The ISO/IEC 11801 cable model is the network model on which
the IEEE 802.3 standards are based:
Campus
distributor�The term
campus refers to a
facility with two or more buildings in a relatively small area. This is the
central point of the campus backbone and the telecom connection point with the
outside world. In Ethernet LANs, the campus distributor would typically be a
gigabit switch with telecom interface capability.
Building
distributor�This is the building's connection point to the campus
backbone. An Ethernet building distributor would typically be a 1000/100- or
1000/100/10-Mbps switch.
Floor
distributor�This is the floor's connection point to the building
distributor. ISO/IEC 11801 recommends at least one floor distributor for every
1000
of floor space in office environments, and, if possible, a separate distributor
for each floor in the building. An Ethernet floor distributor would typically be
a 1000/100/10- or 100/10-Mbps switch.
Telecom
outlet�This is the network connection point for PCs, workstations, and
print servers. File servers are typically colocated with and directly connected
to the campus, building, or floor distributors, as appropriate for their
intended use.
Campus
backbone cabling�This is typically single- or multimode cable that
interconnects the central campus distributor with each of the building
distributors.
Building
backbone cabling�This is typically Category 5 or better UTP or multimode
fiber cable that interconnects the building distributor with each of the floor
distributors in the building.
Horizontal
cabling�This is predominantly Category 5 or better UTP cable, although a
few installations are using multimode fiber.
As with UTP cable selection, the choice of link media and
intermediate network nodes should always be made with an eye to future
transmission rate needs and the life expectancy of the network elements,
unpredictable though they may be. In the 1990s, LAN transmission rates increased
100 times and, by 2002, will increase yet another 10 times.
This does not mean that all�or even some�end stations and
their interconnecting links will require gigabit capability. It does mean,
however, that more central network nodes (such as most campus distributors and
many building distributors) should be equipped with gigabit capability, and that
all floor distributors should have at least 100 Mbps capability. It also means
that all network switches should be nonblocking and that all ports should have
full-duplex capability, and that any new campus backbone links should be
installed with single-mode fiber.
Link Aggregation�Establishing Higher-Speed Network Trunks
Link aggregation is a recent optional MAC capability that
allows several physical links to be combined into one logical higher-speed
trunk. It provides the means to increase the effective data rate between two
network nodes in unit multiples of the individual link transmission rate rather
than in an order-of-magnitude step.
Link aggregation can be a cost-effective way to provide
higher-speed connections in Ethernet LANs that are reaching saturation with 100
Mbps transmission rates but that won't require gigabit capability, at least in
the short term. For example, the maximum length for 62.5
multimode fiber links is 2000 meters at 100 Mbps, and multimode fiber has been
often used for campus backbone links. The logical upgrade would seem to be to
reuse these links for 1000 Mbps operation, but the maximum supportable length
for multimode fiber is only 700 meters and only with 1000Base-LX. If the
existing links are longer than 700 meters, aggregating
existing links
will support an effective transmission rate of (100 Mbps.
Link aggregation should be viewed as a network
configuration option that is primarily used in the few interconnections that
require higher data rates than can be provided by single links, such as
switch-to-switch and in switch-to-file server. It can also be used to increase
the reliability of critical links. Aggregated links can be rapidly reconfigured
(typically in about 1 second or less) in case of link failure, with low risk of
duplicated or reordered frames.
Link aggregation does not affect either the IEEE 802.3 data
frame format(s) or any higher layers in the protocol stack. It is
backward-compatible with "aggregation-unaware" devices and can be used with any
Ethernet data rate (although it does not make sense for 10 Mbps because it would
likely cost less to procure a pair of 100-Mbps NICs). Link aggregation can be
enabled only on parallel point-to-point links and those that support full-duplex
same-speed operation.
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