Difference between SGW initiated and PGW initiated dedicated bearer?

Question

Can someone point out the difference between SGW initiated and PGW initiated dedicated bearer?

Answer 1

There is nothing called SGW or PGW initiated bearer, there is network and user initiated bearer. However there is a bear establishment at PGW - SGW and SGW to MME in case of network initiated bearer.

1) SGW initiated dedicated bearer on Interface S11. A Create Bearer Request message shall be sent from a SGW to a MME as a part of the Dedicated Bearer Activation procedure. This Bearer is responsible for providing the QoS on S11 interface .

2) PGW initiated dedicated bearer on Interface S5/S8. A Create Bearer Request message shall be sent from a PGW to a SGW as a part of the Dedicated Bearer Activation procedure. This Bearer is responsible for providing the QoS on S5/S8 interface.

Comments

In 29.274 3GPP spec, create bearer request direction is always from PGW to SGW and SGW to MME. In first point, it is mentioned that create bearer request message shall be send from SGW to MME as part of dedicated bearer activation procedure.

Answer 2

There are two interfaces (Gx and Gxx) interfaces from PCRF, one ends at PCEF/PGW and second one on SGW/BBERF. Here Gxx is represting Gxa and Gxc interfaces. If access network gateway is 3GPP standard node then interface is known as Gxc and if access network node is trusted non-3GPP then interface is known as Gxa. when PMIP protocol is being used between PGW and SGW then PCRF uses Gxc interface with SGW for policy and charging control. SGW has a component BBERF(bearer binding event reporting function) which interact with PCRF over the Gxc interface.

There are common messages exchange occurs over the Gx and Gxc interface. Credit-Control-Request, Credit-Control Answer, Re-authentication Request and Re-authentication Answers.Message names are same but application id is different.

Dedicated bearer creation doesn't differ since message exchange over the Gxc and Gx interface is same CCR and CCA. Please correct me if I am wrong.