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

Thu Apr 9 09:09:25 CEST 2020

Hello,

if you are designing for over 600.000 concurrent calls, you would probably like to look for a distributed/clustered solution anyway, I guess. And this will bring some more topics related to synchronisation and race-conditions to think about.

Of course not knowing the details about the scenario, but maybe it make sense to tackle this race-condition problem in the client instead of trying to fix it elsewhere. As already pointed out, you can’t control the network transmission anyway, if you use UDP.

Cheers,

Henning

--
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 11:04 PM
To: miconda at gmail.com; Kamailio (SER) - Users Mailing List <sr-users at lists.kamailio.org>; Henning Westerholt <hw at skalatan.de>
Subject: Re: [SR-Users] Kamailio propagates 180 and 200 OK OUT OF ORDER

Hello, Daniel,

I looked into that parameter, but  I need to use with the dialog module, and I'm pretty afraid to use that. I was looking more into the stateless proxy, because I need to process a lot of traffic.

My target is 4200CAPS. with duration between 90s and 210. Let's say, 150 seconds. That would mean 630.000 simultaneous dialogs. I don't think the solution can go that way.

it would really help me to be able to use completely stateless proxy plus Async in reply_route(), to introduce an artificial delay before forwarding 200 OK to Invite.. As someone mentioned, it would help me on request_route(), for race conditions between ACK and Re-Invite.

Any idea why Async is not allowed in reply_route()?

Best regards,

Luis

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>
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From: Luis Rojas G. <luis.rojas at sixbell.com><mailto:luis.rojas at sixbell.com>
Sent: Wednesday, April 8, 2020 3:00 PM
To: Henning Westerholt <hw at skalatan.de><mailto:hw at skalatan.de>; Kamailio (SER) - Users Mailing List <sr-users at lists.kamailio.org><mailto: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

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>
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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 01D60E4E.8FF1E140]

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 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<https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.sixbell.com%2F&data=02%7C01%7C%7C1bde0e5c47434fa230df08d7dbdf4eb4%7Cab4a33c2b5614f798601bc921698ad08%7C0%7C0%7C637219624482013047&sdata=qLbw%2FV%2F45%2BhkIM4hng2DlNpcX2Uko%2Bhgf4suO4SwEwo%3D&reserved=0>

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--

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
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