PDU Session & QoS flow quick answers

Hi NR experts.

  1. As 1 pdu session having multiple QoS flow, is there any number limitations for QoS flow per pdu session?

  2. How many pdu sessions per UE can be established?

  3. How many drb per UE can be established?

Not 100 % sure. I saw it long time ago.


1 pdu per slice (to be confirmed)

Up to 16 or 32 (to be confirmed)


Also: Below message come in what conditions?

  1. pdu session authentication command
  2. pdu session modification request
  3. pdu session release request

Anyone observed it while testing SA?

Comes from SMF when UE try to establish a PDU session.

Comes from UE to modify an existing pdu session ex. to add a flow.

Comes from UE to release an existing pdu session.

Do you know any live flow for such messages?

I’m not able to seen pdu session authentication command in call flow…

Unfortunately not.

Pdu session auth is not mandatory, and is triggered if connection to a DNN needs authentication.

A crude example will be - a corporate sim that has special DNN for connecting to corporate network and that dnn may require additional authentication.

Ok thanks!

So it kind of private 5G network example as well where such messages can be seen as special case?


For dnn auth you can say that, but other 2 are common.

Yes agree :+1:

Pdu modification like eps bearer modification seen
In case of LTE.

Pdu session release is new message for 5G case. Have you seen it earlier?

PDU session release is equivalent to EPS bearer release.

You may have not seen it in LTE because normally default APN and IMS are the 2 EPS bearers setup that are alive for as long UE is active.

Is it seen over the air for 5G case.

In what case this pdu session release seen?

For LTE case EPS bearer release if I’m correct it’s seen in case of UE lost scenario but not over the air it’s seen.

Over the air we have RRC connection release or RRC release in case of NR.

These are NAS procedures carried over the air.

If there is a connection to a DNN, and if UE request release of that DNN. Goes in NAS.

No, to see it UE will need connection to 2 default bearers and release any one.

In what conditions UE request for release of DNN in case of NR?

For LTE like we have 2 APN for IMS case but not seen such release.

Because in LTE both IMS and default APN are active for lifetime of connection.

If you can add another APN , then you can trigger this procedure.

In NR , there is no requirement to have a default pdn connection.

As a test , you can try deleting the DNN in UE to see if the procedure is triggered.

There are many conditions - using specific applications, mobility to a different registration area.

Thanks a lot!

I will check further.

Good discussion with you! :handshake: