---
title: "b2b_sca Module"
description: "This module provides core SCA (Shared Call Appearance) functionality for OpenSIPS. It is designed to work in tandem with the presence_callinfo module."
---

## Admin Guide


### Overview


This module provides core SCA (Shared Call Appearance) functionality
for OpenSIPS.
It is designed to work in tandem with the presence_callinfo module.


The module handles the basic SIP signalling for call controll while
publishing callinfo events to a presence server.
It is built on top of the b2b_logic module and it is using the
'top hiding' scenario to control SIP signalling.


A typical usage example is provided below, where Alice makes a
call to Bob.  The call leg between Alice and the b2b_sca server
is an "appearance" call of the "shared" call between the b2b_sca server
and Bob.


```c
   caller         caller      b2b_sca     callee   presence server
alice1@example alice2@example  server   bob@example watcher@example
     |              |             |           |           |
     |--INV bob------------------>|           |           |
     |              |             |--INV bob->|           |
     |              |             |--PUBLISH(alerting)--->|
     |              |             |<-----200 OK-----------|
     |              |             |           |           |
     |              |             |<-180 ring-|           |
     |<-180 ring------------------|           |           |
     |              |             |           |           |
     |              |             |           |           |
     |              |             |<-200 OK---|           |
     |<-200 OK--------------------|--ACK----->|           |
     |--ACK---------------------->|--PUBLISH(active)----->|
     |              |             |<-----200 OK-----------|
     |              |             |           |           |
     |--INV bob (hold)----------->|           |           |
     |              |             |--INV bob->|           |
     |              |             |--PUBLISH(held)------->|
     |              |             |<-----200 OK-----------|
     |              |             |<-200 OK---|           |
     |<--200 OK-------------------|           |           |
     |              |             |           |           |
     |              |--INV------->|           |           |
     |              |             |--INV bob->|           |
     |<-BYE-----------------------|--PUBLISH(active)----->|
     |--200 OK------------------->|<-----200 OK-----------|
     |              |             |<-200 OK---|           |
     |              |<-200 OK-----|           |

	
```


- Alice calls Bob from her desk IP phone (alice1).
- Bob answers the call.
- Alice decide to carry the conversation from a meeting room
and she put's BOB on hold.
- Alice arrives to the meeting room and retrieves the call on the
conference room IP phone (alice2).


### To-do


Features to be added in the future:


- possibility to handle unlimited number of appearances.


### Dependencies


#### OpenSIPS Modules


The following modules must be loaded before this module:


- *tm* module.
*pua* module.
*b2b_logic* module.


### Exported Parameters


#### hash_size(integer)


The size of the hash table internally used to keep the shared calls.
A larger table means faster acces at the expense of memory.
The hash size is a power of number two.


*The default value is "10".*


```opensips title="Set hash_size parameter"
...
modparam("b2b_sca", "hash_size", "5")
...
```


#### presence_server(string)


The address of the presence server, where the PUBLISH
messages should be sent (not compulsory).
If not set, the PUBLISH requests will be routed based
on watcher's URI.


*The default value is "NULL".*


```opensips title="Set presence_server parameter"
...
modparam("b2b_sca", "presence_server", "sip:opensips.org")
...
```


#### watchers_avp_spec(string)


AVP that will hold one or more watcher URI(s).
If not set, no PUBLISH requests will be sent out.
The watchers_avp_spec MUST be set before calling sca_init_request();


*The default value is "NULL".*


```opensips title="Set watchers_avp_spec parameter"
...
modparam("b2b_sca", "watchers_avp_spec", "$avp(watchers_avp_spec)")
...
route {
	...
	$avp(watchers_avp_spec) = "sip:first_watcher@opensip.org";
	$avp(watchers_avp_spec) = "sip:second_watcher@opensip.org";
	...
}
```


#### shared_line_spec_param(string)


Mandatory parameter.
Opaque string identifing the shared line/call.
The shared_line_spec_param MUST be set before calling sca_init_request();


*The default value is "NULL".*


```opensips title="Set shared_line_spec_param parameter"
...
modparam("b2b_sca", "shared_line_spec_param", "$var(shared_line)")
...
```


#### appearance_name_addr_spec_param(string)


Mandatory parameter.
It must be a valid SIP URI.
It will populate the *appearance-uri* SIP parameter
inside the *Call-Info* SIP header.
The appearance_name_addr_spec_param MUST be set before calling sca_init_request();


*The default value is "NULL".*


```opensips title="Set appearance_name_addr_spec_param parameter"
...
modparam("b2b_sca", "appearance_name_addr_spec_param", "")
...
```


#### db_url(string)


This is URL of the database to be used.


*The default value is "NULL".*


```opensips title="Set db_url parameter"
...
modparam("b2b_sca", "db_url", "[dbdriver]://[[username]:[password]]@[dbhost]/[dbname]")
...
```


#### db_mode(integer)


The b2b_sca module can utilize database for persistent call appearance storage.
Using a database ensure that active call appearances will survive
machine restarts or SW crashes.
The following databse accessing modes are available for b2b_sca module:


- NO DB STORAGE - set this parameter to 0
- WRITE THROUGH (synchronous write in database) - set this parameter to 1


*The default value is 0 (NO DB STORAGE).*


```opensips title="Set db_mode parameter"
...
modparam("b2b_sca", "db_mode", 1)
...
```


#### table_name(string)


Identifies the table name from the defined database.


*The default value is "b2b_sca".*


```opensips title="Set table_name parameter"
...
modparam("b2b_sca", "table_name", "sla")
...
```


#### shared_line_column(string)


The column's name in the database storing the shared call/line id.
See "shared_line_spec_param" parameter.


*The default value is "shared_line".*


```opensips title="Set shared_line_column parameter"
...
modparam("b2b_sca", "shared_line_column", "")
...
```


#### watchers_column(string)


The column's name in the database storing the list of watchers.
See "watchers_avp_spec" parameter.


*The default value is "watchers".*


```opensips title="Set watchers_column parameter"
...
modparam("b2b_sca", "watchers_column", "")
...
```


#### app[index]_shared_entity_column(string)


The column's name in the database storing the shared entity of a
particular appearance.
See "sca_init_request" for more info.


*The default value is "app[index]_shared_entity".*
Index is an integer between 1 and 10.


```opensips title="Set app[index]_shared_entity_column parameter"
...
modparam("b2b_sca", "app1_shared_entity_column", "first_shared_entity")
modparam("b2b_sca", "app2_shared_entity_column", "second_shared_entity")
...
```


#### app[index]_call_state_column(string)


The column's name in the database storing the call state of a
particular appearance.  The following states are stored:


- 1 - alerting,
- 2 - active,
- 3 - held,
- 4 - held-private.


*The default value is "app[index]_call_state".*
Index is an integer between 1 and 10.


```opensips title="Set app[index]_call_state_column parameter"
...
modparam("b2b_sca", "app1_call_state_column", "first_call_state")
modparam("b2b_sca", "app2_call_state_column", "second_call_state")
...
```


#### app[index]_call_info_uri_column(string)


The column's name in the database storing the call info URI of a
particular appearance.


*The default value is "app[index]_call_info_uri".*
Index is an integer between 1 and 10.


```opensips title="Set app[index]_call_info_uri_column parameter"
...
modparam("b2b_sca", "app1_call_info_uri_column", "first_call_info_uri")
modparam("b2b_sca", "app2_call_info_uri_column", "second_call_info_uri")
...
```


#### app[index]_call_info_appearance_uri_column(string)


The column's name in the database storing the call info appearance URI
of a particular appearance.
For each appearance, the value is extracted from the
"appearance_name_addr_spec_param" parameter.


*The default value is "app[index]_call_info_appearance_uri".*
Index is an integer between 1 and 10.


```opensips title="Set app[index]_call_info_appearance_uri_column parameter"
...
modparam("b2b_sca", "app1_call_info_appearance_uri_column", "first_call_info_appearance_uri")
modparam("b2b_sca", "app2_call_info_appearance_uri_column", "second_call_info_appearance_uri")
...
```


#### appindex_b2bl_key_column(string)


The column's name in the database storing the b2b_logic key of a
particular appearance.


*The default value is "app[index]_b2bl_key".*
Index is an integer between 1 and 10.


```opensips title="Set app[index]_b2bl_key_column parameter"
...
modparam("b2b_sca", "app1_b2bl_key_column", "first_b2bl_key")
modparam("b2b_sca", "app2_b2bl_key_column", "second_b2bl_key")
...
```


### Exported Functions


#### sca_init_request(shared_line)


This is the function that must be called by the script writer
on an initial INVITE for which an SCA call must be instantiated
(see the call from alice1 in the above diagram).


Meaning of the parameters:


- *shared_line* (int) - an integer
identifying the call leg as being an "appearnace" call or a "shared" call:
	* 0: "shared" call
	* 1: "appearance" call


```opensips title="sca_init_request() usage"
...
modparam("b2b_sca",
	"shared_line_spec_param","$var(shared_line)")
modparam("b2b_sca",
	"appearance_name_addr_spec_param","$var(appearance_name_addr)")
modparam("b2b_sca",
	"watchers_avp_spec","$avp(watchers_avp_spec)")

...

	# Setting the shared call identifier
	$var(shared_line) = "alice";

	# Setting the watchers
	$avp(watchers_avp_spec) = "sip:alice1@example.com";
	$avp(watchers_avp_spec) = "sip:alice2@example.com";

	if (INCOMING_SHARED_CALL) {
		# The incoming call is a 'shared' call
		$var(shared_line_entity) = 0;
		# Setting the appearance name address
		$var(appearance_name_addr) = $fu;
	}
	else {
		# The incoming call is an 'appearance' call
		# - see Alice's initial call leg in the given example
		$var(shared_line_entity) = 1;
		# Setting the appearance name address
		$var(appearance_name_addr) = $tu;
	}

	# Initiate the call
	if (!sca_init_request($var(shared_line_entity))) {
		send_reply(403, "Internal Server Error (SLA)");
		exit;
	}
...
```


#### sca_bridge_request(shared_line_to bridge)


This is the function that must be called by the script writer on an initial
"appearance" INVITE for an existing shared call.  It will bridge the current
"appearance" call with the existing "shared" call and the old "appearance"
call will be disconnected (see the call from alice2 in the above diagram).


Meaning of the parameters:


- *shared_line_to_bridge* (string) - a string identifying
the shared line/call that was previously set by sca_init_request().


```opensips
...
	if ($rU==NULL && is_method("INVITE") &&
		$fU==$tU && is_present_hf("Call-Info")) {
		# The incoming call is an 'appearance' call
		# - see Alice's call from alice2 in the given example
		$var(shared_line_to_bridge) = "alice";
		if (!sca_bridge_request($var(shared_line_to_bridge)))
			send_reply(403, "Internal SLA Error");
			exit;
		}
	}
...
```


### Exported MI Functions


#### b2b_sca:list


Replaces obsolete MI command: *sca_list*.


It lists the appearances belonging to a shared line/call.


Name: *b2b_sca:list*


Parameters: *none*


MI FIFO Command Format:


```bash
	opensips-cli -x mi b2b_sca:list
```
<!-- CONTRIBUTORS -->

### License

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