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Bug #4558

Why is RRBP set on PACCH Pkt Ul Assignment?

Added by pespin 5 months ago. Updated 3 months ago.

Status:
New
Priority:
Normal
Assignee:
Target version:
-
Start date:
05/20/2020
Due date:
% Done:

0%

Spec Reference:

Description

As far as I cant tell from all TTCN3 PCU tests, osmo-pcu sets always RRBP valid (with N+13) requesting a PACKET CTRL ACK when sending a Packet Uplink Assignment through PACCH towards the MS (as can be seen for instance on TC_mt_mo_ping_pong or f_TC_mo_ping_pong_2phase_access).

So far I don't see the point for doing so, since the purpose of setting that is:
  • During DL data, request DL ACK/NACK
  • During UL ACK/NACK, request PKT CTRL ACK to ACK the ACK.

We need to find in the specs if that's needed for some reason (and also check in the code), and if there's no reason for it, then don't set RRBP during Packet Uplink Assignment.

History

#1 Updated by laforge 5 months ago

On Wed, May 20, 2020 at 04:57:48PM +0000, pespin [REDMINE] wrote:

As far as I cant tell from all TTCN3 PCU tests, osmo-pcu sets always RRBP valid (with N+13) requesting a PACKET CTRL ACK when sending a Packet Uplink Assignment through PACCH towards the MS (as can be seen for instance on TC_mt_mo_ping_pong or f_TC_mo_ping_pong_2phase_access).

it's been ages... but don't you want an ACK for the control message (the assignment itself)?

#2 Updated by pespin 5 months ago

laforge wrote:

it's been ages... but don't you want an ACK for the control message (the assignment itself)?

Well usually the PCU is already setting USF=X for that X being assigned, which means UL blocks will be received before N+13 anyway. Furthermore, I don't see RRBP being set in any of the flow diagrams in book "GPRS from A to Z".

#3 Updated by pespin 3 months ago

There's some references to RRBP in UL Packet Assignment, but when EGPRS is used, not for GPRS:

3GPP TS 44.060 sec 7.1.2.3 Contention resolution at one phase access:

The contention resolution is successfully completed on the mobile station side when the mobile station receives a PACKET UPLINK ACK/NACK message addressing the mobile station with the TFI value associated with the uplink TBF and including the same TLLI value that the mobile station has included in the RLC header of the first RLC data blocks, or alternatively, in EGPRS TBF mode, a PACKET UPLINK ASSIGNMENT message addressing the mobile station with the TFI value associated with the uplink TBF and including the same TLLI value that the mobile station included in the RLC header of the first RLC data blocks. The mobile shall then stop timer T3166 and counter N3104.
The contention resolution has failed on the mobile station side when the counter N3104 reaches its maximum value, or timer T3166 expires. The contention resolution also fails, if the mobile station receives a PACKET UPLINK ACK/NACK message or in EGPRS TBF mode alternatively a PACKET UPLINK ASSIGNMENT message addressing the mobile station with the TFI associated with the uplink TBF and including a TLLI value other than that the mobile station included in the RLC header of the first RLC data blocks; in such a case, the mobile station shall not transmit a PACKET CONTROL ACKNOWLEDGEMENT in the uplink radio block specified if a valid RRBP field is received as part of the PACKET UPLINK ACK/NACK message or in EGPRS TBF mode alternatively as part of the PACKET UPLINK ASSIGNMENT message.

I couldn't find any reference on why it may be useful when sending PACCH Pkt Ul Assignment for GPRS.

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