mid_registrar Module

In "contact mirroring" mode, the mid-registrar will insert itself in the registration flow between end user and main registrar only as a simple proxy registrar, without any other contact processing. The incoming REGISTER requests will be proxied further to the main registrar; the registered contact will be stored in the mid-registrar only on 2xx replies, according to the information returned by the main registrar.

A possible usage of this mode, for example, would be to clone registrations on a SIP front-end that extends the main platform with new services (like adding IM/messaging routing).

In "contact throttling" mode, the mid-registrar can significantly reduce the registration rate on the main registrar side (between mid-registrar and main registrar), while coping with a high registration rate on the end-user side (between end-user and mid-registrar). This is useful in scenarios were the end-users are very dynamic and short-lived (like on mobile devices), but the main registrar cannot cope with large traffic.

Traffic conversion is done in a "per-device" manner, according to each unique SIP Contact header field value. It is achieved by increasing the "expires" parameter value of each contact, when relaying registrations to the main registrar. Once such a registration is completed, subsequent registrations for the same SIP Contact header field value will be continuously absorbed by the mid-registrar until, eventually, the lifetime of the remote registration will have decreased enough that a refresh (i.e. simply forwarding the next REGISTER request) is mandatory.

A common occurence is for some SIP User Agents to lose their network connection (especially when dealing with mobile devices), hence they do not properly de-register from the mid-registrar. In this case, in order to avoid stale registrations on the main registrar (which contains SIP contacts with greatly extended lifetimes!), the mid-registrar will appropriately generate De-REGISTER requests and remove these contacts from the main registrar's location service as soon as it considers them to have expired.

The main practical use for this mode is registration traffic conversion. By minimizing the strain of processing registrations on the main registrar, we allow it to dedicate more system resources to critical areas of the platform, such as advanced SIP calling features and/or media handling.

In "AOR throttling" mode, the mid-registrar helps with handling multiple registrations per user/AOR. This is done by aggregating all the end-user registered contacts from a single AOR under a single registration into the main registrar. This can dramatically reduce the incoming rate of registrations (to a single registration per AOR), but also helps in dealing with registrar servers which are not able to implement parallel forking/ringing.

Traffic conversion is done in a "per-user" manner, according to each unique SIP AOR. It is achieved by providing a contact with a large "expires" parameter value, when relaying registrations to the main registrar. Once such a registration is completed, subsequent registrations to the same Address-of-record will be continuously absorbed by the mid-registrar until, eventually, the lifetime of the remote registration will have decreased enough that a refresh (i.e. simply forwarding the next REGISTER request) is mandatory.

A common occurence is for some SIP User Agents to lose their network connection (especially when dealing with mobile devices), hence they do not properly de-register from the mid-registrar. In this case, in order to avoid stale registrations on the main registrar (which contains SIP AORs with greatly extended lifetimes!), the mid-registrar will appropriately generate De-REGISTER requests and remove these contacts from the main registrar's location service as soon as it considers them to have expired.

Of all three modes, "AOR throttling" potentially offers the best reduction in traffic on the way to the main registrar. By aggregating contacts, it also has the added benefit of reducing the number of contacts that the main registrar must handle.

Regarding SIP request mangling in this mode, the module will always replace all Contact header field values with a single Contact header field value when proxying registrations to the main registrar, indicating that the AOR is local to the front-end, and its contacts can be found there.

The main practical uses for this mode are registration traffic conversion towards the main registrar, as well as taking over its call forking duties. By minimizing the strain of processing registrations / forking calls on the main registrar, we allow it to dedicate more system resources to critical areas of the platform, such as advanced SIP calling features and/or media handling.

This insertion mode will mangle the Contact header field values of all forwarded registration requests, by replacing any original IP and port of a Contact URI with those of one of the mid-registrar's listening interfaces.

The mid-registrar will also append a parameter to each Contact URI ("rid" by default, can be changed through the contact_match_param module parameter) This URI parameter allows reply contacts to be matched with request ones. This same parameter will also be used when routing calls to the users. In this case, it will be taken from the INVITE's Request-URI.

Instructs the module to append a "Path" header field to each forwarded registration request. By recording itself between each user and the main registrar, the mid-registrar allows subsequent calls to be properly routed to the called party.

The following modules must be loaded before this module:

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

Working mode of the module. Refer to Section 1.2, “Working modes” for more details.

The following is true for all working modes:

Each working mode behaves differently, as follows:

Default value is 0 (contact mirroring mode)

modparam("mid_registrar", "mode", 2)

SIP insertion mode of the module. Refer to Section 1.3, “Insertion modes” for more details. Possible values are:

Default value is 0 (route by Contact)

modparam("mid_registrar", "insertion_mode", 1)

The minimum expires value of a Contact, values lower than this minimum will be automatically set to the minimum. Value 0 disables the checking.

Default value is 10 (seconds)

modparam("mid_registrar", "min_expires", 600)

If the processed message contains neither Expires HFs nor expires contact parameters, this value will be used as the expiration interval of any newly created usrloc records.

Default value is 3600 (seconds)

modparam("mid_registrar", "default_expires", 1800)

The maximum expires value of a Contact, values higher than this maximum will be automatically set to the maximum. Value 0 disables the checking.

Default value is 3600 (seconds)

modparam("mid_registrar", "max_expires", 7200)

Only relevant in Contact/AOR throttling modes. Sets a minimal value for the expiration intervals of egressing contacts.

Default value is 3600 (seconds)

modparam("mid_registrar", "outgoing_expires", 3600)

Only relevant in "Contact throttling" mode. Specifies the name of the Contact URI parameter which is used by the module in order to match contacts and route calls.

Default value is “rid”

modparam("mid_registrar", "contact_match_param", "regid")

Sets the default "q" value for new contacts. Because OpenSIPS does not support floating point module parameters, the supplied "q" value must be multiplied by 1000. For example, if you want default_q to be 0.38, set this parameter to 380.

Default value is 0

modparam("mid_registrar", "default_q", 380)

Specifies the message flag to be used to control the module behaviour regarding TCP connections. If the flag is set for a REGISTER via TCP containing a TCP contact, the module, via the mid_registrar_save() function, will set the lifetime of the TCP connection to the contact expire value. By doing this, the TCP connection will stay up as long as its contacts are valid.

Default value is -1 (not set)

modparam("mid_registrar", "tcp_persistent_flag", "TCP_PERSIST_REGISTRATIONS")

In multi-domain user location scenarios ("use_domain" usrloc module parameter set to "1"), this parameter denotes a prefix to be automatically stripped from the hostname part of To header field URIs when doing a save, or Request-URIs when doing a lookup.

It is meant as an alternative to DNS SRV records (not all SIP clients support SRV lookups), a subdomain of the master domain can be defined for SIP purposes (like "sip.mydomain.net" pointing to same IP address as the SRV record for "mydomain.net"). By ignoring the realm_prefix "sip.", at registration, "sip.mydomain.net" will be translated to "mydomain.net".

Default value is NULL (none)

modparam("mid_registrar", "realm_prefix", "sip.")

If set to 1, then AOR comparison will be case sensitive (as RFC3261 instructs), if set to 0 then AOR comparison will be case insensitive.

Default value is 1 (true)

modparam("mid_registrar", "case_sensitive", 0)

The module will store the value of the AVP configured by this parameter in the received column of the user location table. It will leave the column empty if the AVP is empty. The AVP should contain a SIP URI consisting of the source IP, port, and protocol of the REGISTER message being processed.

Default value is "NULL" (disabled)

modparam("mid_registrar", "received_avp", "$avp(rcv)")

The name of the parameter that will be appended to Contacts of 200 OK replies if the received URI is set by nathelper module.

Default value is "received"

modparam("mid_registrar", "received_param", "rcv")

This parameter can be used to limit the number of contacts per AOR (Address-of-Record) allowed at mid-registrar level. A value of 0 disables the check.

This is a global value and will only be used if no other value (for max_contacts) is passed as parameter to mid_registrar_save() (i.e. a "max_contacts" function flag will override this parameter)

Default value is 0 (disabled)

modparam("mid_registrar", "max_contacts", 10)

The mid-registrar can generate 5xx replies to registrations in various situations. It could, for example, happen when the max_contacts parameter is set and the processing of REGISTER request would exceed the limit. In this case, OpenSIPS would respond with "503 Service Unavailable".

If you want to add the Retry-After header field in 5xx replies, set this parameter to a value greater than zero (0 means: do not add the header field). See section 20.33 of RFC3261 for more details.

Default value is 0 (disabled)

modparam("mid_registrar", "retry_after", 30)

Globally disable GRUU handling.

Default value is 1 (GRUUs will not be handled)

modparam("mid_registrar", "disable_gruu", 0)

The string that will be used in XORing when generating temporary GRUUs.

Default value is "0p3nS1pS"

modparam("mid_registrar", "gruu_secret", "my_secret")

Function to be called when handling REGISTER requests. This function decides if a REGISTER should be forwarded to the main registrar and performs all the necessary changes over the registered contacts. The function is also covering the handling of the 2xx REGISTER replies - the contacts confirmed by the main registrar will be automatically saved in the local user location (without any additional scripting).

In Contact/AOR throttling modes (more info about working modes in Section 1.2, “Working modes”), the return value of this function indicates whether the script writer must forward the REGISTER request to the main registrar, or just wrap up any left-over processing and exit script execution, as the current REGISTER request has been answered with 200 OK (absorbed at mid-registrar level).

Depending on the current working mode and insertion_mode, the function may additionally perform the following series of transformations when relaying REGISTER requests:

Meaning of the parameters is as follows:

Return value

This function can only be used from the request route.

...
if (is_method("REGISTER")) {
	mid_registrar_save("location");
	switch ($retcode) {
	case 1:
		xlog("L_INFO", "forwarding REGISTER to main registrar...\n");
		$ru = "sip:10.0.0.3:5070";
		if (!t_relay()) {
			send_reply("500", "Server Internal Error 1");
		}

		break;
	case 2:
		xlog("L_INFO", "REGISTER has been absorbed!\n");
		break;
	default:
		xlog("L_ERR", "mid-registrar error!\n");
		send_reply("500", "Server Internal Error 2");
	}

	exit;
}
...

Function to be called when receiving requests from the main registrar (to be routed to the end-user). It performs the local lookup (in user location) and the necessary RURI processing in order to route the requests further to the end-user registered contacts (note that multiple branches/destinations may result after the lookup).

Depending on the current working mode, the function will behave as follows:

Meaning of the parameters is as follows:

Return value

This function can only be used from the request route.

...
	# initial invites from the main registrar - need to look them up!
	if (is_method("INVITE") and $si == "10.0.0.3" and $sp == 5070) {
		if (!mid_registrar_lookup("location")) {
			t_reply("404", "Not Found");
			exit;
		}

		if (!t_relay())
			send_reply("500", "Server Internal Error 3");

	    exit;
	}
...