8 Apr
2020
8 Apr
'20
3 p.m.
Hello, Henning,
I am worried about this scenario, because it's a symptom of what may
happen in other cases. For instance, I've seen that this operator
usually sends re-invites immediate after sending ACK. This may create
race conditions like 3.1.5 of RFC5407
https://tools.ietf.org/html/rfc5407#page-22
I'd understand that one happens because of packet loss, as it's in UDP's
nature, but in this case it would be artificially created by Kamailio.
if there was no problem at network level (packet loss, packets following
different path on the network and arriving out of order), why Kamailio
creates it?
I'd expect that the shared memory is used precisely for this. If an
instance of kamailio receives a 200 OK, it could check on the shm and
say "hey, another instance is processing a 180 for this call. Let's wait
for it to finish" (*). I know there could still be a problem, the
instance processing the 180 undergoes a context switch just after it
receives the message, but before writing to shm, but it would greatly
reduce the chance.
In our applications we use a SIP stack that always sends messages to the
application in the same order it receives them, even though is
multi-threaded and messages from the network are received by different
threads. So, they really syncronize between them. Why Kamailio instances
don't?
I am evaluating kamailio to use it as a dispatcher to balance load
against our several Application Servers, to present to the operator just
a couple of entrance points to our platform (they don't want to
establish connections to each one of our servers). This operator is very
difficult to deal with. I am sure they will complain something like "why
are you sending messages out of order? Fix that". The operator will be
able to see traces and check that messages entered the Kamailio nodes in
order and left out of order. They will not accept it.
(*) Not really "wait", as it would introduce a delay in processing all
messages. it should be like putting it on a queue, continue processing
other messages, and go back to the queue later.
Well, thanks for your answer.
Luis
On 4/8/20 3:01 AM, Henning Westerholt wrote:
Hello Luis,
as the 1xx responses are usually send unreliable (unless you use
PRACK), you should not make any assumption on the order or even the
arrival of this messages. It can also happens on a network level, if
send by UDP.
Can you elaborate why you think this re-ordering is a problem for you?
One idea to enforce some ordering would be to use the dialog module in
combination with reply routes and the textops(x) module.
About the shared memory question – Kamailio implement its own memory
manager (private memory and shared memory pool).
Cheers,
Henning
--
Henning Westerholt – https://skalatan.de/blog/
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Kamailio services – https://gilawa.com
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*From:* sr-users <sr-users-bounces(a)lists.kamailio.org> *On Behalf Of
*Luis Rojas G.
*Sent:* Tuesday, April 7, 2020 10:43 PM
*To:* sr-users(a)lists.kamailio.org
*Subject:* [SR-Users] Kamailio propagates 180 and 200 OK OUT OF ORDER
Good day,
I am testing the dispatcher module, using Kamailio as stateless proxy.
I have a pool of UAC (scripts in SIPP) and a pool of UAS (also scripts
in SIPP) for the destinations. Kamailio version is
kamailio-5.3.3-4.1.x86_64.
Problem I have is, if UAS responds 180 and 200 OK to Invite
immediately, sometimes they are propagated out of order. 200 OK before
180, like this :
UAS is 172.30.4.195:5061. UAC is 172.30.4.195:5080. Kamailio is
192.168.253.4:5070
Difference between 180 and 200 is just about 50 microseconds.
My guess is that both messages are received by different instances of
Kamailio, and then because of context switches, even though the 180 is
received before, that process ends after the processing of 200.
However, I had the idea that in order to avoid these problems the
kamailio processes synchronized with each other using a shared memory.
I tried using stateful proxy and I obtained the same result.
By the way, anyone has any idea about how Kamailio's share memory is
implemented? It clearly does not use the typical system calls
shmget(), shmat(), because they are not shown by ipcs command.
Before posting here I googled, but I couldn't find anything related to
this. I can't believe I am the only one who ever had this problem, so
I guess I am doing something wrong...
Please, any help. I'm really stuck on this.
Thanks.
--
--
Luis Rojas
Software Architect
Sixbell
Los Leones 1200
Providencia
Santiago, Chile
Phone: (+56-2) 22001288
mailto:luis.rojas@sixbell.com
http://www.sixbell.com
