Ethernet Fundamentals

Question 1

Ethernet Fundamentals

Answer 1

▪ In early computer networks, there were many different network
technologies competing for a portion of the market share
▪ Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), and others
fought for dominance
▪ Currently, Ethernet is dominant for Layer 1
▪ Due to Ethernet’s popularity, it is important to understand the
fundamentals of Ethernet

Question 2

Origins of Ethernet

Answer 2

Was first run over coax cables (10Base5, 10Base2)
▪ Ethernet has changed to using twisted pair cables
▪ 10BASE-T is Unshielded Twisted Pair
● Maximum speed: 10 Mbps
● Maximum distance: 100 meters

Question 3

Carrier Sense Multiple Access/ Collision Detect (CSMA/CD)

Answer 3

▪ Ethernet devices transmit based on a principle called carrier sense
multiple access/collision detect (CSMA/CD)
▪ Carrier sense
● Listen to the wire, verify it is not busy
▪ Multiple access
● All devices have access at any time
▪ Collision detect
● If two devices transmit at the same time, a collision occurs
● Back off, wait a random time, and try again

Question 4

Collision Domains

Answer 4

▪ Comprised of all devices on a shared Ethernet segment (everything on
same cable or hub)
▪ Devices operate at half-duplex when connected to a hub (Layer 1 device)
▪ Devices must listen before they transmit to avoid collisions when
operating as CSMA/CD

Question 5

Collision Domains with Switches

Answer 5

▪ Ethernet switches increase scalability of the network by creating multiple
collision domains
▪ Each port on a switch is a collision domain, no chance of collisions, and
increases speed
▪ Switches can operate in full-duplex mode

Question 6

Speed Limitations

Answer 6

▪ Bandwidth is the measure of how many bits the network can transmit in
1-second (bps)
▪ Type of cable determines the bandwidth capacity of the network