[SR-Users] Kamailio propagates 180 and 200 OK OUT OF ORDER

Luis Rojas G. luis.rojas at sixbell.com
Wed Apr 8 22:17:41 CEST 2020

Hi, Daniel, about this :

A distributor thread (or process) won't help here, if it distributes
traffic to other threads (processes) without waiting for them to finish,
which ends up to be serial processing. The distributor role for UDP
traffic is done by the kernel. For tcp/tls there is a distributor
process for connections.


I disagree. A distributor thread could do something as simple as apply a 
hash to the Call-ID, and use it to select the process to send the 
message to, without waiting. the process will recive all messages for a 
specific call-leg.
it does not need to wait for an answer nor it needs states, as "which 
process is processing which message at any time".

I think the main problem is that it introduces a bottleneck, and break 
the main philosophy of Kamailio's architecture, having only individual 

Best regards,


On 4/8/20 1:07 PM, Daniel-Constantin Mierla wrote:
> Hello,
> you have to keep in mind that Kamailio is a SIP packet router, not a 
> telephony engine. If 180 and 200 replies are part of a call is not 
> something that Kamailio recognize at its core. Its main goal is to 
> route out as fast as possible what is received, by executing the 
> configuration file script. Now, a matter of your configuration file, 
> processing of some SIP messages can take longer than processing other. 
> And the processing is done in parallel, a matter of children parameter 
> (and tcp_children, sctp_children).
> With that in mind, a way to try to cope better with the issue you face 
> is to set route_locks_size parameter, see:
>   * 
> https://www.kamailio.org/wiki/cookbooks/devel/core#route_locks_size 
> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.kamailio.org%2Fwiki%2Fcookbooks%2Fdevel%2Fcore%23route_locks_size&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624481963069&sdata=CWh4qvJwYloHLPCOFUdVXRuge3l2rvuAUDM6FBNjFMA%3D&reserved=0>
> Probably is what you look for.
> But if you want more tight constraints, like when receiving a 180 
> after a 200ok and not route it out, you have to make the logic in 
> configuration file by combining modules such as dialog or htable (as 
> already suggested).
> Cheers,
> Daniel
> On 08.04.20 16:04, Luis Rojas G. wrote:
>> Hi, Henning,
>> No need to be ironic. As I mentioned on my first post, I tried 
>> stateful proxy and I observed the same behavior.
>> /"I tried using stateful proxy and I obtained the same result."/
>> The asynchronous sleep seems promising. I will look into it.
>> Thanks,
>> Luis
>> On 4/8/20 9:30 AM, Henning Westerholt wrote:
>>> Hi Luis,
>>> I see. Well, you want to use Kamailio as a stateless proxy, on the 
>>> other hand it should do things that are inherently stateful. 😉
>>> As mentioned, have a look to the dialog module to track the state of 
>>> dialogs that you process. This will not work in a stateless mode, 
>>> though.
>>> You can also use the htable module to just store some data about the 
>>> processed messages in a shared memory table and use this to enforce 
>>> your ordering. There is also the option to do an asynchronous sleep 
>>> (with the async) module on the message that you want to delay but 
>>> still processing other messages during it.
>>> Cheers,
>>> Henning
>>> -- 
>>> Henning Westerholt – https://skalatan.de/blog/ 
>>> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fskalatan.de%2Fblog%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624481973065&sdata=ISKj4Fc0FlBemyJhLFeDaXPQjpOrjIceeXURx2OccqU%3D&reserved=0>
>>> Kamailio services – https://gilawa.com 
>>> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgilawa.com%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624481983060&sdata=vsVGfGjX4ZgDN%2FyaxzSCmc5BHNa%2Buu0Y%2FFQLbW7ETOc%3D&reserved=0>
>>> *From:* Luis Rojas G. <luis.rojas at sixbell.com>
>>> *Sent:* Wednesday, April 8, 2020 3:00 PM
>>> *To:* Henning Westerholt <hw at skalatan.de>; Kamailio (SER) - Users 
>>> Mailing List <sr-users at lists.kamailio.org>
>>> *Subject:* Re: [SR-Users] Kamailio propagates 180 and 200 OK OUT OF 
>>> 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 
>>> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Frfc5407%23page-22&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624481983060&sdata=FekMqBnzvOj4%2FVFnS9x0X5KdcA0Ov1gcb975iEzfWZE%3D&reserved=0>
>>> 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/
>>>     <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fskalatan.de%2Fblog%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624481993053&sdata=E%2BY%2BNYI0%2FtTIOzOXEKwDkZn%2BexDCKcl2giC%2FKNecLoE%3D&reserved=0>
>>>     Kamailio services – https://gilawa.com
>>>     <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgilawa.com%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624482003051&sdata=nDoL%2BEeMl0r6Kc4gIZ0MaAWWza9Mv8gMlZkWBTCOo80%3D&reserved=0>
>>>     *From:* sr-users <sr-users-bounces at lists.kamailio.org>
>>>     <mailto:sr-users-bounces at lists.kamailio.org> *On Behalf Of *Luis
>>>     Rojas G.
>>>     *Sent:* Tuesday, April 7, 2020 10:43 PM
>>>     *To:* sr-users at lists.kamailio.org
>>>     <mailto:sr-users at 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 UAC is Kamailio is
>>>     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 at sixbell.com
>>> http://www.sixbell.com  <https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.sixbell.com%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624482003051&sdata=tGs20FsV%2FwXvEg1FSIdB7nByjdj0Xw6tVtKlYa5byyU%3D&reserved=0>
>> -- 
>> Luis Rojas
>> Software Architect
>> Sixbell
>> Los Leones 1200
>> Providencia
>> Santiago, Chile
>> Phone: (+56-2) 22001288
>> mailto:luis.rojas at sixbell.com
>> http://www.sixbell.com
>> _______________________________________________
>> Kamailio (SER) - Users Mailing List
>> sr-users at lists.kamailio.org
>> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
> -- 
> Daniel-Constantin Mierla --www.asipto.com
> www.twitter.com/miconda  --www.linkedin.com/in/miconda

Luis Rojas
Software Architect
Los Leones 1200
Santiago, Chile
Phone: (+56-2) 22001288
mailto:luis.rojas at sixbell.com

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