---
title: "Event (based) Routing Module"
description: "The Event (based) Routing module, or shortly the EBR module, provides a mechanism that allows different SIP processings (of messages in script) to communicate and synchronize between through OpenSIPS Events."
---

## Admin Guide


### Overview


The Event (based) Routing module, or shortly the EBR module, provides a 
mechanism that allows different SIP processings (of messages in script) to
communicate and synchronize between through OpenSIPS Events 
(see [Event Interface](../../docs/manual/Interface-Events.md)).


This mechanism is based on the Subscribe-Notify concept. Any SIP processing
may subscribe to various OpenSIPS Events  Upon Event raising, the 
subscriber will be notified, so it will be able to make use of the data
attached to the Event. Note that the Event raising may take place in a
completely different SIP processing context, completely unrelated to the
subscriber processing.


Also, the Events are generated either internally by OpenSIPS (predefined 
Events), either from the script level (custom Events). Please refer to the
Event Interface documentation for more on how the Events are generated 
([Event Interface](../../docs/manual/Interface-Events.md)).


Depending on how the notification is handled by the subscribing processing,
we distinguish two main scenarios:


- The subscriber waits in async. mode for the receiving the notification;
the processing of the subscriber will suspend and it will be fully
resumed when the notification is received (or a timeout occurs).
- The subscriber continues its processing after subscription, without any
waiting. Whenever a notification is received, a script route (armed by
the subscription) will be executed. Note that this notification route
is executed outside any context of the original processing (nothing
is inherited in this route). The Event triggering the notification is
exposed in the notification route, via AVP variables.


So, EBR allows your SIP processing to synchronize or the exchange info
between, even if these processings are completely unrelated from SIP, time
or handling perspective.


With the help of the EBR support, more advanced routing scenarios are 
possible now, scenarios where you need to handle and put together different
processing as type and time, like the handling of various calls with the 
handling of registrations or with the DTMF extraction. For more, see
the [Examples](#usage-examples) section.


### Dependencies


#### OpenSIPS Modules


The following modules are required by this module:


- *TM* - Transaction module


#### External Libraries or Applications


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


- *None*.


### Exported Parameters


This module does not provide any script parameters.


### Exported Functions


#### notify_on_event(event, filter, route, timeout)


This function creates a subscription to a given Event. A filter can be
used (over the attributes of the Event) in order to filter even more
the needed notifications (only Events matching the filter will be
notified to this subscriber).


Upon Event notification, the given script route (usually called 
notification route) will be executed. No variables, SIP message, SIP 
transaction/dialog or any other context related to subscriber will be 
inherited from subscriber processing into this notification route.


The Event attributes will be exposed in the notification route via AVP
variables as *$avp(attr_name) = attr_value*.


As an exception, in the notification route, the EBR module will make 
available the transaction ID from the subscriber context. Note that 
it's not the transaction itself, but its ID. There are some TM 
functions (like *t_inject_branches*) which can 
operate on transactions based on their ID. Of course, you need to 
have a transaction create in the subscriber processing before calling
the  *notify_on_event()* function.


This function can be used from REQUEST_ROUTE.


Parameters:


- *event* (string) -the name of the Event to subscribe for
- *filter* (var) - a AVP variable holding (as multi
value array) all the filters to be applied on the event (before
notification). The filter value has the format "key=value"
where the "key" must match an attribute name of the Event. The
"value" is the desired value for the attribute;  it may be a shell
wildcard pattern. Ex: "aor=bob@*"
- *route* (string) -the name of the script route to be
executed upon Event notification
- *timeout* (int) - for how long the subscription is
active before expiring (integer in seconds). Note: during its 
lifetime, a subscription may be notified several or zero times.


```opensips title="notify_on_event() usage"
...
$avp(filter) = "aor=*@opensips.org"
notify_on_event("E_UL_AOR_INSERT",$avp(filter),"reg_done",60);
...
route[reg_done] {
	xlog("a new user $avp(aor) registered with opensips.org domain\n");
}
```


#### wait_for_event(event,filter,timeout)


Exactly as the async [afunc wait for event](#wait_for_eventeventfiltertimeout-1) function,
but sync/blocking version. The script execution will block and wait
until the event is delivered or the timeout hits


The function return 1 upon success (an event was received), -1 in error
case or -2 in timeout case (no event was received).


This function can be used from any type of route.


```opensips title="wait_for_event usage"
...
# block until the callee to register
$avp(filter) = "aor="+$rU+"@"+$rd
wait_for_event("E_UL_AOR_INSERT",$avp(filter), 40);
if ($rc>0) {
	xlog("user $avp(aor) is now registered\n");
	lookup("location");
	t_relay();
}
```


### Exported Asynchronous Functions


#### wait_for_event(event,filter,timeout)


Similar to the *notify_on_event*, this function
creates an Event subscriber for the given event and filter. But this
function will do async waiting (with suspend and resume) for receiving
the notification on the desired Event.


The meaning of the parameters is the same as for 
*notify_on_event*.


```opensips title="wait_for_event usage"
...
# wait for callee to register
$avp(filter) = "aor="+$rU+"@"+$rd
async( wait_for_event("E_UL_AOR_INSERT",$avp(filter), 40),  resume_call);
# done
...
route[resume_call] {
	xlog("user $avp(aor) is now registered\n");
	lookup("location");
	t_relay();
}
```


### Usage Examples


#### Push Notification


We use *notify_on_event* to capture the events on
new contact registrations for callee. Once the call is sent to callee,
based on the notification (for new contacts) we inject the newly
registered contacts as new branches in the ongoing transaction.


Schematics : when we send a call to a user, we subscribe to see any
new contacts being registered by the user. On such a notification,
we add the new contact as a new branch to the ongoing transaction
(ringing) to user.


```opensips title="Push Notification script"
...
route[route_to_user] {

    # prepare transaction for branch injection; it is mandatory
    # to create the transaction before the subscription, otherwise
    # the EBR module will not pass the transaction ID into the
    # notification route
    t_newtran();

    # keep the transaction alive (even if all branches will 
    # terminate) until the FR INVITE timer hits (we want to wait
    # for new possible contacts being registered)
    t_wait_for_new_branches();

    # subscribe to new contact registration event,
    # but for our callee only
    $avp(filter) = "aor="+$rU;
    notify_on_event("E_UL_CONTACT_INSERT",$avp(filter),
        "fork_call", 20);

    # fetch already registered contacts and relay if any
    if (lookup("location"))
        route(relay);
    # if there were no contacts available (so no branches 
    # created so far), the created transaction will still be 
    # waiting for new branches due to the usage of the 
    # t_wait_for_new_branches() function

    exit;
}

route[fork_call]
{
    xlog("user $avp(aor) registered a new "
        "contact $avp(uri), injecting\n");
    # take the contact described by the E_UL_CONTACT_INSERT
    # event and inject it as a new branch into the original
    # transaction
    t_inject_branches("event");
}
...
```


#### Call pickup


The scenario is Alice calling to bob, Bob does not pickup and Charlie
is performing call pickup (to get the call from Alice)


We use *notify_on_event* to link the two calls: the
one from Alice to Bob  and the one from Charlie to call pickup service.


Schematics: when we send a call to a user within a pickup group, we
subscribe to see if there is any call to the pickup service (from 
another member of the same pickup group). When we have a call to 
the pickup service, we raise from script an event - this event will
be notified to the first call and we cancel the branches to Bob and
inject the registered contacts for the user calling to pickup group
(Charlie).


```opensips title="Call Pickup script"
...
route[handle_call]
    if ($rU=="33") {
        ## this is a call to the pickup service
        ## (Charlie calling 33)

        # reject incoming call as we will generate an back call
        # from the original call (Alice to Bob)
        t_newtran();
        send_reply(480, "Gone");

        # raise the pickup custom event
        # with pickup group 1 and picker being Charlie (caller)
        $avp(attr-name) = "group";
        $avp(attr-val) = "1";
        $avp(attr-name) = "picker";
        $avp(attr-val) = $fu;
        raise_event("E_CALL_PICKUP", $avp(attr-name), $avp(attr-val));

        exit;
    } else {

        ## this is a call to a subscriber
        ## (Alice calls Bob)

        # apply user location
        if (!lookup("location", "method-filtering")) {
            send_reply(404, "Not Found");
            exit;
        }

        # prepare transaction for branch injection; it is mandatory
        # to create the transaction before the subscription, otherwise
        # the EBR module will not pass the transaction ID into the
        # notification route
        t_newtran();

        # subscribe to a call pickup event, but for our group only
        $avp(filter) = "group=1";
        notify_on_event("E_CALL_PICKUP",$avp(filter),
            "handle_pickup", 20);

        t_relay();
    }
    exit;
}

route[handle_pickup]
{
    xlog("call picked by $avp(picker), fetching its contacts\n");
    if (lookup("location","", $avp(picker))) {
        # take the contacts retured by lookup() (for Charlie)
        # and inject them into the original call, but also cancel
        # any existing ongoing branch (ringing to Bob)
        t_inject_branches("msg","cancel");
    }
}
```


## Developer Guide


This modules does not export any internal API.


## Frequently Asked Questions


**Q: Where can I find more about OpenSIPS?**


Take a look at [https://opensips.org/](https://opensips.org/).


**Q: Where can I post a question about this module?**


First at all check if your question was already answered on one of
our mailing lists:

E-mails regarding any stable OpenSIPS release should be sent to 
users@lists.opensips.org and e-mails regarding development versions
should be sent to devel@lists.opensips.org.

If you want to keep the mail private, send it to 
users@lists.opensips.org.


**Q: How can I report a bug?**


Please follow the guidelines provided at:
[https://github.com/OpenSIPS/opensips/issues](https://github.com/OpenSIPS/opensips/issues).
<!-- CONTRIBUTORS -->

### License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0
