This document discusses Ethernet networking. It describes Ethernet's success due to its simplicity, ease of maintenance, and ability to incorporate new technologies reliably and at low cost. It explains that Ethernet uses layer 2 framing to encapsulate data and that each network interface has a unique 48-bit MAC address identifying the device manufacturer and interface. It also details how Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) for network access, including having devices listen for collisions while transmitting and use jamming signals and back-off timers when collisions occur.

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Module 3
Common Types of Networks
By Dr. Percy DIAS

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Introduction to Ethernet
• The success of Ethernet is due to its
simplicity and ease of maintenance, as
well as its ability to incorporate new
technologies, reliability, and low cost of
installation and upgrade.

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Characteristics of Network Media used in Ethernet
3

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Layer 2 Framing
• Framing is the Layer 2 encapsulation process;
a frame is the Layer 2 protocol data unit.
• Generic Frame Format

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Naming
• Each NIC has a burned-in (permanent) MAC
address.
• Ethernet uses MAC addresses that are 48 bits in
length and expressed as 12 hexadecimal digits.
• The first 6 hexadecimal digits, which are
administered by the IEEE, identify the
manufacturer or vendor and thus comprise the
organizational unique identifier (OUI).

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MAC Address Format

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Ethernet - Carrier Sense Multiple Access with
Collision Detection (CSMA/CD)

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CSMA/CD
• The CSMA/CD algorithm in detail:
– Wait until the LAN is silent
– Send a frame
– Transmitting device listens for collisions while
transmitting
– If no collisions occur, process is complete
– All devices whose transmitted frames collided send
a jamming signal (32 bits of 1s and 0s)
– All devices set semi-random collision back-off timers.
– Once the timer expires, a device can begin the
process again

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Cisco Academy 3
Slide 2: CCNA1 6.1.1
Slide 4 – 5: CCNA1 6.1.5
Slide 6 – 7: CCNA1 6.1.4
Slide 8: CCNA1 6.2.2
References
Cisco Academy 4
Slide 2,4,6: Networking
Fundamentals 7.3.1-
7.3.5
Slide 8: Networking
Fundamentals 9.4.1-
9.4.2