Resuming radio connections in a communication network

1 . A user equipment (UE) comprising processing hardware and configured to:

communicate, in an RRC_CONNECTED state, messages with a base station and in accordance with Packet Data Convergence Protocol (PDCP) protocol that corresponds to a first radio access technology (RAT), using a radio connection over a radio interface that conforms to a second RAT;

suspend the radio connection to transition to an RRC_INACTIVE state;

subsequently to the suspending, transmit, to the base station over the radio interface that conforms to the second RAT, an indication that the radio connection has been resumed from the RRC_INACTIVE state to the RRC_CONNECTED state, in accordance with the PDCP protocol that corresponds to the first RAT; and

subsequently to the transmitting, communicate, with the base station, RRC messages associated with an uplink (UL) information procedure, in accordance with the PDCP protocol that corresponds to the first RAT.

2 . The UE of claim 1 , wherein the UE is further configured to:

establish an entity for communicating with the base station in accordance with the PDCP protocol that corresponds to the first RAT;

wherein communicating the messages and transmitting the indication includes using the entity.

3 . The UE of claim 1 , further configured to:

receive, from the base station, a command to release the radio connection;

wherein the suspending of the radio connection is in response to receiving the command.

4 . The UE of claim 1 , further configured to:

transmit, to the base station, a request to resume the radio connection;

receive, from the base station, a command to set up the radio connection; and

resume the radio connection in response to the receiving the command.

5 . The UE of claim 1 , wherein to transmit the indication, the UE is configured to:

set a counter in a header of a data unit that includes the indication to zero.

6 . The UE of claim 5 , further configured to, subsequently to the suspending:

transmit messages to the base station in accordance with the PDCP protocol that corresponds to the first RAT, including:

increment the counter for each of the messages, and

include the counter in headers of respective data units that include the messages.

7 . The UE of claim 1 , wherein:

the first RAT is 5G NR; and

the second RAT is EUTRA.

8 . The UE of claim 1 , further configured to:

subsequently to the suspending, apply a default configuration associated PDCP protocol of the first RAT.

9 . The UE of claim 1 , wherein:

the indication that the radio connection has been resumed includes an RRCConnectionSetupComplete message.

10 . The UE of claim 1 , further configured to:

determine that outbound data is available for transmission to the base station;

wherein the transmitting of the indication that the radio connection has been resumed is in response to the determining.

11 . A user equipment (UE) comprising processing hardware and configured to:

establish a first entity for communicating with a base station in accordance with a format that corresponds to a first radio access technology (RAT);

communicate, in an RRC_CONNECTED state and using the first entity, messages with the base station and in accordance with a format that corresponds to the first RAT, using a radio connection over a radio interface that conforms to a second RAT;

suspend the radio connection to transition to an RRC_INACTIVE state;

release the first entity;

establish a second entity for communicating with the base station in accordance with the format that corresponds to the first RAT; and

subsequently to the suspending, transmit, to the base station over the radio interface that conforms to the second RAT and using the second entity, an indication that the radio connection has been resumed, in accordance with the format that corresponds to the first RAT, to the RRC_CONNECTED STATE.

12 . The UE of claim 11 , wherein the indication is associated with a procedure that is one of:

(i) a security mode procedure to activate access stratum security,

(ii) a downlink (DL) information procedure,

(iii) an uplink (UL) information procedure,

(iv) a connection reconfiguration procedure, or

(v) a measurement reporting procedure.

13 . The UE of claim 11 , further configured to:

receive, from the base station, a command to release the radio connection;

wherein the suspending of the radio connection is in response to receiving the command.

14 . The UE of claim 11 , further configured to:

transmit, to the base station, a request to resume the radio connection;

receive, from the base station, a command to set up the radio connection; and

resume the radio connection in response to the receiving the command.

15 . A user equipment (UE) comprising processing hardware and configured to:

communicate, in an RRC_CONNECTED state, messages with a base station and in accordance with a format that corresponds to a first radio access technology (RAT), using a radio connection over a radio interface that conforms to a second RAT;

suspend the radio connection to transition to an RRC_INACTIVE state; and

subsequently to the suspending, transmit, to the base station over the radio interface that conforms to the second RAT, an indication that the radio connection has been resumed, in accordance with the format that corresponds to the first RAT, to the RRC_CONNECTED STATE; and

use a Packet Data Convergence Protocol (PDCP) protocol of the first RAT to communicate messages with the base station messages via a signaling radio bearer 1 (SRB1).

16 . The UE of claim 15 , further configured to:

receive, from the base station, a command to release the radio connection;

wherein the suspending of the radio connection is in response to receiving the command.

17 . The UE of claim 15 , further configured to:

subsequently to the suspending, apply a default configuration associated with a Packet Data Convergence Protocol (PDCP) protocol of the first RAT.

18 . The UE of claim 15 , further configured to:

determine that outbound data is available for transmission to the base station;

wherein the transmitting of the indication that the radio connection has been resumed is in response to the determining.