Section: 11.2.1.3.2a IPv6 Stateless Address Autoconfiguration for EPC
Content: This subclause describes the signalling flows for the IPv6 Stateless Address Autoconfiguration procedures for EPC, in the case of using GTP-based S5/S8/S2a, and PMIP-based S5/S8/S2a. The procedures are based on the descriptions in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [77] and TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [78]. Subclause 11.2.3.1a lists the use cases between the UE to the P-GW that may trigger the P-GW to interwork with the external PDNs for IPv6 Prefix allocation. IPv6 prefix is delivered to UE in Router Advertisement message from the access router, in the process of IPv6 Stateless Address Autoconfiguration. In the procedure in the cases of using GTP-based S5/S8, P-GW acts as an access router, and allocates to a UE a globally unique /64 IPv6 prefix if the PLMN allocates the prefix, or P-GW retrieves IPv6 prefix from an external PDN if one is allocated by the external PDN and advertises it to the UE. In the latter procedure, P-GW uses RADIUS, Diameter or DHCPv6 protocol for the retrieval of an IPv6 prefix. Following is the flow for IPv6 Stateless Address Autoconfiguration for EPC using GTP-based S5/S8. 1. UE initiates the Attach procedure, indicating ‘IPv6’ or ‘IPv4v6’ for PDN type in PDP type information element. 2. MME requests for Default Bearer creation by sending Create Session Request to the S-GW. 2x. The S-GW sends Create Session Request to the P-GW. 3. P-GW retrieves IPv6 prefix using RADIUS, Diameter, or DHCPv6 mechanism. This procedure is performed when an external PDN allocates an IPv6 prefix. 4. The P-GW sends Create Session Response. It includes the IPv6 interface identifier I IPv6 prefix. 5. S-GW sends Create Session Response message to the MME. It includes the IPv6 interface identifier I IPv6 prefix. 5x. The MME sends Attach Accept message to the UE without the IPv6 prefix. The UE shall ignore the IPv6 prefix if it receives one in the message. 6. After receiving the Attach Accept message, the UE may send a Router Solicitation to the P-GW to solicit a Router Advertisement message. 7. The P-GW sends a Router Advertisement message to the UE, solicited or unsolicited. It shall include an IPv6 prefix in Prefix Information option field of the message. The prefix is the same as the one in the Attach Accept message, if it is provided during the default bearer establishment. For the handling of M, O, L and A flags, and the lifetime of the prefix in the Router Advertisement message, follow the description in subclause 11.2.1.3.2. Figure 11bc: IPv6 Stateless Address Autoconfiguration for GTP-based S5/S8 If PMIP-based S5/S8 is used, S-GW acts as an access router. Therefore, it is responsible for receiving Router Solicitation from and sending Router Advertisement message to the UE. Other than this, procedure is the same as the case of using GTP-based S5/S8; P-GW allocates, or retrieves an IPv6 prefix from the external PDN. The prefix is delivered from the P-GW to the S-GW in the IPv6 Home Network Prefix Option IE of a Proxy Binding Ackowledgement message. In addition, the S-GW shall initiate sending the IPv6 Router Advertisement message (either solicited or unsolicited) to the UE once the PDN connection with PDN type IPv4v6 or IPv6 is setup after the procedure of E-UTRAN initial Attach, UE requested PDN connectivity, intra-3GPP access handover with Serving GW relocation, or handover from non-3GPP IP Access with S2a/S2b to 3GPP Access. Following diagram shows the case where PMIP-based S5/S8 is used. Figure 11bd: IPv6 Stateless Address Autoconfiguration for PMIP-based S5/S8 For trusted non-3GPP accesses, the non-3GPP network supports prefix advertisement for IPv6 prefix received from the P-GW in PMIPv6 Proxy Binding Acknowledgement. If the trusted non-3GPP access network is a WLAN network, for GTP/PMIP –based S2a, TWAN acts as an access router. Therefore, TWAN is responsible for receiving Router Solicitation from and sending Router Advertisement message to the UE. Other than this, procedure is the same as the case of using GTP/PMIP-based S5/S8; P-GW allocates, or retrieves an IPv6 prefix from the external PDN. The prefix is delivered from the P-GW to the TWAN in the IPv6 Home Network Prefix Option IE of a Proxy Binding Ackowledgement message or in the PDN Address Allocation IE of Create Session Response message. Following diagram shows the case for trusted non-3GPP access network for WLAN access where GTP/PMIP-based S2a is used. Figure 11be: IPv6 Stateless Address Autoconfiguration for trusted WLAN access for GTP/PMIP-based S2a The P-GW ensures that the advertised IPv6 prefix is globally unique. Regarding the handling of Duplicate Address Detection, follow subclause 11.2.1.3.2. The UE constructs its full IPv6 address in accordance with RFC 4862[83]. For the handling of IPv6 interface identifier, refer to subclause 11.2.1.3.2. If the P-GW, S-GW and TWAN receive Neighbor Solicitation message from the UE, it shall answer with Neighbor Advertisement message. To renew the allocated IPv6 prefix, the P-GW (GTP based S5/S8), S-GW (PMIPv6 based S5/S8) or TWAN (GTP/PMIP based S2a) shall send an IPv6 Router Advertisement (solicited or unsolicited) to the UE with the same assigned IPv6 prefix and and new non-zero values in preferred and valid lifetime fields for the PDN connection (PDN type IPv4v6 or IPv6), before the Router Advertisement lifetime and prefix lifetime expiry, as specified in IETF RFC 4861 [89]. When sending the IPv6 Router Advertisement message, the S-GW may trigger the paging (e.g. by sending a Downlink Data Notification message to the MME) if the UE is in idle state. In order to reduce paging an idle UE to deliver RA, the Router Advertisement lifetime and IPv6 prefix lifetime shall be configured accordingly. If a UE supports multiple PDN connections functionality, it can connect to multiple P-GWs simultaneously, or it can access multiple PDNs through a single P-GW. In the former case, the IPv6 prefix allocated for its default bearer is used for the UE’s dedicated bearers toward the same PDN. In the latter case, IPv6 Stateless Address Autoconfiguration procedure is applied for each PDN connection.