Concept |
Definition |
|---|---|
CU separation |
Control plane and user plane (CU) separation is to separate the control plane (CP) from the user plane (UP) of multiple BRAS devices. The user management functions of multiple BRAS devices are extracted and centralized to form a new control plane. Other control-plane functions and forwarding-plane functions on the BRAS devices are reserved to form a new forwarding plane for the devices. |
CUSP |
CUSP is a protocol that allows the control and forwarding planes to communicate through standardized open interfaces. CUSP separates the control plane from the forwarding plane and allows the former to manage the latter. |
Controller |
A controller is a CUSP server running on the control plane. |
Forwarder |
A forwarder is a CUSP device running on the forwarding plane. The CUSP agent is a component that is responsible for CUSP protocol management on the forwarder. |
CUSP flow table |
A CUSP flow table is a forwarding table independent of service types. A flow table contains match fields and associated actions. A forwarder matches packets against a specific field in a flow table and performs a specific action associated with the field on matching packets. For example, if a match field in a flow table is set to a source MAC address, and the specified action is to forward packets to a specific interface, the forwarder will forward packets that carry the specified MAC address to the specific interface. CUSP defines device forwarding actions in a flow table. The controller delivers flow table entries to the forwarder to control the actions of the forwarder. |
Traditional network devices have both built-in forwarding and control planes. The forwarding plane varies according to the device and is therefore hard to be opened. In terms of the control plane where forwarding entries are generated, most devices do not allow a third-party control plane to replace the built-in control plane. Hardware and software are closely coupled, reducing the upgrade frequency of network devices but extending the time for the devices to support new technologies. Nowadays, however, various network technologies continuously emerge to meet new requirements. Customers are urged to solve existing network problems with the new network technologies.
To address this issue, CUSP is introduced to provide communication channels for the control and forwarding planes. Using standardized open interfaces, CUSP separates the control plane from the forwarding plane and allows the former to manage the latter.
In a CU separation scenario, CUSP channels are used for the communications between the control and forwarding planes, so that the control plane delivers service entries to the forwarding plane and the forwarding plane reports service events to the control plane.
This feature promotes the standardization and generalization of high-performance forwarding planes through standard interfaces.