Cabletron Systems Cabletron BRIM-F6, Сетевое руководство

Страница: 15 / 132

Fast Ethernet 2-3
Review of Networking
• AUI Length: The maximum Attachment Unit Interface (AUI) cable length is
50 m for connections from a transceiver to an Ethernet device. The 50 m
distance is the allowable maximum for standard AUI, while a maximum
length of 16.5 m has been set for office AUI.
• Number of Stations per Network: IEEE standards specify that the maximum
allowable number of stations per un-bridged network is 1,024, regardless of
media type. The 10BASE5 networks are allowed 100 taps per segment, while
10BASE2 networks are allowed 30 taps per segment with a maximum of
64 devices per tap each. (Fiber optic and twisted pair cable are point-to-point
media which do not allow taps or branches).
• Maximum Signal Path: The maximum allowable signal path is 4 repeaters, 5
segments (with at least 2 segments being unpopulated Inter-Repeater Links),
and 7 bridges for all media types.
There are other limitations involved in the IEEE 802.3 standard and the various
cable specifications, which are more detailed and complex. These limitations are
covered in detail in the Cabletron Systems Cabling Guide and the Cabletron Systems
Ethernet Technology Overview.
Fast Ethernet
Fast Ethernet is a networking technology that grew out of the popular Ethernet
technology described above. Fast Ethernet uses the same CSMA/CD media
access method and basic network operation. The main differences between
Ethernet and Fast Ethernet are the available bandwidth and media limitations.
Fast Ethernet increases the available bandwidth of a single network to 100 Mbps,
ten times faster than normal Ethernet. This increase in transmission speed,
however, comes at a cost to the flexibility of the network. By increasing the speed
of transmission by a factor of 10, the required characteristics of Ethernet links
were likewise reduced.
Fast Ethernet networks only support UTP and multimode fiber optics as standard
transmission media. The two standards for these media are 100BASE-TX for
Category 5 UTP, and 100BASE-FX for multimode fiber optics.
The IEEE 802.3u standard defines two different types of Fast Ethernet repeaters:
Classes I and II. All Cabletron Systems Fast Ethernet products discussed in this
document are Class I repeaters. A Fast Ethernet network designed with Class I
repeaters allows a signal path from one station, through a Fast Ethernet link, to a
Class I repeater, through another Fast Ethernet link, to a receiving station. No
other Class I repeaters may be placed in this signal path.
NOTE
If it becomes necessary to extend the network beyond the IEEE
limit of 1,024 devices, a bridge can be used to connect another
full specification Ethernet network.