6.1 Overview

24.5543GPPProximity-services (ProSe) in 5G System (5GS) protocol aspectsRelease 17Stage 3TS

6.1.1 Transport protocol for PC3a control protocol messages for 5G ProSe direct discovery

The UE and 5G DDNMF shall use HTTP 1.1 as specified in IETF RFC 7230 [3] and IETF RFC 7231 [4] as the transport protocol for 5G ProSe messages over the PC3a interface. The 5G ProSe messages described here shall be included in the body of either an HTTP request message or an HTTP response message.

6.1.2 Handling of UE-initiated procedures

6.1.2.1 General

The following rules apply for UE-initiated procedures:

a) the UE initiates 5G ProSe transactions with an HTTP request message containing the PC3a request(s);

b) the 5G DDNMF responds to the requests with an HTTP response message containing the PC3a response(s) for the PC3a request(s); and

c) HTTP POST methods are used for PC3a direct discovery procedures.

The UE may use UE local configuration or URSP, as defined in 3GPP TS 24.526 [5], to establish a PDU session for reaching the HPLMN 5G DDNMF:

a) if a PDU session for reaching the HPLMN 5G DDNMF is not established yet, the UE shall establish the PDU session for reaching the HPLMN 5G DDNMF and shall send the HTTP request message via the PDU session for reaching the HPLMN 5G DDNMF; and

b) if a PDU session for reaching the HPLMN 5G DDNMF is already established (e.g., either due to other 5G ProSe feature or due to other application), the UE shall send the HTTP request message via the PDU session for reaching the HPLMN 5G DDNMF.

6.1.2.2 5G DDNMF discovery

The IP address or the FQDN of the 5G DDNMF in the HPLMN may be pre-configured in the UE. The FQDN of the 5G DDNMF in the HPLMN may also be self-constructed by the UE, i.e. derived from the PLMN ID of the HPLMN. The FQDN of the 5G DDNMF in the HPLMN may also be provisioned by the PCF as described in clause 5.2.3. The UE may use the pre-configured IP address or the FQDN of the 5G DDNMF in the HPLMN to discover the 5G DDNMF.

6.1.3 Handling of 5G DDNMF-initiated procedures

6.1.3.1 General

The 5G DDNMF address information (i.e. either IP address or FQDN) in the HPLMN may be pre-configured in the UE. The 5G DDNMF address information (i.e. either IP address or FQDN) in the HPLMN may also be provisioned by the PCF as described in clause 5.2.3. The UE may use the IP address or the FQDN of the 5G DDNMF in the HPLMN to discover the 5G DDNMF.

If the UE has neither the pre-configured 5G DDNMF address information in the HPLMN nor the 5G DDNMF address information in the HPLMN provisioned by the PCF, the UE may self-construct the FQDN of the 5G DDNMF in the HPLMN (e.g. deriving the FQDN from the PLMN ID of the HPLMN).

If the UE supports the HTTP long polling, the UE shall include a Network-Initiated Transaction Method set to "HTTP long polling" in the DISCOVERY_REQUEST message to the 5G DDNMF.

Upon receiving a DISCOVERY_REQUEST message containing a Network-Initiated Transaction Method set to "HTTP long polling", if the 5G DDNMF supports the HTTP long polling, the 5G DDNMF shall include a Network-Initiated Transaction Method set to "HTTP long polling" in the DISCOVERY_RESPONSE message.

If the UE receives a DISCOVERY_RESPONSE message including a Network-Initiated Transaction Method set to "HTTP long polling", the UE shall use the HTTP long polling for network initiated procedures. Otherwise, the UE shall assume that the 5G DDNMF uses OMA Push for network initiated procedures.

6.1.3.2 HTTP long polling

The HTTP long polling method is described by the following steps:

a) the UE sends an empty HTTP request message as a polling request when it expects network initiated message(s) over the PC3a interface;

b) the 5G DDNMF defers its response to the UE’s request until;

1) one or more network-initiated PC3a message(s) for the UE are available. The 5G DDNMF encloses the message(s) in an HTTP response message and send it to the UE; or

2) a particular timeout for HTTP polling has occurred. The 5G DDNMF then sends an empty HTTP response message as the polling response to the UE; and

c) after receiving the response from the 5G DDNMF, the UE may keep polling after some waiting period if:

1) the UE receives an empty polling response; or

2) the UE receives 5G DDNMF-initiated message(s) from the 5G DDNMF but still expects additional network-initiated message(s).

NOTE: The implementation of the HTTP polling process can be coordinated with the SUPL (Secure User Plane Location) procedures to synchronize the SUPL location report procedures and the HTTP polling procedure so as to reduce unnecessary wait time of polling.

If the UE is trigged to send a PC3a message to the 5G DDNMF while it has a pending HTTP polling request, the UE shall open another HTTP connection to the 5G DDNMF to send this new request. Alternately the UE may always use a separate dedicated HTTP connection for polling.

6.1.3.3 OMA Push

The OMA Push method is described by the following steps:

a) if one or more network-initiated PC3a message(s) for the UE are available, the 5G DDNMF sends a push message containing a particular URL to the UE via the OMA-Push Architecture as defined in OMA-AD-Push-V2_2-20110809-A [6]. The URL is linked to the PC3a message(s) to be sent to the UE. The 5G DDNMF (performing OMA Push Proxy Gateway functionality) generates a Push Message as specified in OMA-WAP-TS-PushOTA-V2_1-20110405-A [7] with the PDU set according to WAP-168-ServiceLoad-20010731-a [8]. The URL information shall be included in the PDU payload;

b) after receiving the push message, the UE retrieves the URL from the payload of the message and sends an HTTP GET request to the 5G DDNMF with this URL; and

c) the 5G DDNMF sends an HTTP response message containing the PC3a message(s) to the UE.