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The NO_STR is missing, this commit adds it.
Fixes: Jenkins #603
Sponsored-by: On-Waves ehf
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Documentation error (missing docs):
<command id='show tbf all'>
<param name='all' doc='(null)' />
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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());
^
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pcu_vty.c:128:21: warning: implicit declaration of function 'atoi' is invalid in C99 [-Wimplicit-function-declaration]
bts->fc_interval = atoi(argv[0]);
^
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pcu_vty.c:89:3: warning: add explicit braces to avoid dangling else [-Wdangling-else]
else
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Fixes: Coverity CID 1040959
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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.
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Begin to make the BTS a real C++ object with real responsibilities.
The biggest issue will be the pcu_vty.c that might not like C++
at all.
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The initial power control value Alpha must be set in SI13.
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The flow control interval can be set via VTY.
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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)
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The selections are: single slot or multislot
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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".
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