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INTERNET-DRAFT                                                     R. Gu
Intended status: Informational                                     S. Hu
                                                            China Mobile
                                                                 M. Wang
                                                             D. Eastlake
                                                                   F. Hu
Expires: June 11, 2019                                 December 12, 2018

      Control Plane and User Plane Separated BNG Deployment Model


   This document describes the deployment model for a Broadband Network
   Gateway (BNG) device with Control Plane (CP) and User Plane(UP)
   separation. It is intended to give guidance for the deployment of CP
   and UP separated BNG devices in an operators' network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Distribution of this document is unlimited. Comments should be sent
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Table of Contents

      1. Introduction and Overview...............................3

      2. Concept and Terminology.................................5
      2.1 Terminology............................................5

      3. BNG with CP and UP Separation Deployment Model..........6
      3.1 CP and UP of BNG Deployment Within One District........6
      3.2. CP and UP of BNG Deployment in Multiple Districts.....7

      4. The Process of BNG with CUPS in Home Service...........10

      5. High Availability Considerations.......................11

      6. Security Considerations................................12
      7. IANA Considerations....................................12

      Normative References......................................13
      Informative References....................................13

      Authors' Addresses........................................14

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1. Introduction and Overview

   A Broadband Network Gateway (BNG) is an Ethernet-centric IP edge
   router and acts as the aggregation point for the user traffic with
   some additional functions such as address management and cooperating
   with AAA (Radius/Diameter) systems and subscriber management. Because
   of the rapid development of new services, such as 4K, IoT, etc. and
   the increasing numbers of distributed home broadband service users,
   high resource utilization, high-efficiency management, and fast
   service provisioning are required. This calls for a new BNG
   architecture with CP and UP separation, which is also called Cloud
   BNG, as proposed in [BBF-CloudCO] [TR-384].

   The CP and UP separation architecture of the BNG is composed of a
   Control Plane and a User Plane, with the concentrated CP responsible
   for control and management of the UP's resources and subscribers'
   information, and with the distributed UP taking charge of policy
   implementation and traffic forwarding. The obvious advantages of this
   new architecture are listed below.

   Resource Utilization Improvement: A centralized Control Plane
             provides unified management capability for network
             resources and users information. The CP has an overview of
             all the resources and can distribute resources as specific
             users require, thus resources can be totally controlled and

   Management with High Efficiency: A centralized CP provides a unified
             management interface to the outside systems such as EMS,
             DHCP Server, AAA Server, etc. In this situation, management
             can be easier for the centralized CP as it's the only
             device interfacing with the outside systems.

   Dynamic and Flexible: The CP can be virtualized as a VNF with MANO
             management in an NFVI, while the UP can be a virtual
             machine or physical device as needed. A software-oriented
             CP can be designed with flexibility. The CP can handle all
             the situations dynamically over a wide range from few users
             accessing to large numbers of users accessing.

   Fast TTM: The CP and UP can be deployed separately with the CP
             deployed centrally and the UP deployed in distribution
             closer to users. Thus, according to different situations
             such as session overload or extremely high throughput, the
             CP and UP can be extended separately. This can help shorten
             the time to market (TTM).

   As noted, the new BNG architecture has CP and UP separation. The CP
   and UP are deployed with separation due to practical requirements.
   This document gives the CU separation BNG deployment model for actual

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2. Concept and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

2.1 Terminology

   BNG: Broadband Network Gateway. A broadband remote access server
       (BRAS, B-RAS or BBRAS) 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 UP's resources such as the user entry and user's
       QoS policy

   CUPS: Control/User Plane Separation

   UP: User Plane. The 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.

   TTM: Time to Market. It is the length of time it takes from a product
       or a service being conceived until it is available for sale.

   MANO: Management and Orchestration. Functions are collectively
       provided by NFVO, VNFM and VIM.

   VNF: Virtual Network Function. Implementation of a Network Function
       that can be deployed on a Network Function Virtualization
       Infrastructure (NFVI).

   PNF: Physical Network Function

   DHCP: Dynamic Host Configuration Protocol

   PPPoE: Point-to-Point Protocol over Ethernet

   IPoE: Internet Protocol over Ethernet

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3. BNG with CP and UP Separation Deployment Model

3.1 CP and UP of BNG Deployment Within One District

      |                   |
      |       Internet    |
      |                   |
            |       |              +------------------------+
            |   CR  |              |                        |
            |       |              |            +--------+  |
            +---^---+              |     +------+  AAA   |  |
                |                  |     |      +--------+  |
                |                  |  +--+---+              |
            +---+---+              |  |      |  +--------+  |
            |       +---SERVICE----+  |      +--+  DHCP  |  |
            | BNG-UP+---CONTROL----+  | BNG  |  +--------+  |
            |VNF/PNF+----MGNT------+  | -CP  |              |
            +---^---+              |  |  VNF |  +--------+  |
                |                  |  |      +--+   EMS  |  |
                |                  |  |      |  +--------+  |
            +---+---+              |  +--+---+              |
            |       |              |     |      +--------+  |
            |  OLT  |              |     +------+  MANO  |  |
            |       |              |            +--------+  |
            +---^---+              |   Management Network   |
                |                  +------------------------+
            |  USER |

               Figure 1: Cloud BNG Deployed in One District

   Take a one district example as in Figure 1. Here BNG-CP and BNG-UP
   are separated as deployed. Since the CP is computationally intensive,
   a virtualized CP acting as a VNF can meet the requirements of
   flexibility and fast calculation. The UP is traffic intensive, which
   can be virtualized or stay physical depending on traffic. The
   virtualized UP with low expense and high flexibility can be suitable
   for light traffic. In high traffic, special hardware is needed with
   high traffic forwarding performance.

   In order to fulfill the function of a BNG, the BNG-CP needs to
   communicate with outside systems such as a AAA (Radius/Diameter)
   server and many others in the management network. In addition, the

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   BNG-CP has three interfaces with the BNG-UP separated by their
   traffic categories: Service Interface, Control Interface, and
   Management Interface.

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

          Figure 2. Internal Interfaces Between the BNG CP and UP

   The functions of the three interfaces are as follows:

      Service Interface: The CP and UP use this interface to establish
             VXLAN tunnels with each other and transmit PPPoE and IPoE
             packets over the VXLAN tunnels for authentication.

      Control Interface: The CP uses this interface to deliver service
             entries to the UP, and the UP uses this interface to report
             service events to the CP.

      Management Interface: The CP uses this interface to deliver basic
             configurations to the UP. This interface uses NETCONF.

   Several related drafts exist describing these interfaces in detail.
   The VXLAN-GPE extension draft for C/U separated BNG is related to the
   Service Interface [huang-nov3-vxlan-gpe-extension-for-vbng]. The
   draft YANG data model for CU separated BNG focuses on Management
   Interface, seeing in [cuspdt-rtgwg-cu-separation-yang-model]. Another
   two drafts [cuspdt-rtgwg-cusp-requirements] and [cuspdt-rtgwg-cu-
   separation-infor-model] are related to the control interface giving
   an information model abstraction and suitable protocol.

3.2. CP and UP of BNG Deployment in Multiple Districts

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            |                   |
            |       Internet    |
            |                   |
                      |               +------+ +----+ +---+ +----+
                  +---+---+           |Radius| |DHCP| |EMS| |MANO|
                  |       |           +---+--+ +--+-+ +-+-+ +-+--+
                  |       |               |       |     |     |
              +---+   CR  +-----+     +---+-------+-----+-----+--+
              |   |       |     |     |         BNG-CP           |
              |   |       |     |     +---.--.------------.------+
              |   +---^---+     +---------.--.--+         .
              |   ....|....................  .  |         .
              |   .   |           ............  |         .
              |   .   +-------+   .             | .........
            +-+---.-+       +-+---.-+       +---+-.-+
            |       |       |       |       |       |
            | BNG-UP|       | BNG-UP|       | BNG-UP|
            |VNF/PNF|       |VNF/PNF|       |VNF/PNF|
            +---^---+       +---^---+       +---^---+
                |               |               |
                |               |               |
            +---+---+       +---+---+       +---+---+
            |  OLT  |       |  OLT  |       |  OLT  |
            +---+---+       +---+---+       +---+---+
          +-----|-----+         |         +-----|-----+
      +---+---+   +---+---+ +---+---+ +---+---+   +---+---+
      |USER A1|   |USER A2| |USER B1| |USER C1|   |USER C2|
      +-------+   +-------+ +-------+ +-------+   +-------+

             Figure 3: Cloud BNG Deployed in Several Districts

   If subscribers are distributed in several districts, the CP can be
   deployed centrally with the UP deployed in different districts close
   to subscribers as shown in Figure 3. Thus the deployment model can be
   a bit complex.

   Take three districts A, B. and C for example. Here three UPs are
   placed with one shared CP. The CP is usually deployed in a Core Data
   Center such as in a provincial datacenter with UPs in edge Date
   Centers such as city datacenters. In this Data Centers design, we
   have core data centers and edge data centers according to their
   location and responsibility. Core data centers are often planned in
   provinces for control and management, while edge data centers are in
   cities or towns for easy service access.

   In this scenario, a centralized CP interfaces to the subsystems
   outside and communicate with all these UPs for control and

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   Under the CP's control, the corresponding traffic is forwarded by UP
   to the Internet.

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4. The Process of BNG with CUPS in Home Service

   Take a user Bob accessing to the Internet using Home Broadband
   Service as an example. The process includes the service traffic from
   user to the internet and signaling traffic between BNG-UP and BNG-CP.
   Below is the whole process.

   (1) User Bob dials up with packets of PPPoE or IPoE from BNG-UP which
       will be sent to the BNG-CP with the user's information. This is
       signaling traffic.

   (2) The BNG-CP processes the dialup packets. Confirming with the
       outside neighboring systems in the management network, the BNG-CP
       makes the decision to permit or deny of the dial access through
       certification. In this step, the BNG-CP manages resources and
       generates tables with information such as User Info, IP Info, QoS
       Info, etc. This is signaling traffic.

   (3) The BNG-CP sends tables to the corresponding UP or to one UP it
       chooses from the corresponding UPs. This is signaling traffic.

   (4) The BNG-UP receives the tables, matches rules and performs
       corresponding actions.

   (5) If Bob is certificated and permitted, the UP forwards their
       traffic into the Internet with related policies such as limited
       bandwidth, etc. Otherwise, Bob is denied to access the Internet.
       This is service traffic.

   From Step 2 to Step 4, the information model defined in
   [cuspdt-rtgwg-cu-separation-infor-model] can be used.

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5. High Availability Considerations

   As the BNG-CP takes responsibility for control and management, such
   as communicating with outside systems, generating flow tables, and
   managing the UP's resources, high availability of this key component
   should be considered. Some redundancy should be adopted for
   reliability, such as N+N or N+K active standby BNG-CPs. N+N standby
   means 1:1 backup for each BNG-CP, which enables easy rapid switch of
   any number of BNG-CP to their backup but is expensive because it
   requires a large number of backup CPs. N+K means a smaller number of
   backup CPs, for example N2:1 backup where N2<N which is less
   expensive but does not handle more than 1 failure in the N2 subset of
   N BNG-CPs.

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6. Security Considerations


7. IANA Considerations

   This document requires no IANA actions.

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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-

   [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> .in -10

Informative References

   [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.

   [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.

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

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

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Authors' Addresses

      Rong Gu
      China Mobile
      32 Xuanwumen West Ave, Xicheng District
      Beijing, Beijing  100053

      Email: gurong_cmcc@outlook.com

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

      Email: shujun_hu@outlook.com

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

      Email: wangzitao@huawei.com

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

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

      Fangwei Hu
      ZTE Corporation
      No.889 Bibo Rd
      Shanghai  201203

      Phone: +86 21 68896273
      Email: hu.fangwei@zte.com.cn

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   Copyright (c) 2018 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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