Everywhere in LTE call flow and 5G call flow, I see that Sx or PFCP session establishment is triggered upon a initial-attach from UE reaching the control-plane.

My question is, PFCP or SX is node level association, right ? PFCP or SX session can be established even before the UE's anchored/attached to the PDN-GW, right ?

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1 Answer 1


Upon browsing I found out that there are two procedures happening between control-plane and user-plane in CUPS architecture.

  1. Node level association - PFCP association setup and responses.
  2. Subscriber session level PFCP - PFCP session establishment and modification which carries the subscriber's allocated IP addresses via the PDR IE and their QOS properties via QER.

So, the type#1 mentioned above procedures takes place even before any subscriber is attached to the PDN-GW. And the type#2 procedures is per subscriber session level.

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