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