![]() “You can think of the line card as a much lower-cost real estate. “It’s like having real estate in New York City versus Jersey City,” says Ghiasi. “In the lower data rate, a lot of these functionalities are integrated inside higher-level silicon.” “You could even potentially integrate the SerDes or the PHY with these added functionalities inside the MAC or the switch, just like Gigabit Ethernet,” adds Rami Kanama, vice president of sales and marketing at Redfern Integrated Optics (RIO-Santa Clara, CA). The SFP+ enables the integration of functions currently sold in individual ICs, such as the CDR and EDC, into the SerDes, for example. The point is that moving the silicon or most of the ICs out of the optics and onto the line card enables higher integration on the line side, which, in the long run, should give you a cost advantage.” “And it’s really cost neutral from a system perspective. “You could argue this is just a left pocket, right pocket game,” admits Thomas Scheibe, product marketing manager with Cisco Systems’ Transceiver Module Group (San Jose, CA). Isn’t that simply moving cost from one part of the system to another? That said, pulling the silicon out of the module and putting it on the line card appears, on the surface anyway, to be a zero-sum game. But the smaller size of the SFP+ would force some or all of these electronic functions to be housed outside the optical module, directly on the host board or line card, thereby reducing both cost and power consumption of the module. Typically, several electronics functions-such as the clock and data recovery (CDR), some SerDes/PHY functions, and perhaps electronic dispersion compensation (EDC)-reside inside the larger form-factor XFP, X2, and XENPAK optical modules, which are hot pluggable into the back of a switch. The demonstration proved that an SFP+-like form factor could be used for long-reach 40- and 80-km DWDM. “From a component perspective, it’s a very simple E-to-O, O-to-E converter.”Īt OFC last month, Redfern Integrated Optics conducted a feasibility demonstration of an SFP+ transceiver powered by its directly modulated, external-cavity TOSA. “The premise is that you will keep the electronics and optics very simple, just as it is in the case of 1, 2, and 4 gig,” explains Ali Ghiasi, chief architect at Broadcom (Irvine, CA). This design includes only the silicon that needs to be in the module: a laser, a laser driver, a transimpedance amplifier (TIA), and maybe some type of post-amplifier on the receive side. But when you start adding those components inside the module, you start adding cost that the Fibre Channel community was not that eager to adopt.”įor this reason, the industry-specifically the American National Standards Institute (ANSI) Technical Committee T11-opted to return to the simple module design that had worked so well at the lower data rates. “The XFP, for example, has a retimer inside the module in both the transmit and receive directions. “In the past, the way people have attacked that is to put more silicon in the module,” notes Norm Swenson, CTO of ClariPhy Communications (Irvine, CA). Inspired by the success of the 4-Gbit/sec module, the Fibre Channel folks decided to double the speed again with an 8-Gbit/sec design. As a result, the Fibre Channel industry developed a much more widely adopted 4-Gbit/sec version, which is in a similar ballpark, price-wise, to its 1- and 2-Gbit/sec counterparts. But this did not prove to be the case for 10-Gbit/sec Fibre Channel modules, which were priced much higher than 1- and 2-Gbit/sec versions. ![]() Folks in the Fibre Channel world, therefore, are accustomed to purchasing new modules at newer rates for roughly the same price or at only a slight premium over existing modules. ![]() Fibre Channel data rates, by contrast, merely double with each new speed. With every new Ethernet speed, data rates tend to increase by a factor of ten, which typically results in a price premium for new modules. For this reason, vendors in the cost-sensitive 10-Gigabit Ethernet (10-GbE) market are making a strong push to standardize SFP+ for use in 10-GbE applications. Currently under development in the Fibre Channel world for 8-Gbit/sec applications, the SFP+ next-generation form factor promises to be 30% smaller, burn less power, require fewer components, and be less expensive than the XFP form factor.
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