10 Sep
2013
10 Sep
'13
9:41 a.m.
Hi all,
We're moving this discussion to the mailing list, as it seems it is
more generic and complex than we've thought initially.
The issue arose when I started doing load testing of the OsmoTRX
transceiver and disabled all gating in it. As a result, all incoming
noise was processed as valid Normal Bursts and Access Bursts and sent
up to OsmoBTS. This leads to a situation, similar to a RACH flood,
when there are more RACH requests coming, than a BTS could reasonably
process. And this leads to an unbounded increase of the AGCH queue in
the BTS - it consumes a few Mb per minute.
I think that this is the root cause of the issue we've seen at a
Netherlands festival installation, when 20K phones suddenly started
connecting to our station after official networks went down. When the
amount of RACH requests exceeded available CCCH capacity (took <5
seconds), mobile phones stopped answering out IMM.ASS messages.
Hypothesis is that the AGCH queue became so long, requests were sent
too late for a phone to receive it. And thus no phones answered to our
IMM.ASS messages. Unfortunately, I wasn't able to collect enough data
to check this hypothesis during that time and we don't have another
big festival on hands atm.
An attached is a quick fix for the unbounded queue growth. It uses a
hardcoded value for the maximum queue length, which is fine for our
load testing, but not flexible enough for the real life usage. We
should make the AGCH queue long enough to keep high performance. At
the same time, it must not exceed MS timeout or _all_ IMM.ASS messages
will miss their target MS's.
We could make this parameter user-configurable on a BTS side, but it
seems more reasonable to automatically calculate it, depending on the
channel combination and timeout values. But this should be done on the
BSC side. So the questions are:
1) what is a good way to calculate it?
2) should we configure this queue length over OML, or move the queue
from BTS to BSC?
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
10 Sep
10 Sep
11:04 a.m.
Alexander Chemeris wrote:
1) what is a good way to calculate it?
2) should we configure this queue length over OML, or move the queue
from BTS to BSC?
i suggest to use two queues:
* IMM.ASS messages which grant access
* IMM.ASS messages which reject access
the first queue should have higher priority, because giving access to
mobile stations will sooner or later resolve the rach flood.
another suggestion is to use a stack, rather than a fifo. this will
ensure that latest assigned/rejected channels are handled first. we
don't need to consider how long the mobile will wait for the
assign/reject message, so we don't need to define a specific stack size.
the latest messages will always be sent out early enough. the stack
should have a limit, so oldest messages are dropped, if new messages are
added. i still have no good solution for the maximum stack size.
11:21 a.m.
On Tue, Sep 10, 2013 at 11:41:33AM +0400, Alexander Chemeris wrote:
Hi all,
An attached is a quick fix for the unbounded queue growth. It uses a
hardcoded value for the maximum queue length, which is fine for our
load testing, but not flexible enough for the real life usage. We
should make the AGCH queue long enough to keep high performance. At
the same time, it must not exceed MS timeout or _all_ IMM.ASS messages
will miss their target MS's.
We could make this parameter user-configurable on a BTS side, but it
seems more reasonable to automatically calculate it, depending on the
channel combination and timeout values. But this should be done on the
BSC side. So the questions are:
1) what is a good way to calculate it?
2) should we configure this queue length over OML, or move the queue
from BTS to BSC?
I had a quick look at 12.21 and there doesn't appear to be anything
for the AGCH. So we will need to calculate the size from the channel
configuration but this should be fairly easy. The other topic is the
question of fairnes? The first requests will fill the queue, and then
we drop most of the requests.
Can you implement the size calculation?
11:55 a.m.
On Tue, Sep 10, 2013 at 1:21 PM, Holger Hans Peter Freyther
<holger(a)freyther.de> wrote:
On Tue, Sep 10, 2013 at 11:41:33AM +0400, Alexander
Chemeris wrote:
In a flood situation fairness doesn't make much sense, since most of
the requests will be dropped and we will process random requests
anyway. So the best situation for the flood case is actually to have a
very short (zero?) queue to reduce queueing latency. From this point,
Andreas' ide to use a stack instead of a queue makes perfect sense.
Hi all,
An attached is a quick fix for the unbounded queue growth. It uses a
hardcoded value for the maximum queue length, which is fine for our
load testing, but not flexible enough for the real life usage. We
should make the AGCH queue long enough to keep high performance. At
the same time, it must not exceed MS timeout or _all_ IMM.ASS messages
will miss their target MS's.
We could make this parameter user-configurable on a BTS side, but it
seems more reasonable to automatically calculate it, depending on the
channel combination and timeout values. But this should be done on the
BSC side. So the questions are:
1) what is a good way to calculate it?
2) should we configure this queue length over OML, or move the queue
from BTS to BSC?
I had a quick look at 12.21 and there doesn't appear to be anything
for the AGCH. So we will need to calculate the size from the channel
configuration but this should be fairly easy. The other topic is the
question of fairnes? The first requests will fill the queue, and then
we drop most of the requests. Can you implement the size calculation?
I could, but I think you or Andreas will do this cleaner and with much
less effort. I would rather spend my time on looking for other issues
and implementing new features I have more experience with.
PS While you're here - I remind you that I'm still waiting for the
review of the SMS DB schema update code.
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
12:05 p.m.
On Tue, Sep 10, 2013 at 01:55:47PM +0400, Alexander Chemeris wrote:
I will not have time to work on this anytime soon.
Can you implement the size calculation?
I could, but I think you or Andreas will do this cleaner and with much
less effort. I would rather spend my time on looking for other issues
and implementing new features I have more experience with.
12:24 p.m.
On Tue, Sep 10, 2013 at 2:05 PM, Holger Hans Peter Freyther
<holger(a)freyther.de> wrote:
On Tue, Sep 10, 2013 at 01:55:47PM +0400, Alexander
Chemeris wrote:
I will not have time to work on this anytime soon.
If Andreas don't implement the calculation, we'll go with a manually
configured limit. Should be fine for most use cases.
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
Can you implement the size calculation?
I could, but I think you or Andreas will do this cleaner and with much
less effort. I would rather spend my time on looking for other issues
and implementing new features I have more experience with. 
11 Feb
11 Feb
8:13 a.m.
Hi all,
The attached patches for openbsc and osmo-bts finally fix issues which
were discussed above.
There are two parts:
1. Implementation of sending rsl Delete_Ind message (on bts side) and
handling it (on bsc side).
Bts should send rsl Delete Ind message to bsc, if there is no space in
agch queue and bts can not send current imm assign message.
When bsc receives Delete_Ind message from bts, bsc should release
allocated channel, which was specified in dropped imm_assign message.
2. Implemented calculation of agch queue length.
Bts should calculate allowed length of agch queue, because bts should
send imm assign message before immediate assignment procedure will be
aborted by MS.
Imm assign message can be queued no longer than T3126, so agch queue
length should be equal (T3126 / 51 ) * bs_ag_blks_res.
These patches fix critical issues and prevent network failures under
heavy load, so it makes sense to merge them asap.
2013-09-10 16:50 GMT+04:00 Holger Hans Peter Freyther <holger(a)freyther.de>de>:
On Tue, Sep 10, 2013 at 02:24:38PM +0400, Alexander
Chemeris wrote:
--
Regards,
Ivan Kluchnikov.
http://fairwaves.ru
If Andreas don't implement the calculation, we'll go with a manually
configured limit. Should be fine for most use cases.
come on, please don't be so lazy.
11:14 a.m.
On Tue, Feb 11, 2014 at 11:13:35AM +0400, Ivan Kluchnikov wrote:
Good Morning,
The attached patches for openbsc and osmo-bts finally
fix issues which
were discussed above.
what a surprise. Jacob has started implementing AGCH queue handling
as well. So I will let him comment on the BTS part.
OpenBSC:
+
+ /* bts didn't send IMM_ASSIGN, so we should release allocated channel */
+ ia = (struct gsm48_imm_ass *) (rqd_hdr->data + 2);
Please add a size check that the mandatory element actually fits
and use early returns.
+ if (ia->msg_type == GSM48_MT_RR_IMM_ASS) {
+ chan_nr = ia->chan_desc.chan_nr;
+ lchan = lchan_lookup(trx, chan_nr);
same thing for the lchan. Verify it was found and that the state
is actually the right one.
+ rsl_rf_chan_release(lchan, 1, SACCH_DEACTIVATE);
Maybe use rsl_direct_rf_release. By definition there is no one listening
on the SACCH. So there is not point in going through the normal release
procedure.
+/* 8.5.4 DELETE INDICATION */
+int rsl_tx_delete_ind(struct gsm_bts *bts, uint8_t len, uint8_t *val)
+{
+ struct msgb *msg;
+
+ msg = rsl_msgb_alloc(sizeof(struct abis_rsl_cchan_hdr));
+ if (!msg)
+ return -ENOMEM;
+ rsl_cch_push_hdr(msg, RSL_MT_DELETE_IND, RSL_CHAN_PCH_AGCH);
+ msgb_tlv_put(msg, RSL_IE_FULL_IMM_ASS_INFO, len, val);
+ msg->trx = bts->c0;
Have you manually tested this with multi-trx support and the channel
being on the second trx? The lchan_lookup in OpenBSC will be done using
the "bts->c0"?
- msgb_free(msg);
+ rsl_tx_delete_ind(trx->bts, msg->len, msg->data);
+ return -ENOMEM;
Does it leak now? or was it a double free before?
3:07 p.m.
Dear Ivan,
since I've been investigating this topic for some days now, I would like
to share my thoughts about your approach, so that we can resolve this
issue quickly together.
On 11.02.2014 08:13, Ivan Kluchnikov wrote:
1. Implementation of sending rsl Delete_Ind message
(on bts side) and
handling it (on bsc side).
Bts should send rsl Delete Ind message to bsc, if there is no space in
agch queue and bts can not send current imm assign message.
When bsc receives Delete_Ind message from bts, bsc should release
allocated channel, which was specified in dropped imm_assign message.
As far as I understand it is not important to send such messages to
IMMEDIATE ASSIGNMENT REJECT messages. But I like this idea to shorten
the timeout.
2. Implemented calculation of agch queue length.
Bts should calculate allowed length of agch queue, because bts should
send imm assign message before immediate assignment procedure will be
aborted by MS.
Imm assign message can be queued no longer than T3126, so agch queue
length should be equal (T3126 / 51 ) * bs_ag_blks_res.
I'm not sure about the correctness of the max length calculation because of
a) There are other timers/conditions that are influenced by the queue delay:
- T3101 limits channel reservation on the network side.
- Only the last 3 CHANNEL REQUEST messages are matched by the MS
against incoming IMMEDIATE ASSIGNMENT messages.
b) If the queue has the length limited by a) we know that at least
the last (if not every) element of the queue will be delivered too
late.
Since your patch isn't using T3126 but min(T3126) which is based on
T + 2*S, and since this reflects the 3 CHAN-REQ restriction, this is
already solved (T3101 is probably larger that min(T3126)).
I'll use
maxL = (min(T3126) / 51 ) * bs_ag_blks_res
below.
The b) issue is another thing. Because of additional round-trip delays
(DSP queues, BSC<->BTS delay) it might be sensible to reduce the max
queue length by another factor. But AFAICS the main problem with
dropping packets at the queue's input is, that you maintain a queue with
stale messages while throwing away the fresh ones. So under heavy load,
latency increases which is especially bad with IMMEDIATE ASSIGNMENT
messages.
I've two slightly different proposals to fix this:
(1) If the queue is full (e.g. at 0.8 * maxL), flush all IMMEDIATE
ASSIGNMENT REJECT messages. Don't notify the BSC about those. If there
are still too many messages left afterwards one might also drop an
IMMEDIATE ASSIGNMENT (perhaps from the queues input) and notify the BSC
like in your patch.
(2) When taking message from the queue, throw them away if they are
IMMEDIATE ASSIGNMENT REJECTs and the queue is too long (e.g. > maxL/2)
and try the next message until that condition fails (or some low water
mark is reached). A variant would be to drop IA REJECTs based on a queue
usage dependant probability (e.g. p(L) = L / maxL).
I'm not sure, which approach would perform better considering different
scenarios like burst-like accesses and high packet loss. I've done hand
simulations for a single burst case (10 MS compete simultaneously for 4
channels) and both approaches worked well (much better than the current
master). (2) is probably easier to implement.
What do you think about that?
These patches fix critical issues and prevent network failures under
heavy load,
I'm not convinced that this approach will work reliably under overload
(see above). It just guarantees a maximum queue length.
so it makes sense to merge them asap.
What about rebasing on on origin/master? I think that would speed this
up a lot. Is there something missing from jolly's branch beside queue
length accounting?
@@ -50,6 +50,7 @@ struct gsm_bts_role_bts {
uint8_t max_ta;
struct llist_head agch_queue;
int agch_queue_count;
I'd rather not use this name, but agch_queue_length instead. I think
'length' more precise than 'size' or 'count' when asking for the
number
of elements of a list or a queue. 'count' makes me think about the
number of queues. Quite a few libraries have chosen 'size' instead, but
it's ambiguous, whether this refers to memory size or to the number of
elements.
+ uint8_t agch_queue_len;
What about agch_max_queue_length or agch_queue_length_limit?
int bts_agch_enqueue(struct gsm_bts *bts, struct msgb
*msg)
{
struct gsm_bts_role_bts *btsb = bts_role_bts(bts);
+ struct gsm48_system_information_type_3 *si3;
+ uint8_t T, S, agch_num, i;
+ uint8_t T_group = 0;
+ uint8_t ccch_comb = 0;
+
+ /* calculate length of agch queue
+ agch_queue_len = ( min( T3126 ) / 51 ) * bs_ag_blks_res
+ min(T3126) = T + 2*S defined in 04.08 11.1.1
Are you sure? Isn't it
min(T3126) = (T + 2*S) / (RACH slots per second) ?
+ S and T are defined in 04.08 3.3.1.1.2 */
+
+ si3 = GSM_BTS_SI(bts, SYSINFO_TYPE_3);
+ T = si3->rach_control.tx_integer;
+ for (i = 0; i < 15; i++) {
+ if (tx_integer[i] == T) {
+ T_group = i % 5;
+ break;
+ }
+ }
+ if (si3->control_channel_desc.ccch_conf == 1) {
+ ccch_comb = 1;
+ }
+ S = s_values[T_group][ccch_comb];
+ agch_num = si3->control_channel_desc.bs_ag_blks_res;
- if (btsb->agch_queue_count >= 30)
+ btsb->agch_queue_len = ((T + 2 * S) / 51) * agch_num;
This might lead to smaller values than neccessary due to rounding
errors. Why not using agch_queue_len = (??? * agch_num) / 51?
But I think, the max length computation does not yield correct results
anyway because of the number of RACH slots is not taken into account.
I'd rather put the above into an own function
(bts_agch_update_max_queue_length?) that is only called after
config/bs_ag_blks_res is changed/set.
Best wishes
Jacob
13 Feb
13 Feb
12:07 p.m.
Hi,
On 11.02.2014 15:07, Jacob Erlbeck wrote:
> 2. Implemented calculation of agch queue length.
> Bts should calculate allowed length of agch queue, because bts should
> send imm assign message before immediate assignment procedure will be
> aborted by MS.
> Imm assign message can be queued no longer than T3126, so agch queue
> length should be equal (T3126 / 51 ) * bs_ag_blks_res.
My understanding of GSM 05.02 3.3.2.3, 6.5.1 v), and clause 7 table 5
was, that bs_ag_blks_res defines the number of blocks _reserved_ for
AGCH an SI messages per 51-multiframe, but does not _limit_ it.
Is this correct? If yes, is there a reason why the implementations
(master and jolly/trx) do not use PCH blocks when needed?
I'm not sure about the correctness of the max length calculation because of
a) There are other timers/conditions that are influenced by the queue delay:
- T3101 limits channel reservation on the network side.
- Only the last 3 CHANNEL REQUEST messages are matched by the MS
against incoming IMMEDIATE ASSIGNMENT messages.
More precisely, this limits the allowable delay to 3*(S+T/2) while
CHANNEL REQUESTs are being sent. After the last one, T3126 is relevant.
At least, this is my understanding of GSM 04.08, 3.3.1.1.2. So I'd
rather drop that requirement, since 3S+1.5T > 2S+T.
Jacob
1:48 p.m.
Hi Jacob,
Thank you for your comments and ideas!
First I want to summarize you previous ideas, which I think we should implement:
1. we shouldn't send Delete Ind message for IMMEDIATE ASSIGNMENT REJECT messages
2. Just drop IA REJECTs, if L > maxL/2 (am I right?)
3. Use agch_queue_length and agch_max_queue_length names
4. Implement function bts_agch_update_max_queue_length, that is only
called after config/bs_ag_blks_res is changed/set (do you know places
where bs_ag_blks_res is changed/set?)
5. Yes, you are right, we can use PCH blocks when needed, it is good
question, why (master and jolly/trx) do not use PCH blocks when
needed.
Actually we already have function for that:
int paging_add_imm_ass(struct paging_state *ps, const uint8_t *data,
uint8_t len);
Moreover we should also determine when we should start to use PCH for
imm assign messages and what we should do with agch_max_queue_length
in this case, what do you think about it?
6. What do you finally think about calculating agch_max_queue_length?
What is the right way to calculate it from your point of view?
2014-02-13 15:07 GMT+04:00 Jacob Erlbeck <jerlbeck(a)sysmocom.de>de>:
Hi,
On 11.02.2014 15:07, Jacob Erlbeck wrote:
--
Regards,
Ivan Kluchnikov.
http://fairwaves.ru
> 2. Implemented calculation of agch queue
length.
> Bts should calculate allowed length of agch queue, because bts should
> send imm assign message before immediate assignment procedure will be
> aborted by MS.
> Imm assign message can be queued no longer than T3126, so agch queue
> length should be equal (T3126 / 51 ) * bs_ag_blks_res.
My understanding of GSM 05.02 3.3.2.3, 6.5.1 v), and clause 7 table 5
was, that bs_ag_blks_res defines the number of blocks _reserved_ for
AGCH an SI messages per 51-multiframe, but does not _limit_ it.
Is this correct? If yes, is there a reason why the implementations
(master and jolly/trx) do not use PCH blocks when needed?
I'm not sure about the correctness of the max length calculation because of
a) There are other timers/conditions that are influenced by the queue delay:
- T3101 limits channel reservation on the network side.
- Only the last 3 CHANNEL REQUEST messages are matched by the MS
against incoming IMMEDIATE ASSIGNMENT messages.
More precisely, this limits the allowable delay to 3*(S+T/2) while
CHANNEL REQUESTs are being sent. After the last one, T3126 is relevant.
At least, this is my understanding of GSM 04.08, 3.3.1.1.2. So I'd
rather drop that requirement, since 3S+1.5T > 2S+T.
Jacob
1:53 p.m.
Hi Holger,
Thank you for review, I will fix my patches today or tomorrow and send
you new version asap.
2014-02-11 14:14 GMT+04:00 Holger Hans Peter Freyther <holger(a)freyther.de>de>:
On Tue, Feb 11, 2014 at 11:13:35AM +0400, Ivan
Kluchnikov wrote:
Good Morning,
--
Regards,
Ivan Kluchnikov.
http://fairwaves.ru
The attached patches for openbsc and osmo-bts
finally fix issues which
were discussed above.
what a surprise. Jacob has started implementing AGCH queue handling
as well. So I will let him comment on the BTS part.
OpenBSC:
+
+ /* bts didn't send IMM_ASSIGN, so we should release allocated channel */
+ ia = (struct gsm48_imm_ass *) (rqd_hdr->data + 2);
Please add a size check that the mandatory element actually fits
and use early returns.
+ if (ia->msg_type == GSM48_MT_RR_IMM_ASS)
{
+ chan_nr = ia->chan_desc.chan_nr;
+ lchan = lchan_lookup(trx, chan_nr);
same thing for the lchan. Verify it was found and that the state
is actually the right one.
+ rsl_rf_chan_release(lchan, 1,
SACCH_DEACTIVATE);
Maybe use rsl_direct_rf_release. By definition there is no one listening
on the SACCH. So there is not point in going through the normal release
procedure.
+/* 8.5.4 DELETE INDICATION */
+int rsl_tx_delete_ind(struct gsm_bts *bts, uint8_t len, uint8_t *val)
+{
+ struct msgb *msg;
+
+ msg = rsl_msgb_alloc(sizeof(struct abis_rsl_cchan_hdr));
+ if (!msg)
+ return -ENOMEM;
+ rsl_cch_push_hdr(msg, RSL_MT_DELETE_IND, RSL_CHAN_PCH_AGCH);
+ msgb_tlv_put(msg, RSL_IE_FULL_IMM_ASS_INFO, len, val);
+ msg->trx = bts->c0;
Have you manually tested this with multi-trx support and the channel
being on the second trx? The lchan_lookup in OpenBSC will be done using
the "bts->c0"?
- msgb_free(msg);
+ rsl_tx_delete_ind(trx->bts, msg->len, msg->data);
+ return -ENOMEM;
Does it leak now? or was it a double free before?
2:01 p.m.
On Thu, Feb 13, 2014 at 2:48 PM, Ivan Kluchnikov
<Ivan.Kluchnikov(a)fairwaves.ru> wrote:
5. Yes, you are right, we can use PCH blocks when
needed, it is good
question, why (master and jolly/trx) do not use PCH blocks when
needed.
Actually we already have function for that:
int paging_add_imm_ass(struct paging_state *ps, const uint8_t *data,
uint8_t len);
Moreover we should also determine when we should start to use PCH for
imm assign messages and what we should do with agch_max_queue_length
in this case, what do you think about it?
I believe that we should start using PCH for IMM.ASS as soon as we
exhaust capacity of the AGCH.
Imho, IMM.ASS has higher priority than PCH, as paging will lead to
IMM.ASS anyway, and if AGCH is congested, there is no point in sending
any more paging.
6. What do you finally think about calculating
agch_max_queue_length?
What is the right way to calculate it from your point of view?
You could also consider another approach. Instead of limiting the
queue length - limit the age of IMM.ASS in the queue.
I'm not sure about the current implementation, but in general you
should be able to predict when an IMM.ASS is sent out and thus you
could predict whether the phone will receive it or not.
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
2:25 p.m.
On Thu, Feb 13, 2014 at 04:53:27PM +0400, Ivan Kluchnikov wrote:
Dear Ivan,
Thank you for review, I will fix my patches today or
tomorrow and send
you new version asap.
can you please confirm/reject my statements from below. Does the code
have the defect for multi-trx that I lined out?
holger
2:53 p.m.
Hi Ivan,
On 13.02.2014 13:48, Ivan Kluchnikov wrote:
First I want to summarize you previous ideas, which I
think we should implement:
1. we shouldn't send Delete Ind message for IMMEDIATE ASSIGNMENT REJECT messages
2. Just drop IA REJECTs, if L > maxL/2 (am I right?)
I'm not sure about
which factor to use, especially if maxL is very low.
But I think it's a good start. Maybe we need some simulations to
fine-tune. In addition, we should add stat counters for that.
3. Use agch_queue_length and agch_max_queue_length
names
4. Implement function bts_agch_update_max_queue_length, that is only
called after config/bs_ag_blks_res is changed/set (do you know places
where bs_ag_blks_res is changed/set?)
We've to check. If any of the input
values changes, we have to update.
But let's put that call into agch_enqueue initially. Moving this to
other places is just an optimization and I would like to defer it, until
the rest has proved to work.
5. Yes, you are right, we can use PCH blocks when
needed, it is good
question, why (master and jolly/trx) do not use PCH blocks when
needed.
I've just set up a test case with NITB and two phones, and modified
code
where only the PCH blocks are used for AGCH and PCH and it worked pretty
well.
Actually we already have function for that:
int paging_add_imm_ass(struct paging_state *ps, const uint8_t *data,
uint8_t len);
Moreover we should also determine when we should start to use PCH for
imm assign messages and what we should do with agch_max_queue_length
in this case, what do you think about it?
I would use PCH for AGCH messages, when
there is not pending paging
message. And I wouldn't use paging_add_imm_ass() but just call
bts_agch_dequeue() when there is no paging message.
I wouldn't do this in paging_gen_message() but outside of it, since it
is no paging message. agch_max_queue_length should be based on
ag_blks_res + gsm0502_get_n_pag_blocks() (or something delivering the
same result) then.
6. What do you finally think about calculating
agch_max_queue_length?
What is the right way to calculate it from your point of view?
I'm not sure
yet. Since there is a direct relationship between number of
RACH bursts and CCCH blocks per multiframe, there could be a way to
simplify the calculation. One have to adjust it, if there are optional
CCCH blocks that are not AGCH/PCH (like CBCH), but even if that is not
taken into account, the error might be tolerable.
Jacob
14 Feb
14 Feb
11:22 a.m.
On 13.02.2014 14:01, Alexander Chemeris wrote:
Yes, this was my first approach, too. But it is more complex and we
still need to determine max-age which suffers from the same difficulties
like the max-queue-length computation.
I also thought about having to queues:
- One for non-reject messages (IMM.ASS.CMD and IMM.ASS.EXT) that is
unlimited and has a high prio
- Another for the reject messages only with a lower prio, where
messages older that 3(S+T/2) RACH slots are silently dropped
But I have the impression, that a simpler solution (like those I stated
in the other mail) will take us far enough with much less efforts.
Jacob
I believe that we should start using PCH for IMM.ASS
as soon as we
exhaust capacity of the AGCH.
Imho, IMM.ASS has higher priority than PCH, as paging will lead to
IMM.ASS anyway, and if AGCH is congested, there is no point in sending
any more paging.
I'm not so comfortable with that. We would then have a decreasing
probability within a 51-multiframe of having a PCH message being
cannibalized by a AGCH message. That in turn would IMO lead to unfair
treatment of MS because of the paging group they belong to (AFAI
understand GSM 05.02, 6.5.1 vi and 6.5.2). In addition, I didn't
understand the 'extended paging' (see GSM 04.08, 3.3.2.1.1 b) well
enough, to estimate the implications here.
I'd rather prioritize paging messages over IMM.ASS.* to stay on the safe
side until we have measurements or simulations that suggest otherwise.
6. What do you finally think about calculating
agch_max_queue_length?
What is the right way to calculate it from your point of view?
You could also consider another approach. Instead of limiting the
queue length - limit the age of IMM.ASS in the queue.
16 Feb
16 Feb
12:20 p.m.
Jacob,
On Fri, Feb 14, 2014 at 12:22 PM, Jacob Erlbeck <jerlbeck(a)sysmocom.de> wrote:
Yes, this was my first approach, too. But it is more complex and we
still need to determine max-age which suffers from the same difficulties
like the max-queue-length computation.
I was thinking about scheduling IMM.ASS and at the time of its
arrival. May be even replacing a queue with a fixed-size round-robin
"map". In this case there should be no issues with understanding if
IMM.ASS is too late, as we'll know when exactly it's to be sent.
This changes the current code structure, though, and I haven't
estimated the effort required to do that.
On 13.02.2014 14:01, Alexander Chemeris wrote:
Sending more paging messages only increases a number of IMM.ASS
messages being sent out. Thus it doesn't make sense to prioritize PCH
over AGCH.
Another question is how do we schedule IMM.ASS in case we cannibalize
PCH. IIRC, an MS could be sleeping during paging groups it doesn't
belong to and thus might miss the IMM.ASS we're sending. We have to
check this against the standard.
I believe that we should start using PCH for
IMM.ASS as soon as we
exhaust capacity of the AGCH.
Imho, IMM.ASS has higher priority than PCH, as paging will lead to
IMM.ASS anyway, and if AGCH is congested, there is no point in sending
any more paging.
I'm not so comfortable with that. We would then have a decreasing
probability within a 51-multiframe of having a PCH message being
cannibalized by a AGCH message. That in turn would IMO lead to unfair
treatment of MS because of the paging group they belong to (AFAI
understand GSM 05.02, 6.5.1 vi and 6.5.2). In addition, I didn't
understand the 'extended paging' (see GSM 04.08, 3.3.2.1.1 b) well
enough, to estimate the implications here.
I'd rather prioritize paging messages over IMM.ASS.* to stay on the safe
side until we have measurements or simulations that suggest otherwise. 6. What do you finally think about calculating
agch_max_queue_length?
What is the right way to calculate it from your point of view?
You could also consider another approach. Instead of limiting the
queue length - limit the age of IMM.ASS in the queue. But I have the impression, that a simpler solution
(like those I stated
in the other mail) will take us far enough with much less efforts.
Which solution are you referring to?
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
17 Feb
17 Feb
10:59 a.m.
Hello
On 16.02.2014 12:20, Alexander Chemeris wrote:
That might be true for many cases, but there might be other cases like
issuing a paging request at the end of a short term AGCH overload where
it would make sense, to not drop it but some IMM.ASS.REJ instead.
Another case: all IMM.ASS.* messages are about TCH's and the paging
request is for SDCCH (or vice versa). So until there are simulations
covering all sensible combinations and all of them suggest that always
prioritizing AGCH over PCH is really worth the drawbacks, I won't do
that. It is not required by the spec either, which provides AG block
reservation to cope with frequent PCH overloads instead. There might be
reasons, why they didn't suggest this kind of prioritization and I'd
rather be careful until I know that these are not technical ones.
So I've implemented the usage of _free_ PCH blocks for IMM.ASS which is
IMO a big improvement over the current situation and without any
drawback I know of. In addition, I've added dropping of IMM.ASS.REJ
based on AGCH queue length, to further increase the AGCH queue's drain
rate. This is beyond the spec too, but doesn't touch another procedure
at least.
I suggest to gather real live experiences with these changes and
implement more sophisticated solutions when need arises.
See <52FA2E91.1090605(a)sysmocom.de> (1) and (2) and above.
Jacob
On Fri, Feb 14, 2014 at 12:22 PM, Jacob Erlbeck
<jerlbeck(a)sysmocom.de> wrote:
> On 13.02.2014 14:01, Alexander Chemeris wrote:
I'd rather
prioritize paging messages over IMM.ASS.* to stay on the safe
side until we have measurements or simulations that suggest otherwise.
Sending more paging messages only increases a number of IMM.ASS
messages being sent out. Thus it doesn't make sense to prioritize PCH
over AGCH.
Another question is how do we schedule IMM.ASS in case we cannibalize
PCH. IIRC, an MS could be sleeping during paging groups it doesn't
belong to and thus might miss the IMM.ASS we're sending. We have to
check this against the standard.
Paging groups are not relevant for the RR connection establishment
procedure (AFAICS). According to GSM 04.08 3.3.1.1.3.1 and .2 IMM.ASS.*
is only restricted to the "same CCCH timeslot" where the CHANNEL REQUEST
has been sent, "there is no further restriction on what part of the
downlink CCCH" the IMM.ASS.* is sent.
But I have the impression, that a simpler
solution (like those I stated
in the other mail) will take us far enough with much less efforts.
Which solution are you referring to?
3:03 p.m.
Hi Holger,
Yes, you are right, the code had the defect for multi-trx.
We should use arfcn value from immediate assignment message to determine trx.
I sent new version of the patch to openbsc mailing list, please check it.
I also added checks for size and lchan.
2014-02-13 17:25 GMT+04:00 Holger Hans Peter Freyther <holger(a)freyther.de>de>:
On Thu, Feb 13, 2014 at 04:53:27PM +0400, Ivan
Kluchnikov wrote:
Dear Ivan,
--
Regards,
Ivan Kluchnikov.
http://fairwaves.ru
Thank you for review, I will fix my patches today
or tomorrow and send
you new version asap.
can you please confirm/reject my statements from below. Does the code
have the defect for multi-trx that I lined out?
holger
18 Feb
18 Feb
11:58 a.m.
Jacob,
Your implementation (jerbeck/agch-queue branch) looks reasonable.
But from my point of view we should add sending rsl Delete Ind message
to bsc and implement final check (in bts_agch_dequeue function) that
immediate assignment message is still valid for ms.
My plan is to test your code and add sending rsl Delete Ind message to bsc.
After that we can try to implement lifetime parameter for immediate
assignment message.
2014-02-17 13:59 GMT+04:00 Jacob Erlbeck <jerlbeck(a)sysmocom.de>de>:
Hello
On 16.02.2014 12:20, Alexander Chemeris wrote:
That might be true for many cases, but there might be other cases like
issuing a paging request at the end of a short term AGCH overload where
it would make sense, to not drop it but some IMM.ASS.REJ instead.
Another case: all IMM.ASS.* messages are about TCH's and the paging
request is for SDCCH (or vice versa). So until there are simulations
covering all sensible combinations and all of them suggest that always
prioritizing AGCH over PCH is really worth the drawbacks, I won't do
that. It is not required by the spec either, which provides AG block
reservation to cope with frequent PCH overloads instead. There might be
reasons, why they didn't suggest this kind of prioritization and I'd
rather be careful until I know that these are not technical ones.
So I've implemented the usage of _free_ PCH blocks for IMM.ASS which is
IMO a big improvement over the current situation and without any
drawback I know of. In addition, I've added dropping of IMM.ASS.REJ
based on AGCH queue length, to further increase the AGCH queue's drain
rate. This is beyond the spec too, but doesn't touch another procedure
at least.
I suggest to gather real live experiences with these changes and
implement more sophisticated solutions when need arises.
See <52FA2E91.1090605(a)sysmocom.de> (1) and (2) and above.
Jacob
--
Regards,
Ivan Kluchnikov.
http://fairwaves.ru
On Fri, Feb 14, 2014 at 12:22 PM, Jacob Erlbeck
<jerlbeck(a)sysmocom.de> wrote:
> On 13.02.2014 14:01, Alexander Chemeris wrote:
I'd
rather prioritize paging messages over IMM.ASS.* to stay on the safe
side until we have measurements or simulations that suggest otherwise.
Sending more paging messages only increases a number of IMM.ASS
messages being sent out. Thus it doesn't make sense to prioritize PCH
over AGCH.
Another question is how do we schedule IMM.ASS in case we cannibalize
PCH. IIRC, an MS could be sleeping during paging groups it doesn't
belong to and thus might miss the IMM.ASS we're sending. We have to
check this against the standard.
Paging groups are not relevant for the RR connection establishment
procedure (AFAICS). According to GSM 04.08 3.3.1.1.3.1 and .2 IMM.ASS.*
is only restricted to the "same CCCH timeslot" where the CHANNEL REQUEST
has been sent, "there is no further restriction on what part of the
downlink CCCH" the IMM.ASS.* is sent.
But I have the impression, that a simpler
solution (like those I stated
in the other mail) will take us far enough with much less efforts.
Which solution are you referring to?
12:39 p.m.
Dear Ivan,
On 18.02.2014 11:58, Ivan Kluchnikov wrote:
Your implementation (jerbeck/agch-queue branch) looks
reasonable.
But it isn't ;-) It's just a snapshot and not yet finished.
But from my point of view we should add sending rsl
Delete Ind message
to bsc and implement final check (in bts_agch_dequeue function) that
immediate assignment message is still valid for ms.
I thought that your Delete Ind patches could be added as next step,
since they are orthogonal to the queue handling itself.
My plan is to test your code and add sending rsl
Delete Ind message to bsc.
Please wait with testing, the current branch just segfaults and I'll fix
(and rebase) it soon.
After that we can try to implement lifetime parameter
for immediate
assignment message.
What do you mean exactly?
Cheers
Jacob
7:36 p.m.
Your
implementation (jerbeck/agch-queue branch) looks reasonable.
But it isn't ;-)
It's just a snapshot and not yet finished.
But from my
point of view we should add sending rsl Delete Ind message
to bsc and implement final check (in bts_agch_dequeue function) that
immediate assignment message is still valid for ms.
I thought that your Delete Ind patches could be added as next step,
since they are orthogonal to the queue handling itself. My plan is to
test your code and add sending rsl Delete Ind message to bsc.
Please wait with testing, the current branch just segfaults and I'll fix
(and rebase) it soon. After that we
can try to implement lifetime parameter for immediate
assignment message.
What do you mean exactly?
9:01 p.m.
On Tue, Feb 18, 2014 at 10:36 PM, Ivan Kluchnikov
<Ivan.Kluchnikov(a)fairwaves.ru> wrote:
The idea is to save gsm_time for each imm assign message, when we add
this message to agch queue. After that when we are ready to send this
message and dequeue it, we are able to calculate how long this message
was in agch queue and finally decide what to do, send or drop this imm
assign message.
Are you sure that we could rely on the IMM.ASS timestamp to do the
final judgement? From our discussions I was under impression that we
should measure time difference from the original RACH burst, as that's
what MS is measuring. Do I understand the procedure incorrectly?
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
After that we can try to implement lifetime parameter
for immediate
assignment message.
What do you mean exactly?
3739
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23 comments
5 participants
participants (5)
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Alexander Chemeris -
Andreas Eversberg -
Holger Hans Peter Freyther -
Ivan Kluchnikov -
Jacob Erlbeck