Ethernet Hits 40 Gbit, Aims at 100 Gbit
High Levels of Interface Integration to Enable 10, 40 and 100 Gbit/s Ethernet Rates over Optical Nets
New devices are enabling the transport of 10 Gbit Ethernet signals from LANs and WANs over metro and long-haul optical transport networks with less overhead and lower cost.
BY DAVID YEH, APPLIEDMICRO
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Increasing volumes of IP-based network traffic are driving telecommunication carriers and Internet service providers to demand faster transmission speeds of 10 Gigabits per second to 100 Gbit/s and beyond. The long-haul and metro portions of wide area networks are converting from SONET/SDH technology to Optical Transport Network (OTN) technology to send video-rich Ethernet traffic over the fiber-optic infrastructure to meet volume, performance and cost requirements. To make this transition as cost-effective as possible, networking system OEMs have to develop multi-protocol, multi-rate, high-density line cards to support not only the legacy SONET/SDH traffic, but also the surging IP/Ethernet and OTN traffic. Accomplishing that goal requires innovation at circuit, line card and system level design.
OTN optical services offer many of the same protection and management features of SONET/SDH networks, but without the complexity and cost associated with them. OTN optical services are also better for transparent mapping and transport of native client traffic through Metro and long-haul networks. This point is extremely important for client traffic where the preservation of clock and management information is necessary for sustaining end-to-end path link communications, without the degradation of performance. Of course, being able to maintain client transparency is also critical for OTN to be utilized as the common protocol for network convergence.
Another factor driving carrier migration from SONET/SDH to OTN networks is the desire to extend Ethernet, specifically 10 Gbit Ethernet (10GbE), from the local area network (LAN) into the wide area network (WAN). The carriers are able to achieve reduced cost and complexity by preserving the native client signal, particularly 10GbE, through the metro and long-haul transport network.
Standardization is helping to lower the cost of this transition. The 10Gbit Ethernet signal is ideally suited for transmission across metro and long-haul optical transport networks when carriers map it into an optical channel data unit-2 (ODU-2) payload as defined by the International Telecommunication Union (ITU) specification, Sup. 43, Section 7.3. Using this mapping mode, the 10 Gbit Ethernet signal fits entirely into an optical transport unit-2 (OTU-2) signal while maintaining its G.709 standard transmission rate of 10.709 Gbit/s. Additionally, the OTN framing structure also supports forward error correction (FEC) that greatly extends the distances of error-free transmission links, further fueling the rate of adoption for carriers migrating to 10 Gbit services.
The OTN structure also scales nicely for 40 Gbit (OTU-3) and 100 Gbit (OTU-4) signals, thus allowing the multiplexing of 10 Gbit signals into 40 Gbit and 100 Gbit signals. With Internet, voice and data traffic continuing to double every 12 to 18 months, the carriers’ call for 40 Gbit and 100 Gbit transport networks is becoming palpable.
At the device level, the transition is occurring through system-on-chip solutions that provide a rich suite of 10 Gbit client mapping and OTN framing features that enable the multiplexing and transmission of 10 Gbit services over 40 Gbit and 100 Gbit networks.
Higher Transmission Rates
When it comes to meeting the insatiable growth in metro and long-haul traffic, carriers have three basic choices to pursue. They can light more fiber, add more wavelengths to existing fibers, or increase the transmission rates on existing fibers. All have positives and negatives. Lighting up fiber can involve installing additional fiber and/or installing new hardware, a very expensive proposition. Transmitting more wavelengths over a fiber may require narrower channel spacing, which involves more sophisticated modulation schemes and the costly upgrade transmission equipment. In addition, the existing fiber chromatic and polarization mode dispersion characteristics may set limitations to improved channel spacing performance. Finally, the increase in transmission rates involves more sophisticated modulation and forward error correction schemes to address existing fiber dispersion characteristics. New analog-to-digital converter technology and optic modules are under development to enable this level of sophistication.
All three options have drawbacks. However, the path of higher transmission rates offers the greatest advantages in terms of system performance and cost-effective migration paths. By transitioning from 10 Gbit to 40/100 Gbit transmission rates with the integration of enhanced modulation schemes such as Dual Pole – Quadrature Phase Shifting Keying (DP-QPSK), carriers can preserve much of their existing fiber infrastructure, and base transport platforms and repeater equipment. By employing new modulation techniques like DP-QPSK, carriers anticipate transmitting up to 80 channels of 100 Gbit bandwidth over a single fiber, at 50 GHz spacing.
Equipment providers are already in production with 40 Gbit networks, and some are in field trials with 100 Gbit. The ability to efficiently map and multiplex existing 10 Gbit traffic into these larger pipes is also underway. The ITU Study Group 15 has standardized on OTU-4 mapping/framing/clocking schemes, and the Optical Internetworking Forum (OIF) has also standardized on modulation technique DP-QPSK to most efficiently enable the framing, mapping, multiplexing and transmission of 10 Gbit signals into 40 Gbit and 100 Gbit pipes.
A key factor in the transition is highly integrated wide area network SoCs that can provide 4x10 Gbit to 40 Gbit, and 10x10 Gbit to 100 Gbit mapping and multiplex (muxponder) solutions. Among a rich suite of features and integration, these devices should offer support for a generic mapping protocol (GMP) that enables “AnyRate” 10 Gbit client signals to be mapped into 10 Gbit ODTU-23/24 frames, and output them at a common clock rate to allow for easy multiplexing of 10x10 Gbit signals into a 100 Gbit OTU-4 frame.
Highly Integrated Framer/Mapper PHY
To meet the challenge, silicon designers are integrating framing, mapping and physical layer onto devices for LAN/WAN/OTN solutions to meet multiple interface, low-cost and low-power requirements of multi-service transport, dense wave division multiplexing (DWDM) and metro/core switch router applications.
These integrated SoCs offer the most flexible and cost-effective solutions to transport equipment providers and carriers. The devices are designed for a variety of blade applications including 10 Gbit client/line cards, 10 Gbit transponders/muxponder cards, 10 Gbit regenerator cards and even 40 Gbit/100 Gbit muxponder applications. In addition, the serial 10 Gbit interfaces on the devices support programmable pre-emphasis and electronic dispersion compensation (EDC) to interface with both XFP and SFP+ optical modules.
With integrated ITU G.709 FEC and Enhanced FEC (ITU G.975.1.I4), the SoCs enable metro and long-haul transmission of 10GbE over OTN networks in low optical signal noise ratio (OSNR) environments. Additionally, the GFEC and Enhanced FEC also compensate for nonlinear inter-channel impairments, which allows for a narrow channel spacing of 25 GHz for DWDM systems.
A series of devices that integrates 10GbE/10GFC/8Gbit Fibre Channel/OC-192/STM-64 to OTU-2 mapping services, FracN clock synthesizing circuitry, electronic dispersion compensation (EDC), GFEC/Enhanced FEC features and 10 Gbit PHY integration, enables Telecom OEMs to reduce the cost, power and space of their current 10 Gbit LAN/WAN to OTU-2 solutions by up to 50 percent by eliminating external PHYs and interface bridge devices.
Interface flexibility with specialized devices is a key attribute for 10G OTU-2 client/line tributary metro Ethernet and switch/router applications. A flexible system interface supports XAUI/SFI4.P2/SFI-5s protocols and enables the direct connection to network processors, 10Gbit Ethernet switches, 10 Gbit Framers and 10 Gbit MACs, and its 10 Gbit Line XFI Interface enables the direct connection to XFP and SFP+ optic modules.
Designing an SoC with a robust set of interfaces makes it flexible and suitable for multi-service transport and DWDM platforms. These devices need to support a system interface (XAUI/SFI4/P2/SFI-5s) and a dedicated 10 Gbit XFI Line interface. In addition, it should also be designed to support a separate and dedicated 10 Gbit XFI Client interface as well as a 16-bit parallel SFI4.P1 interface that can be used either on the client or line side of the device. The SoC configured this way can be used for 10 Gbit OTU-2 client/line tributary cards, transponder and regenerator applications and support 10 Gbit XFP/SFP+ and 10 Gbit MSA modules. In addition, a rich set of interfaces allows for customer-specific side door functions, such as encryption, to be supported as well as other unique mapping and enhanced FEC modes.
For 10 Gbit transponder applications, serial 10 Gbit backplane applications, and 10x10 Gbit to 100 Gbit muxponder applications, a chip should have two serial 10 Gbit interfaces that are XFP/SFP+ module compliant. Designers in this space should aim to provide a variant of the framer/mapper/PHY SoC to be equipped for the optical networking industry’s continued and inexorable migration to smaller form factor serial 10 Gbit optic modules and 10 Gbit serial backplanes.
To help reduce cost and complexity, silicon companies are tasked with providing OEMs with a clean, thermally efficient and easily routable interface to both the Client side XFP/SFP+ optic module and to the 100 Gbit encoder/decoder/framer device. GMP Mapping and XFI interfaces on the chip-to-chip interface allow for a direct connection to OTU-4 Framer implementations. Also, the 10 Gbit GMP mapping mode integrated into these devices produces a common clock rate, and greatly simplifies the complexity of the OTU-4 framer function.
Future incarnations of framer/mapper/PHY SoCs with further levels of 10 Gbit port integration, and single silicon solutions for 100 Gbit (OTU-4)/FEC functions, will help to provide a downward slope for cost, power and space requirements, enabling 100 Gbit to become ubiquitous in the transport networks (Figure 2).
Figure 2: A highly integrated 10G Framer/Mapper/PHY SoC, seen here as the AppliedMicro Yahara, in a 10x10G to 100G muxponder board level
A family of SoCs with differentiated feature sets enables system OEMs to select the most appropriate set of optical interfaces for their specific applications. As a result, these device families provide system OEMs with a cost/space/power advantage over other multiport, all-encompassing single-chip solutions.
With system OEMs developing metro and long-haul transport solutions utilizing interface-rich WAN SoC devices, they provide carriers and Internet service providers with highly integrated and cost-effective 10 Gbit, 40 Gbit and even 100 Gbit OTN/WAN/LAN system solutions. A flexible architecture and a small footprint provided by high-volume silicon-tested 10 Gbit intellectual property, provides the most robust and effective 10 Gbit transmission solutions over optical-based metro and long-haul networks.