osmocom-net-gprs December 2013

osmocom-net-gprs@lists.osmocom.org

4 participants
4 discussions

Multislot allocation failures and defects
by Holger Hans Peter Freyther 16 Jan '14

16 Jan '14

Dear Andreas, I went through the multislot allocation algorithm and cleaned and structured the code in testable parts that take over parts of the allocation and I have added a unit test for some of the allocation cases (UL first, then DL.. e.g. due a RACH burst and then DL single, UL and DL update). Today morning I added a testcase that tests all PDCH combinations and all MS Classes and verifies that an allocation takes place and that the DL and UL first_common_ts do match. For (xxOxOOxO) and MS_Class=5 this assert is wrong. The alloc/AllocTest of the sysmocom/allocation-cleanups branch should show you this condition. While reading the code I noticed the following things. Could you please explain why these are problems or no problems. * select_first_ts (it exists after the refactoring). It initializes i and compares it but it will never increment it. This means that the code can look at PDCHs _outside_ of the tx_range. * first_common_ts handling. When assigning the DL tbf we pick a first_common_ts but when the actual UL assignment happens there might not be a free USF on the Uplink and at that point the phone might not listen on the TS we think. * Sum for Rx+Tx is not used. I see that in update_rx_win_max you modify the window to make some room. * select_ul_slots. "i" is not incremented in all cases which could potentially lead to using slots outside of the tx_range. For the MS Type == 1 handling you could introduce a different variable that counts how many slots were used? it would be nice if we could fix that during the 30C3. holger -- - Holger Freyther <hfreyther(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * 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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Coverity issues in gsm_rlcmac.cpp
by Holger Hans Peter Freyther 16 Jan '14

16 Jan '14

Dear Ivan, could you please have a look at the coverity issues in the gsm_rlcmac.cpp routines? Uninitialized scalar variable: gsm_rlcmac.cpp:5321 ar.direction not initialized gsm_rlcmac.cpp:5039 ar.direction not initialized gsm_rlcmac.cpp:5155 ar.direction not initialized gsm_rlcmac.cpp:4872 ar.direction not initialized Just initialize it in csnStreamInit? Out-of-bounds read: gsm_rlcmac.cpp:5502 " Overrunning array "data->RLC_DATA" of 20 bytes at byte offset 22 using index "i" (which evaluates to 22)." gsm_rlcmac.cpp:5440 " Overrunning array "data->RLC_DATA" of 20 bytes at byte offset 22 using index "i" (which evaluates to 22)." Maybe just add an assert that dataNumOctets <= 20? -- - Holger Freyther <hfreyther(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * 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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Status of sysmocom/master W50
by Holger Hans Peter Freyther 26 Dec '13

26 Dec '13

Good Afternoon, last week at the sysmocom office Daniel and me continued to work on the window handling. We have now a proper abstraction that allows us to unit test the DL and UL window handling. The encode/decode of the RBB is now compatible to itself. While doing our manual tests (sending a big enough ICMP echo request) we noticed that in the alloc algorithm b case the we get a lot of NACKs. In the same setup (only alloc algorithm is changed) the A algorithm has no NACKs. I am now going to re-write the allocation handling. In terms of operation on the first DL assignment (through the PCH) we can only use a singleslot but when re-using the TBF we might go for multislot. In case the of UL handling we could always try to use multislot assignments. Is this understanding correct? holger -- - Holger Freyther <hfreyther(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * 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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Current list of failures in the pcu
by Holger Hans Peter Freyther 07 Dec '13

07 Dec '13

Good Morning, we at sysmocom continued to add structure/architecture to the PCU code and started to systematically test the code (using something as simple as ICMP ping/reply) Observations: * "alloc algorithm b" has little (3kbit/s) more bandwidth than just using the single slot assignment with CS4. There are also some open coverity issues about this multi slot code. * Congestion is badly handled. When using a ping that creates IP fragments the LLC queue of the TBF gets so long that we expire half the IP fragments before sending them. This means the MS at the downlink never receives all the IP fragments of a PING. We played with the BSVC-FLOW-CONTROL parameters but they don't have any influence here. We have added counting of queue size and calculation of the average queue delay to the LLC class. One option is to drop packages based on the PDU lifetime and the current queue delay. $ sudo ping -s 1800 -i 0.1 10.23.42.6 (CS4, alloc-algorithm a) is enough to re-produce this issue. * RLC V(Q) V(R) handling. It appears that after and before the refactoring the Received Block Bitmap (RBB) is wrongly encoded. The encode and decode are not compatible to each other (thanks to the architecture sysmocom is adding to the code this can now be unit tested!). So as soon as we don't receive a frame from the UL. The send window at the phone and the PCU is going out of sync. After making changes to the window we have also witnesses that on a fully received window V(Q) and V(R) were WindowSize away from each other. <0005> tbf.cpp:1579 UL DATA TFI=0 received (V(Q)=55 .. V(R)=60) <0005> tbf.cpp:1624 - BSN 60 storing in window (55..118) <0005> rlc.cpp:173 - Raising V(R) to 61 <0005> tbf.cpp:1690 - Scheduling Ack/Nack, because 20 frames received. <0005> encoding.cpp:374 Encoding Ack/Nack for TBF(TFI=0 TLLI=0xfa45049d DIR=UL) (final=0) SSN=61 <0005> encoding.cpp:408 - V(N): "RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR" R=Received N=Not-Received This part might be something we broke but we will try to re-produce with a unit test. We will continue to work on unit-testing the RLC window handling if anyone outside sysmocom interested in getting a more stable PCU? holger -- - Holger Freyther <hfreyther(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * 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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osmocom-net-gprs December 2013