Deregulation, the entrance of competitive carriers and a growing number of alternative suppliers of telecommunications systems equipment have forced telecom equipment manufacturers (TEMs) to rethink their reliance on hardware as core intellectual property and to shrink their large hardware development teams to a small, specialized group of engineers. In the process, they are being forced to outsource certain subsystems or modules.

In response, optical-component manufacturers, particularly those working in the 10-Gbit/second DWDM market segment, have moved from selling proprietary designs aimed at one particular TEM to selling standards-based modules to many customers. The most salient example is the development of modular technologies for both tributary and trunk-side optical interfaces.

Traditionally, suppliers have integrated 10-Gbit/s serial optical interfaces with multiplexing and demultiplexing ICs and lower-speed electrical I/O circuits on proprietary line card designs. Today, the DWDM systems engineer can choose from numerous modular options, including 10-Gbit/s DWDM optical-transceiver modules that comply with the 300-pin multisource agreements (MSAs).

Advances in optics, drivers and control ICs enable off-the-shelf transponders that provide full C-band tunability and long-haul transmission performance with footprints as small as 3.5 x 4.5 x 0.5 inches. MSA-based components are now widely accepted in the telecom industry.

Also, the widespread adoption of optical and electrical interface standards from the International Telecommunication Union and Optical Internetworking Forum let TEMs adopt reusable components and line card designs. The modularity trend now extends to firmware communications interfaces.

Using 300-pin MSA transceivers that integrate transmitter and receiver optics removes the need for a hardware designer to route high-speed 10-Gbit/s signals on a line card. Instead, the merchant supplier implements the task in the optical module. This is a useful strategy for high-end DWDM optical interfaces requiring multiple optical components and complex high-speed circuitry.

High-speed interfaces
While component integration and complex high-speed circuit routing on trunk-side optical interfaces drive the use of 16-bit-wide interfaces (SFI-4) in 300-pin MSA-compliant optical transceivers, the XFI standard serial electrical interface provides a serial solution for 10-Gbit/s links. XFP (small-form-factor pluggable) optical transceivers using the XFI interface are being deployed for tributary or client-side optical interfaces based on cost, pluggability and port density. The 10-Gbit/s serial interface eliminates issues with skew across parallel buses but introduces new signal integrity issues. Here, reference designs can be an invaluable aid to design teams as they move to higher transmission speeds.

Standardized optical and electrical interfaces also are enabling the outsourcing of line card design and layout services. The use of reference designs is necessary to enable this transition, particularly for a 10-Gbit/s line card.

The first step in the reference design outsourcing process has been to transfer layout and design-for-manufacturing tasks to a contract manufacturer, letting the systems designer focus on circuit design and characterization and on component selection. The practice cuts R&D spending, speeds time-to-manufacturing and promotes component reuse.

As contract manufacturers and merchant suppliers move up the learning curve, TEMs will begin to outsource the hardware design of an entire line card, including its assembly and test. This practice is happening already at lower data rates and will likely extend to 10 Gbits/s when network designs stabilize.

Component vendors are also beginning to integrate the technologies that are used in various system applications. By mixing and matching key ingredients, the cards can be designed at less cost, qualified with less effort and then handed off for high-volume production.

Craig Thompson is director of marketing, Scott Schube is applications engineering manager and Wei-Chiao Fang is transceiver engineering manager at the Optical Platform Division of Intel Corp. (Santa Clara, Calif.).