A simplified approach to ATM - Digital Lightwave's Network Information Computer eases the installation, test and maintenance of ATM networks - Product Information

Communications News, Sept, 1997 by Mike Watson, Gay Roatch

Many large government and commercial networks already use asynchronous transfer mode (ATM), but we need a more intuitive, simplified approach to ATM test, installation, and verification as more varied users adopt the technology.

Users must provide their own ATM switch and connection to carrier-based ATM services to take full advantage of ATM technology. This hybrid network made up of CPE and carrier services is not new to information technology (IT) organizations.

Adding ATM to the hybrid network brings complexity to a new level, so it's essential to have a test and verification plan for network service and switch configuration. Before accepting the switch and network service, the IT manager should make sure that the switch is configured correctly for the required type of ATM network service.

The complexities of an ATM assurance plan require new skill sets for internal staff, new test procedures, and new ATM test tools. Testing involves verification of T1, T3, or SONET digital network facilities and simulated traffic through the ATM switch.

After each network facility individually demonstrates compliance, the system is tested from the end user switch ports, through the switch, across the network carriers' service, and to the far-end CPE ports.

Test and measurement instruments like Digital Lightwave's Network Information Computer help simplify installation and maintenance of ATM enterprise networks. The test device should be capable of: * Measuring and stressing the quality of digital circuit performance on T-carrier and SONET transmission links. * Simultaneous and independent ATM traffic generation on multiple virtual channels to confirm mapping and network boundaries. * Confirming that agreed-to quality of service (QoS) parameters are being met by generating traffic at the agreed-to service class. * Supporting Recommendation 0.191 for test cell format that provides compatibility between ATM measuring equipment (AME) for out of service (OOS) measurements.

Since ATM is a communications networking technology that requires physical layer transport to function, verifying the connectivity, stability and reliability of the physical layer should be first.

This should encompass testing CPE facilities as well as backbone services. Use established test suites for T1, T3, and SONET to confirm the transmission physical layer. Include tests measuring bit error rate, power, signal level, as well as timing to ensure conformity to specified values for fiber or copper transmission lines.

The next step is verifying ATM connectivity by mapping and error testing. Once you establish and loop back a permanent virtual circuit (PVC), generate and transmit traffic through several virtual channels and paths to confirm that the switches at the customer premises and in the network are properly configured. Then perform error testing to verify the switches can correctly and reliably route traffic.

ATM policing functions are designed to keep the network operating at the agreed-to bandwidth parameters. Stress testing substantiates that the network equipment is performing to defined categories by causing congestion at the switch and monitoring the results.

QoS parameters are the basic connection rules for applications and network optimization. These are agreed to by the service provider for each PVC for the service class contracted.

When traffic is being generated above the provisioned cell rate, it can be confirmed that the ATM switch is dropping the appropriate cells. When traffic is being generated at or below the provisioned rate, it can be confirmed that the QoS parameters are being met.

OOS measurements are used when the connection is dedicated to test activities. For each ATM connection, cells are transmitted across the network at a given service class. For OOS testing, test and background traffic should be programmable to simulate realistic traffic. This allows you to monitor and validate performance characteristics.