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INTERNET-DRAFT                                                     S. Hu
Intended status: Informational                                    F. Qin
                                                                   Z. Li
                                                            China Mobile
                                                                 T. Chua
                                        Singapore Telecommunications Ltd
                                                                V. Lopez
                                                              Telefonica
                                                             D. Eastlake
                                                                 Z. Wang
                                                                 J. Song
                                                                  Huawei
Expires: September 10, 2019                               March 11, 2019


      Architecture for Control Plane and User Plane Separated BNG
        draft-cuspdt-rtgwg-cu-separation-bng-architecture-04.txt


Abstract

   This document defines an architecture for Broadband Network Gateway
   (BNG) devices with control plane (CP) and user plane (UP) separation.
   A BNG-CP is a user control management component while a BNG-UP takes
   responsibility as the network edge and user policy implementation
   component. Both BNG-CP and BNG-UP are core components for fixed
   broadband services and are deployed separately at different network
   layers.


Status of This Memo

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INTERNET-DRAFT                         Architecture for CU Separated BNG


Table of Contents

      1. Introduction............................................3
      1.1 Motivation.............................................3

      2. Terminology.............................................4

      3. CU Separated BNG Architecture...........................5
      3.1 Internal Interfaces Between the CP and UP..............7

      4. Usage of the CU Separation BNG..........................8

      5. Security Considerations................................10
      6. IANA Considerations....................................10

      Normative References......................................11
      Informative References....................................11

      Authors' Addresses........................................12

































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1. Introduction

   A Broadband Network Gateway (BNG) device is defined as an Ethernet-
   centric IP edge router, and the aggregation point for user traffic.
   It performs Ethernet aggregation and packet forwarding via IP/MPLS,
   and supports user management, access protocols termination, QoS,
   policy management, etc.

   This document describes an architecture for BNG devices with control
   plane (CP) and user plane (UP) separation.  A BNG-CP is a user
   control management component while a BNG-UP takes responsibility as
   the network edge and user policy implementation components. Both BNG-
   CP and BNG- UP are core components for fixed broadband services and
   are deployed separately at different network layers in the network.



1.1 Motivation

   The rapid development of new services, such as 4K TV, IoT, etc., and
   increasing numbers of home broadband service users present some new
   challenges for BNGs such as:

   Low resource utilization: The traditional BNG acts as both a gateway
       for user access authentication and accounting and an IP network's
       Layer 3 edge. The mutually affecting nature of the tightly
       coupled control plane and forwarding plane makes it difficult to
       achieve the maximum performance of either plane.

   Complex management and maintenance: Due to the large numbers of
       traditional BNGs, configuring each device in a network is very
       tedious when deploying global service policies. As the network
       expands and new services are introduced, this deployment mode
       will cease to be feasible as it is unable to manage services
       effectively and rectify faults rapidly.

   Slow service provisioning: The coupling of control plane and
       forwarding plane, in addition to a distributed network control
       mechanism, means that any new technology has to rely heavily on
       the existing network devices.

   To address these challenges for fixed networks, the framework for a
   cloud-based BNG with CU separation conception is defined in [TR-384].
   The main idea of Control-Plane and User-Plane separation is to
   extract and centralize the user management functions of multiple BNG
   devices, forming a unified and centralized control plane (CP). And
   the traditional router's Control Plane and Forwarding Plane are both
   preserved on BNG devices in the form of a user plane (UP). Note that
   the CU separation concept has also been introduced in the 3GPP 5G
   architecture [3GPP.23.501].


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2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following acronyms are used as specified below:

   AAA: Authentication Authorization Accounting.

   BNG: Broadband Network Gateway. A broadband remote access server
       (BRAS (Broadband Access Server), B-RAS or BBRAS) that routes
       traffic to and from broadband remote access devices such as
       digital subscriber line access multiplexers (DSLAM) on an
       Internet service provider's (ISP) network. BRAS can also be
       referred to as a Broadband Network Gateway (BNG).

   CP: Control Plane. The CP is a user control management component
       which manages the UP's resources such as the user entry and
       user's QoS policy

   DHCP: Dynamic Host Configuration Protocol.

   EMS: Element Management System.

   IPoE: IP over Ethernet.

   MANO: Management and Orchestration.

   NFV: Network Function Virtualization.

   NFVI: NFV Infrastructure.

   PPPoE: Point-to-Point Protocol over Ethernet.

   UP: User Plane. UP is a network edge and user policy implementation
       component. The traditional router's Control Plane and forwarding
       plane are both preserved on BNG devices in the form of a user
       plane.











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3. CU Separated BNG Architecture

   The functions in a traditional BNG can be divided into two parts: one
   is the user access management function, the other is the router
   function. In a cloud-based BNG, we find that tearing these two
   functions apart can make a difference. The user management function
   can be centralized and deployed as a concentrated module or device,
   called the BNG-CP (Control Plane). The other functions, such as the
   router function and forwarding engine, can be deployed in the form of
   the BNG User Plane. Thus, the Cloud-based BNG architecture is made up
   of control plane and user plane.

   The following figure describes the architecture of CU separated BNG:

    +------------------------------------------------------------------+
    |        Neighboring policy and resource management systems        |
    |                                                                  |
    |   +-------------+   +-----------+   +---------+   +----------+   |
    |   |AAA    Server|   |DHCP Server|   |   EMS   |   |   MANO   |   |
    |   +-------------+   +-----------+   +---------+   +----------+   |
    +------------------------------------------------------------------+

    +------------------------------------------------------------------+
    |                       CU-separated BNG system                    |
    | +--------------------------------------------------------------+ |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |   | Address  |  |Subscriber| | AAA  ||PPPoE/||    UP     |   | |
    | |   |management|  |management| |      ||IPoE  ||management |   | |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |                              CP                              | |
    | +--------------------------------------------------------------+ |
    |                                                                  |
    |                                                                  |
    |                                                                  |
    | +---------------------------+      +--------------------------+  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  | Routing control  |     |      |  | Routing control  |    |  |
    | |  +------------------+     | ...  |  +------------------+    |  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  |Forwarding engine |     |      |  |Forwarding engine |    |  |
    | |  +------------------+  UP |      |  +------------------+  UP|  |
    | +---------------------------+      +--------------------------+  |
   +------------------------------------------------------------------+

                Figure 1. Architecture of CU Separated BNG

   As in Figure 1, the BNG Control Plane could be virtualized and
   centralized, which provides significant benefits such as centralized
   session management, flexible address allocation, high scalability for
   subscriber management capacity, and cost-efficient redundancy, etc.


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   The functional components inside the BNG Service Control Plane can be
   implemented as Virtual Network Functions (VNFs) and hosted in a
   Network Function Virtualization Infrastructure (NFVI).

   The User Plane Management module in the BNG control plane centrally
   manages the distributed BNG User Planes (e.g. load balancing), as
   well as the setup, deletion, and maintenance of channels between
   Control Planes and User Planes. Other modules in the BNG control
   plane, such as address management, AAA, etc., are responsible for the
   connection with outside subsystems in order to fulfill those
   services. Note that the User Plane SHOULD support both physical and
   virtual network functions. For example, BNG user plane L3 forwarding
   related network functions can be disaggregated and distributed across
   the physical infrastructure. And the other control plane and
   management plane functions in the CU Separation BNG can be moved into
   the NFVI for virtualization [TR-384].

   The details of CU separated BNG's function components are as
   following:

   The Control Plane should support:

   (1) Address management: unified address pool management.

   (2) AAA: This component performs Authentication, Authorization and
       Accounting, together with RADIUS/DIAMETER. The BNG communicates
       with the AAA server to check whether the subscriber who sent an
       Access-Request has network access authority. Once the subscriber
       goes online, this component together with the Service Control
       component implement accounting, data capacity limitation, and QoS
       enforcement policies.

   (3) Subscriber management: user entry management and forwarding
       policy management.

   (4) PPPoE/IPoE: process user dialup packets via PPPoE/IPoE.

   (5) UP management: management of UP interface status, and the setup,
       deletion, and maintenance of channels between CP and UP.

   The User Plane should support:

   (1) Control plane functions including routing, multicast, and MPLS.

   (2) Forwarding plane functions including traffic forwarding, QoS and
       traffic statistics collection.






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3.1 Internal Interfaces Between the CP and UP

   To support the communication between the Control Plane and User
   Plane, several interfaces are involved. Figure 2 illustrates the
   internal interfaces of CU Separated BNG.

             +-----------------------------------+
             |                                   |
             |               BNG-CP              |
             |                                   |
             +--+--------------+--------------+--+
                |              |              |
     1. Service |   2. Control | 3. Management|
      Interface |    Interface |    Interface |
                |              |              |
             +--+--------------+--------------+--+
             |                                   |
             |               BNG-UP              |
             |                                   |
             +-----------------------------------+

      Figure 2. Internal Interfaces Between the CP and UP of the BNG

   Service Interface: The CP and UP use this interface to establish
             tunnels with each other and transmit PPPoE and IPoE packets
             over those tunnels. VXLAN is commonly used for such tunnels
             as discussed in
             [hu-nvo3-vxlan-gpe-extension-for-vbng].

   Control Interface: The CP uses this interface to deliver service
             entries, and the UP uses this interface to report service
             events to the CP. The requirements of this interface are
             introduced in [cuspdt-rtgwg-cusp-requirements], and the
             carrying protocol is presented in
             [cuspdt-rtgwg-cu-separation-bng-protocol] which specifies
             the Simple Control and User Plane Separation protocol (S-
             CUSP). The information model of this interface is presented
             in
             [cuspdt-rtgwg-cu-separation-infor-model].

   Management Interface: The CP uses this interface to deliver
             configurations to the UP. This interface uses NETCONF
             [cuspdt-rtgwg-cu-separation-yang-model].









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4. Usage of the CU Separation BNG

   In the CU separated BNG scenario, there are several processes when a
   home user accesses the Internet:

   (1) User dialup packets via PPPoE or IPoE from the BNG-UP are sent to
       the BNG-CP through the BNG-UP's Service Interface.

   (2) BNG-CP processes the dialup packet. Confirming the user's
       authorization with the outside neighboring systems in the
       management network, the BNG-CP makes the decision to permit or
       deny the user access.

   (3) After that, the BNG-CP tells the UP to do perform authorized
       forwarding actions with appropriate QoS policies.

   (4) If the user is certificated and permitted, the UP forwards the
       traffic into the Internet with appropriate QoS policies such as
       limited bandwidth, etc. Otherwise, the user is denied to access
       the Internet.

   In actual deployments, a CU separated BNG device is composed of a CP
   and one or more UPs. The CP is usually centrally deployed and takes
   responsibility as a user control management component managing UP's
   resources such as the user entry and forwarding policy. The UPs are
   distributed and act as a network edge and user policy implementation
   component.

   In order to fulfill a service, neighboring policy and resource
   management systems are deployed outside the BNG. In the neighboring
   systems, different service systems such as RADIUS/DIAMETER server,
   DHCP server and EMS are included. If a BNG-CP is virtualized as a
   NFV, the NFVI management system MANO is also included here. A BNG-CP
   has connections with the outside neighboring systems to transmit
   management traffic.

   The deployment scenario is shown in the following figure:















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INTERNET-DRAFT                         Architecture for CU Separated BNG


   +------------------------------------------------------------------+
   |        Neighboring policy and resource management systems        |
   |                                                                  |
   |   +-------------+   +-----------+   +---------+   +----------+   |
   |   |   AAA Server|   |DHCP Server|   |   EMS   |   |   MANO   |   |
   |   +-------------+   +-----------+   +---------+   +----------+   |
   +------------------------+-----------------------------------------+
                            |
                            |
          +-----------------+-----------------+
          |                                   |
          |              BNG-CP               |
          |                                   |
          +-+-----------+------------+--------+
     Service|    Control|  Management|      |||
   Interface|  Interface|   Interface|          |||
     (VXLAN)|     (CUSP)|   (NETCONF)|               |||
            |           |            |                     |||
          +-+-----------+------------+-+ +---------------------------+
          |                            | |                           |
          |           BNG-UP           | |         BNG-UP...         |
          |                            | |                           |
          +-------+--------------------+ +---------------+-----------+
                  |                                      |
                  |                                      |
    +-------------+-------------+         +--------------+------------+
    |                           |         |                           |
    |       Access Network      |         |       Access Network      |
    |                           |         |                           |
    +-+-----------+-----------+-+         +-+---------+----------+----+
      |           |           |             |         |          |
      |           |           |             |         |          |
   +--+---+  +----+-+     +---+--+     +----+-+  +----+-+     +--+---+
   |User11|  |User12| ... |User1N|     |User21|  |User22| ... |User2N|
   +------+  +------+     +------+     +------+  +------+     +------+

                       Figure 3. Deployment Example















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5. Security Considerations

   The Service, Control, and Management Interfaces between the CP and UP
   might be across the general Internet or other hostile environment.
   Thus, appropriate protections MUST be implemented to provide
   integrity, authenticity, and secrecy of traffic over those
   interfaces.  For example, the implementation of IPSEC, DTLS, or TLS
   as appropriate. However, such security protocols need not always be
   used and lesser security precautions might be appropriate because, in
   some cases, the communication between the CP and UP might be in a
   more benign environment.



6. IANA Considerations

   This document requires no IANA actions.



































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INTERNET-DRAFT                         Architecture for CU Separated BNG


Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, DOI
             10.17487/RFC2119, March 1997, <https://www.rfc-
             editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
             May 2017, <https://www.rfc-editor.org/info/rfc8174>.



Informative References

   [_3GPP.23.501] "System Architecture for the 5G System", 3GPP GPP TS
             23.501 15.0.0, 2018.

   [cuspdt-rtgwg-cu-separation-bng-deployment] Gu, R., "Deployment Model
             of Control Plane and User Plane Separated BNG", draft-
             cuspdt-rtgwg-cu-separation-bng-deployment, work in
             progress, 2018.

   [cuspdt-rtgwg-cu-separation-bng-protocol] Wang, Z., "Control-Plane
             and User-Plane separation BNG control channel Protocol",
             draft-cuspdt-rtgwg-cu-separation-bng-protocol, work in
             progress, 2018.

   [cuspdt-rtgwg-cu-separation-infor-model] Wang, Z., "Information Model
             of Control-Plane and User- Plane separation BNG", draft-
             cuspdt-rtgwg-cu-separation-infor-model, work in progress,
             2018.

   [cuspdt-rtgwg-cusp-requirements] Hu, S., "Requirements for Control
             Plane and User Plane Separated BNG Protocol", draft-cuspdt-
             rtgwg-cusp-requirements, work in progress, 2018.

   [cuspdt-rtgwg-cu-separation-yang-model] Hu, F., "YANG Data Model for
             Configuration Interface of Control-Plane and User-Plane
             separation BNG", draft-cuspdt-rtgwg-cu-separation-yang-
             model, work in progress, 2018.

   [hu-nov3-vxlan-gpe-extension-for-vbng] Huang, L., "VXLAN GPE
             Extension for Packets Exchange Between Control and User
             Plane of vBNG", draft-hu-nvo3-vxlan-gpe-extension-for-vbrg,
             work in progress, 2017.

   [TR-384] Broadband Forum, "Cloud Central Office Reference
             Architectural Framework", BBF TR-384, 2018.



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Authors' Addresses

      Shujun Hu
      China Mobile
      32 Xuanwumen West Ave, Xicheng District
      Beijing, Beijing  100053
      China

      Email: hushujun@chinamobile.com


      Fengwei Qin
      China Mobile
      32 Xuanwumen West Ave, Xicheng District
      Beijing, Beijing  100053
      China

      Email: qinfengwei@chinamobile.com


      Zhenqiang Li
      China Mobile
      32 Xuanwumen West Ave, Xicheng District
      Beijing, Beijing  100053
      China

      Email: lizhenqiang@chinamobile.com


      Tee Mong Chua
      Singapore Telecommunications Limited
      31 Exeter Road, #05-04 Comcentre Podium Block
      Singapore City  239732
      Singapore

      Email: teemong@singtel.com


      Victor Lopez
      Telefonica
      Spain

      Email: victor.lopezalvarez@telefonica.com









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      Donald Eastlake, 3rd
      Huawei Technologies
      1424 Pro Shop Court
      Davenport, FL  33896
      USA

      Phone: +1-508-333-2270
      Email: d3e3e3@gmail.com


      Zitao Wang
      Huawei Technologies
      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China

      Email: wangzitao@huawei.com


      Jun Song
      Huawei Technologies
      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China

      Email: song.jun@huawei.com


























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