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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.
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