FEATURE MID-REACH
busy developing specifications for inexpensive 100 Gig mid-reach QSFP28 modules.
IEEE standard and MSAs Te IEEE set up the 802.3bm Task Force to create a cheaper, 500m interface specification. Four proposals emerged: parallel single mode
(PSM4), coarse WDM (CWDM), pulse amplitude modulation, and discrete multi-tone. But none of the proposals received sufficient backing to pass the required 75 per cent voting threshold, such that no standard was adopted. Tis forced the optical industry to change tack,
The 100 Gig PSM4 differs from the other three designs in its use of a parallel ribbon fibre
pursuing a multi-source agreement (MSA) strategy to bring mid-reach solutions to market. Since January, four single-mode interfaces have emerged: the CLR4 Alliance, CWDM4, PSM4 and OpenOptics. ‘Te MSA-based solutions will have two important advantages,’ said Murray. ‘All will be much less expensive than the 10km, 100-Gig LR4 module, and all can be accommodated by a QSFP28 form factor.’ Te 100 Gig PSM4 differs from the other three
designs in its use of a parallel ribbon fibre. Te PSM4 also has a 500m reach instead of 2km. Te design uses four 25-Gig channels, each sent over a fibre, such that four are used in each direction. In contrast, the CLR4, CWDM4 and OpenOptics all use 4x25-Gig WDM over duplex single-mode fibre. Te PSM4 is technically straightforward to
implement and is likely to be the most economical of the interfaces. But while the PSM4 transceiver cost will likely be the cheapest, parallel fibre is more expensive than duplex such that any module price advantage is eroded the longer the link. A data centre manager will consider using the PSM4-
The main players and alliances MSA CLR4 Alliance
Wavelength/fibres Distance 1 to 2km
Duplex single-mode fibre (SMF), 1310nm window, 20nm spacing
CWDM4 PSM4
Duplex SMF 20nm around 1310nm
1295-1325nm ribbon SMF (4 fibres, one lambda per fibre in each direction)
OpenOptics
1550nm C-band, 4x 25G lambdas, duplex SMF
30 FIBRE SYSTEMS Issue 5 • Autumn 2014 2km 500m Players
3ality Technica, Altera, Aurrion, Brocade, Dell, Ciena, ColorChip, Hewlett-Packard, Fabrinet, Fujitsu, Kaiam, MACOM, NeoPhotonics, Netronome, Oclaro, Oplink, Oracle, SAE Magnetics, Semtech, and Skorpios, Intel, Arista , eBay
Avago Technologies, Finisar, JDSU, Oclaro and Sumitomo.
Avago Technologies, Brocade Delta Electronics, Finisar, JDSU Juniper Networks, Luxtera, MACOM, Microsoft, Oclaro Panduit, US Conec
2km+ Mellanox, Ranovus
@fibresystemsmag |
www.fibre-systems.com
based on such factors as the parallel single mode fibre already deployed or whether the PSM4 is deemed the most cost-effective solution for their requirements. ‘Te PSM approach has secondary applications
which make it very attractive,’ said John D’Ambrosia, chairman of the Ethernet Alliance organisation. Te PSM4’s 25-Gig channels can be used as individual lower speed ‘breakout’ links. Already, a 25-Gigabit Ethernet consortium has been set up with members that include Google, Microsoſt, Arista and Mellanox, while the IEEE has started work to create a 25-Gigabit Ethernet standard. Te PSM4 module could also support the 32-Gig fibre channel and high-density 128-Gig fibre channel. In contrast, the OpenOptics MSA, backed by
Mellanox and start-up Ranovus, uses the 1550nm C-band and dense WDM, whereas the CLR4 Alliance and CWDM4 operate around 1310nm and use coarse WDM technology. Te 100-Gig OpenOptics uses four 25-Gig
channels. Te low channel count means that a far wider spacing can be used – some 800GHz compared to the traditional metro and long-haul DWDM channel spacing of 50GHz. Te wider spacing relaxes the margins, simplifying module manufacturing, but by using DWDM technology, OpenOptics can add more wavelengths in future such that 16-channel (400-Gig) and even higher channel count designs will be possible. ‘Tere is no plan [from competing mid-reach designs] to go from CWDM to eight or 16 channels,’ said Martin. Mellanox has in-house silicon photonics
technology. Its OpenOptics module design uses an array of common gain sources to generate light in the C-band, with individual wavelengths generated using grating-based waveguides. Te company has already demonstrated a
QSFP28 OpenOptics prototype that consumes less than 3W; the QSFP28 has a maximum power rating of 3.5W. ‘We think that silicon photonics in general will be very competitive with VCSELs (used for 100Gig -SR4 and -SR10 multimode solutions),’ said Martin. ‘Tat is our target.’
Driving down costs Meanwhile, the CLR4 Alliance is an Intel and Arista-backed initiative that has garnered wide industry backing (see table). Ciena, an optical transport specialist, has joined the CLR4 Alliance. ‘We want to continue to drive the costs out of 100 Gig interconnects – both within the data centre, and between the data centre and the wide area network,’ said Steve Alexander, senior vice president and CTO of Ciena. Te CLR4 Alliance, unlike the other three, is an industry grouping and not an MSA. Such a
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