Sx interface in 4G Network

Sx interface is the interface between the Control Plane (CP) function and the User Plane (UP) function in 4G Network.

CP function can control the behaviour of the UP function(s) by sending instructions and rules over the Sx interface. This includes policies, Quality of Service (QoS), and other rules that the UP function shall enforce on user's data traffic.

On the other hand, the UP function(s) can report user plane-related information to the CP function over the Sx interface. This information enable the CP function in monitoring user's data, and charging the end user.

There are two Sx interfaces,

  • Sxa interface: Exists between the SGW-C and the SGW-U.
  • Sxb interface: Exists between the PGW-C and the PGW-U.

Sx interface uses the PFCP ptotocol.