Reconfigure networks on the fly
Martin Rowe, Senor Technical Editor -- Test & Measurement World, 4/1/2004
Cisco Systems ONS 15600 multiservice switching platform (MSSP), a digital cross-connect switch for OC-48 (2.5 Gbps) and OC-192 (10 Gbps). An ONS 15600 connects edge switches in a metropolitan area network (MAN) to the network's core.
THE CHALLENGEEngineers needed a flexible, reconfigurable network simulator to test switches for bit-error rate (BER), service disruptions, and connectivity (correct routing). The test bed must simulate 16 10-Gbps metropolitan-area edge networks connected to a core network, thus simulating a traffic load of 160 Gbps.
THE TOOLS- Agilent Technologies OmniBER XM, a SONET multichannel, multiport network simulator and analyzer with up to 192 STS-1 channels in an OC-192 signal. www.agilent.com/find/omniber.
- Glimmerglass System 300T Fiber Connection Server. www.glimmerglass.com.
When testing switches and other network components, engineers at Cisco Systems (Richardson, TX) need to perform tests that produce a 95% or higher confidence level that the component will reliably deliver data and digitized voice, regardless of network topology. To test an ONS 15600 multiservice switching platform (MSSP), they must generate the traffic volume in a typical metropolitan-area edge network, in which telecom switches are connected to form a ring.
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An optical switch connects a multiservice switching platform (MSSP) to a ring of multiservice provisioning platforms (MSPPs) which forms a metro edge network. |
In the past, the engineers configured test networks by manually connecting fibers to the network components through patch panels. Manually connecting the fiber-optic cables takes time, and the cable loses integrity each time a connection is made. Furthermore, cables and connectors break after repeated insertions and removals.
To cut configuration time and minimize cable breaks, Cisco's engineers, led by Chris McKinney, manager of software development engineering, built a reconfigurable test bed for different network topologies. The test bed had to handle a metro network, which could consist of up to 24 rings connected to a single MSSP. Because building such a large network in a lab is impractical, Cisco's engineers used a two-tiered approach. The first tier (see figure) consisted of a single edge network consisting of 15 Cisco ONS 15454 multiservice provisioning platforms (MSPPs). In the second tier, the engineers configured one ring with four MSPPs and 15 rings with one MSPP, all connected to the ONS 15600 under test.
Cisco engineers developed the test bed around two 64-port fiber-connection servers and one SONET tester. The servers let engineers configure edge networks and connect them to the MSSP under test at loads up to 160 Gbps. Patch panels no longer require removal and insertion of optical cables. The connection servers also connect the SONET tester to any network port.
The SONET tester generates the network traffic from which it can measure bit-error rate (BER). Network traffic consists of a pseudorandom bit sequence with 223–1 possible bit combinations (PRBS23). To pass a test, the ONS 15600 had to achieve a BER of 10–10, or no more than one error in 1010 bits. In addition, the fiber-connection servers momentarily break a ring to simulate service interruptions from which the engineers can test a switch's ability to reroute data packets. Software scripts, running on a PC, control the connection servers and the SONET tester.
RESULTSBy building the reconfigurable test bed, Cisco cut configuration time from 1 to 2 days to 1 minute. The drastically shorter setup time and easier configurations let Cisco conduct more testing than was possible with manual setups.
Cisco saved about $320,000 per year, because two engineers now do the work of five. In addition, the company saves time and money because the fiber-connection servers result in fewer damaged, dirty, and misconnected fiber-optic connections. With fewer cabling issues, the company has reduced materials costs as well as the engineering time needed for maintenance.
