CABLING INFRASTRUCTURE

From the December 2006 
issue of Communications News

New roles for media converters

Small form-factor pluggable transceivers expand uses of media conversion.

by Sergiu Rotenstein

Not many years ago, media conversion sat at the lowest level of the optical transport solutions pyramid–the physical layer. Different layers were clearly separated, with distinct platforms serving each main optical application, including media conversion, fiber grooming, services demarcation and wavelength division multiplexing (WDM). Each of these specialized platforms was optimized for its functionality within the hierarchy and was characterized by specific protocols, media, lambdas and optical properties.

The emergence of small form-factor pluggable transceivers (SFP or XFP) and multirate, multi-function converters/transponders has revolutionized this paradigm. These new technologies provide media converters with the chameleon-like ability to adapt to multiple layers of the optical transport domain and to be transformed into a real optical multiservice platform.

These converters seamlessly cover the full range of the optical hierarchy. A basic SFP/XFP gives enterprises easy system and functionality reconfiguration in order to adapt to specific network requirements. Six general categories of solutions are possible.

Pluggable transceivers are the keys to installing a next-generation optical network. Standard SFP and XFP interfaces enable full separation between the networking solution and the physical network interface.

SFP and XFP (10 Gbps) transceivers enable deployment flexibility, while increasing the solution’s density. The same pluggable-enabled converter or transponder can be used for multimode, single mode and single-fiber connections, or for lambda-specific coarse wavelength division multiplexing (CWDM) or dense wavelength division multiplexing (DWDM) connections–depending on the optical transceivers plugged into them.

A simple exchange of the SFP allows a copper-to-fiber media converter to extend its reach from 20 kilometers to 120 kilometers, or to become a WDM transponder tuned to a CWDM or DWDM wavelength. The advanced optical performance monitoring (digital diagnostics) built in the pluggable transceivers improves the optical solution manageability and reduces operational costs.

Quick interface changes
The hot-swappable, plug-and-play nature of SFP transceivers enables an interface to be changed quickly and easily, with minimal network interruption, along with reducing the need for spare inventory. Instead of requiring complete duplication of each application-specific line card, an entire network can be covered with one line card and a small selection of pluggable transceivers covering the range of applications in use.

Converters and transponders, like optical transceivers, originally were designed and configured for specific network types, meaning upgrading a connection required swapping out line cards. Today, transponders can support a wide range of data rates–from 100 Mbps up to 4.25 Gbps.

With multirate transponder line cards, the transition between network protocols becomes as easy as selecting the desired data rate through device management. At the same time, these modules can be transformed from a dual transponder to a redundant repeater or a Layer One signal multi-casting engine by a click on a graphical interface. The same modules can be combined with copper SFPs to convert Ethernet, T-1/E-1 or OC-3/STM-1 from copper/coax cables to fiber-optic cables for backbone networks.

Multirate, multifunction pluggable-optics transponders enable the implementation of a wide range of optical transport functions like media or lambda conversion. For example, using the applicable pluggable transceiver, a Gigabit Ethernet multimode link operating at 850 nm can be connected to a single-mode link operating at 1,550 nm.

Configured with wavelength-specific pluggable optics and connected to a WDM, a multirate transponder can be used to create a static trunk WDM system, a wavelength/trunk switching WDM system or a WDM repeater with or without lambda conversion. Deployed along a WDM trunk at demarcation points, it also can be used to create a sophisticated add/drop topology.

Pluggable-transceiver modules also may come in protocol-optimized versions, serving any 10-Gbps protocol by employing multirate XFP pluggable optics. When combined with CX-4 copper XFP, these modules provide a cost-effective 10-Gigabit Ethernet copper-to-fiber media conversion in which the fiber side is a simple gray 1,550-nm link or a DWDM wavelength.

Other pluggable-transceivers modules are multifunction solutions focused on legacy protocols like Fast Ethernet, Gigabit Ethernet, DS-3/E-3 or T-1/E-1/J-1 with similar capabilities.

Sub-wavelength aggregation modules employ time division multiplexing (TDM) to combine two or more channels of different protocols, like Fast and Gigabit Ethernet, Fiber Channel, DS-3/E-3 and T-1/E-1, thus optimizing fiber transport.

A wide range of demarcation devices run the gamut from 802.3ah-enabled single-service LAN devices to multi-service devices that may, for example, use TDM to combine WAN with an Ethernet data channel. At the top end are devices that incorporate advanced services, such as quality-of-service controls, virtual LAN tagging and multiprotocol label switching.

The demarcation device should support pluggable transceivers for connecting to the carrier network. This feature takes the benefits of optical transport flexibility and serviceability to the edge of the provider network and makes the task of aggregation and grooming at the central office that much easier.

As pluggable-transceiver converters can become WDM transponders by a simple change of an optical transceiver, a true optical multiservice platform asks for accessories to complement the optical transport building blocks.

Passive WDM multiplexers and optical add/drop multiplexer solutions are characteristic of a WDM optical transport network. The transparent operation of passive optical multiplexers and their plug-and-play nature lead to significant flexibility in terms of network deployment and migration. With passive multiplexers, lambda aggregation and separation are abstracted from the underlying data services, making the mix-and-match of multiple services during transport across the network easier. Passive WDM and OADM devices are available for CWDM as well as DWDM applications.

When more optical budget or extended reach is required, an optical link may be amplified through the use of a basic DWDM accessory–the optical amplifier. Single wavelength or full C-band amplifiers are common today in the industry and are intrinsic to the optical multi-service solution.

Sergiu Rotenstein is a vice president with MRV Communications, Chatsworth, Calif.

For more information:
www.rsleads.com/612cn-257