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OSI Layer 2: Data-Link Layer Protocols and Applications

As you can see, there are quite a few technologies to understand, and this

is where we will start.

Ethernet/IEEE 802.3

These two terms actually refer to different things. Ethernet is a communica-
tion technology and IEEE 802.3 is a variety of Ethernet. Ethernet, in the
more specific sense, is a carrier sense, multiple access/collision detection
(CSMA/CD) local area network. This means that the network uses these
attributes--carrier sense, multiple access, and collision detection--to
enhance communication. This definitely does not mean that Ethernet is the
only technology that uses these attributes. In today's technical jargon, how-
ever, Ethernet is getting closer to meaning all CSMA/CD technologies.

Both Ethernet and IEEE 802.3 are broadcast networks. All frames that

cross a given segment can be heard by all machines populating that segment.
Because all machines on the segment have equal access to the physical media,
each station tries to wait for a quiet spot before it transmits its data. If two
machines talk at the same time, a collision occurs.

Ethernet services both the Physical and Data-Link layers, whereas IEEE

802.3 is more concerned with the Physical layer and how it talks to the Data-
Link layer. Several IEEE 802.3 protocols exist; each one has a distinct name
that describes how it is different from other IEEE 802.3 protocols. Table 2.17
summarizes the differences between the different IEEE 802.3 versions.

T A B L E 2 . 1 7

IEEE 802.3 Characteristics

802.3 Values
10Base5

10Base2

1Base5

10BaseT

100BaseT

10Broad36

Data rate
(Mbps)

100

Signaling
Method

Baseband

Broadband

Maximum
Segment
Length (m)

500

185

250

100

1800

Media

50 Ohm coax

50 Ohm
coax

Unshielded
twisted pair

75 Ohm
coax

Topology

Bus

Star

Bus

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