Key refresh for small-data traffic

1. A method of a radio access network (“RAN”) node comprising:

identifying a pattern of small-data traffic of a remote unit, wherein pattern is a frequent pattern of small-data traffic;

starting a counter at the RAN node, said counter corresponding to the remote unit, wherein the counter is for the identified small-data pattern, wherein the counter tracks one of: a number of packet data convergence protocol (“PDCP”) packets received since a security key was issued, a number of radio resource control (“RRC”) connection state transitions of the remote unit since the security key was issued, and an amount of time elapsed since activation of a user plane connection, wherein the small-data traffic is transferred over the user plane connection;

receiving small-data traffic associated with the remote unit;

determining that the security key is valid based on a value of the counter not exceeding a predefined limit;

triggering a key refresh procedure if the value of the counter indicates the security key is invalid; and

relaying the small-data traffic in response to the remote unit having a valid security key.

2. The method of claim 1 , wherein receiving the small-data traffic comprises receiving an RRC message from the remote unit, wherein the RRC message contains the small-data traffic.

3. The method of claim 1 , wherein receiving the small-data traffic comprises receiving the small-data traffic from a session management function.

4. The method of claim 1 , wherein the security key is a access stratum (“AS”) key, wherein triggering the key refresh procedure comprises one of: initiating an AS key refresh procedure and performing RRC connection establishment.

5. The method of claim 1 , wherein the security key protects an air-interface between the remote unit and a base unit.

6. The method of claim 1 , wherein the counter tracks a number of RRC-INACTIVE to RRC-CONNECTED state transitions since the security key was issued.

7. The method of claim 1 , wherein the user plane connection comprises a Protocol Data Unit (“PDU”) session was activated, wherein the small-data traffic is transferred over the PDU session.

8. An apparatus comprising:

a transceiver; and

a processor that:

identifies a pattern of small-data traffic of a remote unit, wherein pattern is an infrequent pattern of small-data traffic;

starts a counter corresponding to a remote unit, wherein the counter is for specific traffic of the identified small-data pattern, wherein the counter track one of: a Non-Access Stratum (“NAS”) counter for small-data packets, and a key refresh timer;

determines that a security key is valid based on a value of the counter not exceeding a predefined limit, in response to the transceiver receiving small-data traffic associated with the remote unit;

triggers a key refresh procedure if the value of the counter indicates the security key is invalid; and

relays the small-data traffic in response to the remote unit having a valid security key, wherein the apparatus comprises an Access and Mobility Management Function (“AMF”).

9. The apparatus of claim 8 , wherein receiving the small-data traffic comprises receiving a non-access stratum (“NAS”) message from the remote unit, wherein the NAS message contains the small-data traffic.

10. The apparatus of claim 8 , wherein the security key is a non-access stratum (“NAS”) key, wherein triggering the key refresh procedure comprises one of: initiating a NAS security mode command (“SMC”) procedure and initiating a NAS key refresh procedure.

11. The apparatus of claim 8 , wherein the key refresh timer tracks an amount of time elapsed since the security key was issued.

12. The apparatus of claim 8 , wherein the counter tracks a number of uplink packets received since the security key was issued.

13. The apparatus of claim 8 , wherein the counter tracks a number of downlink packets received since the security key was issued.

14. The apparatus of claim 8 , wherein the counter tracks a number of non-access stratum (“NAS”) packets received since the security key was issued.

15. A method of an Access and Mobility Management Function (“AMF”), the method comprising:

identifying a pattern of small-data traffic of a remote unit, wherein pattern is an infrequent pattern of small-data traffic;

starting a counter corresponding to a remote unit, wherein the counter is for specific traffic of the identified small-data pattern, wherein the counter track one of: a Non-Access Stratum (“NAS”) counter for small-data packets, and a key refresh timer;

determining that a security key is valid based on a value of the counter not exceeding a predefined limit, in response to the transceiver receiving small-data traffic associated with the remote unit;

triggering a key refresh procedure if the value of the counter indicates the security key is invalid; and

relaying the small-data traffic in response to the remote unit having a valid security key.

16. The method of claim 15 , wherein receiving the small-data traffic comprises receiving a NAS message from the remote unit, wherein the NAS message contains the small-data traffic.

17. The method of claim 15 , wherein the security key is a NAS key, wherein triggering the key refresh procedure comprises one of: initiating a NAS security mode command (“SMC”) procedure and initiating a NAS key refresh procedure.

18. The method of claim 15 , wherein the key refresh timer tracks an amount of time elapsed since the security key was issued.

19. The method of claim 15 , wherein the counter tracks a number of uplink packets received since the security key was issued.

20. The method of claim 15 , wherein the counter tracks a number of downlink packets received since the security key was issued.

21. The method of claim 15 , wherein the counter tracks a number of non-access stratum (“NAS”) packets received since the security key was issued.