MRVC (NBASE) white paper on extended distance Ethernet:
Long Distance Fiber Optic White paper
Extended Distance Ethernet
Link distances have always been a concern for the Network designer from the
first development of centralized mainframe computing until todays distributed
Local Area Networks. While the design criteria for remotely connecting a LAN
are well understood, it is equally well known that when this task occurs, the
simplicity of a LAN goes away. When forced to enter a "cloud" of any
dimension, the cost and the complexity of the elements necessary to
guarantee the same level of service enjoyed by the LAN substantially
increases. This paper addresses this business issue with the intent to
illustrate how one can extend a LAN over substantial distances while
remaining within the ubiquitous standards of Ethernet and TCP/IP.
Like Fast Ethernet and the original 10Mbs Ethernet, Gigabit Ethernet will
support a variety of physical media with various capabilities in terms of link
distances. The IEEE 802.3 High Speed Study Group has identified three
specific objectives for link distances depending on the physical media
employed: copper based Cat 5 link up to 100 meters, a multimode fiber optic
link of up to 500 meters and a single mode fiber optic link of up to 3
Kilometers. Obviously, there is a need for high-speed interfaces to extend
this limitation since even small campus's or multistory buildings easily
exceed this limitation.
Fiber Channel offering up to 1.05 Gps seems to offer an acceptable solution
for up to 20 kilometers but its cost per port often exceeds routed network
designs. Ideally, what is required is a design that retains all of the benefits of
the LAN with a cost structure similar to the port costs of today's LAN's.
NBase Communications, through its heritage of being a world class optical
foundry, has developed a series of products which have extended Ethernet up
to 110 kilometers from the current single mode fiber 3km limitation. Further,
employing a lower cost regeneration device, this distance can be extended
indefinitely. Current tests have validated distances up to 500 miles with no
obstacles to extending the LAN beyond that distance foreseen.
The choice of operating wavelengths to achieve the extended distance
employs terminal components with a wavelength of 1550 nanometers. This
wavelength was selected because 1300 nanometer devices, while moderately
less expensive, are generally limited to distances of 30 to 50 kilometers due
to fiber loss as the distances increases-similar to the fiber channel. 1550
nanometers, on the other hand, with its significant advantage (.19dB/km
versus .34/dB/km fiber loss) offers over two times the distance light may be
reliably detected with economical terminal components
To overcome the performance degradation caused by collisions, NBase
Communications has elected to implement its line of Ethernet switches with
full duplex (collisionless point-to-point connectivity) transmission functionality.
Thus, CSMA/CD is not an issue since two separate fibers are being utilized.
To conserve fiber deployment, full duplex over a single fiber is available by
adding a splitter-combiner device that provides two separate paths on the
single fiber.
Each of the switches employ logic to enable self learning of the network
addresses which improves overall performance by ensuring that only valid
packets destined for another segment will be transferred across the switch.
This feature, together with a VLAN implementation will reduce network
inefficiencies associated with broadcast storms and other bandwidth limiting
issues.
With immediate availability of extended distance Ethernet, it is possible to
implement an extended LAN which would be useful for most organizations.
For example:
A Federal, State or Local Government agency with multiple offices in
the same geographic area could extend the core LAN to the outlying
site. Establishing a VLAN for each autonomous group would insure
security and lower the cost of acquisition and support since all
maintenance could be from the central site.
The Education market (universities and school districts) could employ
this design with significant life cycle cost savings without having to
implement routers to connect the remote buildings to the central site.
Commercial firms with distributed plants in a Metropolitan market
would benefit considerably from this high bandwidth solution. Moreover,
with the rapid acceptance of corporate Intranets, a large percentage of
the IP traffic would remain inside the Corporate LAN without having to
pass through bandwidth limiting firewalls. Employing "Switch Where
You Can, Route Where You Must" in the extended LAN produces a flat
switched network but implements wireline routing where necessary for
security, broadcast containment or address management. Utilizing
techniques like "IP Switching" and "Cut-Through Routing" will produce
dramatic thruput advances and reduced capital outlays.
Telcos could lower their provisioning costs while offering simple LAN
Ethernet and IP services to a variety of businesses. Implementing VPN
functionality creates an environment as if each business appears to
have their own LAN even though the service provider is sharing the fiber
bandwidth with several businesses.
Cable firms can immediately provide competitive IP services by
collapsing their broadband network into an Ethernet backbone without
effecting their video capabilities. By funneling the IP traffic into
redundant Internet Access points will provide reliable and efficient
service advantages over other designs.
In most instances, the alternative to providing the connectivity and bandwidth
for Corporate, Telco, Cable, Government and Educational backbones has
been Asynchronous Transfer Mode or ATM. In a recent survey conducted by
the ATM Forum, 62 percent of the survey respondents' chose ATM to provide
increased bandwidth and another 32 percent elected ATM to support high
volume data traffic. Very few chose ATM to support delay sensitive
applications. ATM has great value for organizations, which seek to implement
applications that demand a Quality of Service for isochronous communication
such as voice and video. Unfortunately, as L. G. Roberts indicated in a report
to the ATM Forum, the current implementation of LANE (ATM emulation of
Ethernet) does not support ATM's QoS features. Therefore without
End-to-End ATM devices at each desktop, ATM cannot utilize its vaunted
QoS features.
These isochronous applications, however, are not the reason why networks
are becoming saturated. Networks are becoming saturated because of
increases in traditional transaction traffic and the aforementioned TCP/IP
traffic. In this instance, ATM is at a significant disadvantage to Gigabit
Ethernet in efficiency. Depending on the packet size, Ethernet offers up to a
thirteen- percent advantage. Primarily, this inefficiency is caused because
ATM must employ, one or more of the following protocols to be installed and
running: MPOA, PNNI, LANE , Q.2931 and ATM/AAL5.
IP Provisioning costs are also lower. Conservative comparisons routinely give
Gigabit Ethernet a five-fold advantage over ATM, in addition to the simplicity
and ease of implementing the Gigabit Ethernet design. Moreover, a common
budgeting rule in the industry is that equipment will cost eight to ten times to
operate as it does to buy. Thus, the life cycle cost advantage of Ethernet can
easily become an order-of magnitude less than ATM.
Since no apparent single architecture completely solves the network
designers' goals, the best long-term solution appears to be a combination of
both ATM and Gigabit Ethernet if the end user has an ATM system
implemented today. The end user would then have choice of both
technologies. Gigabit Ethernet would provide for bandwidth intensive data
applications such as IP Intranets and ATM would provide for real-time
isochronous applications. To facilitate the integration of this hybrid design,
NBase Communications has elected to implement ATM and Gigabit Ethernet
on a single platform. In this design, an ATM uplink is offered to connect to an
established ATM LAN or WAN. High-resolution multimedia, voice and video
would continue to be served in a predictable connection orientated system.
If an ATM backbone is not installed, Gigabit Ethernet can today meet
performance, resiliency and scalability issues once promised by ATM as its
competitive advantage over Ethernet.
For example, the new IP applications will support multi-media features that
ATM once claimed as an advantage. While ATM provides good IP multicast
support, virtual circuit scalability problems will arise. Ethernet does not face
this limitation.
ATM currently scales from 25M to 622M with OC-48 pipes of 2.5G for LAN
implementation targeted for the year 2000. Gigabit Ethernet scales from 10M
to 1000M today with 5G to 10G available at the same time OC-48 arrives.
Thus, Gigabit Ethernet brings more LAN scalability today than ATM-- A
hundred-fold as compared to four for ATM.
Further, the fiber may be combined via the Trunk Group feature of Ethernet to
provide a larger pipe. If one link fails, the multiplexed circuits will still function
and instantly assume the failed links traffic. Present designs provide for a 4 to
1 consolidation.
More important, if the Gigabit Ethernet link is designed to remain under 60%
peak utilization, (same capability as a 100 percent utilized OC-12 circuit)
QoS for isochronous applications can be delivered with dependability
comparable to ATM. IEEE 802.1p/q provides for data stream analysis and
flow classification. More important is that it performs this function without
changes to the O/S or application. Further, with proper queuing and buffering
by end-stations, this traffic does not need to be sheltered in dedicated
pipes.
Moreover, new advances in Gigabit Ethernet filtering, prioritization and traffic
rerouting will allow higher design goals that meet the safety thresholds of QoS
but further expand Gigabit Ethernet's performance advantage.
Clearly, the 1000Mbps architecture with Industry unique extended distance
capabilities has proven itself in the marketplace. With the growing availability
of fiber, the ability to design a contiguous LAN within a Metropolitan area or
campus provides a network designer with cost effective backbone alternatives.
With over 80 percent of all network nodes worldwide being Ethernet, it is a
technology most network managers understand. The simplest way of doing
Things are the best way of doing things. This familiarity coupled with scalable
thruput plus overcoming the distance barrier assures NBase Communications
family of Gigabit Ethernet switches a place in every network. |
