| rtgwg | S. Hu |
| Internet-Draft | China Mobile |
| Intended status: Informational | V. Lopez |
| Expires: January 3, 2019 | Telefonica |
| F. Qin | |
| Z. Li | |
| China Mobile | |
| T. Chua | |
| Singapore Telecommunications Limited | |
| M. Wang | |
| J. Song | |
| Huawei | |
| July 2, 2018 |
Requirements for Control Plane and User Plane Separated BNG Protocol
draft-cuspdt-rtgwg-cusp-requirements-02
This document introduces the Control Plane and User Plane separated BNG architecture and defines a set of associated terminology. What's more, this document focuses on defining a set of protocol requirements for the BNG-CP and BNG-UPs communication in the Control Plane and User Plane Separated BNG.
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This Internet-Draft will expire on January 3, 2019.
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BNG is an Ethernet-centric IP edge router, and the aggregation point for the 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, which is responsible for user access authentication and setting 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).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
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 supports to manage UP’s resources such as the user entry and user's QoS policy
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.
The following figure describes the architecture of CU separated BNG
+------------------------------------------------------------------+
| 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| |
| +---------------------------+ +--------------------------+ |
+------------------------------------------------------------------+
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 supports to manage UP's resources such as the user entry and user's 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 VNFs and hosted in a 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]. And the User Plane (UP) is a network edge and user policy implementation component. It can support the forwarding plane functions on traditional BNG devices, 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].
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 |
| |
+----------------------------------+
Internal interfaces between the CP and UP of the BNG device
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 runs 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 which specified in [draft-cuspdt-rtgwg-cu-separation-infor-model].
-----------------
//// \\\\
//// \\\\
// Cloud \\
| |
| |
| |
| |
| +-----------------+ |
| | Control Plane | |
\\ | | //
\\\\ +------+----------+ ////
\\\\ | ////
----+------------
| Control Interface (CUSP)
+--------+----------+-------------+-----+
| | | |
User's information IP address QoS: .......
May Including: | CIR; :
User ID; | PIR; |
User MAC; | CBS; |
Access method(PPPoE, | PBS; |
IPoE, etc) | ......
..... | | |
+-------------------V--------------+
|
+-----------+
| -------
| /// \\\
+------+ +-------v---------+ +--------+ | |
| OLT | | User Plane | | Core | | Internet |
| +-------+ +-------+ Routing+-----+ |
+------+ +-----------------+ +--------+ \\\ ///
-------
CU Separation BNG protocol usage
As shown in above figure, when users access to the BNG network, the control plane solicits these users' information (such as user's ID, user's MAC, user's access methods, for example via PPPoE/IPoE), associates them with available bandwidth which are reported by User planes, and based on the service's requirement to generate 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 planes receive these tables, parse them, match these rules, and then perform corresponding actions.
This section specifies some of the requirements that the CU separation protocol SHOULD support.
The Control Plane and User Plane Separation Protocol MUST allow the CP to send tables to each User Plane device.
The CU Separation protocol MUST provide a means to express the protocol message priorities.
Heartbeat is a periodic signal generated by hardware or software to indicate normal operation or to synchronize other parts of network system.
In CU separation BNG, the heartbeat is sent between CP and UPs at a regular interval in 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 monitor 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.
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, it MUST be supported to ensure the integrity of all CU Separation protocol messages and protect against man-in-the-middle attacks.
And the CP Separation protocol should support multiple security mechanisms to satisfy various scenarios. For example, when the special lines are implemented between the CP and UPs, the key chain SHOULD be supported. And if some VPNs are deployed between the CP and UPS, the TLS SHOULD be supported. In case of the CP and UPs cross several domains (i.e. cross third-party network), the IPsec SHOULD be supported.
The CU separated BNG may consist of different vendors' devices. Since different vendors’ device may implement different versions of protocol, therefore, the CU separation protocol should provide some mechanisms to perform the version negotiation.
The 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.
The UP Capability Report displays the devices profile, service capability, and other assigned capabilities within the CU separated BNG. The CU separation protocol should provide some mechanism to exchange the UP device’s capability
A backup CP for disaster recovery is required for the CU separated BNG network. And the CUSP should provide some mechanism to implement the backup CP:
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 which may initiate the event notification list as follows.
The CUSP protocol MUST provide a means for the CP to be able to query statistics (performance monitoring) from the UP.
None.
None.
| [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", Internet-Draft draft-cuspdt-rtgwg-cu-separation-bng-deployment-00, 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", Internet-Draft draft-cuspdt-rtgwg-cu-separation-infor-model-00, 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. |