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Week # 06 ANDSF 與 Non- 3GPP Access

Explore ANDSF and Non-3GPP access technologies in wireless communication systems in this educational course by National University of Kaohsiung. Join Prof. Wu Junxing and TA Yang Wenjian to delve into trusted/untrusted non-3GPP access, handovers, and network trust mechanisms.

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Week # 06 ANDSF 與 Non- 3GPP Access

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  1. 教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心 示範課程:行動與無線區網整合 Week #06ANDSF與Non-3GPPAccess 助理教授：吳俊興 助教：楊文健 國立高雄大學 資訊工程學系

  2. Outline • Introduction of ANDSFand Non-3GPP Access • Trusted/Untrusted non-3GPP Access • Information Exchanged By ANDSF • Handover from 3GPP Access to Non-3GPP Access

  3. Introduction of ANDSF • Access Network Discovery and Selection Function (ANDSF) is a network element specified in 3GPP TS 23.402 [6] • The term ANDSF is used to refer to both Home and Visited ANDSF • ANDSF rules refers to the set of ANDSF policies defined in 3GPP TS 24.312 [13] for WLAN access selection and traffic routing between E-UTRAN or UTRAN and WLAN • ANDSF rules can contain RAN validity conditions for RAN-assisted WLAN interworking

  4. Introduction of ANDSF(Cont.) • The UE-ANDSF interaction can take place via non-seamless WLAN offload or via any 3GPP or non-3GPP access technology that can be used by the UE to access EPC • The UE shall support receiving OMA DM commands with bodies encoded as XML formatted as described in OMA-TS-DM_TNDS-V1_2 [5B]

  5. Introduction of non-3GPP accesses The 3GPP standard defines two types of access • trusted and untrusted non-3GPP access • Non-3GPP access includes access from for instance Wi-Fi, WiMAX, fixed and CDMA networks • The Mobility mechanisms supported between 3GPP and non-3GPP accesses within an operator and its roaming partner's network would depend upon operator choice • The EPS supports the use of non-3GPP IP access networks to access the EPC

  6. Trusted/Untrusted non-3GPP Access • Non-3GPP accesses can be split into two categories: • the "trusted" ones and the "untrusted" • The biggest difference between trusted access and untrusted access would be the requirement of authentication requirement • 3GPP does not specify which non-3GPP technologies should be considered trusted or untrusted • This decision is made by the operator

  7. Untrusted non-3GPP Access • Untrusted non-3GPP accesses interwork with the EPC via a network entity called the ePDG (for Evolved Packet Data Gateway) • The main role of the ePDG is to provide security mechanisms such as IPsec tunnelling of connections with the UE over an untrusted non-3GPP access

  8. Trusted non-3GPP Access • In Trusted non-3GPP Access, UE would not need any separate authentication/security process when it switches from 3GPP access to non-3GPP access (WiFi) since UE already has gone through this process when it was camping on the 3GPP access and network trust the process and assume that the non-3GPP access can be protected by the same security procedure • In this access, it is highly likely that Network Operator distribute their own WiFi Access points and let UE get access through those Access Point

  9. Trusted/untrusted non-3GPP access network detection • Access During initial attach or handover attach a UE needs to discover the trust relationship (whether it is a Trusted or Untrusted Non-3GPP Access Network) of the non-3GPP access network in order to know which non-3GPP IP access procedure to initiate. The trust relationship of a non-3GPP access network is made known to the UE with one of the following options: • If the non-3GPP access supports 3GPP-based access authentication, the UE discovers the trust relationship during the 3GPP-based access authentication • The UE operates on the basis of pre-configured policy in the UE

  10. Why we need ANDSF • Access Network Discovery and Selection Function (ANDSF) • It can help UE to know which network (3GPP or Non-3GPP) are available • When UE detected 3GPP network and WiFi network, which network UEhave to get access to

  11. Information Exchanged By ANDSF • ANDSF can be used to provide the following category of information to UE, based on operator configuration : • Discovery Information • Inter-System Mobility Policy (ISMP) • Inter-System Routing Policy (ISRP) • Inter-APN Routing Policy (IARP) • RuleSelectionInformation and WLAN Selection Policy (WLANSP) • VPLMNs with preferred WLAN Selection Rules • Home Network Preferences • Visited Network Preferences • The ANDSF communicates with the UE over the S14 reference point, which is essentially a synchronization of an OMA-DM management object (MO) specific to ANDSF

  12. Access Network Discovery Information • It consists of a list of access networks, such as WiFi, that may be available in the vicinity of a UE • This information is received in response to the UE’s request which contains its location and capability, such as types of supported interfaces, among others • The received information assists the UE to expedite the connection to these networks

  13. Access Network Discovery Information • ANDSF response may contain the following information: • Access the technology type, such as WiFi, WiMAX • Radio access network identifier, such as SSID of WLANs • Technology-specific information, such as one or more carrier frequencies • The suggested list of access networks may also include networks which are not owned by the same operator, but that have a roaming agreement with that operator

  14. Inter-System Mobility Policy (ISMP) • ISMP is valid for those UEs which cannot have more than one active access network connection at a time • For example, a UE that supports LTE as well as WiFi interface, but only one of them can be active at a time • ISMP consists of rules which can be used by UEs to select the most preferable access technology type • Such rules decide if a specific access technology is preferable to another (e.g. WiMAX is preferable to WLAN or WLAN SSID-1 is preferable to WLAN SSID-2, etc.) or not

  15. Inter-System Routing Policy (ISRP) • ISRP is valid for the UEs which can have more than one active access network connection simultaneously, and can also route IP traffic concurrently over multiple radio access interfaces • The UE can use this information to select the most preferable (or restricted) access technology/access network or APNs to direct a given traffic (per flow) • Thus, it defines IFOM (per flow mobility) policies and can be used by UEs implementing seamless mobility protocols such as DSMIPv6

  16. Inter-System Routing Policy (Cont.) • All of this received information comes along with some validity conditions which indicate when it shall be valid, such as a location area condition, time-of-day condition, etc. • For example, based on a UE’s location (home network or roaming), it can either latch on to H-ANDSF (home) or V-ANDSF (visitors)

  17. Introduction of Inter-APN Routing Policies (IARP) • IARP information to control and assist a UE with selecting a prioritised APN which is associated with an existing PDN connection for routing different IP flows • The IARP provided by ANDSF can also include information for identifying IP flows applicable for non-seamless WLAN offload

  18. WLAN Selection Policy (WLANSP) • The WLAN Selection Policy (WLANSP) is a set of operator-defined rules that determine how the UE selects and reselects a WLAN access network • The UE may be provisioned with WLANSP rules from multiple PLMNs

  19. VPLMNs with preferred WLAN Selection Rules • The "VPLMNs with preferred WLAN Selection" Rules is a list of PLMNs that is used by the UE when roaming • When the UE is roaming to one of the PLMNs in the list, the UE is configured to prefer the WLANSP rules provided by this PLMN over the WLANSP rules provided by the HPLMN • When the UE is roaming to any other PLMN, the UE is configured to prefer the WLANSP rules provided by the HPLMN

  20. VPLMNs with preferred WLAN Selection Rules(Cont.) • The home operator may provide "VPLMNs with preferred WLAN Selection" rules to UE via the H-ANDSF or may pre-configure the UE with "VPLMNs with preferred WLAN Selection" rules • The "VPLMNs with preferred WLAN Selection" rules provided to UE via the H-ANDSF shall take precedence over the pre-configured "VPLMNs with preferred WLAN Selection" rules in the UE

  21. Home Network Preferences • The Home Network Preferences may be provided by the UE's home operator and include information that assists the UE to select a WLAN access network and to select a PLMN for 3GPP-based authentication over WLAN • The Home Network Preferences may be provided by the HPLMN or an equivalent HPLMN or may be statically provisioned in the UE • The UE shall ignore the Home Network Preferences if provided by any other PLMN

  22. Architecture for Access Network Discovery Support Functions(Non-Roaming)

  23. Architecture for Access Network Discovery Support Functions(Roaming)

  24. Visited Network Preferences • The Visited Network Preferences may be provided by a PLMN-x, which is different from the UE's HPLMN and all equivalent HPLMNs • They include information that assists the UE (when roaming to PLMN-x) to select a PLMN for authentication over WLAN • The UE shall ignore the Visited Network Preferences if provided by HPLMN or any equivalent HPLMN

  25. ANDSF Discovery • In non-roaming scenario, the H‑ANDSF is discovered through interaction with the Domain Name Service function or the DHCP Server function • The H‑ANDSF address may also be provisioned to the UE • In roaming scenario, the UE shall be possible to retrieve both the H‑ANDSF and V‑ANDSF addresses • The ANDSF may not be contactable in certain PDNs

  26. Procedure for Inter-System Change with ANDSF ANDSF UE 3GPP Access Non-3GPP Access UE connect to 3GPP Access Inter-System Mobilty Policy pre-provisioned in UE ANDSF Discovery ANDSF Discovery Inter-System Mobilty Policy Update Policy Update

  27. Procedure for Inter-System Change with ANDSF ANDSF UE 3GPP Access Non-3GPP Access Evaluate non-3GPP access networks for HO Access Network Discovery Access Network Information Request Access Network Information Response

  28. Procedure for Inter-System Change with ANDSF ANDSF UE 3GPP Access Non-3GPP Access Turn ON Non-3GPP radio and check availability of non-3GPP access network Network Selection Network Sclection and HO Decision Inter-System Change proceduer Inter-System Change proceduer

  29. Simplify Handover with Access Network Discovery and Selection

  30. Procedure for Inter-System Change with ANDSF-Step1~3 • Initial connectivity • The UE is connected to 3GPP network. The current applications are supported over the 3GPP access network • Pre-provisioned policies • The inter-system mobility policy is pre-provisioned on the UE. Based on pre-provisioned operator policies the UE has preference for different non-3GPP networks such as WLAN, and WiMAX. The UE can select these access networks when they are available • ANDSF Discovery • The UE can discover ANDSF using DHCP query options as specified in IETF RFC 6153 [37], where ANDSF may be identified with a specific sub-option code

  31. Procedure for Inter-System Change with ANDSF-Step4~6 • Policy Update based on Network Triggers • The Based on network triggers the ANDSF sends an updated inter-system mobility policy to the UE. The inter-system mobility policy includes validity conditions, i.e. conditions indicating when the policy is valid. Such conditions can include time duration, location area, etc. • Evaluate which non-3GPP networks to discover • The inter-system mobility policies specify the access networks that the UE can select; the UE has both WLAN and WiMAX radios. In this case, the inter-system mobility policy provided by the operator allows the UE to select either WLAN or WiMAX networks under all conditions • Access Network Information Request • The UE sends a request to ANDSF to get information about available access networks. The UE also includes its location information in the request. ANDSF can limit the information sent to UE based on internal settings

  32. Procedure for Inter-System Change with ANDSF-Step7~9 • Access Network Information Response • The ANDSF sends a response to the UE which includes the list of available access networks types (in order of operator preferences), access network identifier and PLMN identifier • Evaluate candidate non-3GPP networks • Based on the received information and UE's local policy, the UE evaluates if it is within the coverage area of the available access networks in the order of preferences • Non-3GPP Network Selection • The UE selects the most preferred available access network for inter-system mobility

  33. Procedure for Inter-System Change with ANDSF-Finally Step • Inter-system change Procedure • The UE initiates inter-system change procedure to the selected non-3GPP access network

  34. Access Authentication in non-3GPP Accesses • Non-3GPP access authentication signalling is executed between the UE and the 3GPP AAA server/HSS • The authentication signalling may pass through AAA proxies • 3GPP based access authentication is executed across a SWa/STa reference point as depicted in the EPS architecture diagram. Following principles shall apply in this case: • Transport of authentication signalling shall be independent of the non-3GPP IP Access technology • The 3GPP based access authentication signalling shall be based on IETF protocols, for e.g., Extensible Authentication Protocol (EAP) as specified in RFC 3748 [11]

  35. Handover from 3GPP Access to Trusted Non-3GPP Access

  36. Handover-Step1~3 • The UE is connected in the 3GPP Access and has a PMIPv6 or GTP tunnel on the S5 interface • The UE discovers the trusted non-3GPP IP access system and determines to transfer its current sessions (i.e. handover) from the currently used 3GPP Access to the discovered trusted non-3GPP IP access system • The UE performs access authentication and authorization in the non-3GPP access system. The 3GPP AAA server authenticates and authorizes the UE for access in the trusted non-3GPP system

  37. Handover-Step4~6 • After successful authentication and authorization, the attach procedure is triggered • The Trusted Non-3GPP IP Access initiates a Gateway Control Session Establishment Procedure with the PCRF as specified in TS 23.203 [19] • The entity in the Trusted non-3GPP IP Access acting as a MAG sends a Proxy Binding Update (MN-NAI, Lifetime, Access Technology Type, Handover Indicator, APN, GRE key for downlink traffic) message to the PDN GW in order to establish the new registration

  38. Handover-Step7 7) • The PDN GW executes a PCEF-Initiated IP CAN Session Modification Procedure with the PCRF as specified in TS 23.203 [19e] • The PDN GW can decided to allocate a new IP address/prefix instead of preserving the old IP address/prefix • The PDN GW informs the 3GPP AAA Server of its PDN GW identity and the APN corresponding to the UE's PDN Connection and obtains authorization information from the 3GPP AAA Server

  39. Handover-Step8~9 • The PDN GW responds with a PMIP Binding Acknowledgement (MN NAI, Lifetime, UE Address Info, Additional Parameters, GRE key for uplink traffic, Charging ID) message to the Trusted Non-3GPP IP Access • The Lifetime indicates the duration the binding will remain valid • The Charging Id provided is the Charging Id previously assigned to the PDN connection if the source access is a PMIP-based access or to the Default Bearer if the source access is GTP-based • L3 attach procedure is completed at this point • The IP address(es) assigned to the UE by the PDN-GW is conveyed to the UE

  40. Handover-Step10 • The PDN GW executes a PCEF-Initiated IP CAN Session Modification Procedure with the PCRF as specified in TS 23.203 [19e]

  41. Handover from 3GPP Access to Untrusted Non-3GPP Access

  42. Handover-Step1~3 • The UE is initially attached to the 3GPP Access network • The UE moves and attaches to an untrusted non-3GPP IP access network • Access authentication procedure between UE and the 3GPP EPC • When the 3GPP AAA server has WLAN Location Information about the UE, it provides it over SWm to the ePDG together with the Age of this information • The WLAN Location information is provided to the ePDG when the 3GPP AAA server considers that location information coming from the WLAN AN used by the UE is trustable

  43. Handover-Step4 • The IKEv2 tunnel establishment procedure is started by the UE • The ePDG IP address to which the UE needs to form IPsec tunnel • After the UE is authenticated, UE is also authorized for access to the APN • As part of access authentication the PDN GW identity is sent to the ePDG by the 3GPP AAA server

  44. Handover-Step5 • The ePDG sends the Proxy Binding Update (MN-NAI, Lifetime, Access Technology Type, Handover Indicator, GRE key for downlink traffic, UE Address Info, Additional Parameter) message to the PDN GW • Access Technology Type is set to a value matching the characteristics of the non-3GPP access • The UE Address Info shall be set according to the CFG_Request in step 3. The ePDG shall not change the requested address(es) in the CFG_Request sent by the UE, and encode such address(es) in PBU and send to the PDN GW

  45. Handover-Step6 6) • If PCC is supported, the PDN GW requires configuration for enforcing policy, the PDN GW executes a PCEF-Initiated IP CAN Session Modification Procedure with the PCRF • The PDN GW informs the 3GPP AAA Server of its PDN GW identity and the APN corresponding to the UE's PDN Connection and obtains authorization information from the 3GPP AAA Server

  46. Handover-Step7 • The PDN GW processes the Proxy Binding Update message from the ePDG, updates the binding cache entry for the UE and responds with a Proxy Binding Acknowledgement (MN_NAI, Lifetime, GRE key for uplink traffic, UE Address Info, Charging ID, Additional Parameters) message • In the Proxy Binding Ack, the PDN GW replies with the same IP address and/or prefix that was assigned to the UE earlier • At this point a PMIPv6 tunnel exists between PDN GW and ePDG • The Charging Id provided is the Charging Id previously assigned to the PDN connection if the source access is a PMIP-based access or to the Default Bearer if the source access is GTP-based

  47. Handover-Step8~10 • The ePDG and the UE continue the IKEv2 exchange and IP address configuration. • At the end of the handover procedure there is a default bearer for the UE that consists of an IPsec tunnel between the UE and the ePDG and a PMIPv6 tunnel between the ePDG and the PDN GW. • For connectivity to multiple PDNs, the UE establishes connectivity to each PDN that is being transferred from 3GPP access, besides the PDN connection that was established in the steps 3-8, by executing the UE-initiated Connectivity to Additional PDN procedure specified in clause 7.6.1.

  48. References • 3GPPTS23.402 • 3GPPTS24.302 • http://www.sharetechnote.com/html/Handbook_LTE_WiFi_Offload.html • https://www.aptilo.com/solutions/mobile-data-offloading/3gpp-wifi-access/

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