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Feature Article
July 2002

Steps For Success In Testing IP Telephony


Phenomenal growth in the IP sector is reshaping the future of voice traffic, driving the integration of multimedia, and leading to network convergence. Network equipment manufacturers and service providers are rapidly creating IP telephony products and services, deploying them into the marketplace even as IP standards continue to evolve. To be successful, equipment manufacturers must ensure that their new products are compliant with the appropriate standards, are compatible with other network devices and can provide the necessary performance. The complexity of today�s networks � owing to their greater size, their need to support rapidly evolving communication standards, and the dictates of legacy infrastructure � makes testing network equipment more challenging than ever.

Faced with this challenge, what measures need to be taken in order to deliver IP telephony products that integrate smoothly and perform reliably? Although there are many approaches to testing, the following steps are almost always required for success:

  • Verify features and functions. As IP products have become more complex, basic product testing has become more critical than ever. Each design feature must be individually checked and each function must be individually proven to work. Typically this is done by comparing the manufacturer�s product design specifications against the operating characteristics of the product under development.
  • Confirm compliance with industry standards. Today IP standards are mainly being set by the Internet Engineering Task Force (IETF) and the International Telecommunication Union (ITU). Products must be tested for compliance with the relevant specifications produced by these organizations. If compliance can be shown, a first level of confidence can be established that the product can work with other standards-compliant equipment. One way to confirm compliance to standards is to use a third party to provide an independent assessment. Standards are being revised and upgraded frequently so attention to this topic must be ongoing.
  • Verify network interoperability. New IP products must communicate with network nodes that may be produced by multiple vendors. One approach to interoperability testing is to buy or lease those network node products � sometimes a prohibitively expensive proposition. A more economical approach is to acquire a test system that can emulate those same network nodes. Strong interoperability testing in the lab generally spells interoperability in the field.
  • Load-test the product. Networks are expanding in size and traffic loads are growing rapidly. So a critical question is: �What is the load capacity of a new product and what happens when that load is exceeded?� By using an appropriate test system, the new product can be driven to produce load data. Moreover, the test system can be used to stress-test the product to determine when load saturation occurs and what happens when that saturation level is exceeded. Based on this data, the manufacturer can determine whether the new product can handle the required load or not.
  • Perform installation and acceptance testing. It is impossible to test everything in a laboratory environment, and the risk of real world surprises can be great. So even though a new product passes the above tests in the laboratory equipment, a test system can be used to further test and/or monitor the new product as it is being installed in the field. Appropriate beta testing and phased roll-outs are accepted ways to reduce the risks of field deployment.

Today, both H.323 and Session Initiation Protocol (SIP) standards coexist in the IP world. This coexistence adds complexity in that IP telephony networks must be able to support a variety of networking scenarios. Besides supporting IP to IP communications, both H.323 and SIP networks must be able to interwork with legacy Public Switched Telephone Networks (PSTN) and advanced cellular networks. This interworking involves a variety of call scenarios (Figure 1).

For example, consider a manufacturer that is developing a SIP Media Gateway Controller (MGC) to provide IP internetworking with the PSTN network. The MGC must communicate with the other SIP network nodes such as the Media Gateway, Signaling Gateway, and SIP Agent. Recognizing the limited time and resources available to develop internal test tools, the manufacturer has acquired a third-party system to emulate these nodes (Figure 2). As usual, there is heavy pressure to get the new MGC to market as soon as possible. Nevertheless, the manufacturer is committed to quality and will not stint on the necessary testing steps.

Step 1. Verify the features and functions of the MGC. The new MGC must perform the required features and functions of a MGC including, for example, registration, admission, and resource allocation. By using the test system to simulate a SIP Agent, a Signaling Gateway, and a Media Gateway, the manufacturer can test the MGC in a standalone environment.

Step 2. Confirm that the MGC complies with industry standards. More specifically, the MGC must conform to the signaling protocol (SIP), the signaling transport protocol (SIGTRAN), and the media gateway control protocol (H.248/Megaco). Without this conformance the new product is very likely be a proprietary solution with career limiting implications. By building the required SIP, SIGTRAN, and H.248/Megaco protocols on the test system, the manufacturer can perform the necessary tests to prove protocol compliance.

Step 3. Test that the MGC can support interoperability between the IP network and the PSTN. Instead of spending the time to develop internal test tools or the money to purchase the actual network equipment, the manufacturer can use the third-party test system to emulate a SIP Agent (to establish SIP calls), a Signaling Gateway (to generate SIGTRAN signaling), and Media Gateway (to create IP traffic). These emulations allow the manufacturer to quickly and cost-effectively confirm interoperability.

Step 4. Test the traffic-handling capability of the MGC. The new MGC must be able to support a required level of traffic. The test system can be used to monitor the performance of the MGC under varying load conditions. By analyzing the data in terms of BHCA (Busy Hour Call Attempts), MPS (Messages Per Second), and TPS (Transactions Per Second), the manufacturer can determine whether or not the MGC can meet the required load levels and what will happen under extreme load.

Step 5. Test the MGC as it is being installed in the field. The test system can be used to monitor the performance of the MGC after it is installed into the network and to perform additional product, compliance, and interoperability tests as necessary.

Each of these five steps is time and resource intensive. Manufacturers may be tempted to develop internal tests. However, for a variety of reasons � i.e., the growing complexity of the tests that are required, the desire for an independent assessment, and the urgency of getting to market � the acquisition of external test tools is often the best approach. Accordingly, manufacturers should heed the old adage: �Get the right tool for the job.� By availing themselves of today�s advanced network test tools, manufacturers can reconcile time-to-market pressures with the accelerating pace and complexity of new networking standards. As a result, products can get to market faster and better meet customer expectations.

Comprehensive testing is the only way to ensure that IP-based network equipment will perform reliably in real world networks. There is no better ROI than to find and resolve issues such as feature shortcomings, protocol non-conformance, interoperability problems, and load limitations throughout the product life cycle. The complexity of today�s networks and the dictates of legacy infrastructures make testing network equipment more challenging than ever � but with the right test methodology and the right test tools, success can be achieved.

Guy Simpson is vice president of applications development at Catapult Communications. Catapult Communications provides advanced test systems to equipment manufacturers and service providers for the design, integration, installation, and acceptance testing of a broad range of digital telecommunications equipment and services. For more information, visit the company�s Web site at www.catapult.com.

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