PCU scheduling and PACCH timeout question

Saurabh Sharan Saurabh.Sharan at radisys.com
Fri Feb 26 20:23:15 UTC 2016


Hello Max,
Please find below chart that indicate time skew is happening in the setup.
I have also attached the excel sheet used for this analysis here for reference.
TS4 in downlink is considered for drawing the plot. Please note that block duration value of 18 and 23 milliseconds are acceptable as transmission FNs increment by pattern of 4,4,5,4,4,5,..and so on.
4FN duration is 18.4ms and 5 FN is 23 ms approx.
But the spikes in the system as high as 26.8ms may result in incorrect air interface behavior from L1.


[cid:image002.png at 01D17101.8DA5BBD0]

Regards
Saurabh
From: Max [mailto:msuraev at sysmocom.de]
Sent: Friday, February 26, 2016 10:37 PM
To: Saurabh Sharan <Saurabh.Sharan at radisys.com>; osmocom-net-gprs at lists.osmocom.org
Subject: Re: PCU scheduling and PACCH timeout question

I'm not sure what to make of this timing difference. I'm using sysmoBTS hw to test different osmoPCU versions (including ssharan/egprs) and I can see pacch timeouts on all of those I've tried. For some phones it really breaks connectivity, others seems to be able to ignore it somehow. I do not see a pattern yet.

Do you have some test setup where you try it and see if it's the same for you?
On 02/26/2016 04:13 PM, Saurabh Sharan wrote:
Hello Max,
Though I have not analyzed the missing UL poll response, few of my observations from the pcap file attached is mentioned below
1.       There seems to be difference in FN UL versus DL being processed at any given time by the order of approx. 10 FNs, example given below
a.       Packet 7174 , FN 1137361 in DL @ 15:33:22.511809393
b.      Packet 7190,  FN 1137361 in UL @ 15:33:22.559427972
c.       From above example difference in time is 48milliseconds or approx.. 10FN duration
2.       For processing DL timeslots 2 to 6 at any given DL FN time taken seems to be approx. 3milliseconds, example given below
d.      Packet 7174 , FN 1137361 in DL @ 15:33:22.511809393 for TS 2
e.      Packet 7178, FN 1137361 in DL @ 15:33:22.514310379 for TS 6

Please let me know if these are known behavior in your integration environment ?
These time variations may have an impact on the poll response behavior from MS as well.

Regards
Saurabh

-----Original Message-----
From: Max [mailto:msuraev at sysmocom.de]
Sent: Thursday, February 25, 2016 3:58 PM
To: osmocom-net-gprs at lists.osmocom.org<mailto:osmocom-net-gprs at lists.osmocom.org>; Saurabh Sharan <Saurabh.Sharan at radisys.com><mailto:Saurabh.Sharan at radisys.com>
Subject: PCU scheduling and PACCH timeout question

Hello.

I'm trying to debug issue with current OsmoPCU master when some basebands ignore polling requests.

The debug output from RLCMAC layer and corresponding .pcap files are attached.
The issue appears somewhere after line 112 in debug.log The corresponding packet in pcu.pcapng is 6866

After receiving PACKET_CONTROL_ACK from phone we're trying to schedule polling at FN 1137123 (see packet 6869 in pcap) and than at FN 1137127 (packet 6874) which subsequently fails.
This seems suspiciously close but I have not found in the spec yet if this is legitimate thing to do.

There are several other occurrences like that in both log and pcap.

Have you experienced something like this? Do you have an idea why only some basebands are affected while others work fine?

--
Max Suraev <msuraev at sysmocom.de<mailto:msuraev at sysmocom.de>> http://www.sysmocom.de/ =======================================================================
* sysmocom - systems for mobile communications GmbH
* Alt-Moabit 93
* 10559 Berlin, Germany
* Sitz / Registered office: Berlin, HRB 134158 B
* Geschaeftsfuehrer / Managing Directors: Holger Freyther, Harald Welte





--

Max Suraev <msuraev at sysmocom.de><mailto:msuraev at sysmocom.de> http://www.sysmocom.de/

=======================================================================

* sysmocom - systems for mobile communications GmbH

* Alt-Moabit 93

* 10559 Berlin, Germany

* Sitz / Registered office: Berlin, HRB 134158 B

* Geschaeftsfuehrer / Managing Directors: Holger Freyther, Harald Welte
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