Current Telecom Networks provide functions that implement offline and/or online charging mechanisms on the bearer (e.g.GPRS), subsystem (e.g. IMS) and service (e.g. MMS) levels. In order to support these charging mechanisms, the network performs real-time monitoring of resource usage on the above three levels in order to detect the relevant chargeable events.
Offline charging is a process where charging information for network resource usage is collected concurrently with the resource usage. The charging information is processed offline to charge the subscriber post resource usage at periodic billing dates. The subscribers are generally billed for the resource usage at a later scheduled billing date. However in certain circumstances, a telecom operator may still impose an upper threshold limit on resource usage beyond which usage is restricted unless the subscriber clears the outstanding dues to date.
Offline charging thus presents a mechanism where charging information does not affect, in real-time, the service rendered.
Online charging is a process where charging information for network resource usage is collected concurrently with that resource usage in the same fashion as in offline charging. However, authorization for the network resource usage must be obtained by the network prior to the actual resource usage to occur. The authorization phase generally involves reservation of charges for the desired resource/service followed by an actual charge to the subscriber immediately after its usage. This authorization is granted by the Online Charging System (OCS) upon request from the network (Charging Trigger Function ; CTF) . The resource usage authorization may be limited in its scope (e.g. volume of data or duration), therefore the authorization may have to be renewed from time to time as long as the user’s network resource usage persists. The Online Charging system thus imposes the end-users to have a prior authorization in terms of account balance or pre-paid subscriptions etc to use a service/resource.
Online charging is a mechanism where charging information can affect, in real-time, the service rendered and therefore a direct interaction of the charging mechanism with the control of network resource usage is required.
Charging Systems – Architecture
For Online systems, the Charging Trigger Function (CTF) generates charging events based on the observation of network resource usage. The charging events are forwarded to the Online Charging Function (OCF) in order to obtain authorization for the chargeable event / network resource usage requested by the user. The CTF must be able to delay the actual resource usage until permission by the OCS has been granted. The CTF must be able to track the availability of resource usage permission (“quota supervision”) during the network resource usage. The CTF must be able to enforce termination of the end user’s network resource usage when permission by the OCS is not granted or expires
The Online Charging Function (OCF) consists of two distinct modules, namely the Session Based Charging Function (SBCF) and the Event Based Charging Function (EBCF).
The Session Based Charging Function is responsible for online charging of network / user sessions, e.g. voice calls, GPRS PDP contexts or IMS sessions.
The Event Based Charging Function performs event-based online charging.
The Rating Function (RF) determines the monetory/non-monetory charge value of the network resource usage received by the OCF from the network on behalf of the OCF. The OCF furnishes the necessary information,obtained from the charging event, to the RF and receives in return the rating output (monetary or non-monetary units). The RF may handle a wide variety of rateable instances, such as:
• Rating of data volume (e.g. based on charging initiated by an access network entity, i.e. on the bearer level);
• Rating of session / connection time (e.g. based on charging initiated by a SIP application, i.e. on the subsystem level);
• Rating of service events (e.g. based on charging of web content or MMS, i.e. on the service level).
The Account Balance Management Function (ABMF) is the location of the subscriber’s account balance within the OCS.
Online Charging Systems generally support two modes of Rating and Charging.
• Event Based Charging: The requested resource is determined and billed in a single shot. The resource usage is debited in a single shot from the subscriber account immediately after processing the charging event, and the permission for the resource usage is returned to the network. An example of this is charging a fixed cost from the end user for downloading an MMS.
• Session Based Charging: the OCS cannot a priori know the amount of resources that the end user may eventually consume, or it cannot be assumed a priori that the resource usage request can be (completely) fulfilled. In this case, a certain amount of (monetary or non-monetary) units is blocked, or reserved, on the subscriber’s account on the OCS, and permission to use an amount of resources that matches the unit reservation is returned to the network. When the granted units have been used or a new, not yet authorized chargeable event occurs, the network must send a new request for unit allocation to the OCS. When resource usage has been executed, the actual amount of resource usage (i.e. the used units) must be returned by the Network to the OCS so that eventually over-reserved amounts can be recredited to the subscriber account, assuring that the correct amount gets debited.
Thus for Online Session Based Charging Systems, there are multiple Resource-Request and Resource-Grants message exchanges during the session until the session ceases on account of unit exhaustion or voluntary termination by user.
Online Charging Systems and Network generally implement fixed Resource-Request and Resource-Grant UNITS for handling a session. Eg An OCS system may have a definite value of “Time” units, that it might grant in response to all the Network requests during voice sessions. Similarly they might have another fixed “Volume” units that it might grant in response to all the Network requests during Data sessions.
The fixed Unit Request-Grant based approach results in following anomalies
1. Sessions in which the actual desired/consumable units are much less than the standard units requested by Network and granted by OCS ; an over-reservation of monetory/non-monetory units at OCS results in un-necessary locking of units that might have been used in other concurrent sessions initiated by the end-user.
2. Sessions in which the actual desired/consumable units are much more than the standard units requested by Network and granted by OCS ; an under-reservation of monetory/non-monetory units at OCS results in un-necessary request-grant messages being exchanged between the Network and OCS. This results in undesirable OCS Overloading and poor utilization of network resources.
The following invention presents an exponential smoothing based statistical model for deriving Optimum value of Request-Grant Units for each OCS-Network exchange in session based charging systems. This ensures most optimum network utilization by minimizing message exchanges between the OCS and Network Systems , in addition to optimizing the extent of unit reservations for an end-user per request.
The simplest form of exponential smoothing is given by the formulae:
S1 = x0
S t = α xt-1 + (1- α) s t-1 = s t-1 + α (x t-1 – s t-1) ; t>1
Where α is the smoothing factor and 0 t is a simple weighted average of the previous observation x t-1 and the previous smoothed statistic. Values of “α” close to one have less of a smoothing effect and give a greater weight to recent changes in the data., while the values of “α” closer to zero have a greater smoothing effect and are less responsive to recent changes.
Variable End-User Consumption Rate Sessions :
These refer to the Online charging Sessions such as internet browsing where the consumption of units (i.e Volume) varies according to the end-user access frequency and available bandwidth. i.e consumption is non linear with time.
The exponential smoothening formulae may be used to derive an optimum value of Request-Grant Units for each OCS-Network exchange in a Variable End-User Consumption Rate session based charging scenarios.
The exponential smoothing formulae may be re-written as :
1. (Expected unit consumption rate at T=1) 1 = Standard-Operator chosen value
2. (Expected unit consumption rate at T=t) = α (Actual Recorded Consumption Rate at T=t-1) +(1- α) (Calculated Expected unit consumption rate at T=t-1)
3. (Variable Granted units value for request at T=t) : Desired message spacing in time space * Calculated Expected unit consumption rate at T=t.
(e.g A desired message spacing of 100 sec implies that it is desired to have a space of 100 seconds between each outgoing request-grant message exchange between the OCS and the network.
Illustration, comparing the standard unit Request-Grant Approach and the proposed Variable Units Request-Grant Approach :
Standard Fixed Unit Request-Grant based Approach
1. Standard Granted Units per request = 1000 KB
2. Consumption Rate = (Granted Units per request / time lag between two subsequent network requests)
Request-Grant Exchange Times between OCS and Network: See Attached Calculation Sheet (Image 4 and 5)
Image 1 Message Exchanges in the given time space for delivering a 20000 Kb Payload using Standard Fixed Unit Request-Grant based Approach
Variable Unit Request-Grant based Approach
To achieve best possible evenly spaced message exchanges between the OCS and Network in the given time space for delivering a definite payload to the end subscriber.
Let’s assume that the desired spacing between the message exchanges in 100 seconds.
And α = 0.6
Consumption Rate = (Granted Units per request / time lag between two subsequent network requests)
The Variable Granted Units per request are calculated as : See Attached Calculation Sheet Image 4 and 5
Figure 2 Message Exchanges in the given time space for delivering a 20000 Kb Payload using Variable Unit Request-Grant based Approach
Number of Message Exchanges for delivering a payload of 20000Kb using Standard Fixed Unit Request-Grant based Approach = 20
Number of Message Exchanges for delivering a payload of 20000Kb using Variable Unit Request-Grant based Approach = 12
Bandwidth Improvisation : (20-12)/20 % = 40 %
Fixed End-User Consumption Rate Sessions
These refer to the Online Charging sessions such as Voice Calls where the consumption of units (i.e Time) is time linear :
For deriving the request-grant unit value for Fixed End-User Consumption Rate Sessions , exponential smoothing may be applied to the historical usage patterns of the end user to derive a standard request-grant unit value for the complete session.
In one implementation, an operator may define various levels of users based on service usage pattern and corresponding weights.
For instance, depending on Telecom Operator Choice end users making an average voice calls of less than 2 minutes may be termed as Very Light Users , while those making an average voice calls of more than half hour may be termed as Very Heavy Users.
Very Light Usage
Very Heavy Usage
Granted unit Values M (eg in sec)
The exponential smoothing formulae may be re-written as :
1. (Expected Usage Weight for the first session) 1 = Standard-Operator chosen value (eg :1 )
2. (Expected Usage Weight for the current session) = α (Actual Usage Weight for the previous session depending on how long the session continued) +(1- α) (Expected Usage Weight for the previous session)
3. (Granted units value per request, for a session) : “M” * Expected Usage Weight for the current session where “M” is the standard Grant units value chosen by the operator.
Consider the Following 10 voice sessions of a subscriber. M=60 ; a=0.6 See Image 4 and 5
The Actual Usage weights have been assigned according to the actual usage of the end user.
Total Number of Requests over 10 sessions as per fixed – standard request-grant unit value approach = 257
Total Number of Requests over 10 sessions as per fixed – standard request-grant unit value approach = 97
Bandwidth Improvisation : (257-97)/257 % = 62.2 %