5 FTT-IMS protocol

24.3223GPPRelease 17Stage 3TSTunnelling of IP Multimedia Subsystem (IMS) services over restrictive access networks

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.1 General

The FTT-IMS protocol consists of the UE requested FTT-IMS establishment procedure, the IP packet transport FTT-IMS procedure, the UE requested FTT-IMS release procedure and the EFTF requested FTT-IMS release procedure.

5.2 UE requested FTT-IMS establishment procedure

5.2.1 General

The purpose of the UE requested FTT-IMS establishment procedure is to establish an FTT-IMS between the UE and the EFTF.

5.2.2 UE procedures

5.2.2.1 UE requested FTT-IMS establishment procedure initiation

If the UE is not configured with an HTTP proxy address, the UE shall follow the procedures in subclause 5.2.2.2.

If the UE is configured with an HTTP proxy address, the UE shall follow the procedures in subclause 5.2.2.3.

NOTE: UE configuration of an HTTP proxy address is out of scope of 3GPP.

5.2.2.2 UE requested FTT-IMS establishment procedure initiation via restrictive non-3GPP access network type I

In order to establish an FTT-IMS, the UE shall establish a TCP connection to the EFTF address and destination port 443.

If the TCP connection establishment is successful, the UE shall establish a TLS connection over the TCP connection according to the TLS profile specified in 3GPP TS 33.310 [14] annex E. If the EFTF address is a FQDN, the UE shall include a TLS extension of type "server_name" in the TLS client hello message according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

5.2.2.3 UE requested FTT-IMS establishment procedure initiation via restrictive non-3GPP access network type II

If the UE is configured with HTTP proxy address, in order to establish an FTT-IMS, the UE shall send HTTP CONNECT request to the HTTP proxy address according to IETF RFC 2817 [8]. The UE shall populate Request-URI of the HTTP CONNECT request with the EFTF address and port 443.

Upon receiving HTTP 2xx response to HTTP CONNECT request, the UE shall establish TLS connection according to the TLS profile specified in 3GPP TS 33.310 [14] annex E over the TCP connection used for the HTTP CONNECT request transport. If the EFTF address is a FQDN, the UE shall include a TLS extension of type "server_name" in the TLS client hello message according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

5.2.2.4 UE requested FTT-IMS establishment procedure accepted

When valid TLS Finished message is received over the TCP connection, the UE shall use the connection as the FTT-IMS.

5.2.3 EFTF procedures

The EFTF shall handle the TCP connection setup and the TLS connection establishment according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

When TLS Finished message is sent over the TCP connection according to the TLS profile specified in 3GPP TS 33.310 [14] annex E, the EFTF shall use the connection as the FTT-IMS.

5.3 IP packet transport FTT-IMS procedure

5.3.1 General

The purpose of the IP packet transport FTT-IMS procedure is to transport an IPv4 packet or IPv6 packet over an FTT-IMS.

5.3.2 UE procedures

5.3.2.1 IP packet sending

In order to send an IPv4 packet or IPv6 packet, the UE shall create an IP packet envelope according to subclause 7.1.2.2, and shall populate the IP packet field of the IP packet envelope with the IPv4 packet or the IPv6 packet and shall send the IP packet envelope as TLS application data over the FTT-IMS.

5.3.2.2 IP packet receiving

Upon receiving the IP packet envelope as TLS application data over the FTT-IMS, the UE shall:

– if the UE supports IPv4 and the field in the four most significant bits of the first octet of the IP packet field of the IP packet envelope according to subclause 7.1.2.2 contains 4, handle the IP packet as an IPv4 packet according to IETF RFC 791 [5];

– if the UE supports IPv6 and the field in the four most significant bits of the first octet of the IP packet field of the IP packet envelope according to subclause 7.1.2.2 contains 6, handle the IP packet as an IPv6 packet according to IETF RFC 2460 [7]; and

– if the field in the four most significant bits of the first octet of the IP packet field of the IP packet envelope according to subclause 7.1.2.2 indicates not supported IP version, discard the IP packet envelope.

NOTE: The field in the four most significant bits of the first octet of both the IPv4 packet and the IPv6 packet indicates the IP version.

5.3.3 EFTF procedures

5.3.3.1 IP packet sending

In order to send an IPv4 packet or IPv6 packet, the EFTF shall create an IP packet envelope according to subclause 7.1.2.2, and shall populate the IP packet field of the IP packet envelope with the IPv4 packet or the IPv6 packet and shall send the IP packet envelope as TLS application data over the FTT-IMS.

5.3.3.2 IP packet receiving

Upon receiving the IP packet envelope as TLS application data over the FTT-IMS, the EFTF shall:

– if the EFTF supports IPv4 and the field in the four most significant bits of the first octet of the IP packet field of the IP packet envelope according to subclause 7.1.2.2 contains 4, handle the IP packet as an IPv4 packet according to IETF RFC 791 [5];

– if the EFTF supports IPv6 and the field in the four most significant bits of the first octet of the IP packet field of the IP packet envelope according to subclause 7.1.2.2 contains 6, handle the IP packet as an IPv6 packet according to IETF RFC 2460 [7]; and

NOTE: The field in the four most significant bits of the first octet of both the IPv4 packet and the IPv6 packet indicates the IP version.

5.4 UE requested FTT-IMS release procedure

5.4.1 General

The purpose of the UE requested FTT-IMS release procedure is to release an FTT-IMS when FTT-IMS is no longer needed.

5.4.2 UE procedures

In order to release the FTT-IMS, the UE shall send TLS close_notify alert according to the TLS profile specified in 3GPP TS 33.310 [14] annex E

5.4.3 EFTF procedures

The EFTF shall handle the TLS close_notify alert according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

5.5 EFTF requested FTT-IMS release procedure

5.5.1 General

The purpose of the EFTF requested FTT-IMS release procedure is to release an FTT-IMS when FTT-IMS is no longer needed.

5.5.2 EFTF procedures

In order to release the FTT-IMS, the EFTF shall send TLS close_notify alert according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

5.5.3 UE procedures

The UE shall handle the TLS close_notify alert according to the TLS profile specified in 3GPP TS 33.310 [14] annex E.

5.6 Procedure for unknown FTT-IMS envelope types

5.6.1 General

The purpose of this procedure is forward compatibility.

5.6.2 UE procedures

Upon receiving a generic FTT-IMS envelope with the type field indicating an envelope type other than the envelope types defined by this version of specification in subclause 7.1.2, the UE shall discard the generic FTT-IMS envelope.