Network Design and Layout As in previous Ethernet standards, 40 Gb/s and 100 Gb/s define several different Physical layer (PHY) implementations for transmitting information over various distances and media types. These media types include multimode and singlemode optical fiber cabling and some form of copper cabling. Additionally, various transceiver types are defined, distinguished by which media they are intended for and how far they transmit.
Table 1 above lists the PMD devices that were adopted by IEEE 802.3ba, along with their media type and minimum expected reach. For both 40 Gb/s and 100 Gb/s, the minimum reach for short-reach applications on multimode optical
fiber is 100 m (328 ft) over OM3 fiber and 150 m (492 ft) over OM4 fiber. The PMD solution for multimode optical fiber described in the previous section is based on a parallel optics technology that has already been
proven in the marketplace (e.g., InfiniBand), entailing simultaneoustransmission of one 10 Gb/s signal on each of four or 10 fibers (for 40 Gb/s and 100 Gb/s, respectively).
Aggregating these parallel signals may sound complex. However, from a user perspective, it is the same approach that has been used for copper-based systems for years. The array of VCSELs and the array of detectors are built onto a single chip connected to the optical fibers with one MPO connector. The MPO connector connects 12 optical fibers as a unit, simplifying the interconnection of both 40 and 100 Gb/s parallel solutions proposed for multimode optical fiber. The result is that for a given link, all detectors are connected to all the transmitters with a single optical cable.
As mentioned, PMDs involving
singlemode optical fiber use WDM
technology, where multiple wavelengths are transmitted over a single
optical fiber. For example, 40 Gb/s
40GBASE-KR4 Backplane 1 m
40GBASE-CR4 Copper Twinax 7 m
40GBASE-SR4 Multimode Optical Fiber 100 m OM3
150 m OM4
40GBASE-LR4 Singlemode Optical Fiber 10 km
100GBASE-CR10 Copper Twinax 7 m
100GBASE-SR10 Multimode Optical Fiber 100 m OM3
150 m OM4
100GBASE-LR4 Singlemode Optical Fiber 10 km
100GBASE-ER4 Singlemode Optical Fiber 40 km
PMD MeDia Link Length table 1: PMD devices adopted by IEEE 802.3ba Electronic reprint with permission from BICSI News Magazine-September/October 2012 Issue can be achieved by multiplexing four wavelengths that are each carrying 10 Gb/s. Similarly, 100 Gb/s can be obtained by combining four wavelengths operating at 25 Gb/s each. Using parallel optics with multimode optical fiber is less complex and less expensive than using WDM over one singlemode optical fiber.
The IEEE Next Generation 40 Gb/s and 100 Gb/s Optical Ethernet Study Group is developing requirements for alternative implementations of both 40 Gb/s and 100 Gb/s Ethernet. Plans include a longer reach (30 to 40 km [18.6 to 25 mi]) singlemode 40 Gb/s PMD, a short-reach (0.5 to 2 km [0.3 to 1.2 mi]) singlemode 100 Gb/s PMD and a short-reach (100 to 150 m [328 to 492 ft]) multimode 4×25 100 Gb/s PMD.
The short-reach 4×25 multimode PMD will allow a simple upgrade from today’s 4×10 40 Gb/s links without requiring additional optical fibers or cable.
