Connection establishment in inter-RAT communication system

1. An apparatus, comprising:

at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

detect, from a user equipment, a connection request to a first radio access technology (RAT), wherein the apparatus is or is comprised in an access node of the first RAT;

determine, before the user equipment is switched to a connected state in the first RAT, whether a second RAT is more suitable to serve the user equipment than the first RAT; and

upon determining that the second RAT is more suitable, provision connection information of the second RAT to the user equipment, wherein the connection information is configured to cause the user equipment to directly connect with the second RAT instead of the first RAT, and comprises an indication of allocated resources of the second RAT for the user equipment to be used in contention-free connection establishment with the second RAT without first entering the connected state with the first RAT.

2. The apparatus of claim 1 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

detect the connection request in an initial access procedure; and

allocate the connection information of the second RAT to the user equipment in an RRCConnectionSetup-message of the initial access procedure.

3. The apparatus of claim 1 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

detect an establishment cause for the connection request, wherein the determination whether the second RAT is more suitable to serve the user equipment than the first RAT is based on the establishment cause.

4. The apparatus of claim 1 , wherein the determination whether the second RAT is more suitable to serve the user equipment than the first RAT is based on at least one of the following with respect to the first and/or the second RAT: available resources, traffic load, type, available bandwidth, available bandwidth with respect to applicable bandwidth for the user equipment.

5. The apparatus of claim 1 , wherein the apparatus is not collocated with a network node serving the second RAT, and wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

negotiate over an interface between the first and the second RAT regarding characteristics of the second RAT; and

compare those to characteristics of the first RAT for determining whether the second RAT is more suitable to serve the user equipment.

6. The apparatus of claim 1 , wherein the provided connection information causes the user equipment to perform a connection request with the second RAT in a 2-step contention free initial access procedure.

7. An apparatus, comprising:

at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

obtain, from an access node of a first radio access technology (RAT), an enquiry of connection information of a second RAT for a user equipment attempting to connect to the first RAT, wherein the apparatus is or is comprised in an access node of the second RAT;

determine connection information of the second RAT for the user equipment based on the request and provide the connection information to the first RAT, wherein the connection information comprises an indication of allocated resources of the second RAT for the user equipment to be used in contention-free connection request with the second RAT without first entering a connected state with the first RAT; and

detect a connection request to the second RAT from the user equipment based on the connection information and establish a connection with the user equipment.

8. An apparatus, comprising:

at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

cause a transmission to a first network node of a connection request with respect to a first radio access technology (RAT), wherein the first network node is an access node of the first RAT;

cause reception of connection information of the second RAT from the first network node before the apparatus is switched to a connected state in the first RAT, wherein the connection information comprises an indication of allocated resources of the second RAT for the user equipment to be used in contention-free connection request with the second RAT without first entering the connected state with the first RAT; and

establish a connection directly with the second RAT based on the received connection information, instead of establishing a connection with the first RAT.

9. The apparatus of claim 8 , wherein the connection request is for re-questing a switch to a radio resource control (RRC) connected state either from an RRC idle state or from an RRC inactive state.

10. The apparatus according to claim 8 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

provide the connection request in an initial access procedure; and

cause reception of the connection information of the second RAT in an RRCConnectionSetup-message of the initial access procedure from the first network node.

11. The apparatus according to claim 8 , wherein the direct connection establishment with the second RAT comprises a switch either from an RRC idle state or from the RRC inactive state in the first RAT to an RRC connected state in the second RAT, and wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

perform a connection request with the second RAT in a 2-step contention free initial access procedure based on the connection information.

12. The apparatus according to claim 8 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus further to:

provide to the first network node an indication of at least one RAT the apparatus is capable to operate with.

13. The apparatus of claim 8 , wherein the apparatus is a user equipment.