100 Gigabit for the metro

ADVA Optical Networking has launched a 100 Gigabit transmission card designed for metro wavelength-division multiplexing (WDM) applications.

The firm claims this is an industry first: a direct-detection-based 100 Gigabit-per-second (Gbps) design using four, 28Gbps channels rather than current 10x10Gbps schemes.

"Data centre operators want to make best use of the fibre insfrastructure and get lower overall cost, footprint and power consumption"

Jörg-Peter Elbers, ADVA Optical Networking

The card, designed for the FSP 3000 platform, delivers a 2.5x greater spectral efficiency compared to 10Gbps dense WDM (DWDM) systems. In turn, the 100Gbps metro card has half the cost of a 100 Gigabit coherent design while requiring half the power and space.

ADVA Optical Networking is using a CFP optical module to implement the 100Gbps metro design. This allows the card to use other CFP-based interfaces such at the IEEE 100 Gigabit Ethernet (GbE) standards. The design also benefits from the economies of scale of the CFP as the module of choice for 100GbE, and from future smaller modules such as the CFP2 and CFP4 being developed as the 100GbE market evolves.

The 100Gbps metro CFP's four, 28Gbps signals are modulated using optical duo-binary. By choosing duo-binary, cheaper 10Gbps optics can be used akin to a 4x10Gbps design. Duo-binary is also more resilient to dispersion than standard on-off keying.

The CFP-based card requires 200GHz of spectrum for each 100Gbps light path. This is 2.5x more spectrally efficient than 10x10Gbps based on 50GHz channel spacings. However, while the design is cheaper, denser and less power hungry than 100Gbps coherent, it has only a quarter of the spectral efficiency of coherent (see chart).

Jörg-Peter Elbers, vice president, advanced technology at ADVA Optical Networking, says duo-binary delivers closer channel spacing such that a doubling in spectral density will be possible in a future design (100Gbps in a 100GHz channel). The 100Gbps metro card supports 500km links using dispersion-compensated fibre.

Non-coherent designs for the metro are starting to appear despite 100Gbps optical transport being in its infancy. Besides ADVA Optical Networking's design, a component vendor is promoting a 100Gbps direct detection DWDM design for the metro. The 10x10 MSA has also announced a DWDM extension that will support four and eight 100Gbps channels.

The 100G metro card showing the CFP. Source: ADVA Optical Networking

Metro direct-detection also faces competition from system vendors developing coherent designs tailored for the metro.

System vendors, module makers, optical and IC component companies all believe there is a market for lower cost 100Gbps metro transport. This is backed by keen interest from service providers and large content providers that want cheaper 100Gbps interfaces to connect data centres.

Elbers highlights two such applications that will first likely use the 100 Gigabit metro card.

One is connecting the data centres of enterprises that use rented fibre. "They have a multitude of interfaces and services - 10GbE, 8 Gigabit Fibre Channel - and they often rent fibre," says Elbers. "They need to get as much capacity as possible to make the fibre rent worthwhile while being constrained on rack space and power."

The second application is to connect 100GbE-enabled IP routers across the metro. Here service providers may not have heavily loaded DWDM networks and can afford to use a 100Gbps metro link rather than the more spectrally efficient, if more expensive, 100Gbps coherent interface. Equally, such links may be less than 500km while coherent is designed for long-haul links, 1000km or greater.

Elbers says samples of the metro card are available now with volume production beginning at the end of 2011.

Introducing 100G Metro (ADVA Optical video)