Summary of osmo-pcu failures/defects

Holger Hans Peter Freyther hfreyther at
Tue Nov 26 08:22:56 UTC 2013

On Mon, Nov 25, 2013 at 08:24:27AM +0100, Andreas Eversberg wrote:

> generally there is always a re-send due to delay between pcu and the
> radio interface. if all rlc/mac data blocks of an llc frame have been
> sent to the phone, a packet downlink ack control block is requested and
> scheduled. the pcu repeats all unacknowledged data blocks in a loop
> until it receives that requested control block. this way the pcu starts
> re-sending data blocks that might got lost, before it actually knows if
> and which blocks still need to be resend. (this procedure is described
> in TS 04.60.)

Are you referring to "Acknowledge state array V(B) for GPRS
TBF Mode"?

 If there are no further RLC data blocks available for transmission
 (i.e. the RLC data block with BSN= V(S) does not exist), the sending
 side shall transmit the oldest RLC data block whose corresponding
 element in V(B) has the value PENDING_ACK, then the next oldest block
 whose corresponding element in V(B) has the value PENDING_ACK, etc. 

With statistics in place it appears that for CS4 close to 50% of the
sent RLC blocks are re-sends. Is that what you expected when implementing


- Holger Freyther <hfreyther at>
* sysmocom - systems for mobile communications GmbH
* Schivelbeiner Str. 5
* 10439 Berlin, Germany
* Sitz / Registered office: Berlin, HRB 134158 B
* Geschaeftsfuehrer / Managing Directors: Holger Freyther, Harald Welte

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