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Chapter 2

Connecting the Switch Block

DEC, Intel, and Xerox pushed Ethernet, while Burroughs, Concord Data

Systems, Honeywell, Western Digital, and later, General Motors and Boe-
ing, pushed 802.4. IBM took on 802.5.

The IEEE then created the 802.3 subcommittee to come up with an Ether-

net standard that happens to be almost identical to the Ethernet_II version of
Ethernet. The two differ only in their descriptions of the Data Link layer.
Ethernet_II has a Type field, whereas 802.3 has a Length field. Even so,
they're both common in their Physical layer specifications, MAC addressing,
and understanding of the LLC layer's responsibilities.

See CCNA: Cisco Certified Network Associate Study Guide by Todd Lammle

(Sybex, 2000) for a detailed explanation of Ethernet frame types.

Ethernet_II and 802.3 both define a bus-topology LAN at 10Mbps, and

the cabling defined in these standards are identical:

10Base2/Thinnet Segments up to 185 meters using RG58 coax at
50 ohms.

10Base5/Thicknet Segments up to 500 meters using RG8 or 11 at
50 ohms.

10BaseT/UTP All hosts connect using unshielded twisted-pair (UTP)
cable to a central device (a hub or switch). Category 3 UTP is specified to
10Mbps, category 5 to 100Mbps, category 6 to 155Mbps, and category
7 to 1Gbps.

Switched Ethernet

Ethernet is the most popular type of network in the world and will continue
to be so. It is important to understand how hubs and switches work within
an Ethernet internetwork.

By using switched Ethernet in layer 2 of your network, you no longer have

to share bandwidth with the different departments in the corporation. With
hubs, all devices have to share the same bandwidth, which can cause havoc
in today's networks.

Remember that layer 2 switches break up collision domains, but the net-

work is still one large broadcast domain. Switched Ethernet has replaced
shared hubs in the networking world because each connection from a host to

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