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

Henning Westerholt hw at skalatan.de
Wed Apr 8 15:30:21 CEST 2020

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.



Henning Westerholt – https://skalatan.de/blog/
Kamailio services – https://gilawa.com<https://gilawa.com/>

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 ORDER

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


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.


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).



Henning Westerholt – https://skalatan.de/blog/<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fskalatan.de%2Fblog%2F&data=02%7C01%7C%7C9909a729fd8a426f81aa08d7db8aab0a%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C1%7C637219260993836600&sdata=ZLmPqvbWKbsXY49s870sElN2I0uIn0DtDQSqJOoxr6I%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%7C9909a729fd8a426f81aa08d7db8aab0a%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C1%7C637219260993836600&sdata=Hdgzfwgu80wiwJBOjh9N70hvXSvWjt8abuKFjVRsavo%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 :

[cid:image001.png at 01D60DBA.9CBC1BA0]

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.




Luis Rojas

Software Architect


Los Leones 1200


Santiago, Chile

Phone: (+56-2) 22001288

mailto:luis.rojas at sixbell.com

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