Thursday, April 26, 2012

'Missed' Call Revenue

Huge chunk of GSM operators’ revenue gets wasted in the current implementation where missed calls remain uncharged.  Proposed idea suggests modification of existing GSM billing solutions by charging missed voice calls optimally so that revenue of GSM Service Provider is not lost by being unable to charge even though radio spectrum/core network resources are wasted in establishing a GSM voice missed call, and at the same time the common man can avail affordable mobile connectivity.

User will additionally pay for network usage during a missed call depending upon how far and how long the radio connection was established. Software architecture enhancements are required on the existing accounting framework related RADIUS protocol or its extension: DIAMETER client/server based protocol’s Ro interface for pre-paid online charging and Rf interface for post-paid offline charging. RADIUS/DIAMETER protocols work on application layer of OSI model and Attribute Value Pairs codes form the basic unit inside these messages .AVPs need to be extended to issue following new missed call related command codes, to be used for both requests and answers:
1. Credit lost in sending missed calls
2. Missed calls related tariff plan information
3.   Calling and called party initiating missed call
4. Life cycle of missed call activity
5. Free missed call quota reached / Missed call balance after tariff plan change

Application error handling and Finite State Machines for RADIUS/DIAMETER protocol will be further extended to support missed call accounting related messages. Credit control of subscriber’s account under different billing scenarios like normal call / missed call charging, SMS, internet usage etc. should have a single account balance.

SW should be able to analyze a mobile originated missed call in real time by intelligently interpreting the termination reason of the GSM voice call and compute the network usage time during the missed call flow. The missed call rating unit should be the number of milliseconds after the ringing bell starts echoing in the calling party’s mobile. The minimum rating units required in user’s account balance to initiate a complete missed call will be similar to existing normal call’s minimum rating units. Charging rates for missed call further need to be classified under following criteria:
1. QoS precedence classes for mobile user
2. Area/Country code, Time (peak hours/night hours)
3. No. of audible ring tones to calling party before disconnection (linear pricing model)

SW changes are also required at the network elements which help in evaluating a call as missed call as per missed call criteria specified below and the existing rating and mediation engine where complete information about mobile originated missed calls is received for further charge computation for the mobile subscriber depending upon his tariff plan.


1. Mobile A initiates a voice call, Intelligent Network Application Part checks sufficient balance in the calling mobile account. If exists, connection is established and duration of the call is monitored, else Service Control Point is informed to reject the request  which is having direct interaction with the charging mechanism.
2. If the call remains unanswered, the ringing duration, type of service (roaming, call to PSTN, PLMN, national/international call etc.) is stored temporarily in the database for calculating last missed call charges later.
3. If the call is returned as busy/unattended, various missed call criteria are evaluated If fulfilled, in addition to the normal pre-paid billing process, the caller’s balance account is further updated by making appropriate deduction as per subscriber’s tariff plan.
4. The missed call count and the type of missed call i.e. Local/National/international is also maintained for maintaining different tariff plans provisions.
5. Before mobile A makes any other next call, the updated balance account is further checked as described in step 1.



For post-paid subscribers, there is no need to check the balance before subscriber wants to use the network.
In addition to the normal post-paid billing process, the missed called criteria evaluation and billing related information is also captured in the Call Detail Record. The missed call count as explained for pre-paid is also maintained.
Based on the information stored in the CDR, the call parameters are further analyzed in the mediation engine if it can be charged as per missed call specifications.

Following scenarios should not be treated as missed call:
A call missed while the called party was on another call.
Missed calls to India’s national emergency number 2611 or other national/regional emergency numbers like 100 (POLICE), 101 (FIRE) etc.
Missed calls to Customer Care numbers should not be charged as these numbers may be busy or unattended/ legalized services providing free information via SMS to mobile user who give a missed call to their special numbers.
False bell ringing due to network error/Call ringing discontinued due to sudden loss of radio network.
All other scenarios, where call is not picked by called party or discontinued by calling or called party should be considered as missed call. If the called party does not respond in the complete call duration, then though ignoring misuse of this waiver by mobile user, it should be treated as a missed call as of now.


  Various sub-plans can be introduced to offer different number of free missed calls as per user’s usage just like free SMS and free talk-time. When user exceeds that count, he should be sent an alert SMS.
  The missed call charging rate range should be fixed by GSMA authorities for all service providers, to avoid exploitation of common man by different SP; users should be educated about SMS usage as alternative to missed call which comparatively takes less GSM resources.


The missed call record sent from mobile should be available to user to report any suspected fraud, normally routed via a VOIP system. Swindlers hire many premium rate numbers from different SP and using automated systems keep giving missed calls to people on a random basis. Even if 1/3rd of the called parties call back, they make profit by making callers pay a higher charge and playing automated reply messages to attract further. Using Q.931 codes, ways can be devised to detect such automated missed call flows to public.


1. Enhanced radio spectrum usage, increased SP revenue, more availability of radio spectrum to needy subscribers in emergency
2. Helps curbing eve-teasing activities/phishing activities initiated via missed calls


DIAMETER Credit Control Application- RFC 4006;  3GPP TS 32.299;
Created awareness against GSM misuse at  web- link: