Mobility management for relaying

1. A method of operation of a first mobility management entity in a cellular communications network, the method comprising:

when said first mobility management entity is serving a first User Equipment, UE, obtaining information about a second UE that is being used as a relay by the first UE or that may be used as the relay by the first UE;

obtaining further information in the event that there is data to be sent to the first UE; and

responsive to there being data to be sent to the first UE:

sending a request to a second mobility management entity serving the second UE to forward a paging message to the first UE, in response to determining that the first UE is in an idle mode, and

sending downlink signalling to the first UE via the second UE.

2. A method according to claim 1 , wherein the step of obtaining information about the second UE comprises:

receiving the information in a message from a radio access network, RAN, node serving the first UE.

3. A method according to claim 2 , comprising:

receiving the information from the RAN node serving the first UE as part of a non-access stratum message.

4. A method according to claim 2 , comprising:

receiving the information from the RAN node serving the first UE in a separate message containing the information.

5. A method according to claim 1 , wherein the step of obtaining information about the second UE comprises:

receiving the information in a message from the second mobility management entity serving the second UE.

6. A method according to claim 1 , wherein the step of obtaining information about the second UE comprises:

receiving the information in a message from the first UE.

7. A method according to claim 1 , wherein obtaining the further information in the event that there is data to be sent to the first UE comprises receiving a notification from a core network node serving the first UE that there is data to be sent to the first UE.

8. A method according to claim 1 , wherein obtaining the further information in the event that there is data to be sent to the first UE comprises receiving a request from a radio access network node serving the first UE.

9. A method according to claim 1 , wherein obtaining the further information in the event that there is data to be sent to the first UE comprises determining that the first mobility management entity wishes to send signaling data to the first UE.

10. A method of operation of a second mobile management entity in a cellular communications network, the method comprising:

when said second mobile management entity is serving a second User Equipment, UE, that is being used as a relay by a first UE or that may be used as the relay by the first UE, receiving a first request from a first mobile management entity serving the first UE to one of forward a paging message to the first UE or find the second UE;

determining that the second UE is in a connected mode; and

if the received first request is a request to forward the paging message to the first UE, sending to the second UE a second request to forward the paging message to the first UE, in response to determining that the second UE is in the connected mode.

11. A mobile management entity in a cellular communications network configured to operate in accordance with a method according to claim 10 .

12. A method of operation of a second mobile management entity in a cellular communications network, the method comprising:

when said second mobile management entity is serving a second User Equipment, UE, that is being used as a relay by a first UE or that may be used as the relay by the first UE, receiving a request from a first mobile management entity serving the first UE to one of forward a paging message to the first UE;

determining that the second UE is in an idle mode; and

if the received request is a request to forward the paging message to the first UE, sending a message to a radio access node serving the second UE, requesting said radio access node to page the second UE, in response to determining that the first UE and the second UE is in an idle mode, wherein the message to the radio access node serving the second UE is a paging message comprising identities of the second UE and of the first UE in a linked list.

13. A method according to claim 12 , further comprising, after establishing a signaling connection between the second mobility management entity and the second UE, sending to the second UE a request to forward the paging message to the first UE.