This change add support for the recently-introduced GPRS Gb interface
auto-configuration using the NS IP Sub-Network Service (SNS) procedures.
It requires a Change-Id I84786c3b43a8ae34ef3b3ba84b33c90042d234ea of
libosmocore.
Related: OS#3372
Depends: I84786c3b43a8ae34ef3b3ba84b33c90042d234ea (libosmcore)
Change-Id: I256b40ac592d3b6e75dd581bf7b9512f69b11e83
The PDCH class and corresponding functions are rather self-contained and
independent from BTS implementation. Let's move them into separate file
to make bts.cpp more manageable. As additional benefit it allow us to
somewhat untangle all the different cross-dependent includes.
Change-Id: Ie05e25361e6741a81b024679f9675c98d4923683
Related: OS#1539
vty_install_default() and install_default() will soon be deprecated.
Depends: I5021c64a787b63314e0f2f1cba0b8fc7bff4f09b
Change-Id: I6c9f928f4a4d7fd6bf37c64a64ee5d843ad5bb7a
We have seen that UL MCS5- MCS9 link adaptation has not been implemented in current PCU implementation.
If the MS slowly moves far away from the BTS, the UL MCS will always stick at MCS9 no matter UL link quality values leading to poor data service experience.
The UL MCS is expected to adapt from MCS9 -> MCSx due to bad UL quality.
Below PCU traces indicate that UL MCS is quickly increasing to MCS9 (max MCS 9 was used in this test) and it never changes to other UL MCS due zero thresholds.
<0004> gprs_ms.cpp:670 MS (IMSI ): Link quality 23dB (23dB) left window [0, 0], modifying uplink CS level: MCS-6 -> MCS-7
<0004> gprs_ms.cpp:670 MS (IMSI 000): Link quality 23dB (23dB) left window [0, 0], modifying uplink CS level: MCS-7 -> MCS-8
<0004> gprs_ms.cpp:670 MS (IMSI 000): Link quality 23dB (23dB) left window [0, 0], modifying uplink CS level: MCS-8 -> MCS-9
Change-Id: I9272c337ad6399da4a47cc6e2736e25f24e099d8
osmo-bts already supports configuring a different path for the bts<->pcu
socket by using the 'pcu-socket' config field.
Change-Id: I9b3e1171da467519750b201849ec892a1e318129
When looking at GSMTAP output so far, one is easily overwhelmed by way
too much information being presented. A lot of is consists of DUMMY
frames, which are probably of lowest interest, ever.
A concept similar to the "gsmtap-sapi" of OsmoBTS is introduced, by
which the user can configure which particular categories (uplink or
downlink control or data, gprs or egprs, ...) he actually wants to
see in his logs.
Change-Id: I297183690e98a7234dfc1608c18847d8981306e4
Modify the EGPRS DL TBF flow to support Split block during
Retx. This patch will also Upgrade the test suite with test cases
to validate the EGPRS Downlink SPB for Retransmission
Scenarios like MCS6->MCS3, MCS4->MCS1, MCS5->MCS2, MCS9->MCS3
MCS7->MCS2, MCS8->MCS3 have been simulated and Integration tested
in NuRAN 1.0 hardware thoroughly.
Change-Id: I242afdd8ae7622dec8593b26382ad66bad5b9516
This warning is not valid since the PCU is not failing when EGPRS is
activated. So removing this trace
Change-Id: I62278f998adc691b9a3563ac2a46d756e7bfb66c
This adds the following VTY command (config-pcu node):
- mcs <1-9> sets initial DL and UL MCS to the same value
- mcs <1-9> <1-9> sets initial DL and UL MCS separately
- no mcs sets the default values
Sponsored-by: On-Waves ehf
Currently the window size is fixed to 64 even for EGPRS.
Support dynamic window sizes depending on the number of PDCH. The
WS can be set to b + f * N_PDCH. If the result is not valid according
to TS 44.060, Table 9.1.9.2.1, the value will be corrected to use the
next lower valid value (or 64).
The following VTY commands are added (config-pcu node):
window-size <0-1024> set base (b) value and leave f unchanged
window-size <0-1024> <0-256> set base (b) and factor (f)
Sponsored-by: On-Waves ehf
Currently the plain 'egprs' command enables EGPRS but doesn't prevent
phones from being served in GPRS mode if they do not support EGPRS.
This involves complex frame allocation implementations in dynamic
mode, especially if 8PSK is being used. This is due to the inability
of non-EGPRS phone to decode 8PSK USF and ES/P altogether. Since
polling has a higher priority than USF, collisions will have to be
prevented by the PCU by never using an GPRS USF if it refers to a FN
that is already being used for polling.
This commit just disables mixed usage by ignoring GPRS-only request
if EGPRS is enabled.
The following VTY command (config-pcu node) is changed:
egprs -> egprs only
Sponsored-by: On-Waves ehf
This sets the maximum MCS encoding used for EGPRS RLC data blocks
in either direction.
The following VTY command are added to node config-pcu:
- mcs max <1-9> set maximum for both, uplink and downlink
- mcs max <1-9> <1-9> set maximum for downlink and uplink (in that
order)
- no mcs max do not limit
Note that using a value of 4 or below for each direction implies
that a GMSK-only TBF may be assumed, which for instance would allow
the use of the GPRS MS class instead of the possibly more restrictive
EGPRS MS class.
Sponsored-by: On-Waves ehf
LListHead does basically the same like llist_pods, but more C++ish
and with type safety.
This commit turns the former list field of gprs_rlcmac_tbf into a
private field, provides accessors, moves the related code from
pcu_vty.c to pcu_vty_functions.cpp, and removes the llist_pods
type and related code.
Sponsored-by: On-Waves ehf
Enable the TBF to use EGPRS if the bts->egprs_enabled config variable
has been set via the VTY "egprs" command and if the MS has signaled a
EGPRS multislot class.
Tell the MS to use EGPRS if the condition above holds.
Note that this will cause the MS to use EGPRS RLC block formats for
further messages which are not yet understood by the PCU.
Sponsored-by: On-Waves ehf
Add a global config flag to enable the use EDGE/EGPRS.
The following VTY commands are added to node config-pcu:
- egprs Enables EGPRS
- no egprs Disable EGPRS
Note that enabling EGPRS is experimental and will most likely break
packet transmission until a minimal required set of EGPRS
functionality is implemented.
Sponsored-by: On-Waves ehf
This commit fixes the go_parent_cb API according to libosmocore's
commit of the same name.
Fixes:
pcu_vty.c:799:2: warning: initialization from incompatible pointer
type [enabled by default]
.go_parent_cb = pcu_vty_go_parent,
Sponsored-by: On-Waves ehf
Currently packets are only dropped if they have reached their maximum
life time. This leads to LLC queues being constantly filled under
load, increasing the latency up to the maximum life time. This kind
of bufferbloat hinders TCP's congestion avoidance algorithms. To keep
the queues short, the CoDel active queue management algorithm can be
used.
This commit changes to llc_dequeue method to apply the CoDel
algorithm to selectively drop LLC frames before they passed to the
TBF layer to be encoded in BSNs. This feature is currently disabled
by default.
The CoDel state is managed per MS since the LLC queues are also kept
in the MS objects.
Note that there is still some buffering in the TBF objects, in the
worst case (CS4) 3.5kByte + LLC-MTU octets are stored there. The
resulting additional packet delay is not (yet) taken into account for
CoDel.
Also note that configuration changes are applied to new MS objects
only.
The following VTY commands are added to the 'pcu' node:
- queue codel activates CoDel, the interval is selected by
the implementation
- queue codel interval <1-1000>
activates CoDel with a fixed interval given
in centiseconds (10ms-10s)
- no queue codel deactivates CoDel
Which interval value to use is still an open issue. For high speed
links (e.g. Ethernet), CoDel suggests 100ms. For slower links, the
expected RTT is recommended. The current implementation uses a
default value of 2000ms.
Measurements:
Note that the following measurements depend on several other factors,
most notably the interaction with the SGSN's flow control. They are
just examples to give an idea how CoDel might influence some
parameters.
The measurements have been done with a single E71, first with a
running ping only (Idle), then with an additional TCP download
of a 360k file (Busy). The CoDel interval was set to 1s.
- Idle :
ping ~400ms, avg queue delay 0ms, dropped 0
- Busy, No CoDel:
ping ~6s, avg queue delay 4-6s,
dropped 0, scheduled 948, duration 54s
- Busy, CoDel:
ping 500-1500ms, avg queue delay ~600ms,
dropped 77, scheduled 1040, duration 60s
More measurements with two MS downloading in parallel (two
independant measurements per case).
- Busy, No CoDel:
dropped 0, scheduled 1883, duration 121s
dropped 19, scheduled 2003, duration 133s
- Busy, CoDel:
dropped 22, scheduled 1926, duration 116s
dropped 22, scheduled 1955, duration 108s
Sponsored-by: On-Waves ehf
The idea behind this meta algorithm is to automatically select one of
the other algorithms based on the system state. Basically algorithm B
will be selected if the PDCH usage is low to improve throughput and
latency. Algorithm A will be selected to support more concurrent MS.
This commit adds a first simple state-less version of this algorithm
that always tries B first and only if that fails A is tried
afterwards.
The following VTY command is added to the 'pcu' node:
- alloc-algorithm dynamic
Ticket: #1934
Sponsored-by: On-Waves ehf
If just a few bytes are left to send to the MS, it makes sense to
reduce the coding scheme level to increase the throughput. This
has been shown by Chen and Goodman in their paper "Theoretical
Analysis of GPRS Throughput and Delay". See their throughput over C/I
measurement graphs (figures 4 and 5 in the paper) for details.
This commit implements a simplified CS downgrade feature for the
downlink. The coding scheme will be downgraded if there are only a
few octets are left to be send over the TBF (see the
downgrade-threshold command below) and the NACK rate is not low (the
CS will not get degraded on a high quality RF link). As an exception,
CS-3 will be degraded to CS-1, since CS-2 does not improve the
throughput in general when a few small packets are sent and the
signal fades slowly (see Chen/Goodman).
The following VTY command is added to the config-pcu node:
- cs downgrade-threshold <1-10000>
- cs no downgrade-threshold
to set the threshold of the number of remaining bytes to be RLC/MAC
encoded. The CS will only be reduced, if the number is below the
threshold. The 'no' command disables this feature completely. The
default value is 200 octets.
Sponsored-by: On-Waves ehf
Currently the UL CS values are set to the corresponding DL CS value,
eventually limited by a maximum value. This approach does not reflect
the general situation of the RF link between ME and BTS, which is
rather asymmetric e.g. due to a lower degree of TX efficiency of the
built-in antenna. This means, that UL and DL CS control should be
decoupled for better results.
This commit adds automatic UL CS selection based on the link quality
measurement parameter. Each coding scheme is mapped to a link quality
range. If the link quality value leaves that range, the current UL CS
value is increased/decreased accordingly. This value will be copied
when the next PACKET_UPLINK_ACK_NACK or PACKET_UPLINK_ASSIGMENT is
sent to the MS.
The following VTY command will be added to the config-pcu node:
- cs link-quality-ranges cs1 <0-35> cs2 <0-35> <0-35>
cs3 <0-35> <0-35> cs4 <0-35>
which sets the ranges for the four coding schemes. For instance the
example below reflects the current default values:
cs link-quality-ranges cs1 6 cs2 5 8 cs3 7 13 cs4 12
set the following ranges, where the overlapping is used to configure
a hysteresis:
CS1: -inf .. 6
CS2: 5 .. 8
CS3: 7 .. 13
CS4: 12 .. inf
Sponsored-by: On-Waves ehf
This commit extends the "show ms" command to display an extended set
of information for a single MS.
The following VTY commands are added:
- show ms tlli TLLI
- show ms imsi IMSI
Sponsored-by: On-Waves ehf
Currently the CS values can be increased to CS4 even when the "cs"
configuration command has been used with a lower value. The "cs"
command just sets the initial coding scheme, so other means are
needed to limit the selection. One approach is to use the CS flags
passed in SI, but these are currently ignored.
To make it possible to limit the CS selection by configuring the PCU,
this commit adds the following VTY commands to config-pcu:
- cs max <1-4> Limit DL and UL CS to the given value
- cs max <1-4> <1-4> Limit DL and UL CS separately (DL first)
- no cs max Don't limit
Ticket: #1674
Sponsored-by: On-Waves ehf
This commit adds the following VTY commands to config-pcu:
- cs threshold <0-100> <0-100> Enables adaptive CS selection
- no cs threshold Disables it
The "cs threshold LOW HIGH" command sets the water marks
(cs_adj_lower_limit and cs_adj_upper_limit) used to
decide about switching coding schemes.
Ticket: #1739
Sponsored-by: On-Waves ehf
This command lists the entries of the ms_store by a line per MS.
Beside TLLI and IMSI, some measurement and state information is
shown.
A ms_list() getter method is added to GprsMsStorage to obtain a list
of the MsGprs objects.
The following VTY command is added to the 'enable' node:
- show ms all
Sponsored-by: On-Waves ehf
Currently the pcu_vty.c doesn't compile with C++. Thus C++ object
cannot be access directly there.
This commit adds a helper C++ file that exports all functions with C
calling conventions and naming to work around that limitation until
the transition of pcu_vty.c is completed.
Sponsored-by: On-Waves ehf
This commit sets the MS timeout when the MS object is created. The
value is taken from the ms_idle_sec field in gprs_rlcmac_bts which
can be changed by the VTY commands shown below.
The following VTY commands are added to the config-pcu node:
- ms-idle-time <1-7200> Set the timeout in seconds
- no ms-idle-time Disable the timeout
Another timer that is related is T3314 (Ready Timer, default 44s, GSM
24.008, 11.2.2) which requires the SGSN to use paging after its
expiry. Longer timeouts can help if adaptive coding scheme selection
is used (not yet implemented). On the other hand, measurement values
(TA, signal quality) can get invalid after some time, especially with
a moving MS. So a value slightly above T3314 is probably a good value
to start with.
Sponsored-by: On-Waves ehf
Currently the bucket size is by default being computed based on the
leak rate and the expected life time of LLC frames. The latter is
either taken from 'queue lifetime' (if given) or a fixed value is
used. Using 'queue lifetime' has the drawback that it sets a 'hard'
limit, since frames will be dropped if they stay in the queue
for a longer time.
This commit adds a VTY command to specifically set the time used for
the computation of the bucket size advertised to the SGSN. It does
not affect the PCUs queue handling in any way. If the bucket time is
not set (or if the 'no' command has been used), the old behaviour
(see above) is applied.
The following VTY commands are added (config-pcu node):
- flow-control bucket-time <1-65534> Sets the time in centisecs
- no flow-control bucket-time Don't use this time
Ticket: OW#1432
Sponsored-by: On-Waves ehf
Currently the FLOW-CONTROL_BVC message contains fixed values: The tag
is 1, the BVC bucket size is 6MB, the BVC bucket leak rate is
820kbit/s, the MS bucket size is 50kB, and the MS leak rate is
50kbit/s.
This commit makes the BVC parameters configurable and adds the
following VTY commands:
- flow-control force-bvc-bucket-size <1-6553500>
- no flow-control force-bvc-bucket-size
- flow-control force-bvc-leak-rate <1-6553500>
- no flow-control force-bvc-leak-rate
- flow-control force-ms-bucket-size <1-6553500>
- no flow-control force-ms-bucket-size
- flow-control force-ms-leak-rate <1-6553500>
- no flow-control force-ms-leak-rate
The 'no' variants restore the default behaviour.
Sponsored-by: On-Waves ehf
Currently an uint8_t csec variable is used to temporarily store
the number of centiseconds which can be set within the range
1 - 65535. This way values above 255 cannot be set properly. This
affects the VTY commands "queue lifetime", "queue hysteres", and
"queue idle-ack-delay".
This commit replaces the uint8_t by an uint16_t.
Sponsored-by: On-Waves ehf
This commit adds missing includes to pcu_vty.c and fixes the
llist_head type (missing struct keyword) used by tbf_print_vty_info.
Sponsored-by: On-Waves ehf
This commit applies to following changes to pcu_vty.c:
- Use vty_install_default() instead of install_default()
- Add a blank after the '#' of the prompt
- Rename the 'pcu' configuration node to 'config-pcu'
Sponsored-by: On-Waves ehf
If the protocol layers above LLC (e.g. TCP) need an acknowledgement
to continue, it can take up to 400ms (single TS) until the MS is
polled for Ack/Nack which it can use to request an uplink TBF
quickly. The 400ms result from requesting an DL Ack/Nack every 20 RLC
blocks until all pending LLC frames have been sent.
Especially TCP's slow start mechanism can lead to a high delay at the
start of the connection, since the sender will eventually stop after
having sent the first packets (up to 4 (RFC2581) or 10 (RFC6928)).
This commit modifies append_data() to (re-)start
a timer every time it handles an LLC packet and to request an
Ack/Nack every time it expires. So if the server ceases to send IP
packets, the MS is polled in the assumption, that the server is
waiting for an ACK.
The following VTY commands are added (pcu node):
- queue idle-ack-delay <1-65535> timeout in centiseconds
- no queue idle-ack-delay disable this feature (default)
A sensible value is 10 (100ms) that at gave promising results when
testing locally.
Sponsored-by: On-Waves ehf
Currently single LLC blocks are discarded when the PDU lifetime
expires. If an IP packet has been fragmented either on the IP or on
the LLC layer and is therefore distributed over several LLC frames,
the kept fragments are transmitted and then discarded by the MS
because of the missing PDU. This can cause massive IP packet loss
when there are many fragmented packets (e.g. when trying 'ping
-s1800' or if the GGSN chops downlink IP packets into several SNDCP
packets).
On the other hand, discarding too many packets might disturb the
congestion handling of TCP. Dropping plain TCP ACKs might also hinder
flow control and congestion avoidance.
This commit adds a hysteresis algorithm to the LLC discard loop. If
an LLC message's age reaches the high water mark, further message's
with an age above the low water mark are discarded, too. This is
aborted, if a GMM, a non-UI, or a small message is detected. In
these cases, that message is kept.
The following VTY commands are added (pcu config node):
- queue hysteresis <1-65535> set the difference between high
(lifetime) and low watermark in
centiseconds
- no queue hysteresis disable this feature (default)
Since the SGSN will most probably send all fragments of a single
N-PDU without much delay between them, a value slightly above the
average transmission delay jitter between SGSN and PCU is probably a
sensible value to discard all fragments of a single IP packet.
This is an experimental feature that might be replaced by more
advanced means of active queue management in the future.
Sponsored-by: On-Waves ehf
Currently a DL TBF is immediately closed, when the LLC queue is
drained. This will lead to a new DL assignment if data is received
afterwards. In addition, it is not possible to keep the PACCH open
to poll the MS for UL establishment requests there.
GSM 44.060, 9.3.1a suggests to delay the release of an inactive TBF
for some time (max 5s).
This commit mainly changes create_new_bsn() to send LLC dummy
commands as filler if no LLC data is available until keep_open()
returns false. The keep_open() functions returns true unless a
configurable time has passed after the LLC data store drained. By
default, that time is not set which causes keep_open() to always
return false, so that delayed release is effectively disabled.
The following VTY commands are added:
- dl-tbf-idle-time <1-5000> to set the delay in ms
- no dl-tbf-idle-time to disable delayed release
Ticket: #556
Sponsored-by: On-Waves ehf
pcu_vty.c:285:2: warning: implicit declaration of function 'vty_out_rate_ctr_group' is invalid in C99 [-Wimplicit-function-declaration]
vty_out_rate_ctr_group(vty, "", bts_main_data_stats());
^
pcu_vty.c:128:21: warning: implicit declaration of function 'atoi' is invalid in C99 [-Wimplicit-function-declaration]
bts->fc_interval = atoi(argv[0]);
^
Compared to the previous code there will be a branch to get the
global pointer so the code will be slightly slower than the previous
version but it allows us to start creating objects but still use
the code from C. It is best approach I have found so far.
One downside of C++ is that by default talloc will not be used
(unless we override the new operator to use talloc. Right now
we need to memset the C data structure by hand. The benefit of
enforcing a better structure should is more important though.
It is mandatory to support it because MS may request a single block.
In this case the network must assign a single block.
It is possible to force single block allocation for all uplink requests
on RACH. (VTY option)
If lifetime expires of queued LLC frames, they are discarded. The number
of discarded frames and the sum of their octets are reported to SGSN
via LLC-DISCARDED message.
The lifetime can be overridden via VTY. The value can be centi-seconds
or "infinite".
Harald Welte
Max
Pau Espin
Neels Hofmeyr
Daniel Willmann