Saturday, November 21, 2009

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.

User and Control 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.
Sample Layer Stack
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.

 User and Control Plane used with Layers
Figure 3. User and Control Plane used with Layers

11 comments:

  1. Very good.Really helpful for beginners.

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  2. 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."

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    Replies
    1. 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.

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    2. Excellent .. Thanks for the examples Bro..

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  3. hi ....can i know that Layer2 Control Plane protocols in LTE?

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