Application server (AS): Ass are responsible for user interface, billing and data storage. They indicates miniSipServer ( MSS ) to establish Callback connections.

MiniSipServer (MSS): MSS is responsible for receiving instructions from ASs and initiate, maintain and release VOIP connections. And most important, MSS is responsible for maintaining Callback service.

Peer SIP Server (PSS): provided by VOIP providers. PSSs are responsible for VOIP connections and media gateways.

1.1 Service descriptions

Callback service is a special service. The service is not initiated from a UE as normal but from an AS. AS will indicate MSS to establish VOIP connections with two user numbers and a maximum duration.

When MSS receives this instruction, MSS should establish a VOIP connection towards to user1 firstly. When the user answers the call, MSS will start a timer to monitor the call and begin to establish a VOIP connection towards to user2. When user2 answers the call, MSS should merge two call segments and establish connections between user1 and user2.

After the call is disconnect, MSS will response it to AS with the real duration.

Following sections describe the interface between AS and MSS.

1.1.1 IIF definition

IIF is text-encoded message. An IIF message is either a request message from AS to MSS, or a response message from MSS to AS.

IIF message = Method: SP Parameters.

‘Method’ should be uppercase and ‘Parameters’ should be lowercase.

1.1.2 IIF Method

In current version, there are three methods: REQUEST, ACK and RESPONSE.

REQUEST message is used by AS to indicate MSS establish callback service.

ACK is a response message to indicate AS that MSS has parsed the REQUEST message and begin to establish call sections.

RESPONSE is from MSS. It carries the real duration of current call

1.1.3 IIF parameters

Parameters have two parts. One is parameter name and another is parameter value. They are always formatted as following.

Parameter = “parameter name=parameter value”.

Parameters are separated with ‘;’

For an example, here is a demo parameters string. “id=1234;user1=100;user2=101”. In this demo, there are three parameters: ‘id’, ‘user1’ and ‘user2’.

Following sections define details parameters for IIF methods.

1.1.3.1 Parameters in REQUEST message

Parameter Name	Unit	Length	Description
id	string	less than 32 characters	Call section identity
user1	string	less than 32 characters	User 1. The called party in the first call.
user2	string	less than 32 characters	User 2. The called party in the second call.
duration	integer		It indicates how many seconds current call section can process.

For example:

REQUEST: id=1234;user1=100;user2=101;duration=3600;

It means AS request a CALLBACK service. The service or the call is identified by call ID ‘1234’. In this request, the first called party is ‘100’, and the second called party is ‘102’. After the first called party answers the call, the whole call process can continue about 3600 seconds.

1.1.3.2 Parameters in ACK message

Parameter Name

Unit

Length

Description

string

less than 32 characters

Call section identity. It is the same parameter in REQUEST message.

code

string

It indicates whether the request message is processed.

There are only two values.

ok or fail.

For example:

(1) ACK: id=1234;code=ok;

(2) ACK: id=1234;code=fail;

1.1.3.3 Parameters in RESPONSE message

Parameter Name	Unit	Length	Description
id	string	less than 32 characters	Call section identity. It is the same parameter in REQUEST message.
real_duration	integer	-	It indicates how many seconds current call continues.

For example:

RESPONSE: id=1234;real_duration=180;

It means both users have talk for about 180 seconds and then the call is released.

1.2 Definitions, symbols and abbreviations

AS Application Server

IIF Inner Interface

MSS miniSipServer

OAM Operator and Administrator Management

PSS Peer SIP Server

UE User End

2 Configuration

There are three kinds of configurations we shall prepare for callback service.

(1) Callback service configuration; This is service configuration.

(2) External line configuration; this is configuration for establishing connection with PSS.

(3) Peer servers configuration; this is configuration for establishing connection with AS.

2.1 Callback service

Please click menu ‘serviceàcall back service’, then below dialog shall be showed and configured.

Items	Description
Local listen port*	This is the port which MSS will open to receive instructions from AS. When this item is updated or modified, we should restart MSS to enable it.
Audio codec	It indicates audio codec which MSS is able to transfer. We suggest you to select ‘G711a’ or ‘G711u’ since most VOIP providers cannot support G.729.
External line mode	It indicates whether MSS shall connect to VOIP providers with external line.
Default caller	It can be NULL if ‘external line mode’ is selected, and then the caller number will be the external line number. But if ‘external line mode’ is un-selected, it means MSS will connect to VOIP providers’ server as ‘server to server’ mode and the ‘default caller’ should not be NULL since some VOIP providers’ reject NULL caller number.

2.2 External line

In above configuration, if ‘external line mode’ is selected, then we must configuration external line to connect VOIP providers.

Please click menu ‘dataàexternal lines’ to continue this configuration. We have to mention that the external line must be set to share outgoing call with other local users, then CALLBACK service logic can use this external line to initiate outgoing call.

Please refer to chapter 5 of MSS manual document for details.

2.3 Peer server

MSS will only receive the instruction form the servers which have been configured in ‘Peer server’. Then, we must add AS host and port into ‘Peer server’

Please click menu ‘dataàPeer servers’ to continue this configuration. We have to mention that server host address and port shall be configured rightly; otherwise, MSS will reject the CallBack request instruction.

Please refer to chapter 7 of MSS manual document for details.