Kamailio module

Overview

Kamailio module들 내용 설명

Dispatcher

• https://www.kamailio.org/docs/modules/devel/modules/dispatcher.html

Kamailio 에서 트래픽 로드 밸런싱을 수행할 수 있는 모듈이다.

ETC

Kamailio 4.4.7 버전에서 이슈가 있었다. 새롭게 Asteri

Dispatcher 모듈에 여러개의 Asterisk IP 가 설정되어 있는 상황에서, 어느 하나의 IP 가 flag 4(Disabled) 로 설정되게 되면 정상적으로 로드 밸런싱을 수행하지 않는 문제가 있었다.

MAXFWD

• https://www.kamailio.org/docs/modules/5.0.x/modules/maxfwd.html#maxfwd.f.mf_process_maxfwd_header

Max-Forward SIP header 와 관련된 기능을 수행할 수 있는 모듈이다.

The SIP Max-Forward header is used to prevent loops in a SIP network. Every server that process and forward a SIP request lowers the Max-Forward value with one. When the value reaches zero, the request is not forwarded and an error response is sent to the UAC.

Parameters

max_limit(integer)

Set an upper limit for the max-forward value in the outgoing requests. If the header is present, the decremented value is not allowed this max_limits - if it does, the header value will by decreased to "max_limit". This check is done when calling the maxfwd_process() function.

The range of values stretches from 1 to 256, which is the maximum MAX-FORWARDS value allowed by RFC 3261. The value can be changed at runtime.

Default value is "70"

modparam("maxfwd", "max_limit", 32)

Functions

maxfwd_process(max_value)

If no Max-Forward header is present in the received request, a header will be added having the original value equal with "max_value". If a Max-Forward header is already present, its value will be decremented(if not 0). The parameter can be a variable.

This function can be used from REQUEST_ROUTE.

Variables

• max_value: Value to be added if there is no Max-Forward header field in the message.

Return code

• 2 (true): header was not found and a new header was successfully added.
• 1 (true): header was found and its value was successfully decremented (had a non-0 value).
• -1(false): the header was found and its value is 0(cannot be decremented).
• -2(false): error during processing.

The return code may be extensivly tested via script variable "retcode" (or "$?").

...
# initial sanity checks --- messages with
# max_forwards==0, or excessively long requests
if (!maxfwd_process("10") && $retcode==-1) {
  sl_send_reply("483", "Too Many Hops");
  exit;
};
...

SL

• https://kamailio.org/docs/modules/5.3.x/modules/sl.html

SL 모듈을 이용하면 Kamailio 를 stateless UA server 로 사용할 수 있도록 해준다.

The SL module allows the SIP server to act as a stateless UA server and generate replies to SIP requests without keeping state. That is beneficial in many scenarios, in which you wish not to burden server's memory and scale well.

The SL module needs to filter ACKs sent after a local stateless reply to an INVITE was generated. To recognize such ACKs, Kamailio adds special "signature" in to-tags. This signature is sought for in incoming ACKs, and if included the ACKs are absorbed.

To speed up the filtering process, the module uses a timeout