How an eNodeB gets connected to the Core Network ? (Architecture Level Representation)


When it comes to representing the RAN side of LTE network the usual representation is shown below most commonly.



Simplistic RAN representation in LTE



We put the core network in a cloud and represent the connection of the core network with the RAN side with a straight line representing user plane and dotted line representing control plane.


The bigger question is how does an eNodeB gets connected with packet core. ? 

The simple answer is; it depends on the configuration of the operator.

Let’s discuss some common configurations of the commercial deployment how the network is deployed in the network. The exact implementation is operator dependent however, we can discuss some general implementation structures.

The general connection or implementation structure of an eNodeB with the core network is shown as below.



How an eNodeB gets connected to the Core Network ?



In the above configuration, as you can see, each site router is being fed to the Metro Ethernet. Not all operators will have metro Ethernet solution. Instead, many will have other solutions rather than metro Ethernet. No matter whatever is your solution, other solutions are equally valid. Few North American Telecommunication operators have solutions of this sort.


Generic description and connection setup:

Different flavors for connection to the core network are available. The ultimate decision lies with the operator how and when they are going to deploy the network and with what characteristics.

From the perspective of deployment even though logically we consider there are two interfaces going towards the core network

  • S1- Control plane
  • S1-User plane


However, in reality, physically there is just one interface going from Base station towards the core network. This interface is the actual transport network interface going towards the core network. This same transport interface is actually carrying the control and user plane information,  operation and maintenance related information and clock synchronization information etc.


Market and Regional Level Implementations

The above discussion of the eNodeB and connection to the core node, can be summarized as the diagram below for market to market level.



Market Level Representations of eNodeBs getting connected to the core network !

In the above deployment architecture. Each market’s sites have site routers followed by IP access provider and aggregate router.  Aggregate router ends up in IP backbone. IP backbone finally terminates into Regional IP backbone.  Markets eventually end up at Regional Market level.


Simplistic Diagram


As an RF engineering professional, you may not deal with the overall architecture every day, apart from working on the RAN side. Therefore, it is easy and to the point for symbolism that RAN is represented with an eNodeB.  In this world of information overload, where less is more. Therefore usually for simplicity RAN side is shown as figure below.



Simplicity is easy to digest and understand the big picture



What is the solution for  eNodeB getting connected to Core Network in your market ?

Share your thoughts in the comments below.


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  • vel says:

    Very nice description for people working on the network and RF side

  • David Reynell says:

    Getting the physical connection to eNodeB sites is typically the major challenge for network deployment teams. RF is the easy part is comparison to resolving the transmission solution for connecting sites to the network.

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