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Distributed Mobility Management                          Kyoungjae Sun
Internet Draft                                            Younghan Kim
Intended status: Informational                     Soongsil University
Expires: April 2018                                       Jaehwoon Lee
                                                    Dongguk University
                                                      October 30, 2017

    Gap Analysis for Adapting the Distributed Mobility Management
                   Models in 4G/5G Mobile Networks

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 29, 2018.

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   In this document, we provide a gap analysis to apply DMM deployment
   models to a 3GPP mobile core network. The DMM deployment models are
   described into five models for separation control and data plane,
   and the 3GPP mobile core network is a 4G-based extended architecture
   and 5G core network study architecture. We conduct the gap analysis
   to describe the technology that requires current standards-based
   applicability and extension for technical interoperability between
   two standardization organizations.

Table of Contents

   1. Introduction ................................................ 2
   2. 3GPP 4G/5G Studies Overview ................................. 3
   3. Gap Analysis for Adapting DMM in 4G/5G Mobile Core Network .. 5
      3.1. Split Home Anchor Model ................................ 5
      3.2. Separated Control and User Plane ....................... 6
      3.3. Centralized Control Plane .............................. 6
      3.4. Data Plane Abstraction ................................. 8
      3.5. On-demand Control Plane Orchestration .................. 8
      3.6. Mapping DMM Deployment Model in to 4G/5G Core Network
           Architecture ........................................... 9
   4. Security Considerations...................................... 9
   5. IANA Considerations ......................................... 9
   6. References ................................................. 10
      6.1. Normative References....................................10
      6.2. Informative References..................................10
   7. Acknowledgments .............................................10

1. Introduction

   The Distributed Mobility Management (DMM) solution has been
   investigated to re-locate the current anchor functions in a
   distributed manner and to provide different IP session management
   characteristics for each mobile node session. For deploying DMM,
   five different models are described in [dmm-deployment-models] based
   on the network entities according to the location(access or home)
   and functionality(control or data).

   3GPP has the responsibility to standardize cellular mobile networks,
   and the functional separation of the gateway in 4G Evolved Packet
   Core(EPC) network has also been studied to divide the gateway into
   a control and data plane, defining an interface between them, and

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   configuring a data path from the control plane entities to the data
   plane entities by exchanging signaling messages between the control
   plane entities. Furthermore, future mobile core network architecture
   called 5G NextGen has been also studied. For flexible service
   continuity, 5G NextGen have integrated the current distributed
   gateway entities (SGW and PGW) that are deployed in a hierarchical
   manner into a combined gateway to separate the control and data
   plane function. In addition, to provide on-demand session
   management, they separate the attachment procedure of the mobile
   node and the session establishment procedure so that different
   sessions of the mobile node with different service characteristics
   can connect through a network slice. However, mobility management
   solution when the IP anchor function is changing is not described
   clearly yet.

   This document provides a gap analysis to adapt the DMM deployment
   model into the 4G/5G mobile network architectures studied in 3GPP.
   Based on studies of the network architecture evolution in 3GPP, we
   analyze whether each scenario of the DMM deployment model can be
   adapted to the 3GPP network architecture under study by showing the
   corresponding mapping table.

2. 3GPP 4G/5G Studies Overview

   The 4G EPC network includes several components that provide IP
   connectivity to mobile subscribers and accommodate the use of
   various network access technologies. In mobility management, many
   different kinds of handover can occur in the EPC network
   architecture. IP mobility is occurred in the Inter-MME handover,
   which occurs between different SGWs, the traffic forwarding path
   between the SGW and PGW should be changed, so the IP mobility scheme
   should be needed. For this, the 3GPP standard can use the GTP or
   PMIP protocol to update the location of the mobile node, establish
   the tunnel between the SGW and PGW, and forward data traffic.

   To improve the flexibility during deployment and operation of the
   mobile core network, 3GPP provides several options to modify the
   gateway deployment. First, the combined gateway entity is defined
   by integrating the SGW and PGW function into a single component in
   [3GPP TR 23.401]. Second, the control plane and the data plane are
   separated for the gateway functions in [3GPP TR 23.714]. The
   operation of the interface between control plane and data plane
   includes managing the state of the data plane in the control plane,
   configuring the session path between the GW-DPs according to the
   service request of the mobile node, and reporting the measurement
   information from the data plane to the control plane.

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      +-----+   +-----+   +-----+   +-----+   +----+
      | NEF |   | NRF |   | PCI |   | UDM |   | AF |
      +-----+   +-----+   +-----+   +-----+   +----+
         |         |         |         |         |
          |          |          |
       +-----+   +-----+    +-----+
       | AUF |   | AMF |    | SMF |
       +-----+   +-----+    +-----+
                  :    :            :     control-plane
                  :      :              :   user-plane
             +----+    +-----+         +-----+       +----+
             | UE |----| RAN |---------| UPF |-------| DN |
             +----+    +-----+         +-----+       +----+

                    Fig 1. 5G Core Network Architecture

   The 5G mobile core network architecture is designed in a service-
   oriented manner described in Fig.1. 5G mobile core network design
   separates control and user plane functions for allowing independent
   scaling of both functions and it allows control plane dynamically
   configures user-plane functions to provide the traffic handling
   functionality. Unlike SGW/PGW in 4G network, user plane function of
   5G is defined as a unified entity. All the control plane functions
   are separated into different standalone entities to enable
   independent scalability and flexibility. For example, unlike the 4G
   mobile core network, authentication and mobility management function
   which were combined into the MME are separated and also mobility
   management and session management function are separated. The
   interfaces between control functions are defined as a service-based
   interface which is independent on the communication protocol so that
   the interoperation in the control plane is more flexible that the 4G
   mobile core network.

   For the mobility management, since that mobility management and
   session management functions are separated, they consider supporting
   different levels of data session continuity based on the mobility on
   demand concept as similar with DMM works. It allows selection of
   anchor point to achieve efficient user plane path, as well as
   enablement of reselection of anchor point to achieve efficient user
   plane path with minimum service interruption. In the 5G mobile core
   architecture, IP anchor function is separated into control and user
   plane function. Control plane of anchor function which is allocation
   of UE IP address is performed by the Session Management Function
   (SMF) and user plane of anchor functions such as external PDU
   session point, packet forwarding, and anchor point for mobility are
   assigned to user plane function. When the IP mobility of the mobile

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   nodes traffic occurs between the different access networks or by
   changing the IP anchor in the core network, the SMF processes the
   signaling to provide session mobility for the mobile node and
   configures the forwarding policies to the data plane. There is more
   than one data plane functions in the core network, and these are
   included in the path of the mobile nodes traffic to the data network
   but it may not perform the separate roles as with the SGW/PGW in the
   existing 4G network.

3. Gap Analysis for Adapting DMM in 4G/5G Mobile Core Network

   Following five deployment models in [dmm-deployment-model], we
   provide a conformance and gap analysis to apply the IETF DMM
   deployment model to 4G/5G mobile network architectures. Detailed
   description of DMM deployment model is not provided in this

3.1. Split Home Anchor Model

   In the 4G EPC network, we can deploy the PGW as the home anchor with
   CP/DP separation and the SGW as an Access Node with a legacy entity
   without CP/DP separation. For that, terminology of Home-CPA is
   mapped to PGW-CP, Home-DPA to PGW-DP, Access-CPN to SGW-CP, and
   Access-CPN to SGW-DP. In this case, the current interface between
   SGW and PGW is separated into two interfaces for the control and
   data planes. However, since the SGW is implemented as an existing
   CP/DP combined entity, the destinations of the control and data
   packets must be set differently in the SGW. Figure 2 describes
   architecture of this model in EPC network. Between PGW-CP and
   PGW-DP, several protocols can be used to configure forwarding
   policy. Mobility management signaling such as GTP-C or PMIP will be
   exchanged using S5-C interface and data traffic will be forwarded on
   the S5-D using various forwarding method such as GTP/PMIP tunnel,
   SDN-based forwarding, etc.

                  +-------+ S5-C (GTP/PMIP) +-------+
                  |       |-----------------| PGW-C |
                  |       |                 +---^---+
                  |  SGW  |                     : FPC / OpenFlow /...
                  |       |  S5-D (tunnel)  +---v---+
                  |       |-----------------| PGW-D |
                  +-------+                 +-------+

              Figure 2. Split Home Anchor Model for 4G EPC

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   In the 5G core network study architecture, the data plane functions
   are not separated into Home and Access. Even though one or more data
   plane functions may be included in the data traffic path of the
   mobile node between the access network and the data network, it is
   not clear whether this separates the roles of Access and Home.

3.2. Separated Control and User Plane

   This model separates the control plane and the data plane from both
   the Access and Home nodes, and it can be applied as a CP/DP
   separation architecture between the SGW and the PGW when applied in
   the 4G EPC network. The parameters for the tunnel configuration,
   such as the TEID according to the bearer information generated
   through the control plane and the QoS-related information, are
   transmitted to the data plane by using the interface between the
   control plane and the data plane, and traffic measurement
   information is transmitted to the control plane for billing and
   policy management. Figure 3 describes EPC network architecture
   using this model.

                  +-------+  S5-C (GTP/PMIP) +-------+
                  | SGW-C |------------------| PGW-C |
                  +---^---+                  +---^---+
                      :   FPC / OpenFlow /...    :
                  +---v---+                  +---v---+
                  | SGW-D |------------------| PGW-D |
                  +-------+  S5-D (tunnel)   +-------+

     Figure 3. Separated Control and User Plane Model for 4G EPC

   Since there is no definition for an access node in the 5G core
   architecture, we cannot find a clear adaptable scenario to apply
   that model. By considering the network slice concept, the 5G
   architecture separates the mobile node attachment and the service
   request process for the authentication and connection state
   management according to the attachment of the mobile node through
   the Common CP function and selects an appropriate network slice when
   the mobile node requests session connectivity to the network. In
   this case, several control planes can exist in the core network, but
   this is not related to mobility management and there is no data
   plane function that is mapped with the Common CP.

3.3. Centralized Control Plane

   In [3GPP TR 23.401], the 3GPP standard allows to integrate the SGW

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   and PGW into a single entity called Combined GW. In the CP/DP
   separation architecture, each plane entity can be deployed as a
   combined or separated entity, and the architecture with a combined
   control plane and separate data plane entities can be applied. For
   the combined GW-CP function, the interface between control plane
   functions is no longer required because the SGW-CP and PGW-CP
   functions are combined as a single physical entity. Figure 4 shows
   EPC architecture using this model.

                  |        SGW-C + PGW-C        |
                      : FPC / OpenFlow /... :
                  +---v---+             +---v---+
                  | SGW-D |-------------| PGW-D |
                  +-------+     S5-D    +-------+

       Figure 4. Centralized Control Plane Model for 4G EPC

   With the 5G core architecture, there may be an architecture for a
   single control plane entity to manage multiple data plane entities,
   even without an access node definition. According to
   [3GPP TS23.501], 3GPP specifications support deployments with a
   single User Plane Function(UPF) or multiple UPFs for a given PDU
   session. In the latter case, UPF in the middle of path may be
   performed as a access data plane node. When mobility is occurred,
   session management function can assign other access UPF to forward
   packet to the anchor UPF. Figure 5 is described this model for 5G
   core network architecture.
   In particular case, [3GPP TR 23.799] defines a data plane branching
   a GW entity between the access network and the different data plane
   functions. The branching GW maintains the session between the
   respective anchor data plane nodes and uses the tunnels for traffic

                           |  SMF  |
                               : FPC / OpenFlow /...
           +---v---+       +---v---+      +---v---+
           |  UPF  |_______|  UPF  |______| Anchor|
           |       |       |       |      |  UPF  |
           +-------+       +-------+      +-------+

        Figure 5. Centralized Control Plane Model for 5G Core

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3.4. Data Plane Abstraction

   SDN-based EPC networks and forwarding configuration schemes between
   the data plane entities can be possible.  In several studies, all
   EPC control plane functions, including the SGW-CP and the PGW-CP,
   are implemented in the SDN controller as an SDN application, and the
   data traffic path in the data plane network is set utilizing
   southbound protocol such as the OpenFlow. The SDN-based EPC
   architecture has an advantage in that the traffic path between the
   data plane entities can be abstracted from the control plane while
   maintaining each GW role, so a flexible forwarding path
   configuration may be possible.

   The 5G core network architecture document also considers SDN-based
   data plane abstraction. In [3GPP TR23.799], they described about
   SDN-based approach for user plane forwarding. In that document, the
   CP function updates the forwarding table of the switches in the path
   between access network and UP function. When UE moves to another
   access network node, the CP-Function determines which switch need to
   be updated and do the forwarding table update accordingly. Even
   though there is no definition for Anchor and Access node, the data
   plane GW entities and the switches in the core network are
   abstracted through the SDN controller to manage the traffic path
   from the access network to the data network. FPC protocol defined in
   [draft-ietf-dmm-fpc-cpdp-08] may be used for configuring forwarding
   policy and mobility policy to UP functions.

3.5. On-demand Control Plane Orchestration

   This model can be deployed through an EPC network structure with an
   NFV-based virtualization environment and Management & Orchestration
   (MANO) function. In an NFV-based virtualized EPC (vEPC) environment,
   all control plane functions can be installed on a general-purpose
   cloud server using a Virtualized Network Function (VNF), and the
   data plane entities can be physically located in the switch or
   router. Regarding mobility, the Mobility Controller defined in the
   DMM deployment model is an entity that provides mapping information
   of the mobility control plane and data plane functions as needed.
   This is a method to generate mobility services by including VNFs
   according to the mobility in the network.

   The 5G architecture research also discusses methods to provide
   on-demand services in a virtualization-based environment. In
   different sets of core network functions by selecting network slices
   according to the type of traffic for a given service, even if they
   are from the same mobile node.

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   Network slicing is a one of key technology of 5G and it can provide
   customized network to optimize for different network services.
   Network slicing has the advantage of providing QoS to meet various
   service requirements. From mobility management perspective,
   different network slice can support different kinds of mobility
   management. For example, network slice for vehicle network needs to
   support mobility management functions enhanced for reducing handover
   latency by locating the anchor function closed to the access
   network. In other case, for traditional mobile core network, they
   can make network slice including one or more anchor UPF depending on
   their needs. Thus, for the various services and subscriber types,
   network operator can support on-demand mobility management using
   different network slices.

3.6. Mapping DMM Deployment Model in to 4G/5G Core Network Architecture

   Table 1 shows whether five DMM deployment models are applicable to
   the 4G EPC network and 5G core network study architecture.

   |              |   DMM Deployment Models (Described Chapter)       |
   |     3GPP     +---------------------------------------------------+
   |              |  3.1    |   3.2   |   3.3   |    3.4   |    3.5   |
   | 4G EPC Core  |         |         |         |    YES   |    YES   |
   | with CP/DP   |   YES   |   YES   |   YES   |   with   |   with   |
   | Separation   |         |         |         |    SDN   |    NFV   |
   | 5G Core      |         |         |         |    YES   |    YES   |
   | Network Study|    NO   |    NO   |   YES   |   with   |   with   |
   | Architecture |         |         |         |    SDN   |    NFV   |
   Table 1: Mapping DMM Deployment Model in to 3GPP Mobile Core Network

4. Security Considerations


5. IANA Considerations


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6. References

6.1. Normative References

   [dmm-deployment-models] S. Gundavelli, and S. Jeon, "DMM Deployment
             Models and Architectural Considerations", I.D. draft-ietf
             -dmm-deployment-models-02, Aug. 2017.

   [3GPP TR 23.401] 3GPP, "LTE: General Packet Radio Service(GPRS)
             enhancements for Evolved Universal Terrestrial Radio
             Access Network (E-UTRAN) access", 3GPP TR 23.401
             (v.14.2.0), Dec. 2016.

   [3GPP TR 23.714] 3GPP, "Study on Control and User Plane
             Separation of EPC nodes", 3GPP TR 23.714 (v.14.0.0).

   [3GPP TR 23.799] 3GPP, "Study on Architecture for Next Generation
             System", 3GPP TR 23.799 (v.1.0.2), Sep. 2016.

   [draft-ietf-dmm-fpc-cpdp-08] S. Matsushima, L. Bertz, M. Liebsch,
             S. Gundavelli, D. Moses and C. Perkins, "Protocol for
             Forwarding Policy Configuration (FPC) in DMM", I.D.
             draft-ietf-dmm-fpc-cpdp-08, Sep. 2017.

6.2. Informative References

7. Acknowledgments

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Authors' Addresses

   Kyoungjae Sun
   Soongsil University
   369, Sangdo-ro, Dongjak-gu
   Seoul 156-743, Korea

   Email: gomjae@ssu.ac.kr

   Jaehwoon Lee
   Dongguk University
   26, 3-ga Pil-dong, Chung-gu
   Seoul 100-715, KOREA

   Email: jaehwoon@dongguk.edu

   Younghan Kim
   Soongsil University
   369, Sangdo-ro, Dongjak-gu
   Seoul 156-743, Korea

   Email: younghak@dcn.ssu.ac.kr

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