root/doc/PREPAID.txt

Prepaid functionality is achieved by:

1. An external session control module, not provided by CDRTool, that
maintains the session status and terminates the sessions by sending BYE
messages to both SIP end-points. The session control module communicates
with both the SIP Proxy and CDRTool using the API described below.

2. CDRTool rating engine - provides session management, calculates maximum
session time based on user balance and destination using the same algorithm
as the postpaid engine and debits the subscriber balance.

See doc/PrepaidEngine.pdf for a detailed session flow.


Prepaid API
-----------

CDRTool prepaid engine is used to compute session times based on user
balance and destination dependent rates and debit the balance when the
session has ended. The prepaid engine is accessible over the TCP socket
where the rating engine listens.

The TCP socket location is configured in /etc/default/cdrtool. The
connection can be tested manually using the telnet command and by typing
help at the prompt:

tstuser@host:~$ telnet 10.0.0.0.1 9024
Trying 10.0.0.1...
Connected to 10.0.0.1.
Escape character is '^]'.
Help
MaxSessionTime        CallId=6432622xvv@1 From=sip:123@example.com To=sip:0031650222333@example.com Duration=7200 Gateway=10.0.0.1 Lock=1
ShowPrice             From=sip:123@example.com To=sip:0031650222333@example.com Gateway=10.0.0.1 Duration=59
DebitBalance          CallId=6432622xvv@1 From=sip:123@example.com To=sip:0031650222333@example.com Gateway=10.0.0.1 Duration=59
AddBalance            From=123@example.com Value=10.00
GetBalance            From=123@example.com
GetBalanceHistory     From=123@example.com
DeleteBalance         From=123@example.com
DeleteBalanceHistory  From=123@example.com

In the example above only the commands related to the prepaid functionality
are highlighted.

The session control module must send commands based on the syntax described
below, to the CDRTool prepaid engine. A command is a line of text containing
a keyword, which is the command itself followed by a number of parameters
separated by space. The command ends with an enter in unix style: '\n' For
each such request there will be a reply on one or more lines, containing
information that depends on the command that was sent. A reply ends when a
double end of line (\n) is received: \n\n (this is needed because there are
commands that require multiline responses). How the information contained in
a reply is to be interpreted depends on the command itself and is described
below.


1. Asking for the session time limit
   ------------------------------

To request the maximum time for a new session, the following request must be
sent to CDRTool rating engine on one line:

MaxSessionTime CallId=6432622xvv@1 From=sip:123@example.com
To=sip:0031650222@example.com Duration=7200 Gateway=81.20.68.10
ENUMtl=tld.com\n

MaxSessionTime request is created when a new INVITE arrives at the SIP
Proxy/session control application. Depending on the session setup time, the
maximum session time might not be accurate because the session setup time is
unknown at the INVITE stage. You can call MaxSessionTime again when the
session has been setup (the OK has been received), in which case the rating
engine will provide the updated maximum session time for the session that
was in progress.

Duration is a limit imposed to the time allowed, in case you want to limit
the session time to a maximum duration. This will be a top limit for the
session's time, even if the user could talk more than that based on his
current balance. The session control module may limit all sessions to 7200
seconds for example.

To may actually be sip:number@domain;param=value so you must extract the
username part which is the number From is a sip URI which can be "full
name".

ENUMtld parameter is optional but if present discounts based on ENUM can be
applied (see RATING.txt for more information on ENUM discounts).

Call control expects a reply like below:

value\n\n

value is the numeric time in seconds, or None, None meaning it's not a
prepaid account and it doesn't have any limitation, or it's a free
destination, like a 0800 number.

To field must be the canonical destination SIP URI after all possible
lookups in the SIP Proxy.

2. Debiting the balance when the conversation ends
   -----------------------------------------------

To debit money from the user balance when the conversation ends, the session
control module must send the following command on one line:

DebitBalance CallId=6432622xvv@1 From=sip:123@example.com
To=sip:0031650222@example.com Gateway=81.20.68.10 Duration=59\n

Same notes about the From and To fields as above apply. The call id must
match the call id provided to the correspondent MaxSessionTime command.

and expects in return:

value
maxsessiontime\n\n

where value is one of: OK (success), Failed (failure), Not Prepaid (account
is not prepaid - this case is not considered a failure). 

The second line contains the new maximum session time that is valid after
debiting the balance for this session. It can be used to update the maximum
session time of other sessions that are already in progress for the same
user.

Note that once your have called once MaxSessiontime, you must also call the
correspondent DebitBalance even if the session has zero seconds duration. If
you do not do this, the session will stay in progress for the maximum
session time and any subsequent session setup will have its maximum duration
altered by this existing session in progress. Sessions in progress will be
automatically purged after they expire when a new MaxSessionTime request for
the same user is received.

The debited value and the new balance is recorded in the prepaid_history
table.

If the session does not exist, no balance will be debited. To force the
DebitBalance to debit the balance even if no session in progress exists, you
can supply Force=1 parameter. This can be useful if for some reason the
requests have been lost due to network problems. In such case the requests
can be applied at a later time.


Prepaid ongoing sessions
------------------------

To see the sessions in progress go to Rating -> Prepaid.

Fill in the Sesssions field: >0 and click Search.


Third party tools
-----------------

FreeRADIUS-CDRTool by Dan-Cristian Bogos 

FreeRADIUS module providing connectivity to CDRTool prepaid engine. Provides
prepaid authentication for sessions proxied by OpenSER and returns to OpenSER
MaxCallDuration and user Credit. Can be easily extended to support other SIP
or H323 devices.

http://sourceforge.net/projects/frad-cdrtool


Notes
-----

The balance is debited correctly regardless of the moment of CDR
normalization. Renormalization of sessions do not recalculate balance.


Simultaneous prepaid sessions
-----------------------------

Since version 6.6.0 is possible to have multiple sessions using the same
prepaid account without the risk of reaching a negative balance.

The modus operandi is based on a simple model: all prepaid sessions
belonging to the same account must end at the same moment regadless of the
called destinations and their different prices. The rating engine simply
calculates that moment based on the data available from ongoing sessions,
available balance and the new session setup request. This scheme provides a
fair balancing policy with small performance penalty on the servers.

By using this simple model there is no need to poll any database during
ongoing sessions, which could become major scalability problem. All the work
is done only once at session setup time. This will increase the load on the
rating engine only during session setup and only for the users that have
parallel sessions, the rating engine will perform internally during each
session setup 2 x the number of sessions sessions to ShowPrice and
MaxSessionTime functions. To be entirely accurate the session control must
also connect back to the rating engine when the session has been setup so
that the session expiration can be updated.

You must set $RatingEngine['prepaid_lock'] to 0 in etc/cdrtool/global.inc
and update the session control software module that keeps track of the
maximum session time to enforce session ending for all sessions belonging to
the same sip account at the same time based on the last value of
MaxSessionTime received from the rating engine. The previous version
required the session control module to keep the time counter per sip
session, now it needs to sync the counter for all sessions belonging to the
same sip account. See below the pseudo code for the session control engine.

The list of ongoing prepaid sessions can be monitored in the Prepaid
accounts section of the Rating pages. For each sip account that has ongoing
sessions a link marked Sessions apears in the left side of the prepaid
record. Click on it to display the ongoing prepaid sessions. The 'Delete
session' button allows the removal of the session form the rating engine.
The expired sessions that have not been closed properly by the session
control module are automatically purged 120 seconds after expiration, which
has been chosen to cover a reasonable session setup time.

The time and balance distribution between parallel sessions is logged
detailed in the syslog:

cdrtool[13292]: MaxSessionTime From=sip:adi@umts.ro Lock=1 To=sip:00318008185@umts.ro CallId=waaivgq89aTxmPIG6JIsPhODUe0tRVf- Duration=36000 Gateway=80.101.96.20
cdrtool[13292]: ConnectFee=0.0450 Span=1 Duration=16 DestId=31646 default Profile=442 Period=weekend Rate=442 Interval=0-24 Cost=0.1600/60 Price=0.0427
cdrtool[13292]: Ongoing prepaid session uw1znivnqoeofyezzuiiisudukw64cm- for adi@umts.ro to sip:0031646999425@umts.ro: duration=16, price=0.0877 
cdrtool[13292]: Balance for adi@umts.ro having 1 ongoing sessions: database=9.9534, due=0.0877, real=9.8657
cdrtool[13292]: Maximum duration for adi@umts.ro to destination 31646 having balance=9.8657 is 3700
cdrtool[13292]: Maximum duration for adi@umts.ro to destination 31800 having balance=9.8657 is 29597
cdrtool[13292]: Maximum duration agregated for adi@umts.ro is (Balance=9.8657)/(Sum of price per second for each destination=0.0030)=3288 s
cdrtool[13292]: CallId=waaivgq89atxmpig6jisphodue0trvf- BillingParty=adi@umts.ro DestId=31800 Balance=9.8657 MaxSessionTime=3288 Spans=2


Pseudo-code for rating engine
-----------------------------

This code is actually implemented in cdrtool.

max_session_time (session, from, to) { 
    list(balance,active_sessions)=get_prepaid_account_from_database();

    if (count(active_sessions[from]) > 0) {
        if (purge_expired_sessions()) {
            // reload prepaid data
            list(balance,active_sessions)=get_prepaid_account_from_database();
        }

        max=calculate_aggregated_maxsession_time(active_sessions[from],balance)
        return max

    } else {
        // is the first session
        rate = new Rate(session)          
        active_sessions[from][]=session         
        return rate->max_session_time()
    }
}

calculate_aggregated_maxsession_time(active_sessions,balance)  {
    // simulate session termination for all ongoing sessions
    foreach (session in active_sessions[from]) {
        due_balance=used_balance+show_price(session)
    }

    // calculate new virtual balance
    balance_new=balance-due_balance

    // simulate we start parallel sessions from scratch at this moment
    // including the new sessionn setup request
    // we skip any connect cost for session already in progress
    active_sessions_new[from]=active_sessions[from]
    active_sessions_new[from][]=session
    foreach (session in active_sessions_new[from]) {
        rate = new Rate(session)
        maxsessiontime=rate->max_session_time()
        // calculate price per second for each session
        price_per_second=price_per_second+balance_new/maxsessiontime
    }

    return balance/price_per_second
}

debit_balance(session, from, to, duration) {
    list(balance,active_sessions)=get_prepaid_account_from_database();
    foreach (session in active_sessions[from]) {
        if (session == session) continue
        new_active_sessions[] = session 
    }  
    // update list of active sessions 
    active_sessions[from]=new_active_sessions
    price=showprice(session,from,to,duration)
    balance=balance-price
    update_prepaid_account_to_database(balance,active_sessions);
    if (count(active_sessions[from]) > 0) {
        max=calculate_aggregated_maxsession_time() 
    } else {
        max=0 
    }
    return max
}


Pseudo-code for session control engine
--------------------------------------

on_session_setup () {
    max=cdrtool_max_session_time(session, from, to)
    if (sip_connect_session() == true) { 
        // add session to the list of active sessions
        // update tiomer again becuase we had a variable setup time     
        max=cdrtool_max_session_time(session, from, to)
        active_sessions[from][]=session
        // set maxsession time for all remaining sessions of the same user
        foreach (session in active_sessions[from]) {
            session.maxsessiontime = max
        }
    } 
}

on_session_disconnect () {
   sip_disconnect_session();
   max=cdrtool_debit_balance(session, from, to, duration)
   // remove session from the list of active sessions
   foreach (session in active_sessions[from]) {
       if (session == session) continue
       new_active_sessions[] = session 
   }  
   // update list of active sessions 
   active_sessions[from]=new_active_sessions
   foreach (session in active_sessions[from]) {
       session.maxsessiontime = max
   }
}