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Case Study: Risk Assessment of an Enterprise Call Accounting Solution


Part 1: Background of the Analyzed System

Abstract

This paper describes a customer case study of a threat analysis for a next generation call accounting solution. Campton College, a private medical school, needed to replace an aging call accounting system, which frequently lost call records and lacked the capability to provide unified campus-wide telephony billing features. Campton wanted to create an integrated Web based call accounting system that would service student dorms and administrative departments. The institution contracted with TACS, a call accounting solution provider, to replace the old software and provide a modern, Web-based solution that would be cheaper to own and easier to use. Faced with a steep bill for information security, Campton contracted with Software Associates in order to find a way to reduce liability at the lowest possible cost. By using the PTA risk assessment tool, Software Associates was able to demonstrate to Campton how to reduce risk from 250% to 50% at less than half the original InfoSec budget proposed by the vendor.

The TACS managed call accounting service in a nutshell

TACS offers small to mid-sized clients a managed service for call accounting that includes basic billing functionality and is capable of collecting and processing call detail records from variety of sources. The user interface is Web-based and caters to four different types of users: PBX technicians, administrators, phone users and organization managers.

Technicians - TACS technicians are responsible for installing the CDR (call detail records) buffer devices connected to the PBXs for accumulating the calls. A technician defines the parameters of the protocols used by the buffer, data collection schedule, format of call records and performs initial testing of data collection in order to validate that the calls are collected and parsed successfully by TACS data back-end data processing systems.

Administrators - Customer administrators handle ongoing management of the telephone switch resources and subscribers as follows:

  • Allocate phone-extensions and other telephony resources, such as cellular phones etc.
  • Set the pricing programs that calculates and attaches a price tag to each call
  • Define phone users and system users
  • Associate users with telephony resources and pricing programs
  • Manage system access permissions

Subscribers (phone users) - Subscribers can view and print the detailed listings of their private calls and their monthly bills.

Managers - User department Managers can produce reports that summarize calls traffic and the usage of telephony resources in the organization. They also monitor the billing and payments of phone users.

System Architecture

The TACS system ASP architecture is based on Microsoft Windows Server 2003 that runs several .Net applications responsible for the call accounting processing, and a suite of web applications that interact with users via browsers (IE 5.5 and higher). The system’s database is managed by a stand alone MS SQL 2000 machine connected to the application server via LAN.


Database

The TACS MS SQL Server 2000 stores all types of system data, including call records, pricing programs, users, organizational structure and system configuration. The CDR tables can handle several million records per month and are indexed by a multiple fields to support rich reporting.

The SQL Server scheduler mechanism is used to schedule and dispatch the data collection activities.

Processing

The processing of CDRs has 3 stages:

- Data Collection – collecting the calls from the CDR buffers. The output is blocks of raw CDR data.
- Parsing and reformatting - the output is structured call records in a uniform format invariant to origin of the calls.
- Load to database - call record are associated with the corresponding end point device, subscriber id and telecom provider and then inserted to the database.

The implementation is based on a several Windows services that use worker components to implement the required functionality. For example, the data collection service operates several different ‘collector’ components to collect the call records from different data sources via the appropriate protocols. Campton College operates 3 PBXs from different vendors: Avaya, Siemens and a small Cisco VoIP switch. The operating parameters of the components are kept in the database.

The data is transferred between the 3 processing stages via MSMQ private queues that serve as non-volatile buffers for data in process.

The service processes and some of the worker components were developed using .NET technology. Other worker components are legacy Win32 components wrapped with .NET Interop layer.

Web applications

The Web Applications are implemented in ASP.NET combined with Microsoft reporting engine. Some of the applications are capable of directly viewing and editing data tables in the database via ASP.NET server side controls.

In the TACS system, all Web applications share the same infrastructure for user login and secure access to the database.

Pricing, database maintenance and data exchange

The pricing, database maintenance and data exchange tasks are implemented with a Windows service that uses worker components to perform the actual tasks, similar to the call records processing architecture. The tasks are executed in a periodical manner according to the system’s schedule.

Download the Threat Analysis of the Enterprise Call Accounting Solution
 

The PTA threat analysis and risk assessment project of the Enterprise Call Accounting and Billing Solution is packed in a WinZip archive CallAccountingCaseStudy.zip. The archive contains the sample threat model database (a file with thm extension) and a few document files relevant to the project (doc and pdf). After downloading the archive, please extract the files to a dedicated folder according to your convenience and than invoke PTA* and open the thm database using the File / Open PTA Project dialog.

*Note: to view the sample threat model you should have the PTA Risk Assessment Tool installed on your computer.

 

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Next (part 2): Conducting the Security Risk Assessment
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