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Can Your Layer 1 Switch Do This?

Value-added features that provide more of a good thing

by Eli Laufer, Co-founder Lepton Systems

There are many, well-documented ways a Layer 1 (Physical Layer) Switch can help you save time and money in your test lab: Enable programmable/remote access to the physical layer of a test lab infrastructure, eliminate manual cabling configurations, and share expensive equipment. Check here for a refresher of these primary benefits.

As data rates increased, the technology of Layer 1 switches changed to accommodate the increased bandwidth. Technologies based on an all-fiber switching fabric (OOO), or robotic switching, were introduced to support these increased rates, but these technologies leave out some critical features used to make a test lab even more efficient. Lepton’s ColdFusion Optical-Electrical-Optical (OEO) Layer 1 switch supports data rates to 128 Gbps, and supports these value-added features available only to the OEO technology. Specifically, media support flexibility, port mapping options, and Fibre Channel (a Storage Area Networks (SAN) protocol) support: these features expand the efficiency and functionality of a Layer 1 switch and provide additional savings in CAPEX and OPEX.

Media Flexibility

A test lab environment is filled with many different types of media. Think about the devices under test, test equipment, and any ancillary equipment used in the configuration of the test scheme, as well as how you will establish the connectivity architecture. Some equipment only supports one type of media, some media is less expensive to implement, and for some technologies, fibre channel, for instance, 95% of SAN labs use only multimode optics. The Layer 1 switch chosen to automate your test lab, should be able to support whatever media is actually in your test lab.

Single mode (SM) vs. multimode (MM) fiber - Single mode fiber and associated transceivers are much more expensive to deploy. In long-distance networks, it serves its purpose, however, in a test lab, it is typically unnecessary. Comparing the cost of singlemode and multimode transceivers at higher data rates, you’ll find single mode transceivers can be two to three times more expensive than its multimode counterpart. This chart shows some clear examples of how deploying multimode can save a significant amount of money in a test lab environment.

Additionally, ColdFusion’s architecture can perform media conversion; converting single mode signals to multimode (and vice versa) thus allowing mappings from a single mode port to a multimode port. Think of the flexibility of being able to use test sets that only support one media throughout your test lab. 

What about AOC, DAC PSM4?

Not as ubiquitous in test lab infrastructure, these technologies are viable alternatives to standard SM and MM cabling/transceiver options when supported by your Layer 1 switch.

Active Optical Cable (AOC) - AOC is an alternative to stand-alone optical transceivers, which eliminates the separable interface between transceiver module and optical cable. AOC have significantly lower cost and power consumption and due to the fact that each transceiver pair only has to operate at a pre-defined cable length and with one specific optical transceiver spliced to the other end of the cable.

Direct Attached Cable (DAC) - There is an overall mindset that copper technology has little application since the advent of fiber optics.This is not true for direct attach copper cable. In fact, direct attach copper cable has a much lower cost and power consumption, and provides an excellent alternative for in-rack connections supporting 1/10G Ethernet, 8G FC, FCoE and InfiniBand.

PSM4 is short for Parallel Single Mode technology that uses 4x25 Gbps lanes in QSFP28 form-factor to implement 100G network connections. This technology results in greater port density and overall system cost savings. It also supports 10G Ethernet, Fibre Channel, InfiniBand, SAS and SONET/SDH standards with different data rate options.

Mapping Flexibility


The basic function of a Layer 1 switch is to provide software controlled mappings at the physical layer. In OOO and robotic L1 switch technologies, the only mapping method available is point-to-point. ColdFusion offers additional mapping capabilities that can add value to your testing schemes by reducing test time and number of test equipment ports necessary to support your lab. This is especially important because of the increase in cost of test equipment that supports higher data rates.

Multicast/Mirroring - The ability to have multicast mappings (1 to n) at wire speed is only supported by OEO L1 switches. One transmit port can multicast/mirror a signal to any number of ports within the system with a user-settable return path to the test port. This allows one port of a very expensive test set to simultaneously generate a test signal to any number of ports in the switch. In reverse, mirroring allows sending the same signal to many test devices for analysis. This saves test time and reduces the number of test sets/ports needed to support your test lab.

Port/Link Flapping - Electronic simulation of intermittent connections or fiber cuts allows precise, controlled testing of these situations in a test lab. Programmable start/stop, duration, and repetition of the simulated break allows testing of real-life situations.

Fiber Cut Simulation - Fiber cut simulation typically assumes that both fibers (Tx and Rx) are cut, but in real life, sometimes only a single fiber is affected. Unidirectional fiber cut simulation will allow you to make sure a single fiber cut will trigger the switch over necessary in these situations.

Many of today's high speed networks, connections are based on multiple microfiber lanes carrying traffic belonging to single physical port. If only one of the microfiber lanes is cut, it may not trigger the port redundancy fail over mechanism that typically relies on an optical power measurement.
ColdFusion can simulate a microfiber lane cut to insure that the device under test responds correctly in this real-world scenario.

Long Fiber Span Network Delay Simulation - Application performance can change dramatically based on network delays. Varying lengths of fiber spools, along with the optical transceivers appropriate to drive the specific fiber length can be pre-wired to ColdFusion. These ports can then be used within the test configuration to simulate an increase or decrease in delay, to test for network performance. Other L1 technologies cannot perform this simulation because they do not regenerate the optical signal.

Fibre Channel Support


Fibre Channel is the prominent protocol used in Storage Area Networks (SAN) and addresses the need for very fast transfers of large volumes of information. Unique to the SAN industry, it provides one standard for networking, storage and data transfer. Lepton’s Cold Fusion Layer 1 switch supports 4, 8, and 16G, 4 x 32G and 64G (gen 6) Fibre Channel data rates.

Flexibility is Key

When choosing a Layer 1 switch for your test lab, making sure it is flexible enough to handle the data rates and number of ports is only part of the decision. Consideration of the type of lab infrastructure, and specific testing and simulation requirements can make your Layer 1 switch an even more powerful tool in your test automation deployment.