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Beyond LAN: 10GbE for high bandwidth metro systems

Posted: 16 Jun 2002 ?? ?Print Version ?Bookmark and Share

Keywords:ethernet? 10gbe? mac? oem? lan?

Even during the Telecom meltdown, bandwidth requirements are still growing. Enterprise applications such as Internet, extranet and VPN access, emerging business-to-business and peer-to-peer applications as well as broadband consumer access via DSL and cable modems continue to drive carrier and ISP bandwidth needs. To support these requirements, system designers are looking for cost effective 10Gb packet-based solutions for building, metropolitan optical access and transport networks.

A number of high-speed data solutions are available to network designers, from OC-192c PoS to the emerging standard for 10Gb Ethernet (10GbE). Today, OC-192c PoS is used for high-speed packet links to interconnect routers. 10GbE is providing a Layer 2 alternative that can be either switched or routed and is anticipated to lower the cost of 10 Gigabit metropolitan optical, access and transport systems.

As the IEEE P802.3ae 10GbE draft standard is ratified, designers now have the challenge of incorporating 10GbE functionality into their systems.

10GbE overview

To service these broad applications, the IEEE is defining a 10GbE standard that can support WAN physical layer (PHY) and 10GbE LAN PHY. A common misconception is that the LAN PHY has a short reach and the WAN PHY has a long reach. This is not the case as both LAN and WAN PHY can support any distance. Rather, the names refer to the physical coding options chosen and not link distance.

The main differences between the LAN and WAN PHYs are in the data rate, physical coding sub-layer (PCS) and physical medium dependent (PMD) interface and link management. The LAN PHY is intended to maximize the data rate to 10Gbps, while the WAN PHY frame format and rate are compatible with the existing OC-192 (9.95328Gbps) MAN and WAN infrastructure. In order to match the different rates of 10Gbps at the media access control (MAC) and the WAN PHY line rate of 9.95328Gbps, the MAC will insert extra spaces (idle characters) between Ethernet frames to slow the data rate down. The idle characters are then deleted to allow the Ethernet frame stream to be packed into a SONET/SDH payload. Compared to the LAN PHY, there is a small (4 percent) reduction of throughput.

The WAN PHY employs a basic SONET frame and scrambling to transport Ethernet frames. The 64B/66B code characters generated from the same coding scheme used by the LAN PHY are encapsulated in SONET frames rather than being directly fed to the optics.

While the WAN PHY SONET frame inherently provides many mechanisms for system management, the 10GbE LAN PHY had additional fiber management functions added to facilitate longer reach applications. The line rate of the LAN PHY depends on the coding scheme employed. The serial LAN PHY uses 64B/66B coding. This results in data rates of 10.3Gbps and 4 lanes of 3.125Gbps respectively.

Multiple component architectures

10GbE components fall into two main categories that support either integrated or discrete functions. On the one hand, some switch vendors build their own 10G MAC as a stand-alone discrete device or as an integrated function within a larger Layer 2 ASIC. For these cases, system vendors would use discrete PCS devices to complete their solution.

On the other hand, switch and router vendor preference for integrated components is becoming increasingly common as value-added features move up the layer stack. In this architecture, the system vendors want the MAC and PCS to be integrated within a merchant market physical layer device so that they can focus their resources on developing higher layer value-added features such as Layer 2 switching, Layer 3 routing, packet classification and traffic management. Vendors who have already invested in developing 10GbE MAC technology must consider the cost of bringing their MAC up to compliance with the evolving IEEE P802.3ae standard when deciding which architecture to use.

10GbE delivery

System designers are under significant pressure to incorporate 10GbE functionality in their products. The emergence of multiple vendors supporting 10GbE components helps system designers by providing 10GbE building blocks. Key design considerations include: whether to provide 10GbE support for LAN PHY, WAN PHY or both, which optical interface to use and which multi-source agreement to support.

A large part of Ethernet's strength comes from a wide range of vendors providing interoperable component and system solutions. 10GbE is well along this familiar path with the first interoperability demonstration sponsored by the 10GbE Alliance at the September 2001 Networld+Interop. Going forward, the continued demonstration of standards compatibility and multi-vendor interoperability will be a base for product differentiation and success for 10GbE solutions.

? Stuart Robinson

PMC-Sierra Inc.

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