Protocols, interfaces, User Plane and Control Plane

When two devices would like to communicate with each other they would use a defined protocol. Protocol is set of rules describing how those two devices can communicate in way that receiver would understand what sender “had in mind” while sending message. Protocol description is usually description of messages (signals) that can be sent and received, it is also description for particular procedures and functions.Now, our two devices know “how to talk” to each other, but they need to be connected somehow. For this purpose an Interface would be defined. Interface would be generally another device, with or without dedicated software, that would allow connecting, inter-working and changing messages(signals) between our devices – connected using this interface.Sometimes when connecting two devices using interface there is a need for two protocols. First protocol would allow first device to control how works the second one. This kind of protocol is part of control plane. Second protocol would send just raw data from one device to another. This would be a part of user plane.

Figure 1. User and Control Plane.

Often when two devices connected over the interface not one protocol would be used but set of protocol divided into layers. Each layer with its specific dedicated tasks.

Figure 2. Sample Layer Stack.

Important to mention that each layer may has its own user and control plane. What is control plane for one protocol can be (would be) user plane for protocol located below in stack.

 Figure 3. User and Control Plane used with Layers

Hi there,Can anyone please explain this, i really don't understand.

"Important to mention that each layer may has its own user and control plane. What is control plane for one protocol can be (would be) user plane for protocol located below in stack."

An example:You are carrying a box, a gift for someone. You know whom you want to give this box, and try to deliver it for this person. In this case you are the control plane, and the box is the user plane.But this person lives a few miles away, so you have to take a bus.When you get on the bus, the busdriver does not know who you are, or what you are carrying, but he knows the destination of the bus. In this case you and your box are the user plane, and the busdriver is the control plane.

Difference Between Control Plane & Data Plane

Control Plane

Makes decisions about where traffic is sent Control plane packets are destined to or locally originated by the router itself The control plane functions include the system configuration, management, and exchange

of routing table information The route controller exchanges the topology information with other routers and

constructs a routing table based on a routing protocol, for example, RIP, OSPF or BGP Control plane packets are processed by the router to update the routing table information. It is the Signalling of the network Since the control functions are not performed on each arriving individual packet, they do

not have a strict speed constraint and are less time-critical

Data Plane

Also known as Forwarding Plane Forwards traffic to the next hop along the path to the selected destination network

according to control plane logic Data plane packets go through the router The routers/switches use what the control plane built to dispose of incoming and

outgoing frames and packets

Example 1

The protocol or application itself doesn’t really determine whether the traffic is control, management, or data plane, but more importantly how the router processes it. Consider a 3 router topology with routers R1, R2 and R3. Lets say a Telnet session is established from R1 to R3. On both of these routers the packets need to be handled by the control/management plane. However from R2′s perspective this is just data plane traffic that is transiting between its links.

Example 2

Control Plane => Learning what we will do

Our  planning stage, which includes learning which paths the buses will  take, is similar to the control plane in the network. We haven’t picked up people yet, nor have we dropped them off, but we do know the paths and stops due to our plan. The control plane is primarily about the learning of routes.

Data Plane => Actually moving the packets based on what we learned.

The data plane is the actual movement of the customers data packets over the transit path we learned in the control plane stage.