Information Technology Reference
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and switches that operate at either 10 or 100 Mbps (referred to as 10/100BaseT) have
become ubiquitous. Then we will point out the things that make 100 and 1000BaseT
different. Copper 10 Gbps networking, called 10GBaseT, is covered in another chapter,
but it essentially is just a faster version of 1000BaseT4. Other 10-Gig copper variations
and the fiber-optic 10-Gig standards are covered in the same chapter.
10/100BaseT Networking
The 10/100BaseT (and 1000BaseT) Ethernet topology is an active star, rather than
the Tapped Bus topology of 10Base5 and 10Base2 (see Appendix B). The operation
of 100BaseT is identical to 10BaseT. 1 This star topology is quite compatible with
the standard home-run method of commercial telephone-style wiring. Although the
use of existing telephone wiring was originally the goal of a twisted-pair Ethernet,
the standards now recommended that special LAN-certified twisted-pair wire be
used exclusively for the LAN network connection. Telephone wiring should be done
using a separate cable to be totally in step with the standard.
10/100BaseT Hubs. A typical 10/100BaseT installation is shown in Fig. 2.2. The
center of the star topology is a 10/100BaseT hub. Each workstation (or server) has
a 10/100BaseT network adapter port that is connected to the hub over a twisted-
pair cable. The standard specifies a maximum 90-m distance for each cable leg, plus
a total of 10 m for interconnection, both at the workstation and at the hub.
Modular cords, jacks, punchdowns, cross-connects, and patches are all allowed.
While these wiring devices resemble their telephone counterparts, there are impor-
tant differences that make them “data grade.” Some of these differences are evident
by the performance certifications needed to meet the standards for LAN wiring.
A significant difference between 10/100BaseT and Ethernet coax topologies is
the addition of an active hub device. 10/100BaseT still uses the CSMA/CD signal-
ing method. Remember, with the Ethernet coax topologies, any transmission by a
station is passively distributed by the coax cable to all the other connected stations.
In 10/100BaseT, however, a transmission by a workstation first goes to the hub,
which then repeats (retransmits) the signal to all of the other connected stations.
Each port thus acts as a transceiver (repeater hop). 2
1 In fact, most Ethernet hubs/switches today are dual 10/100 speed ports, often with a high-speed (giga-
bit) uplink. All-gigabit switches are available, as well as modular switches that let you mix speeds as
needed.
2 Ethernet switches do not necessarily repeat all packets received to every other port, unless it is a
broadcast packet. But, for purposes of topology, each port-to-port link “counts” as a repeater hop.
Switches, or switch-hubs, will be covered later in this section.
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