LTE user plane

Questions. More questions!

This time focus in on LTE user plane and SGW load balancing. Picture this. eNB, MME and SGW. Control plane between MME and SGW, User plane between eNB and SGW controlled by MME. Perfect.

SGW : How many interfaces does an SGW have. When I read about ALU bringing in LTE device (ALU 7750) I went and checked out their website. Read here. A SGW is going to be a blade which will sit in a 7750 router. So is the case with Cisco. When I say a blade, how many interfaces will that blade have? Next how many blades can sit in a device? And how will the blades be controlled? Each blade will have its own software to control?

More elaboration: MME sends out a create session request to SGW. It picks up the SGW from SGW selection function. So a create session request will be sent to a particular SGW. Particular SGW mean a "Particular IP". Now SGW may respond to request with a Create Session Response. Note that Create Session response has FTEID of SGW, where in SGW can send information about another blade of SGW that is another interface, if it exists. That way SGW can balance the load? Say if 7750 has 10 SGW blades, then how will this load balancing be done. One main interface and having several other interfaces? How are all these blades controlled? Because there has to be a TEID mapping.

User Plane: When we say user plane is segregated from control plane, what do we mean here. Is user plane traffic going to hit the same interface of SGW where control plane is established. If yes, how good is this implementation? Again same question, if there exists multiple blades how are they controlled?

Below find SGW with little boxes which are nothing but blades. Will the blades be controlled by master software running on SGW or will there be a software for each blade. Say if two blades have to communicate how will they do it?

How it started: I am working a product which is supposed to test SGW. As there is no SGW available to test dev guys gave us a dummy implementation of SGW. Here both user plane and control plane traffic hit the same interface. I decided to write my own SGW. The problem is my SGW runs on a linux box and I wrote only control plane communication. After control data is supposed to flow. I noticed that data was hitting the same interface where control plane was established. Thats where my quest for separating the data and user plane began.

Folks any clue on how it is done? I really want to know how is the SGW made. Your reply's are appreciated and greatly welcomed.

LTE Protocol Stack

LTE Control Plane
The control plane consists of protocols for control and support of the user plane functions:-

• controlling the E-UTRA network access connections, such as attaching to and detaching from E-UTRAN;
• controlling the attributes of an established network access connection, such as activation of an IP address;
• controlling the routeing path of an established network connection in order to support user mobility;
• controlling the assignment of network resources to meet changing user demands.

The Communication between MME and S-GW, MME and MME is taken care by GTP-C v2. This is again used to communicate with other nodes in UMTS and GERAN networks too. Eloboration soon!

LTE User Plane