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rtgwg                                                              S. Hu
Internet-Draft                                              China Mobile
Intended status: Informational                                  V. Lopez
Expires: April 25, 2019                                       Telefonica
                                                                  F. Qin
                                                                   Z. Li
                                                            China Mobile
                                                                 T. Chua
                                    Singapore Telecommunications Limited
                                                        Donald. Eastlake
                                                                 M. Wang
                                                                 J. Song
                                                                  Huawei
                                                        October 22, 2018


  Requirements for Control Plane and User Plane Separated BNG Protocol
                draft-cuspdt-rtgwg-cusp-requirements-03

Abstract

   This document introduces the Control Plane and User Plane separated
   BNG (Broadband Network Gateway) architecture and defines a set of
   associated terminology.  It also specifies a set of protocol
   requirements for communication between the BNG-CP and the BNG-UPs in
   the Control Plane and User Plane Separated BNG.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 25, 2019.








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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Concept and Terminology . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  CU Separated BNG Model  . . . . . . . . . . . . . . . . . . .   3
     3.1.  Internal interfaces between the CP and UP . . . . . . . .   5
   4.  The usage of CU separation BNG protocol . . . . . . . . . . .   6
   5.  Control Plane and User Plane Separation Protocol Requirements   7
     5.1.  Transmit information tables . . . . . . . . . . . . . . .   7
     5.2.  Message Priority  . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Reliability . . . . . . . . . . . . . . . . . . . . . . .   7
     5.4.  Support for Secure Communication  . . . . . . . . . . . .   8
     5.5.  Version negotiation . . . . . . . . . . . . . . . . . . .   8
     5.6.  Capability Exchange . . . . . . . . . . . . . . . . . . .   9
     5.7.  CP primary/backup capability  . . . . . . . . . . . . . .   9
     5.8.  Event Notification  . . . . . . . . . . . . . . . . . . .   9
     5.9.  Query Statistics  . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   A Broadband Network Gateway (BNG) is an Ethernet-centric IP edge
   router and the aggregation point for user traffic.  To provide
   centralized session management, flexible address allocation, high
   scalability for subscriber management capacity, and cost-efficient
   redundancy, the CU separated BNG is introduced [TR-384].  The CU
   separated Service Control Plane could be virtualized and centralized;



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   it is responsible for user access authentication and sending
   forwarding entries to user planes.  The routing control and
   forwarding plane, i.e. BNG user plane (local), could be distributed
   across the infrastructure.

   This document introduces the Control Plane and User Plane separated
   BNG architecture and modeling.  This document also defines the
   protocol requirements for Control Plane and User Plane Separated BNG
   (CUSP).

2.  Concept and 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.

2.1.  Terminology

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

   CUSP: Control Plane and User Plane Separated BNG Protocol.

   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.

3.  CU Separated BNG Model

   Figure 1 shows the architecture of CU separated BNG












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

    +------------------------------------------------------------------+
    |                       CU-separated BNG system                    |
    | +--------------------------------------------------------------+ |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |   | Address  |  |Subscriber| |Radius||PPPoE/||    UP     |   | |
    | |   |management|  |management| |      ||IPoE  ||management |   | |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |                              CP                              | |
    | +--------------------------------------------------------------+ |
    |                                                                  |
    |                                                                  |
    |                                                                  |
    | +---------------------------+      +--------------------------+  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  | Routing control  |     |      |  | Routing control  |    |  |
    | |  +------------------+     | ...  |  +------------------+    |  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  |Forwarding engine |     |      |  |Forwarding engine |    |  |
    | |  +------------------+  UP |      |  +------------------+  UP|  |
    | +---------------------------+      +--------------------------+  |
    +------------------------------------------------------------------+
                     Figure 1. Architecture of CU Separated BNG


   Briefly, a CU separated BNG is made up of a Control Plane (CP) and a
   set of User Planes (UPs) [TR-384], [I-D.cuspdt-rtgwg-cu-separation-
   bng-deployment].  The Control Plane is a user control management
   component which manages UP's resources such as the user entry and
   user's Quality of Service (QoS) policy, for example, the access
   bandwidth and priority management.  This Control Plane could be
   virtualized and centralized.  The functional modules inside the BNG
   Service Control Plane can be implemented as Virutl 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, update, and maintenance
   of channels between control planes and user planes [TR-384], [I-
   D.cuspdt-rtgwg-cu-separation-bng-deployment].  The User Plane (UP) is
   a network edge and user policy implementation component.  It can
   support the forwarding plane functions on traditional BNG devices,



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   such as traffic forwarding, QoS, and traffic statistics collection,
   and it can also support the control plane functions on traditional
   BNG devices, such as routing, multicast, etc [TR-384], [I-D.cuspdt-
   rtgwg-cu-separation-bng-deployment].

3.1.  Internal interfaces between the CP and UP

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

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

          Figure 2. Interfaces between the BNG-CP and the BNG-UP

   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.

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

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

   The CUSP (Control plane and User plane Separated BNG protocol)
   defines the control interface, and specifies the communication
   between the centralized control plane and user planes.  This protocol
   should be designed to support establishing and maintaining a
   conversation between CP and UPs, and transporting the tables that are
   specified in [draft-cuspdt-rtgwg-cu-separation-infor-model].






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4.  The usage of CU separation BNG protocol


                     -----------------
                 ////                 \\\\
             ////                         \\\\
           //          Cloud                  \\
          |                                     |
         |                                       |
        |                                         |
        |                                         |
         |        +-----------------+            |
          |       |  Control Plane  |           |
           \\     |                 |         //
             \\\\ +------+----------+     ////
                 \\\\    |            ////
                     ----+------------
                         | Control Interface (CUSP)
                +--------+----------+-------------+-----+
                |                   |             |     |
          User's information     IP  address     QoS:  .......
          May Include:            |            CIR;         :
          User ID;                  |            PIR;   |
          User MAC;                 |            CBS;   |
          Access method(PPPoE,      |            PBS;   |
          IPoE, etc)                |            ......
          ..... |                   |              |
                +-------------------V--------------+
                                    |
                        +-----------+
                        |                                    -------
                        |                                 ///       \\\
 +------+       +-------v---------+       +--------+     |             |
 | OLT  |       | User Plane      |       | Core   |    |    Internet   |
 |      +-------+                 +-------+ Routing+-----+             |
 +------+       +-----------------+       +--------+      \\\       ///
                                                             -------
                 Figure 3. CU Separation BNG protocol usage


   As shown in Figure 3, when users access the BNG network, the control
   plane solicits user information (such as user's ID, user's MAC,
   user's access methods, for example via PPPoE/IPoE), associates users
   with available bandwidth which is reported by User planes, and, based
   on the service's requirement, generates a set of tables, which may
   include user's information, UP's IP segment, and QoS, etc.  Then the
   control plane can transmit these tables to the User planes.  User




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   planes receive these tables, parse them, and then perform
   corresponding actions.

5.  Control Plane and User Plane Separation Protocol Requirements

   This section specifies the requirements for the CU separation
   protocol.

5.1.  Transmit information tables

   The Control Plane and User Plane Separation Protocol MUST allow the
   CP to send tables to each User Plane device.

      a) The current BNG service requires that the UP should support at
      least 2000 users being accessed every second.  And every user
      requires at least 2000 bytes.  To achieve high performance, the CU
      Separation protocol SHOULD be lightweight.

      b) CU separation protocol should support data encoded as either
      XML or binary.  It allows user information data to be read, saved,
      and manipulated with tools specific to XML or binary.

      c) In order to provide centralized session management, high
      scalability for subscriber management capacity, and cost-efficient
      redundancy, batching ability should be provided.  The CU
      Separation protocol should be able to group an ordered set of
      commands to a UP device.  Each such group of commands SHOULD be
      sent to the UP in as few messages as practical.  Furthermore, the
      protocol MUST support the ability to specify if a command group
      MUST have all-or-nothing semantics.

      d) The CU Separation protocol SHOULD be able to support at least
      hundreds of UP devices and tens of thousands of ports.  For
      example, the protocol field sizes corresponding to UP or port
      numbers SHALL be large enough to support the minimum required
      numbers.  This requirement does not relate to the performance of
      the system as the number of UPs or ports in the system grows.

5.2.  Message Priority

   The CU Separation protocol MUST provide a means to express the
   protocol message priorities.

5.3.  Reliability

   Heartbeat is a periodic signal generated by hardware or software to
   test for some aspects of normal operation or to synchronize other
   parts of network system.



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   In the CU separation BNG, a heartbeat is sent between CP and UPs at a
   regular interval on the order of seconds.  If the CP/UP does not
   receive a heartbeat for a time--usually a few heartbeat intervals--
   the CP/UP that should have sent the heartbeat is assumed to have
   failed.

   The CU separation protocol should support some kind of heartbeat
   monitoring mechanism.  And this mechanism should have ability to
   distinguish whether the interruption is an actual failure.  For
   example, in some scenarios (i.e.  CP/UP update, etc), the connection
   between the UP and CP need to be interrupted.  In this case, the
   interruption should not be reported.

5.4.  Support for Secure Communication

   As mentioned above, CP may send some information tables to the UP
   which may be critical to the network function (e.g, User Information,
   IPv4/IPv6 information) and may reflect the business information (e.g,
   QoS, service level agreements, etc).  Therefore, supporting the
   integrity of all CU Separation protocol messages and protecting
   against man-in-the-middle attacks MUST be supported.

   The CP Separation protocol should support security in a variety of
   scenarios.  For example, the connections between the CP and UPs could
   be dedicated lines, VPNs within one domain, or could cross several
   domains, that is, cross third party networks.  Thus it is likely that
   more than one security mechanism SHOULD be supported.  TLS and IPsec
   are good candidates for such mechanisms.

5.5.  Version negotiation

   The CU separated BNG may consist of different vendors' devices
   implementing different versions of protocol.  Threfore, the CU
   separation protocol MUST provide some mechanisms to perform the
   version negotiation.

   Version negotiation is the process that the CU separated BNG's
   Control-Plane uses to evaluate the protocol versions supported by
   both the control-plane and the user-plane devices.  Then a suitable
   protocol version is selected for communication in CUSP.  The process
   is a "negotiation" because it requires identifying the most recent
   protocol version that is supported by both the control-plane and the
   user-plane devices or determining that they have no version in
   common.







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5.6.  Capability Exchange

   The UP Capability Report displays the device's profile, service
   capability, and other assigned capabilities within the CU separated
   BNG.  The CU separation protocol should MUST provide some mechanism
   to exchange the UP device's capabilities.

5.7.  CP primary/backup capability

   A backup CP for failure recovery is required for the CU separated BNG
   network.  And the CUSP should provide some mechanism to implement the
   backup CP:

      a) In some scenarios, there may be two CP devices both declaring
      the primary CP.  Thus the CUSP should support or associate with
      some mechanisms to determine which CP is the primary device.

      b) In the scenario of the primary CP down, the CUSP should support
      switching between primary and backup CP.

5.8.  Event Notification

   The CUSP protocol SHOULD be able to asynchronously notify the CP of
   events on the UP such as failures and changes in available resources
   and capabilities.  Some scenarios that may initiate event
   notifications are listed below.

      a) Sending response message: As mentioned above, the control plane
      solicits users' information, associates them with available
      bandwidth, and generates a set of tables based on the service's
      requirement.  Then the control plane transmits these tables to the
      conresponding User plane.  The UP should respond with an event
      notification to inform the CP that the tables are received.

      b) User trace: The user trace mechanism can support the Control
      Plane tracing and monitoring the network status for users (for
      example the real-time bandwidth, etc), to help debug the user's
      application.  Therefore, the UPs SHOULD be able to notify the CP
      with the User trace message.

      c) Sending statistics parameters: In CU separation BNG, the User-
      plane will report the traffic statistics parameters to the
      Control-plane, such as the ingress packets, ingress bytes, egress
      packets, egress bytes, etc.  These parameters can help measure the
      BNG network performance.  Available network resources can be
      allocated basing on the statistics parameters by the BNG-CP.
      Therefore, the UPs SHOULD be able to notify the CP with statistics
      parameters.



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      d) Report the result of User Detect: "User Detect" message will be
      send periodically to detect user dial-up and disconnect.  The UPs
      SHOULD be able to notify the CP with the result of User Detect.

5.9.  Query Statistics

   The CUSP protocol MUST provide a means for the CP to be able to query
   statistics (performance monitoring) from the UP.

6.  Security Considerations

   As this is an Informational requirements document, detailed technical
   Security Considerations are not included.  However, Section 5.4
   covers general security requirements and Section 5.7 covers backup
   requirements relevant to some denial of service scenarios.

7.  IANA Considerations

   This document requires no IANA actions.

8.  References

8.1.  Normative References

   [I-D.cuspdt-rtgwg-cu-separation-bng-deployment]
              Gu, R., Hu, S., and Z. Wang, "Deployment Model of Control
              Plane and User Plane Separation BNG", draft-cuspdt-rtgwg-
              cu-separation-bng-deployment-00 (work in progress),
              October 2017.

   [I-D.cuspdt-rtgwg-cu-separation-infor-model]
              Wang, Z., Gu, R., Lopezalvarez, V., and S. Hu,
              "Information Model of Control-Plane and User-Plane
              separation BNG", draft-cuspdt-rtgwg-cu-separation-infor-
              model-00 (work in progress), February 2018.

   [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>.







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8.2.  Informative References

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

Authors' Addresses

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

   Email: shujun_hu@outlook.com


   Victor Lopez
   Telefonica
   Sur 3 building, 3rd floor, Ronda de la Comunicacion s/n
   Madrid  28050
   Spain

   Email: victor.lopezalvarez@telefonica.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










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

   Email: teemong@singtel.com


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

   Email: d3e3e3@gmail.com


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

   Email: wangzitao@huawei.com


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

   Email: song.jun@huawei.com

















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