling and controlling overload in a network. The MME may comprise an Overload Protection (OLP) function. If the MME is overloaded, the overload protection function is triggered, the MME may for example move the calls to another MME in a given pool, re-locate radio base station associations to other device boards or it may send an Overload Start message to the radio base station asking it not to forward any calls of a specific kind to the MME. If necessary resources are available then MME may send Overload Stop indicating that it is ready to accept new calls. An MME pool, as mentioned above, is a pool of MMEs which serves a common geographical area. The single MME may be overloaded when its load is above a threshold, i.e. when the signalling load is too high. Figure 1 illustrates an Overload Start procedure involving the MME and the radio base station. The purpose of the Overload Start procedure is to inform a radio base station to reduce the signalling load towards the concerned MME, i.e. to inform the radio base station that the MME is overloaded. The procedure uses non-UE associated signalling. The MME sends an OVERLOAD START message to the radio base station. The radio base station receiving the OVERLOAD START message may assume the MME from which it receives the message as being in an overloaded state. The OVERLOAD START message comprises an Overload Action Information Element (IE) providing information about which action the radio base station shall take when receiving the message, i.e. when there is an overload situation in the network. The radio base station may reject/permit the indicated signalling traffic if the Overload Action information element in the OVERLOAD START message is set to - "reject all Radio Resource Control (RRC) connection requests for non-emergency mobile originated data transfer ", or

- "reject all new RRC connection requests for signalling ", or

- "only permit RRC connection establishments for emergency sessions".

The RRC mentioned above is a protocol handling control plane signalling between the user equipment and the radio base station.

The Overload Control procedure is not enough in a pool scenario due to the fact that the MME's have no control over which radio base station to contact with the message without risking radio network "black-outs". "Black-out" is the case when all MMEs in an MME pool chooses to send the Overload Start message to the same radio base station.

Typically, it is not possible to distinguish specific hot spots which should always be covered even in overload situations. A hot spot is a geographical location comprising one or more access points providing public broadband network services to user equipment's. Hotspots typically have a short access range. There is no way for the MME pool to divide the radio base station between them to get faster/safer access for public warning messages, which could probably also be used in evolved Multimedia Broadcast Multicast Services (eMBMS) cases. eMBMS is a point-to- multipoint service in which data is transmitted from a single source to multiple destinations over the radio network. Transmitting the same data to multiple recipients allows network resources to be shared.

Emergency calls, for example related to the E9-1 -1 system in the United States or the emergency phone number 1 12 in Sweden, allows a caller to contact the emergency services for assistance. Previously, emergency calls were routed over special dedicated circuits. Today, emergency calls are mixed with ordinary telephone traffic. There are several requirements for emergency calls, for example regarding the response time, coverage, roaming, delay, acknowledgement etc. However, there are still a number of issues that are not solved relating to emergency calls. For example, an emergency call could be lost or disregarded when the network is overloaded. There exists no

overload/load control which takes ongoing Emergency calls into account.

A Self-Organizing Network (SON) is a network comprising the following functionalities:

• Self-configuration

· Self-optimization

• Self-healing.

Self-configuration is a process where newly deployed network elements, e.g. radio base stations, are configured in an automatic installation procedure to get the necessary basic configuration for system operation, i.e. the process of bringing the network element into service requires minimal human operator intervention or none at all. Self-optimization is a process where user equipment and radio base station measurements, in addition to performance measurements are used to auto-tune configuration data to optimize the network. Self-healing is a process related to automatic detection and localization of failures and mechanism to solve the failures. SON has to be taken into account which disqualifies local configuration in the MME. When the local configuration in the MME is disqualified, the network is not self-organizing anymore. Instead it is configured.

Public Warning System (PWS) is a system for issuing public warnings over 3GPP mobile systems. PWS alerts and updates the user of emergency situations in a timely, secure, and geographically selective manner. The Earthquake and Tsunami Warning System (ETWS) relates to broadcasting of emergency information such as earthquake warnings provided by a local or national governments to many user equipments as quickly as possible by making use of the characteristic of the widespread mobile communication networks. However, there exist no safe way to load distribute PWS/ETWS signaling in an MME Pool to achieve faster End-To-End (e2e) transport.

SUMMARY

An object of embodiments herein is therefore to provide an improved overload control in the communications network.

According to a first aspect, the object is achieved by a method in a MME for handling signaling overload in a communications network. The MME is connected to a plurality of radio base stations. The MME comprises at least a connection to a first radio base station and a connection to a second radio base station. The MME obtains priority information associated with the first radio base station and the second radio base station indicating whether the first radio base station and the second radio base station can be

disconnected from the MME to reduce signaling load in case of a signaling overload.

According to a second aspect, the object is achieved by a method in a network node for handling signaling overload in a communications network. The network node provides priority information associated with a first radio base station and a second radio base station to the MME. The priority information indicates whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signaling overload.

According to a third aspect, the object is achieved by a MME for handling signaling overload in a communications network. The MME is connected to a plurality of radio base stations. The MME comprises at least a connection to a first radio base station and a connection to a second radio base station. The MME comprises an obtaining unit configured to obtain priority information associated with the first radio base station and the second radio base station indicating whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signaling overload.

According to a fourth aspect, the object is achieved by a network node for handling signaling overload in a communications network. The network node comprises a providing unit configured to provide priority information associated with a first radio base station and a second radio base station to a MME. The priority information indicates whether the first radio base station and the second radio base station can be

Since the MME comprises the priority information, it can determine whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signaling overload, thus overload control in the communications network is improved. Ongoing emergency calls shall also be taken into account before disconnecting any radio base stations.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows: The embodiments herein enable the advantage of prioritizing a geographical area in an overload situation.

The embodiments herein is easy to implement, and requires a small amount of signaling. The embodiments herein use an intelligent overload control mechanism.

The embodiments herein disconnect pre-determined radio base stations in a pool or parts of a pool as part of a network recovery situation. Another advantage of the embodiments herein is that they ignore/discard/shed user equipment individual messages based on importance of the radio base station.

In a PWS/ETWS scenario, an advantage of the embodiments herein is to avoid causing OLP in the system and to faster, more reliable, get the warning out to the user equipments. The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will now be further described in more detail in the following detailed description by reference to the appended drawings illustrating the embodiments and in which:

Fig. 1 is a signaling diagram illustrating embodiments of an overload start

procedure. Fig. 2 is a schematic block diagram illustrating embodiments of a

communications network.

Fig. 3 is a signaling diagram illustrating embodiments of a method. Fig. 4 is a signaling diagram illustrating embodiments of a S1 setup procedure.

Fig. 5 is a schematic block diagram illustrating embodiments of area priority in a communications network. Fig. 6 is a schematic block diagram illustrating embodiments of a primary and secondary MME in a communications network.

Fig. 7 is a flow chart illustrating embodiments of a method in a MME. Fig. 8 is a schematic block diagram illustrating embodiments of a MME.

Fig. 9 is a flow chart illustrating embodiments of a method in a network node.

Fig. 10 is a schematic block diagram illustrating embodiments of a network node. The drawings are not necessarily to scale and the dimensions of certain features may have been exaggerated for the sake of clarity. Emphasis is instead placed upon illustrating the principle of the embodiments herein.

DETAILED DESCRIPTION

Figure 2 depicts a communications network 200 in which embodiments herein may be implemented. The communications network 200 may in some embodiments apply to one or more radio access technologies such as for example Long Term Evolution (LTE), LTE Advanced, Code Division Multiple Access (CDMA), CDMA2000, Time Division CDMA (TD-CDMA) Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM), or any other Third Generation Partnership Project (3GPP) radio access technology. The communications network 200 is a Self-Organizing Network (SON).

The communications network 200 comprises a user equipment 201 connected to the Evolved Packet Core (EPC) over Evolved-Universal Terrestrial Radio Access Network (E- UTRAN). The EPC is connected to the external networks, which may comprise the IP Multimedia Core Network Subsystem (IMS). The EPC comprises a plurality of network elements, such as a MME 203.

The MME 203 is a core network element in the EPC, the core network of the LTE system. The EPC comprises a plurality of other network elements, but they will not be described in this context. The MME 203 deals with the control plane. It handles the signaling related to mobility and security for E-UTRAN access. The MME 203 is responsible for the tracking and the paging of the user equipment 201 in idle-mode. It is the termination point of the Non-Access Stratum (NAS). The MME 203 may be comprised in an MME pool. The MME pool comprises a plurality of MMEs 203. The MME 203 comprises a memory 207 configured to store data such as for example priority information. The MME 203 may be connected to a Domain Name System or Server (DNS) 210 which translates domain names into Internet Protocol (IP) addresses. A plurality of radio base stations 205, such as a first radio base station 205a and a second radio base station 205b, are comprised in E-UTRAN of the communications network 200. The first radio base station 205a and the second radio base station 205b each serves a cell (not shown). The first radio base station 205a and the second radio base station 205b may be radio base stations such as a NodeB, an eNodeB, or any other network unit capable to communicate over a radio carrier with the user equipment 201 being present in the cell.

The MME 203 is connected to and serves the plurality of radio base stations 205, such as the first radio base station 205a and the second radio base station 205b.

The user equipment 201 may be any suitable communication device or computational device with communication capabilities capable to communicate with a radio base station 205 over a radio channel, for instance but not limited to mobile phone, smart phone, personal digital assistant (PDA), tablet computer, laptop, MP3 player or portable DVD player (or similar media content devices), digital camera, or even stationary devices such as a PC. A PC may also be connected via a mobile station as the end station of the broadcasted/multicasted media. The user equipment 201 may also be an embedded communication device in e.g. electronic photo frames, cardiac surveillance equipment, intrusion or other surveillance equipment, weather data monitoring systems, vehicle, car or transport communication equipment, etc.

The method according to some embodiments will now be described with reference to the combined signalling diagram and flowchart depicted in Figure 3. The method comprises the following steps, which steps may as well be carried out in another suitable order than described below.

Step 301

The MME 203 obtains priority information from a network node, e.g. from the first radio base station 205a, the second radio base station 205b, the memory 207 comprised in the MME 203 or from the DNS 210. If the priority information is obtained from the first radio base station 205a or the second radio base station 205b, the priority information is pushed by one of the radio base stations 205. If the priority information is obtained from the memory 207 or the DNS 210, the MME 203 pulls the information from them. The priority information comprises a plurality of parameters represented by information elements, such as one or more of the following three:

• Area Priority

• Primary MME

5 · Secondary MME

The Area Priority information element provides information to the MME 203 about the importance of a geographical area. An example of a geographical area may be an operator office, city hall, police office etc. The geographical area comprises a plurality of radio base stations 205. In the example shown in figure 3, the MME 203 obtains area

10 priority information relating to the first radio base station 205a and the second radio base station 205b. The priorities of the geographical areas may have values between e.g. 1 - 15, where 1 indicates the lowest priority and 15 indicates the highest priority. In this example, the geographical area associated with the first radio base station 205a has a high priority and the geographical area associated with the second radio base station

15 205b has a low priority.

The primary MME information element and the secondary MME information element provide information to the MME 203 whether it is a primary or secondary MME for a radio base station 205 such as the first radio base station 205a and/or the second radio base 20 station 205b. A primary MME has higher priority than a secondary MME, and therefore the MME should maintain the connection to the radio base station 205 as far as possible if it is a primary MME.

During the initial signaling between the RAN, i.e. the radio base station 205, and the MME 25 203, the radio base station 205 may convey the priority information to the MME 203.

The priority information may be conveyed using the S1 Setup Request procedure, as exemplified in Figure 4. The S1 Setup Request message may be provided from the RBS 205 comprising new additional fields, or use private extensions, to convey the priority 30 information related to radio base station priority, i.e. area priority, Primary MME and

Secondary MME. The purpose of the S1 Setup procedure is to exchange application level data needed for the radio base station 205 and the MME 203 to interoperate correctly on the S1 interface. This procedure shall be the first S1 AP procedure triggered after the Transport Network Layer (TNL) association has become operational. The procedure uses non-user equipment associated signalling.

This procedure may erase any existing application level configuration data in the two nodes and replace it by the one received. This procedure may also re-initialise the E- UTRAN S1 AP user equipment related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do, and clear MME 203 overload state information at the radio base station 205. If the radio base station 205 initiating the S1 Setup procedure supports a Closed Subscriber Group (CSG) cell, the procedure shall report the CSG ID(s) of the supported CSGs.

The S1 Setup procedure exemplified in Figure 4 comprises the following steps, which steps may be performed in any suitable order: Step 401

The radio base station 205 initiates the procedure by sending a S1 SETUP REQUEST message comprising the appropriate data to the MME 203. The message is sent by the radio base station 205 to transfer information for a TNL association. The direction of the message is from the radio base station 205 to the MME 203. The S1 SETUP REQUEST message may be as exemplified in Table 1 below. The IE/Group Name column in table 1 comprises the name of the information element or group. The Presence column comprises the presence of the information elements, where M indicates that the information element is mandatory, i.e. it shall always be in the message and where O indicates that the information element is optional, i.e. it may or may not be comprised in the message. Range column in table 1 indicates the allowed number of copies of repetitive IEs/IE groups. The information element type and reference column indicates which type the information element is and where in the document 3GPP TS. 36.413 further information about the type may be found. The semantics description column provides a semantic description of the information elements. The critically column indicates the criticality of each information element, where yes indicates that criticality information is applied. - indicates that no criticality information is applied explicitly and GLOBAL indicates that the information element and all its repetitions together have one common criticality information. The assigned criticality column provides the actual criticality information, whether is rejected or ignored. In table 1 below, the priority information is located in the three bottom rows, emphasized with underline. The priority information is piggy backed on the existing S1 setup request message. All three information elements are optional, indicated with an O in the presence column. The Area priority may have a range of 1 - 15. More information about the MME Code is found in the section 9.2.3.12 in 3GPP TS 36.413 and this reference describes that the MME Code uniquely identifies an MME 203 within an MME pool area. The semantic description of the Area Priority is Area Importance. The semantic descriptions of the two MME Codes are Primary MME and Secondary MME. All three information elements have critical information and the assigned criticality is "ignore".

Table 1

IE/Group Range IE type and Semantics Assigne Name reference description d

Criticalit y

P^resence

Message Type M 9.2.1.1 YES reject

Global eNB ID M 9.2.1 .37 YES reject eNB Name 0 PrintableString YES ignore

(1 ..150,...)

Supported 1 ..<maxnoo Supported reject TAs fTACs> Tas in the

eNB

>TAC M 9.2.3.7 Broadcasted

TAC

>Broadcast 1 ..<maxnoo Broadcasted

PLMNs fBPLMNs> PLMNs

»PLMN M 9.2.3.8

Identity

CSG Id List 0..1 reject

C GO GO^iiliLBA^L _LBA^Lttrcay

>CSG Id M 1 to < 9.2.1.62

maxnoofCS

Glds >

Default paging M 9.2.1 .16 YES ignore DRX

Area Priority 0 1 -15 Area YES ignore

Importance

MME Code 0 9.2.3.12 Primary MME YES ignore

MME Code 0 9.2.3.12 Secondary YES ignore

MME Range bound Explanation maxnoofTACs Maximum no. of TACs. Value is 256.

Range bound Explanation

maxnoofBPLMNs Maximum no. of Broadcasted PLMNs. Value is 6.

Range bound Explanation

maxnoofCSGIds Maximum no. of CSG Ids within the CSG Id List.

Value is 256.

Step 402

The MME 203 responds by sending a S1 SETUP RESPONSE message comprising the appropriate data back to the radio base station 205.

The exchanged data shall be stored in respective node and used for the duration of the TNL association. When this procedure is finished S1 interface is operational and other S1 messages may be exchanged.

If the radio base station 205 initiating the S1 SETUP procedure supports one (or more) CSG cell(s), the S1 SETUP REQUEST message shall contain the CSG ID(s) of the supported CSG(s).

If the S1 SETUP REQUEST message comprises the base station name information element the MME 203 may use this information element as a human readable name of the radio base station 205. If the S1 SETUP RESPONSE message comprises the MME name information element the radio base station 205 may use this information element as a human readable name of the MME 203.

After the MME 203 has obtained the priority information it may receive updated priority information, e.g. from a network operator. For example, if an emergency situation occurs, the network operator may change the priority information related to the geographical area of the emergency situation. Returning to figure 3.

Step 302

The MME 203 detects that it is overloaded and an overload protection function is triggered in the MME 203. The MME 203 may start to use Overload Control messages. The overload protection function may be triggered by the MME 203 itself or it may receive the trigger from e.g the SGW. Step 303

Based on the priority information, the MME 203 determines whether it should maintain or disconnect the connection to the first radio base station 205a and the connection to the second radio base station 205b. The priority information related to primary and secondary MME makes it possible for each individual MME 203 in an MME pool to have its own selection of RAN nodes, i.e. radio base stations 205. The MME 203 may also prioritize "its own" radio base station 205 during public warning scenarios. The priority information also makes it possible for the MME 203 to have a defined primary area such as e.g.

operator offices, city hall, police etc... The MME 203 may then prioritize which radio base station 205 to disconnect in a pre-defined order, again if needed. The MME 203 shall also take ongoing Emergency calls into consideration before disconnecting a radio base station 205.

The MME 203 may not typical maintain the connection of all radio base stations 205 served by the MME 203 or disconnect all radio base stations 205 served by the MME 203. Thus, it is assumed that least one radio base station 205 is maintained and that at least one radio base station 205 is disconnected.

Step 304

Based on the result of step 303, the connection to the first radio base station 205a is maintained, i.e. it is excluded from the overload procedure.

Step 305

The connection to the second radio base station 205b is disconnected based on the result of step 303. The MME 203 may then disconnect all other radio base stations 205 if needed, i.e. send overload control messages to them. However if an emergency call or a public warning is ongoing then that connection should also be excluded from the Overload procedure even if it's not a "primary", "secondary" connection.

Figure 5 illustrates an embodiment of the communications network 200 where the

5 network 200 is overloaded. As mentioned above, the MME 203 comprises the overload protection function that enables the MME 203 to disconnect radio base stations 205 to avoid incoming traffic. The overload protection function takes the priority information into account to determine whether radio base stations 205 should be disconnected or not. It may be the MME 203 itself that triggers the disconnection or the MME 203 may receive a 10 trigger from e.g. the Serving GateWay (SGW). In the embodiments exemplified in Figure 5, the area priority is taken into account. The area comprises one or more radio base station 205 serving the area. Therefore, the area priority may be also referred to as a radio base station priority, implicitly. The area may also be seen as a geographical area, e.g. a cell, such as an operator office, city hall, police etc.

15

The SGW mentioned above, is a network node which is responsible for handovers with neighbor radio base stations, it handles data transfer across the user plane. The SGW acts as the mobility anchor or interface for mobility between LTE and other 3GPP technologies. The SGW also monitors and maintains context information related to the 20 user equipment during idle state and generates paging requests when data for the user equipment arrives from the network on the downlink. The SGW also performs replication of the user traffic in case of lawful interception.

In figure 5, the cloud illustrates an MME pool comprising a plurality of MMEs 203. In 25 figure 5, the MME pool is exemplified with four MMEs 203, a first MME 203a, a second MME 203b, a third MME 203c and a fourth MME 203d. However, the MME pool may comprise any other suitable number of MMEs 203.

The first MME 203a, the second MME 203b, the third MME 203c and the fourth MME 30 203d each has priority information stating that they shall have a priority one S1 connection with a first area in case of overload control in the network 200. The priority one S1 connection is illustrated with a broken line in figure 5. In figure 5, the first area comprises the first radio base station 205a, and the first radio base station 205a is represented by three radio base stations to illustrate that there may be more than one radio base station 35 in the first area. The first MME 203a, the second MME 203b, the third MME 203c and the fourth MME 203d each has priority information stating that they shall have a priority two S1 connection with a second area in case of overload control in the network 200. The priority two S1 connections are illustrated with a dotted line in figure 5. In figure 5, the second area comprises the second radio base station 205b, and the second radio base station 205b is represented by three radio base stations 205 to illustrate that there may be more than one radio base station 205 in the second area. The first MME 203a, the second MME 203b, the third MME 203c and the fourth MME 203d each has priority information stating that they shall have a normal priority S1 connection with a third and fourth area in case of overload control in the network 200. The normal priority connections are illustrated with continuous lines in figure 5. In figure 5, the third area comprises a third radio base station 205c, and the third radio base station 205c is represented by three radio base stations to illustrate that there may be more than one radio base station 205 in the second area. Similarly, the fourth area comprises a fourth radio base station 205d, and the fourth radio base station 205d is represented by three radio base stations 205 to illustrate that there may be more than one radio base station in the fourth area.

The first area should be prioritized by all MMEs 203 in this example embodiment. The second area should be prioritized after the first area by all MMEs 203. The third and fourth area should have normal prioritizing. In other words, the connection between the MMEs 203 and the first area and the second area should be kept in case of overload and the connection between the MMEs 203 and the third and fourth area will be disconnected in case of overload.

The Area priority comprised in the MME 203 provides the possibility to have a

configurable option in the MME 203 on how to react, how to apply OLP, for different kinds of priorities. Assuming that all MMEs 203 in the Figure 5 above is overloaded, then they may go through the priority for each, in the radio base station 205, configured area and maintain the ones with highest priority until last. This may be referred to as radio base station sub pooling. Figure 6 illustrates an embodiment of the communications network 200 where the network 200 is overloaded. As mentioned above, the MME 203 comprises the overload protection function that enables the MME 203 to disconnect radio base stations 205 to avoid incoming traffic in case of overload in the network 200. The overload protection 5 function takes the priority information into account to determine whether radio base stations 205 should be disconnected or not. It may be the MME 203 itself that triggers the disconnection or the MME 203 may receive a trigger from e.g. the SGW. In the embodiments exemplified in Figure 6, the priority information regarding primary MME and secondary MME is taken into account. A primary MME is an MME 203 whose connection 10 to a certain radio base station which should be highly prioritized in an overload scenario,

In figure 6, the cloud illustrates an MME pool comprises a plurality of MMEs 203. In figure 6, the MME pool is exemplified with four MMEs 203, a first MME 203a, a second MME 203b, a third MME 203c and a fourth MME 203d. However, the MME pool may comprise 15 any other suitable number of MMEs 203.

The broken lines represent a primary S1 connection in case of load control. The dotted lines represent a secondary S1 connection in case of load control. The continuous bold lines represent a normal connection to get full mesh in the pool.

20

In figure 6, the priority information provides information regarding the first MME 203a being a primary MME for a fourth radio base station 205d, as seen from the broken line towards the fourth radio base station 205d. Thus, the S1 connection between the first MME 203a and the fourth radio base station 205d may be seen as a primary S1

25 connection. Furthermore, the priority information provides information regarding that the first MME 203 is a secondary MME for the first radio base station 205a, as seen by the dotted line in figure 6. The remaining connections of the first MME 203a, i.e. towards the second radio base station 205b and the third radio base station 205c, does not have any priority and is considered having "normal" priority. In an overload situation, the first MME

30 203a will maintain its connections towards the fourth radio base station 205d and the first radio base station 205a and disconnect the connections towards the second radio base station 205b and the third radio base station 205c, i.e. by sending overload control messages only to the second radio base station 205b and the third radio base station 205c. This way, black spots are avoided in the network 200.

35 In figure 6, the priority information further provides information regarding the second MME 203b being a primary MME for the first radio base station 205a, as seen from the broken line towards the first radio base station 205a. Thus, the S1 connection between the second MME 203a and the first radio base station 205a may be seen as a primary S1 5 connection. Furthermore, the priority information provides information regarding that the second MME 203b is a secondary MME for the second radio base station 205b, as seen by the dotted line in figure 6. The remaining connections of the second MME 203b, i.e. towards the third radio base station 205c and the fourth radio base station 205d, does not have any priority and is considered having "normal" priority. In an overload situation, the 10 second MME 203b will maintain its connections towards the first radio base station 205a and the second radio base station 205b and disconnect the connections towards the third radio base station 205c and the fourth radio base station 205d, i.e. by sending overload control messages only to the third radio base station 205c and the fourth radio base station 205d. This way, black spots are avoided in the network 200.

15

The priority information further provides information regarding the third MME 203c being a primary MME for the second radio base station 205b, as seen from the broken line towards the second radio base station 205b. Thus, the S1 connection between the third MME 203c and the second radio base station 205b may be seen as a primary S1

20 connection. Furthermore, the priority information provides information regarding that the third MME 203c is a secondary MME for the third radio base station 205c, as seen by the dotted line in figure 6. The remaining connections of the third MME 203c, i.e. towards the first radio base station 205a and the fourth radio base station 205d, does not have any priority and is considered having "normal" priority. In an overload situation, the third MME

25 203c will maintain its connections towards the second radio base station 205b and the third radio base station 205c and disconnect the connections towards the first radio base station 205a and the fourth radio base station 205d, i.e. by sending overload control messages only to the first radio base station 205a and the fourth radio base station 205d. This way, black spots are avoided in the network 200.

30

With regards to the fourth MME 203d, the priority information further provides information that the fourth MME 203d is a primary MME for the third radio base station 205c, as seen from the broken line towards the third radio base station 205c. Thus, the S1 connection between the fourth MME 203d and the third radio base station 205c may be seen as a 35 primary S1 connection. Furthermore, the priority information provides information regarding that the fourth MME 203d is a secondary MME for the fourth radio base station 205d, as seen by the dotted line in figure 6. The remaining connections of the fourth MME 203d, i.e. towards the first radio base station 205a and the second radio base station 205b, does not have any priority and is considered having "normal" priority. In an 5 overload situation, the fourth MME 203d will maintain its connections towards the third radio base station 205c and the fourth radio base station 205d and disconnect the connections towards the first radio base station 205a and the second radio base station 205b, i.e. by sending overload control messages only to the first radio base station 205a and the second radio base station 205b. This way, black spots are avoided in the network 10 200.

The MME 203 may, in some embodiments, provide internal prioritization of messages. The embodiments described above may then be used when discarding messages, Initial user equipment, from specific RAN nodes, radio base stations 205.

15

The embodiments herein may be used to evenly spread the message load on the MMEs 203 and also radio base stations 205 in case of a Public Warning System (PWS) and/or Earthquake and Tsunami Warning System (ETWS) scenario. The benefit of this is to avoid causing OLP in the network 200 and to faster, more reliable, get the warning out to 20 the user equipment's 201 .

The method described above will now be described seen from the perspective of the MME 203. Figure 7 is a flowchart describing the present method in the MME 203 for handling signaling overload in the network 200. The MME 203 is connected to a plurality

25 of radio base stations 205. The MME 203 comprising at least a connection to a first radio base station 205a and a connection to a second radio base station 205b. The plurality of radio base stations 205 may typically comprise many more radio base stations 205 than the first radio base station 205a and the second radio base station 205b, e.g. more than 5 or 10 or 100 or 1000 but below 10 000. The method comprises the following steps to be

30 performed by the MME 203, which steps may be performed in any suitable order:

Step 701

This step corresponds to step 301 in figure 3. The MME 203 obtains priority information associated with the first radio base station 205a and the second radio base station 205b indicating whether the first radio base station 205a and the second radio base station 205b may be disconnected from the MME 203 to reduce signaling load in case of a signaling overload in the communications network 200.

The obtained priority information may e.g. indicate that the MME 203 is the primary MME or the secondary MME for the first radio base station 205a, or that the first radio base station 205a serves a prioritized geographical area. In some embodiments, the priority information is comprised in an S1 setup request message.

In some embodiments, the information is obtained from the first radio base station 205a and/or the second radio base station 205b, a DNS 210, or from a memory unit 207 comprised in the MME 203.

Step 702

This step corresponds to step 302 in figure 3. In some embodiments, the MME 203 detects that an amount of signaling from the plurality of radio base stations 205 exceeds a threshold indicating the signaling overload. The signaling may comprise "payload" signaling e.g. such as speech, images, movies, data files or similar, and/or "control" signaling e.g. such as signaling required to establish bearers, execute handovers or similar. In some embodiments, the MME 203 may detect that an amount of signaling from the plurality of radio base stations 205 exceeds a threshold by receiving a trigger from the SGW indicating overload.

The above mentioned threshold may be any suitable threshold corresponding to a signaling load. The threshold may e.g. be a predetermined threshold, e.g. indicating the signaling load in bit/s or allocated bandwidth or similar. Also, the signaling load may be the combined signaling load from all the radio base stations 205 served by the MME 203 or at least the signaling load from a majority of the radio base stations 205 served by the MME 203. The signaling overload from the radio bases stations 205 must not necessarily occur with respect to the MME 203 or at least not exclusively with respect to the MME 203. Similarly; the signaling overload may not necessarily be detected by the MME 203 itself. In other cases the signaling overload from the radio bases stations 205 served by the MME 203 may occur towards some other network node, e.g. the signaling overload may occur with respect to a Serving Gateway (SGW) (not shown) or similar serving at least a part of said plurality of radio base stations 205, and the signaling overload may be detected by that other node, e.g. the SGW, and reported to the MME 203. Step 703

This step corresponds to steps 303 and 304 in figure 3.

In some embodiments, the MME 203 maintains the connection to the first radio base station 205a based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload.

Step 703a

This step is a substep of step 703. In some embodiments, the MME 203 maintains the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates a high priority. It is preferred that the second radio base station 205b is disconnected based on the obtained priority information, e.g. since the priority information indicates that the second radio base station 205b has a lower priority than the first radio base station 205a, e.g. that the MME 203 in question is neither the primary nor the secondary MME for the second radio base station 205. This will be described in more detail with reference to step 704 below.

Step 703b

This is a substep of step 703, and a step performed before or after step 703a or instead of step 703a.

In some embodiments, the MME 203 maintains the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates that the MME 203 is a primary MME or a secondary MME. In other words, the first base station 205a is maintained because the priority information indicates that the MME 203 is the primary or secondary MME for this radio base station 205. The second radio base station 205b will still be disconnected based on the obtained priority information, e.g. since the priority information indicates that the second radio base station 5 205b has a lower priority than the first radio base station 205a, e.g. that the MME 203 in question is neither the primary nor the secondary MME for the second radio base station 205. This will be described in more detail with reference to step 704 below.

Step 703c

0 This is a substep of step 703, and a step performed before or after step 703a, before or after step 703b.

In some embodiments, the MME 203 maintains the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a5 indicates that the first radio base station 205a handles an emergency call or when the MME 203 detects that the first radio base station 205a handles the emergency call. The first radio base station 205a is maintained because the first radio base station 205a handles an emergency call. The second radio base station 205b will still be disconnected based on the obtained priority information, e.g. since priority information indicates that the0 second radio base station 205b has a lower priority than the first radio base station 205a, e.g. in that the MME 203 in question is neither the primary nor the secondary MME for the second radio base station 205b, and/or in that there is no emergency call handled by the second radio base station 205b. 5 Preferably, the second radio base station 205b is still disconnected based on the obtained priority information, e.g. since the priority information indicates that the second radio base station 205b has a lower priority than the first radio base station 205a, e.g. that the MME 203 in question is neither the primary nor the secondary MME for the second radio base station 205. This will be described in more detail with reference to step 704 below.

0

Step 703d

This is a substep of step 703, and a step performed before or after step 703a, before or after step 703b, before or after step 703, instead of step 703a, instead of step 703b or instead of steps 703a and step 703b.

5 In some embodiments, the MME 203 maintains the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates that the first radio base station 205a serves a prioritized geographical area. The prioritized geographical area may e.g. be defined by the cell or cells covered by the first 5 radio base station 205a, and/or by the identity of the first radio base station 205a, or by one or more Public Land Mobile Networks (PLMN) or similar to which the first radio base station 205a belongs, or by one or more Tracking Areas (TA) or similar and/or by one or more Location Areas (LA) or similar or by some other geographical area(s) to which the first radio base station 205a belongs.

10

Step 704

This step corresponds to step 303 and 305 in figure 3.

In some embodiments, the MME 203 disconnects the connection to the second radio 15 base station 205b based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload.

Step 704b

This is a substep of step 704.

20

In some embodiments, the MME 203 disconnects the connection to the second radio base station 205b when the priority information associated with the second radio base station 205b indicates a low priority. The second radio base station 205b may e.g. be disconnected when the priority information indicates that the second radio base station 25 205b has a lower priority than the first radio base station 205a, e.g. that the MME 203 in question is neither the primary nor the secondary MME for the second radio base station 205b and/or in that there is no emergency call handled by the second radio base station 205b.

30 To perform the method steps shown in figure 7 the MME 203 comprises an arrangement as shown in Figure 8. The MME 203 is connected to the plurality of radio base stations 205. The MME 203 comprises at least a connection to the first radio base station 205a and a connection to the second radio base station 205b. The MME 203 comprises an obtaining unit 801 which is configured to obtain priority information associated with the first radio base station 205a and the second radio base station 205b indicating whether the first radio base station 205a and the second radio base station 205b may be disconnected from the MME 203 to reduce signaling load in case of a signaling overload. In some embodiments, the priority information is comprised in an S1 setup request message. In some embodiments, the obtaining unit 801 is configured to obtain the priority information from the first radio base station 205a and/or the second radio base station 205b, the DNS 210, or from the memory 207 comprised in the MME 203.

In some embodiments, the MME 203 comprises a processor 803 configured to detect that an amount of signaling from said plurality of radio base stations 205 exceeds a threshold indicating the signaling overload. The processor 803 is further configured to maintain the connection to the first radio base station 205a based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload, and to disconnect the connection to the second radio base station 205b based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload. In some embodiments, the processor 803 is further configured to maintain the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates a high priority, and to disconnect the connection to the second radio base station 205b when the priority information associated with the second radio base station 205b indicates a lower priority.

In some embodiments, the processor 803 is further configured to maintain the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates that the MME 203 is a primary MME or a secondary MME.

In some embodiments, the processor 803 is further configured to maintain the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates that the first radio base station 205a handles an emergency call or when the MME 203 detects that the first radio base station 205a handles an emergency call. In some embodiments, the processor 803 is further configured to maintain the connection to the first radio base station 205a when the priority information associated with the first radio base station 205a indicates that the first radio base station 205a serves a prioritized geographical area. The processor 803 may comprise Radio Frequency (RF) circuitry and baseband processing circuitry (not shown).

The memory 207 comprised in the MME 203 comprises one or more memory units. The memory 207 is arranged to be used to store data, received data streams, power level measurements, priority information, threshold values, time periods, configurations, schedulings, and applications to perform the methods herein when being executed in the MME 203.

The MME 203 may further comprise a receiver 810 and a transmitter 813 configured to receive and transmit data traffic, signaling etc.

In particular embodiments, some or all of the functionality described above as being provided by the MME 203 may be provided by the processor 803 executing instructions stored on a computer-readable medium, such as the memory 207 shown in Figure 8. Alternative embodiments of the MME 203 may comprise additional components beyond those shown in Figure 8 that may be responsible for providing certain aspects of the MME's functionality, comprising any of the functionality described above and/or any functionality necessary to support the embodiments described above. The method described above will now be described seen from the perspective of a network node. Figure 9 is a flowchart describing the present method in the network node 203 for handling signalling overload in the network 200. The network node may be a radio base station 205, the DNS 210 or the memory 207 comprised in the MME 203. The method comprises the following steps to be performed by the network node, which steps may be performed in any suitable order:

Step 901

In some embodiments, the network node receives the priority information from a network operator. Step 902

This step corresponds to step 301 in figure 3.

The network node provides priority information associated with the first radio base station 5 205a and a second radio base station 205b to the MME 203. The priority information indicates whether the first radio base station 205a and the second radio base station 205b may be disconnected from the MME 203 to reduce signaling load in case of a signaling overload. The priority information may be preconfigured in the network node. 0 Step 903

In some embodiments, the network node receives updated priority information from a network operator.

To perform the method steps shown in figure 9 the network node comprises an

5 arrangement as shown in Figure 10. The network node may be a radio base station 205, a DNS 210, or a memory 207 comprised in the MME 203.

The network node comprises a providing unit 1001 configured to provide priority information associated with the first radio base station 205a and the second radio base0 station 205b to the MME 203. The priority information indicates whether the first radio base station 205a and the second radio base station 205b may be disconnected from the MME 203 to reduce signaling load in case of a signaling overload.

In some embodiments, the network node comprises a receiver 1003 which is configured5 to receive updated priority information from a network operator. The receiver 1003 may be further configured to receive the priority information from a network operator. In some embodiments, the priority information is preconfigured in the network node.

As shown in Figure 10, the example network node further comprises a memory 1005 and0 a processor 1007 and a transmitter 1010. The memory 1005 comprises one or more memory units. The memory 1005 is arranged to be used to store data, received data streams, power level measurements, priority information, threshold values, time periods, configurations, schedulings, and applications to perform the methods herein when being executed in the network node. The processor 1005 may comprise RF circuitry and baseband processing circuitry (not shown). In particular embodiments, some or all of the functionality described above as being provided by the network node may be provided by the processor executing instructions stored on a computer-readable medium, such as the memory 1005 shown in Figure 10. Alternative embodiments of the network node may comprise additional components responsible for providing additional functionality, comprising any of the functionality identified above and/or any functionality necessary to support the

embodiments described above.

Some embodiments described above may be summarised in the following manner:

One embodiment is directed to a method in a mobility management entity, MME, for handling signaling overload in a communications network. The MME is connected to a plurality of radio base stations. The MME comprises at least a connection to a first radio base station and a connection to a second radio base station. The first radio base station and the second radio base station are comprised in the plurality of radio base stations 205. The method comprises: obtaining priority information associated with the first radio base station and the second radio base station indicating whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signaling overload. The method may further comprise: detecting that an amount of signaling from said plurality of radio base stations exceeds a threshold indicating the signaling overload; and maintaining the connection to the first radio base station based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload; and disconnecting the connection to the second radio base station based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload.

The maintaining of the connection to the first radio base station based on the obtained priority information may comprise: maintaining the connection to the first radio base station when the priority information associated with the first radio base station indicates a high priority; and wherein the disconnecting the connection to the second radio base station based on the obtained priority information may comprise: disconnecting the connection to the second radio base station when the priority information associated with the second radio base station indicates a low priority.

The maintaining of the connection to the first radio base station based on the obtained priority information may comprise: maintaining the connection to the first radio base station when the priority information associated with the first radio base station (205a) indicates that the MME (203) is a primary MME or a secondary MME.

The maintaining of the connection to the first radio base station based on the obtained priority information may comprise: maintaining the connection to the first radio base station when the priority information associated with the first radio base station indicates that the first radio base station handles an emergency call or when the MME detects that the first radio base station handles the emergency call.

The maintaining of the connection to the first radio base station based on the obtained priority information may comprise: maintaining the connection to the first radio base station when the priority information associated with the first radio base station indicates that the first radio base station serves a prioritized geographical area.

The priority information may be comprised in an S1 setup request message.

The priority information may be obtained from the first radio base station and/or the second radio base station, or a domain name server, DNS, or from a memory comprised in the MME.

Some other embodiments described above may be summarised in the following manner:

One other embodiment is directed to a method in a network node for handling signaling overload in a communications network.

The method comprises: providing priority information associated with a first radio base station and a second radio base station to a mobility management entity, MME, which priority information indicates whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signalling overload. The method may further comprise: receiving updated priority information from a network operator.

The priority information may be preconfigured in the network node. The method may further comprise: receiving the priority information from a network operator.

The network node may be a radio base station, or a domain name server, DNS, or a memory comprised in the MME.

One other embodiment is directed to a mobility management entity, MME, for handling signaling overload in a communications network. The MME is configured to be operatively connected to a plurality of radio base stations. The MME comprises at least a connection to a first radio base station and a connection to a second radio base station. The MME comprises: an obtaining unit configured to obtain priority information associated with the first radio base station and the second radio base station indicating whether the first radio base station and the second radio base station can be disconnected from the MME to reduce signaling load in case of a signaling overload.

The MME may comprise a processor configured to:

detect that an amount of signaling from said plurality of radio base stations exceeds a threshold indicating the signaling overload; and to maintain the connection to the first radio base station based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload; and to disconnect the connection to the second radio base station based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload. The processor may be configured to: maintain the connection to the first radio base station when the priority information associated with the first radio base station (205a) indicates a high priority; and to disconnect the connection to the second radio base station when the priority information associated with the second radio base station indicates a lower priority.

Additionally or alternatively, the processor may be configured to maintain the connection to the first radio base station when the priority information associated with the first radio base station indicates that the MME (is a primary MME or a secondary MME.

Additionally or alternatively, the processor may be configured to maintain the connection to the first radio base station when the priority information associated with the first radio base station indicates that the first radio base station handles an emergency call or when the MME detects that the first radio base station handles an emergency call.

Additionally or alternatively, the processor may be configured to maintain the connection to the first radio base station when the priority information associated with the first radio base station indicates that the first radio base station serves a prioritized geographical area.

The priority information may e.g. be comprised in an S1 setup request message.

The obtaining unit may be configured to obtain the priority information from at least one of: the first radio base station or the second radio base station or from a domain name server, DNS or from a memory comprised in the MME.

Some other embodiments described above may be summarised in the following manner: One other embodiment is directed to a network node for handling signaling overload in a communications network. The network node comprises: a providing unit configured to provide priority information associated with a first radio base station and a second radio base station to a mobility management entity, MME, which priority information indicates whether the first radio base station and the second radio base station can be

disconnected from the MME to reduce signaling load in case of a signaling overload. The network node may comprise a receiver configured to receive updated priority information from a network operator. The network node may comprise a receiver configured to receive the priority information from a network operator.

The priority information may be preconfigured in the network node. The network may be a radio base station or a domain name server, DNS, or a memory comprised in the MME.

The embodiments herein may be implemented through one or more processors, such as the processor 803 in the MME 203 depicted in Figure 8 and a processor 1007 in the network node depicted in Figure 10, together with computer program code for performing the functions of the embodiments herein. The processor may be for example a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC) processor, Field- programmable gate array (FPGA) processor or microprocessor. 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

embodiments herein when being loaded into the MME 203 and/or network node. 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 MME 203 and/or network node.

The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the embodiments.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements.

It should also be emphasised that the steps of the methods defined in the appended claims may, without departing from the embodiments herein, be performed in another order than the order in which they appear.

Claims

1 . A method in a mobility management entity, MME (203), for handling signaling overload in a communications network (200), the MME (203) is connected to a plurality of radio base stations (205), the MME (203) comprising at least a connection to a first radio base station (205a) and a connection to a second radio base station (205b), which first radio base station (205a) and second radio base station (205b) are comprised in the plurality of radio base stations (205), the method comprising:

obtaining (301 , 701 ) priority information associated with the first radio base station (205a) and the second radio base station (205b) indicating whether the first radio base station (205a) and the second radio base station (205b) can be disconnected from the MME (203) to reduce signaling load in case of a signaling overload.

2. The method according to claim 1 , further comprising

detecting (302, 702) that an amount of signaling from said plurality of radio base stations (205) exceeds a threshold indicating the signaling overload;

maintaining (303, 304, 703) the connection to the first radio base station (205a) based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload; and

disconnecting (303, 305, 704) the connection to the second radio base station

(205b) based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload.

3. The method according to claim 2, wherein the maintaining (703) of the connection to the first radio base station (205a) based on the obtained information comprises:

maintaining (303, 304, 703a) the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates a high priority; and

wherein the disconnecting (704) the connection to the second radio base station (205b) based on the obtained information further comprises:

disconnecting (303, 305, 704a) the connection to the second radio base station (205b) when the priority information associated with the second radio base station (205b) indicates a low priority.

4. The method according to any one of claim 2 - 3, wherein the maintaining (703) of the connection to the first radio base station (205a) based on the obtained information comprises:

maintaining (703b) the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the MME (203) is a primary MME or a secondary MME.

5. The method according to any one of claim 2 - 3, wherein the maintaining (703) of the connection to the first radio base station (205a) based on the obtained information comprises:

maintaining (703c) the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the first radio base station (205a) handles an emergency call or when the MME (203) detects that the first radio base station (205a) handles the emergency call.

6. The method according to any one of claim 2 - 3, wherein the maintaining (703) of the connection to the first radio base station (205a) based on the obtained information comprises:

maintaining (703d) the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the first radio base station (205a) serves a prioritized geographical area.

7. The method according to any one of the preceding claims, wherein the priority information is comprised in an S1 setup request message.

8. The method according to any one of the preceding claims, wherein the information is obtained from at least one of the first radio base station (205a), or the second radio base station (205b), or a domain name server, DNS (210), or from a memory (207) comprised in the MME (203).

9. A method in a network node for handling signaling overload in a communications network (200), the method comprising:

providing (902) priority information associated with a first radio base station (205a) and a second radio base station (205b) to a mobility management entity, MME (203), which priority information indicates whether the first radio base station (205a) and the second radio base station (205b) can be disconnected from the MME (203) to reduce signaling load in case of a signaling overload.

10. The method according to claim 9, further comprising:

5 receiving (903) updated priority information from a network operator.

1 1. The method according to any one of claim 9 - 10, wherein the priority information is preconfigured in the network node.

10 12. The method according to any of claim 9 - 10, further comprising:

receiving (901 ) the priority information from a network operator.

13. The method according to any one of claim 9 - 12, wherein the network node is a radio base station (205), a domain name server, DNS (210), or a memory (207)

15 comprised in the MME (203).

14. A mobility management entity, MME (203), for handling signaling overload in a communications network (200), the MME (203) being connected to a plurality of radio base stations (205), the MME (203) comprising at least a connection to a first radio base

20 station (205a) and a connection to a second radio base station (205b), the MME (203) comprising:

an obtaining unit (801 ) configured to obtain priority information associated with the first radio base station (205a) and the second radio base station (205b) indicating whether the first radio base station (205a) and the second radio base station (205b) can be

25 disconnected from the MME (203) to reduce signaling load in case of a signaling

overload.

15. The MME (203) according to claim 14, comprising

a processor (803) configured to

30 detect that an amount of signaling from said plurality of radio base stations

(205) exceeds a threshold indicating the signaling overload;

maintain the connection to the first radio base station (205a) based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload; and to disconnect the connection to the second radio base station (205b) based on the obtained priority information when the amount of signaling exceeds the threshold indicating the signaling overload.

16. The MME (203) according to claim 15, wherein the processor (803) is configured to: maintain the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates a high priority; and to

disconnect the connection to the second radio base station (205b) when the priority information associated with the second radio base station (205b) indicates a lower priority.

17. The MME (203) according to any one of claim 15 - 16 wherein processor (803) is further configured to maintain the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the MME (203) is a primary MME or a secondary MME.

18. The MME (203) according to any one of claim 15 - 16, wherein the processor (803) is further configured to maintain the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the first radio base station (205a) handles an emergency call or when the MME (203) detects that the first radio base station (205a) handles an emergency call.

19. The MME (203) according to any one of claim 15 - 16, wherein the processor (803) is further configured to maintain the connection to the first radio base station (205a) when the priority information associated with the first radio base station (205a) indicates that the first radio base station (205a) serves a prioritized geographical area.

20. The MME (203) according to any one of claim 14 - 19, wherein the priority information is comprised in an S1 setup request message.

21. The MME (203) according to any one of claim 14 - 20, wherein the obtaining unit (801 ) is configured to obtain the priority information from the first radio base station (205a) and/or the second radio base station (205b), a domain name server, DNS (210), or from a memory (207) comprised in the MME (203).

22. A network node for handling signaling overload in a communications network (200), the network node comprising:

a providing unit (1001 ) configured to provide priority information associated with a 5 first radio base station (205a) and a second radio base station (205b) to a mobility management entity, MME, (203), which priority information indicates whether the first radio base station (205a) and the second radio base station (205b) can be disconnected from the MME (203) to reduce signaling load in case of a signaling overload.

10 23. The network node according to claim 21 , further comprising:

a receiver (1003) configured to receive updated priority information from a network operator.

24. The network node according to any one of claim 22 - 23, further comprising:

15 a receiver (1003) configured to receive the priority information from a network operator.

25. The network node according to any one of claim 22 - 23, wherein the priority information is preconfigured in the network node.

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26. The network node according to any one of claim 22 - 25, wherein the network node is a radio base station (205), a domain name server, DNS (210), or a memory (207) comprised in the MME (203).

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