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Top Choices for high-performance 10 Gb/s transport. (Special Feature: Telecommunications).

While the Internet has cemented the dominance of TCP/IP as the routing protocol for data, the transport environment remains segmented: Ethernet in the enterprise, SONET rings in the MAN and Packet-Over-SONET and ATM in the WAN. This segmentation is supported by the divergent requirements of data communication and telecommunication networks. However, with speeds now reaching 10 Gigabit in the enterprise, MAN, and WAN, telecommunication and data communication expectations are intersecting at the same rate for the first time. This provides an opportunity for convergence of best-of-breed technologies.

Faced with a confluence of standards and ever-increasing customer expectations, the leading questions facing 10 Gb/s network equipment designers are: how to select the right protocol for their application; how to meet the time-to-market, performance and cost requirements of the marketplace; and how to protect their design investment in a rapidly changing environment.

Designers have two solid choices for data transport applications at 10 Gb/s: 10 Gigabit Ethernet (10GbE) and 10 Gigabit Packet-Over-SONET (POS). However the abundance of standards at 10 Gb/s can lead to some confusion about why these might be the most appropriate protocols for today's networking environments. A quick explanation of the benefits of 10GbE and POS -- as well as new methods in integrating these protocols -- goes a long way towards gaining an understanding of their strengths in building today's high-speed communication networks.

10 Gigabit Ethernet

Since its inception in Xerox's Palo Alto Research Center in 1973, Ethernet has grown to a position of dominance in the LAN by providing low cost, high performance and extreme ease of use. 10 Gigabit Ethernet is the next generation of Ethernet technology, poised to expand from the enterprise into the MAN and WAN primarily because of its ease of management and cost effectiveness.

The technical challenge with Ethernet has been to increase performance, reliability, and scalability to meet the requirements of next-generation backbones, while maintaining maximum compatibility with the large installed base and simple management model of IEEE 802.3 Ethernet. 10 Gigabit Ethernet retains the MAC layer virtually unchanged, ensuring that expectations for software compatibility and ease of network configuration will be met while crafting new Physical Layers to meet the performance, reliability and scalability requirements of next-generation networks.

The standardization of a variety of Physical Media Dependents, including short-reach and parallel versions that capitalize on short-term cost advantages, will allow designers to select the lowest-cost option appropriate for their application. The WAN Interface Sublayer (WIS), based on SONET, provides 1OGbE with a path to robust Phy management for MAN and WAN applications. WIS will also enable Ethernet networks to scale past prior limits.

10 Gigabit Ethernet promises to be a good choice for applications focused on ease-of-management and compatibility with installed Enterprise equipment and networks. Such applications occur primarily in the Enterprise and MAN, and include premises routers, edge aggregators and storage area networks. For long-haul WAN applications, the monitoring and efficiency benefits of POS make it a better choice.

10 Gigabit Packet-Over-SONET

The Internet Engineering Task Force (IETF) first standardized Packet-Over-SONET in 1994 as a low-overhead protocol for transporting packet-based data over SONET links. POS is defined by IETF RFCs 1661, 1662, and 2615. POS uses the Point-to-Point Protocol (PPP) and High-level Data Link Control (HDLC) protocols to encapsulate and encode data packets for transmission.

Like Ethernet, POS spans the first two layers of the OSI model, and it is designed to directly encapsulate IP. Unlike Ethernet, POS is not suitable for building bridged or switched layer 2 networks. It is specifically designed for point-to-point links within routed networks, and provides only the Data Link layer features required for protocol identification and transmission error detection. This focus allows a simpler encapsulation than that required by the Ethernet MAC, leading to increased efficiency for IP traffic.

The Physical coding used by POS is also extremely efficient. Packets are subjected to a process called transparency processing, which reduces the number of values used within packet bytes from 256 to 254 by encoding all occurrences of the two reserved byte values as two-byte strings. In normal operation, transparency processing incurs a coding overhead of only 0.8 percent. After coding, the POS data stream is mapped into SONET payloads.

POS does not support the flat switching model that gives Ethernet its reputation for ease of use. However, its full-fledged SONET transport provides the scalability and reliability required to satisfy WAN and MAN requirements, and its efficiency gives it an advantage in applications where transport is expensive. In addition, SONET has a proven track record of delivering the reliability and scalability required for telecommunication networks. This success is based on a history of careful equipment design and stringent qualification processes. By delivering on the cost benefits of concatenated operation, protocols built on top of SONET, such as POS, will have a substantial advantage in the MAN and WAN.

The Next Step: Multi-Protocol, Modular Equipment

To build the full spectrum of 10 Gb/s devices -- ranging from optical Internet equipment (such as high-performance switch routers) to datacom edge equipment (including campus backbone switches, servers and aggregators) -- network equipment providers are beginning to use flexible, high-performance, modular subsystems for established functions in optical networking equipment. A modular architecture eliminates the need for external support chips, promoting higher reliability and trimming system design time and cost. Optical networking modules can pave the way to faster, less expensive 10 Gb/s optical networking equipment development without forcing designers to compromise on performance or reliability.

Leveraging plug-and-play module technology that supports multi-protocol Layer 1 and 2 functionality, equipment vendors can take a standardized approach to building systems for multiple applications. A single module that can switch among multiple protocols under software control -- such as 10 Gigabit Ethernet, Packet-over-SONET (POS) and SONET/SDH -- allows a single line card design to fit into a variety of applications. In an environment of rapid change, with multiple standards aligned to meet identical market requirements, equipment builders who provide their customers with the flexibility to provision services according to demand will have the competitive advantage.

One of the most efficient and cost-effective strategies for building high-speed optical networking equipment is to adopt a more flexible, horizontal approach to system design. This means incorporating modular subsystems to handle common networking functionality. Plug-and-play modules with multi-protocol optical and protocol processing support provide system designers with the essential tools necessary to negotiate the demands of 10 Gb/s design while ensuring their investment will not be eroded by shifts in the highly dynamic network infrastructure marketplace.



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Author:Denton, Claude
Publication:ECN-Electronic Component News
Date:Nov 15, 2002
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