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Content for  TS 23.402  Word version:  16.0.0

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4  Architecture Model and ConceptsWord‑p. 17

4.1  Concepts

4.1.0  General Concepts

The EPS supports the use of non-3GPP IP access networks to access the EPC.
The EPS supports network-based mobility management mechanism based on PMIP or GTP and host-based mobility management mechanism (e.g., MIP) over S2 reference points.
The EPS supports IETF-based network-based mobility management mechanism (i.e. PMIP) over S5 and S8 reference points.
When host-based mobility protocol (DSMIPv6, RFC 5555 [10]) is used within the EPS and the UE camps on a 3GPP access network, in this specification the UE is considered to be on its home link.
The mobility management procedures specified to handle mobility between 3GPP and non 3GPP accesses shall include mechanisms to minimize the handover latency due to authentication and authorization for network access. This applies to UEs either supporting simultaneous radio transmission capability or not supporting it. EPS-based mobility between GERAN/UTRAN access and non-3GPP access requires S4-based SGSNs.
For multiple PDN-GWs connecting to the same PDN, all the PDN GWs shall support the same mobility protocols.
The EPC supports local breakout of traffic whether a roaming subscriber is accessing the EPC via a 3GPP or a non 3GPP access network according to the design principles described in clause 4.1 of TS 23.401.
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4.1.1  General Concepts for Interworking Between E-UTRAN and CDMA2000

The mobility management procedures specified to handle mobility between E-UTRAN and CDMA2000 accesses (as required by TS 22.278) shall include mechanisms to minimize the service interruption during handover and where possible support bidirectional service continuity.
  • This applies to UEs supporting either single or dual radio capability.
  • The mobility management procedures should minimize any performance impacts to the UE and the respective accesses, for example, UE battery consumption and network throughput.
  • The mobility management procedures should minimize the coupling between the different accesses allowing independent protocol evolution in each access.
The operator may configure an indicator in HSS which is delivered to the BBERF in HSGW within the Charging Characteristics and used by the BBERF to not establish the Gateway Control Session during the IP-CAN session establishment procedure.
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4.1.2  General Concepts for Interworking Between 3GPP Accesses and WiMAXWord‑p. 18
The mobility management procedures specified to handle mobility between 3GPP Accesses and WiMAX (as required by TS 22.278) shall include mechanisms to minimize the service interruption during handover and where possible support bidirectional service continuity.
  • This applies to UEs supporting either single or dual radio capability.
  • The mobility management procedures should minimize any performance impacts to the UE and the respective accesses, for example, UE battery consumption and network throughput.
  • The mobility management procedures should minimize the coupling between the different accesses allowing independent protocol evolution in each access.
Furthermore, the mobility management procedures specified to handle mobility between 3GPP accesses and WiMAX should minimize the impact on legacy systems (i.e. UTRAN and GERAN).
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4.1.3  IP Mobility Management Selection Principles

The Mobility mechanisms supported between 3GPP and non-3GPP accesses within an operator and its roaming partner's network would depend upon operator choice.

4.1.3.1  Static Configuration of Inter-technology Mobility Mechanism

For networks deploying a single IP mobility management mechanism, the statically configured mobility mechanism can be access type and/or roaming agreement specific. The information about the mechanism to be used in such scenario is expected to be provisioned into the terminal (or the UICC) and the network. IP session continuity between 3GPP and non-3GPP access types may not be provided in this case if there is a mismatch between what the UE expects and what the network supports. For example service continuity may not be possible if the user switches to a terminal supporting a different IP mobility management mechanism than provisioned in the network.
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4.1.3.2  Networks Supporting Multiple IP Mobility Mechanisms

IP Mobility management Selection (IPMS) consist of two components:
  • IP MM protocol selection between Network Based Mobility (NBM) and Host based mobility (HBM - MIPv4 orDSMIPv6).
  • Decision on IP address preservation if NBM is selected.
IPMS does not relate to the selection between PMIPv6 and GTP over S5/S8/S2b/S2a.
Upon initial attachment to a 3GPP access, no IPMS is necessary since connectivity to a PDN GW is always established with a network-based mobility mechanism.
Upon initial attachment to a trusted non-3GPP access or ePDG and upon handover from 3GPP to a trusted non-3GPP access or ePDG, IPMS is performed before an IP address is allocated and provided to the UE.
The UE support for a specific IP Mobility Management protocol and/or IP address preservation mechanism for inter-access mobility may be known by the network-based on explicit indication from the UE.
Upon attachment to a trusted non-3GPP access or ePDG, if the access network (supporting at least NBM) is not aware of the UE capabilities and the home and access network's policies allow the usage of NBM, then NBM is used for establishing connectivity for the UE to the EPC.
When a NBM mechanism is used for establishing connectivity in the target access upon inter-access mobility, IP address preservation for session continuity based on NBM may take place as per PMIPv6 specification (RFC 5213 [8]) or according to clause 8.6 for GTP, and additionally based on the knowledge in the network of UE's capability (if available) to support NBM. Such knowledge may be based on an explicit indication from the UE upon handover that IP address preservation based on NBM management can be provided.
IP address preservation for session continuity based on HBM may take place if the network is aware of the UE capability to support DSMIPv6 or MIPv4. Such knowledge may be based on an indication to the target trusted non-3GPP access or ePDG from the HSS/AAA (e.g. in case of DSMIPv6, the UE performed S2c bootstrap before moving to the target trusted non-3GPP access or ePDG). In such a case, the trusted non-3GPP access network or ePDG provides the UE with a new IP address, local to the access network if IP mobility management protocol selected is DSMIPv6. In that case, in order to get IP address preservation for session continuity, the UE shall use DSMIPv6 over S2c reference point. This IP address shall be used as a care-of address for DSMIPv6. If the IP mobility management protocol selected is MIPv4, the address provided to the UE by the non-3GPP access network is a FACoA and IP address preservation is performed over S2a using MIPv4 FACoA procedures.
The final decision on the mobility management mechanism is made by the HSS/AAA upon UE authentication in the trusted non-3GPP access system or ePDG (both at initial attachment and handover), based on the information it has regarding the UE, local/home network capabilities and local/home network policies. If the UE provided an explicit indication of the supported mobility mechanisms, the network shall provide an indication to the UE identifying the selected mobility management mechanism.
Support of different IP mobility management protocols at local/home network is known by the AAA/HSS in one of the following ways:
  • through static pre-configuration, or
  • through indication of the supported IP mobility management protocols (NBM and/or MIPv4 FA CoA mode) by the trusted non-3GPP access system or ePDG as part of the AAA exchange for UE authentication.
Upon selecting a mobility management mechanism, as part of the AAA exchange for UE authentication in the trusted non-3GPP access system or ePDG, the HSS/AAA returns to the trusted non-3GPP access system or ePDG an indication on whether a local IP address shall be allocated to the UE, or if instead NBM shall be used to establish the connectivity, or the HSS/AAA returns to the trusted non-3GPP access system an indication that the address of the MIPv4 Foreign Agent shall be provided to the UE.
IPMS is performed in the following scenarios:
  • Upon initial attach to a trusted non-3GPP access or ePDG, the IPMS is performed to decide how to establish IP connectivity for the UE.
  • Upon handover without optimization from a 3GPP access to a non-3GPP access, the IPMS is performed to decide how to establish IP connectivity for the UE over the trusted non-3GPP access or ePDG.
  • Upon change of access between a non-3GPP access and a 3GPP access or between two non-3GPP accesses, if the IP MM protocol used to provide connectivity to the UE over the trusted non-3GPP access or ePDG is a NBM protocol, then a decision is performed on whether IP address preservation is provided or not as per PMIPv6 specification, (RFC 5213 [8]) or according to clause 8.6 for GTP and additionally based on the knowledge in the network of UE's capability (if available) to support NBM.
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4.1.3.2.1  IP Mobility Management Selection During Initial Attach to a Non-3GPP AccessWord‑p. 20
The IPMS decision is performed as described in the following:
  • If the UE indicates DSMIPv6 support only, and the network supports and selects DSMIPv6, the trusted non-3GPP access network or ePDG provides a local IP address to the UE to be used as CoA for DSMIPv6/S2c.
  • If the UE indicates MIPv4 support only, and the network supports and selects MIPv4, then the trusted non-3GPP access network provides a FACoA to the UE.
  • If the UE indicates DSMIPv6 or MIPv4 support only, and the network selects NBM for providing connectivity, then NBM is used for providing connectivity.
  • If the UE does not indicate any capabilities, it is assumed that the UE is not able to support DSMIPv6 or MIPv4, and NBM is used for providing connectivity if the network supports NBM.
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4.1.3.2.2  IPMS solutions
On handover to 3GPP access, UE shall request for IP address preservation by setting Request Type flag to "handover" during the attach procedure.
When the UE provides an indication of its supported mobility modes either during initial attach or on handover, the UE provides such information to the entity performing IPMS during network access authentication, for trusted non-3GPP accesses, or during authentication for tunnel establishment with ePDG, for untrusted non-3GPP accesses.
The network then makes the decision on what mobility protocol to be used for connectivity as described in further clauses depending on the scenario.
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4.1.3.2.3  IP Mobility Management Selection on Handover between accesses
On handover to non-3GPP accesses, the IPMS decision is performed as described in the following:
  1. If the UE only indicates NBM support between the two access technologies involved in the handover and the network supports NBM between those two access technologies involved in the handover, then NBM is used for providing connectivity, and IP address preservation is provided with S2a or S2b procedures.
  2. If the UE indicates DSMIPv6 support and the network supports and selects DSMIPv6, the trusted non-3GPP access network or ePDG provides a local IP address to the UE to be used as CoA for DSMIPv6, and IP address preservation is provided with S2c procedures.
  3. If the UE indicates DSMIPv6 support only and the network does not support DSMIPv6, then NBM is used for providing basic connectivity to the existing PDN GW if NBM is supported by the trusted non-3GPP access network or ePDG. In this case, the decision for IP address preservation is made as per PMIPv6 specification, (RFC 5213 [8]) or according to clause 8.6 for GTP.
  4. If the UE indicates support for both NBM and DSMIPv6, and the network based on policies selects NBM to establish the connectivity, then NBM is used to establish connectivity, and IP address preservation is provided with S2a or S2b procedures.
  5. If the UE indicates support for both NBM and DSMIPv6, and the network based on policies selects DSMIPv6 to establish the connectivity, then the trusted non-3GPP access network or ePDG provides a local IP address to the UE to be used as CoA for DSMIPv6, and IP address preservation is provided with S2c procedures.
  6. If the UE does not indicate any capabilities, then NBM is used for establishing connectivity if NBM is supported by the trusted non-3GPP access network or ePDG. In this case, the decision for IP address preservation is made as per PMIPv6 specification, (RFC 5213 [8]) or according to clause 8.6 for GTP.
  1. Preserve the IP address based on a timer; If the connection through the old access system is not torn down before the timer expires then a new prefix is assigned, or
  2. Immediately assign a new prefix.
    This decision can be based on operator's policies.
The UE indication of DSMIPv6 support may be implicit, e.g. having bootstrapped a security association via the old access network. The same applies to NBM, since the network can collect information about NBM support from other sources.
On handover to 3GPP access, the only decision that needs to be made is whether IP address preservation needs to be provided or not.
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4.1.4  Trusted/untrusted non-3GPP access network detectionWord‑p. 21
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:
  1. If the non-3GPP access supports 3GPP-based access authentication, the UE discovers the trust relationship during the 3GPP-based access authentication.
  2. The UE operates on the basis of pre-configured policy in the UE.
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4.1.5  Non-seamless WLAN offload |R10|

Non-seamless WLAN offload is an optional capability of a UE supporting WLAN radio access in addition to 3GPP radio access.
A UE supporting non-seamless WLAN offload may, while connected to WLAN access, route specific IP flows via the WLAN access without traversing the EPC. These IP flows are identified via user preferences, the Local Operating Environment Information defined in TS 23.261, and via policies that may be statically pre-configured by the operator on the UE, or dynamically set by the operator via the ANDSF. For such IP flows the UE uses the local IP address allocated by the WLAN access network and no IP address preservation is provided between WLAN and 3GPP accesses.
For performing the non-seamless WLAN offload, the UE needs to acquire a local IP address on WLAN access, and it is not required to connect to an ePDG.
Also, in the case the WLAN access is EPC connected, it is possible for a UE which also supports seamless WLAN offload to perfom seamless WLAN offload for some IP flows and non seamless WLAN offload for some other IP flows simultaneously.
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