Options for building a high-speed network

There are a number of technologies available for building the high speed network of the future. The network interfaces include Gigabit Ethernet and Fibre Channel

As IT becomes more and more prevalent for complex business processes, today's corporate networks are being made to transfer huge amounts of data. As the businesses expand, more PCs, workstations and servers are added to the existing network. But unchecked, this can have a detrimental affect on network performance.

This is why system administrators are toying with the idea of a wholesale upgrading of the network rather than the traditional piecemeal approach. There are a number of technologies available for building the high speed network of the future. Many of these have already been implemented successfully by various organisations with varying degrees of success. One of the most promising high speed networking technologies is Gigabit Ethernet.

Building on the near-universal acceptance of Ethernet, Fast Ethernet, and 100Base-T, Gigabit Ethernet has become the leading choice among the high-speed LAN technologies available today. The growing use of 100Base-T connections to servers and desktops, however, is creating a clear need for an even higher-speed network technology at the backbone and server level.

Gigabit Ethernet (GbE) is the solution to which network administrators are turning to address this need for speed. Gigabit Ethernet will provide 1000Mb-per-second, or 1Gb-per-second, bandwidth for campus networks with the simplicity of Ethernet and at a lower cost than other technologies of comparable speed.

Gigabit Ethernet addresses three key issues confronting today's network administrators: performance, flexibility and cost of ownership.

Higher throughput at the server and backbone level is being required as network applications embrace video, graphics, and other content-rich data types. Gigabit Ethernet brings 1Gb-per-second bandwidth capability to local area networks, satisfying the demand for greater overall network performance. Moreover, it supports full-duplex operating modes for switch-to-switch and switch-to-server connections and introduces shared media full-duplex repeaters or buffered distributors. A half-duplex operating mode for shared connections using repeaters and the carrier sense multiple access/collision detection (CSMA/CD) access method has been specified, but it is not expected to experience significant deployment.

Flexibility and simplicity are the hallmarks of Gigabit Ethernet. Gigabit Ethernet supports existing 10 and 100Base-T interfaces and provides network managers with the flexibility to select an upgrade scenario that best meets their needs. For example, instead of upgrading an entire network, a network manager might decide to install Ethernet switches with gigabit ports to target specific troublespots for gigabit-level speed, while utilising existing switches and hubs to maintain performance levels in other areas of the network. Users can continue to run existing Ethernet and Fast Ethernet applications, systems, and networking hardware while preserving a simple, cost-effective migration path to higher network bandwidth.

Gigabit Ethernet offers a natural upgrade path for current Ethernet installations by utilising existing stations, training, and management tools. Gigabit Ethernet employs the same protocol, same frame format, and same frame size of traditional Ethernet and Fast Ethernet, meaning users can cost-effectively migrate to gigabit speeds with existing applications, network operating systems, protocols, and network management products. Gigabit Ethernet requires only incremental investments in personnel training and troubleshooting tools.

The IEEE 802.3z Gigabit Ethernet specification calls for three transmission media - short-wavelength laser, or 1000Base-SX for general connectivity, long-wavelength laser, or 1000Base-LX for long-haul switch-to-switch connections and coaxial Copper, or 1000Base-CX for switch-to-switch daisy chaining

The 1000Base-SX specification supports transmission over multimode fibre (MMF) only. Link distances for this technology are 300 meters over 62.5-micron fibre and 550 meters over 50 micron fibre. Target areas for 1000Base-SX are MMF runs in horizontal and shorter backbone applications.

The 1000Base-LX specification calls for transmission over both single (SMF) and multimode fibre. The link distances for long-wavelength laser are 550 metres over 62.5 and 50-micron MMF and 3000 metres over 9-micron SMF. 1000Base-LX is targeted at longer multi-mode building fibre backbones and single-mode campus backbones.

The 1000Base-CX specification supports transmission over coaxial copper only. Link distances for this technology are limited to 25 metres. Target areas for 1000Base-CX are wiring closet applications and system clusters.

Of the high-speed networking alternatives available for today's local area networks, Gigabit Ethernet is expected to become the solution of choice. For networks experiencing congestion at the server and backbone level, Gigabit Ethernet provides 1Gb-per-second of bandwidth relief while maintaining full compatibility with the installed base of over 70 million Ethernet nodes. Gigabit Ethernet is Ethernet, only much faster.

Another competing technology for high speed networks is Fibre Channel. Fibre Channel is an efficient low-latency, high-bandwidth channel network solution for critical high bandwidth applications. These applications include:

Backbones: Fibre Channel provides the parallelism, high bandwidth, and fault tolerance needed for high-speed backbones. It is the ideal solution for mission critical internetworking. The scalability of Fibre Channel makes it practical to create backbones that grow as one's needs increase, beginning with a few servers and expanding to an entire enterprise network.

Workstation clusters: Fibre Channel is a natural choice to enable supercomputer-power processing at workstation costs. For example, in imaging, Fibre Channel provides the "bandwidth-on-demand" needed for high-resolution medical, scientific, and prepress imaging applications, among others.

Scientific/Engineering: Today's new breed of visualisation, simulation, CAD, and other scientific and engineering applications demands megabytes of bandwidth per node. Fibre Channel delivers the needed throughput and more.

Mass Storage: Current mass storage access is limited in rate, distance, and addressability. Fibre Channel provides mass storage attachments of up to 100 megabytes/sec at distances up to several kilometres. Fibre Channel will interface with SCSI, HIPPI, and IPI-3, among others.

Fibre Channel is a high-speed data transfer technology - an integrated standards set developed by a committee operating under the American National Standards Institute (ANSI). Fibre Channel's primary task is to transport data extremely quickly with the least possible delay. "Fibre" is a generic term referring to all supported media types, while "fibre" refers to the optical fibre transmission medium. The Fibre Channel standard is proving the most useful in interconnecting servers, storage devices, and workstation users. Its success is based on its transfer speeds, flexible topology, and flexible upper-layer protocols. Fibre Channel easily handles both networking and peripheral input/output (I/O) communication over a single channel, resulting in fewer I/O ports and fewer unique ports - the traditional bottlenecks of other server connection technologies.

Business, government, and academic institutions are unable to use traditional network technology to deliver the high-bandwidth, low-latency I/O required for the new breed of client/server applications. These client/server applications include high-speed mass storage networks, scientific and medical imaging, visualisation, parallel processing, multimedia communication, transaction processing, distributed computing, and distributed database processing. A new network paradigm is necessary - one that brings forward the enabling technology needed to make innovative network applications and architectures a practical, affordable reality. This new network paradigm is here today. It is channel networking using Fibre Channel.

A channel generally provides connection, or point-to-point, service. The primary task of a channel is to transport data from one point to another at the highest speed with the least latency (delay), performing error correction in hardware. Channels, being hardware intensive, have much lower overhead than networks. Unfortunately, until now it was difficult to cost-effectively provide channel connectivity to many clients. Channels also had a problem handling small-packet bursty traffic. Networks, on the other hand, provide a shared service designed to handle unpredictable, bursty traffic. The very nature of this service means that networks are inherently software intensive. The acute problem with these networks is an inability to provide the I/O bandwidth required by today's applications and client/server architectures.

Fibre Channel combines the best attributes of a channel with those of a network to provide channel networks for the high bandwidth, low latency I/O needs of the client/server model. Now performance will be measured in transactions per second instead of packets per second.

Switch-based systems provide optimum bandwidth for the best client/server architectures. Switches come in two forms: packet for low-latency and circuit for high-bandwidth. Key to the high performance of Fibre Channel, besides raw transmission speed, is the use of a flexible circuit and packet-switched topology. Through the switch, Fibre Channel is uniquely able to establish multiple simultaneous direct-connect (channel) and shared-connect (network) links. Devices attached to the switch do not have to contend for the transmission medium. Two dimensional switching provides simultaneous circuit and packet switching - third generation networking with unequalled performance.

One of the reasons traditional LANs are so software intensive is that each node must be capable of recognising error conditions on the network and provide the error management needed to recover from them. This is known as station management, and it is a burden that channels do not have to bear. Telephone companies have provided a complete, low-cost connectivity solution for years. When a caller picks up a telephone and dials a number, the telephone company routes the call and makes all of the intermediate connections needed to ring the number dialled. If the phone is answered, the route is confirmed all the way back to the caller. If a switch fails along the way, the telephone company reroutes calls onto other circuits. Error recovery is not the responsibility of the caller. Similarly, Fibre Channel employs a switch to connect devices. The switch relieves each Fibre Channel port of the responsibility for station management. All a Fibre Channel port has to do is manage a simple point-to-point connection between itself and the switch.

There is another reason for adopting principles similar to those practised by the telephone systems. A parallel can be drawn between a LAN and a party line in that the more users each supports, the less bandwidth that is available to each user. At some point, therefore, LAN performance can be improved only by changing to a technology that runs at a faster data rate, or by breaking a single LAN into multiple LANs. In contrast, a Fibre Channel switch provides multiple concurrent circuit and packet switched paths between points. If more bandwidth is needed, more paths are added, and bandwidth is increased through more parallelism. As an analogy, doubling the number of lanes in a freeway is a far safer and more practical approach than doubling the speed limit.

The major drawback of Fibre Channel at the moment is its cost. Despite the claims of Fibre Channel adapter manufacturers, the technology is still far too expensive to be used on a wholesale basis. So far, many of the organisations who have adopted Fibre Channel are in the digital imaging field where file sizes could run into gigabytes. For instance, many of the post-production special effects companies in London's Soho district have recently adopted Fibre Channel. For such companies, the advantages outweigh the high cost. However, other organisations that want to preserve their existing networks might well be better off with Gigabit Ethernet.

Ajith Ram

Future Network Interface solution I.S. Department 19/07/99 09:49

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