Messaging: SMS, MMS


Short Message Service (SMS) is a communication service component of the GSM mobile communication system, using standardized communications protocols that allow the exchange of short text messages between mobile phone devices.

Call scenario in which Aparty (sender) of a mobile operator (Home network) send SMS to Bparty(Receiver) at same network.

SMS traffic routing

At MSC:

1: MO SMS CDR will generate for Aparty(sender) .which includes Sender ,Receiver information (MSISDN),Time stamp, date and time.

2: MT SMS CDR will generate for B party (Receiver) end.

SIMBOX fraud detection


What is SIMBOX:

A SIM box is device that maps the call from VoIP to a SIM card (in the SIM box) of the same mobile operator of the destination mobile,so that international call terminating as home call to subscriber country and usually cheap compared to the cost of terminating the international call.This is to just bypass international traffic.Commonly, SIM boxes are used to perpetrate bypass fraud, so we shall use this technique for illustration.

Normal call flow from Visitor country to home country Subscriber

In case of SIM BOX, call routing like

In this figure sim box is working as a ‘plug-in and work’ box that contains a mobile SIM card that is connected to a PBX or router. It can automatically reroute a call that would take place on a mobile network to a lower cost fixed or IP network.

Detection of fraud can be some what tricky because in some cases.

  1.  Some SIM boxes uses IMEI management.. which changes their IMEI constantly making it difficult to detect.
  2.  MSISDN’s are also changes regularly.

In general, the fraud can be analyzed with constantly looking various calling parameters. Further these parameters can classified into Indicators. These indicators can be used to analyze frequent usage of MSISDN and IMSI for RA perspective  .

The Indicators are based on;

  1. High volume of calls from the same MSISDN’s and IMEI’s.
  2. High volume of calls from the same cell id (this boxes are located in an office).
  3. Last recourse would be to call terminating customers and try to find out about the quality of the calls.

For shake we divide indicators.

  1. Indicator 0 – Flags high incoming calls from other carriers for potential simbox terminating to Aparty.
  2. Indicator 1 – Flags high outgoing calls for potential simbox operators and other form of fraud/abuse in usage
  3. Indicator 2 – Flags high SMS for potential abuse in usage or virus mobile phones
  4. Indicator 3 – Use to detect high usage subscribers for potential fraud/abuse in usage
  5. Indicator 4&5 – related IMEI/IMSI stuffing

Telecom Mediation


Mediation is the process of collecting and processing usage data from networked devices, usually for billing purposes.

At Mediation there are following tasks performed.

  • Collecting and validating CDR from network elements (Switches / MSC’s)
  • Filtration (non billing CDR’S)
  • Correlation of different input sources CDR’s
  • Aggregation of partial CDRs related to the same call.
  • CDR normalization.
  • Transformation of data as per business logic.
  • Downstream Format mapping ,header and trailer generation
  • Downstream Distribution

Mediation Flow

Function of Mediation system

Whenever a Subscriber / Customer uses communication services (Voice, Call,SMS ,Data transfer etc ) from a Service Provider,Usage Data are generated at the network element.
The usage data is called as Call Detail Record (CDR) in the traditional voice network environment or Internet Protocol Detail Record (IPDR) in the data network environment. Some of the Service Usage Data sources in the network are:

GSM telephony Network Elements
    GSM telephony
    Voice calls – MSC
    SMS traffic – SMSC
    Data traffic – GGSN
    MMS traffic – MMSC
    Roaming CDRs from business partners
    Interconnect CDRs from partners

The CDRs are normally pushed to or pulled from the switches. The switch generates a CDR file. These file contains header or trailer records containing the number of CDRs in a particular file. The files are generated as they reach a specified count or at regular time intervals.

There are various protocol supported namely  FTP, SFTP, FTAM, X.25.SNMP.SFTP provides a secured way of collecting the CDRs as it uses SSL.

Once CDR file received mediation software pre process  the CDR, This process involves removal of header and trailer , adding extra filed in CDR to process and finally parsed to check with switch format to validate CDR.

Some mediation software collect CDR from network element at physical path then process it, while some collect the same in buffer and after process , one final CDR is sent for further process and one file sent to Archive directory.

A typical mediation workflow:

Interconnect Billing


The Interconnection refers to scenarios where traffic crosses different networks. When the call enters the home network the operator charges the Interconnect partner for using his network. When the call leaves the home network the operator has to pay the Interconnect Partner for using his network.

If any operator is sending/receiving of calls to/from other operators (outside the network) then both the operators needs to be interconnected i.e. both operators should have a network based interconnect to send/receive calls to/from the network. The routing of call based on trunks (a physical wire connected at switch level). When the call comes from other network to home network this call treated under inbound and the operator charges the Interconnect partner for using his network.  When the call goes to home network to the other operator network  is termed at outbound and the operator has to pay the Interconnect Partner for using his network.. This setup requires some kind of billing mechanism to monitor the actual amount of data (send/received).

Network diagram:  A party (Home network) calling to B party at another interconnected network:


The operator who finally receives data (Voice or SMS)  from other B Party operator is know as Terminating partner and call detail of A Party is treated as Mobile terminating call (MTC) while Bparty operator is known as Originating Partner and call details (call type) of Bparty is treated as Mobile originating calls (MOC).

Beside this operator can works as Transit Network i.e. it receives data (voice or SMS) from one operator and delivers it (as it is) to any other operator.  To transfer data (voice or SMS) to various destinations, general purpose carriers are used that sends data according to the country code.

In Interconnect scenario. Mobile operator has agreement with various business partners for routing the calls.

The agreement is all about:

  1. Handling the call
  2. Rating terms
  3. Paying terms
  4. Billing terms.
  5. Data Exchange terms

When a home subscriber calls a number which is routed through external network of business partners, the external network invoices the home network for a call depending on the traffic volume and may send call details. The home network pays the invoices and bills this to customers. This is called interconnect outbound

When a home subscriber receives a call from external network the external network pays the invoices in terms of volume usage of home network .This is called interconnect inbound.

Traffic scenarios  discussion:

Interconnect outbound:In this case A party of home network calling to B party of external network.

AT home location:

  • MOC CDR generated which contains Information of A party IMSI, ICCID, Mobile number,Calling party number,Cell ID, Timestamps, duration of calls, Trunks groups information.
  • An Transit CDR is generated for calling party at each additional MSC. This contains information about routing trunk group.

Interconnect Inbound: In this scenario B party from external network call to A party at home network and thus home network trunks is needed to terminate this call.

At home network:

  • Mobile terminating call record generated.
  • Roaming call forwarding (RCF) generated at very first MSC.

Billing process:

Consider a call originating in the home network of the subscriber, and terminating at a destination in a different network. Several transit networks can be involved. Each network collects CDR‘s at its own switches for billing and reconciliation. Basically, incoming traffic will be billed for, and outgoing traffic relates to reconciliation.

When a new telecom operator is registered, a contract is signed. Contract is signed for both Incoming and outgoing calls. Trunks are configured at switch level to routing the calls and trunks group is defined for various operators (Inbound/Outbound). In general two types of charging policies:

  • Distance based charging
  • Destination based charging

Rates depend on the charging policy, if it is destination based billing then rates is specified according to the area code of terminating destination. While In distance based billing, rates are specified according to different zones.

CDR Collection process for billing

In general billing (Inbound/outbound) is done using total answer minutes routed through trunks. The incoming trunk and out trunk information is taken from call details (CDR’s). We also analyze traffic and monitor utilization trunks over switch.

Interconnect SMS scenario