Network Fundamentals: Ch9 - Ethernet

Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Network Fundamentals
Abdelkhalik Elsaid Mousa
abdu.elsaid@yahoo.com
http://abdelkhalik.staff.scuegypt.edu.eg/

IEEE - Standards
• The first LAN in the world was the original version of Ethernet.
• The first Ethernet standard (802.3) was published in 1980.
• Ethernet is the predominant LAN technology in use today.
• Ethernet standards define both L2 protocols and L1 technologies.

Ethernet- L1 and L2

Logical Link Control – Connecting to the upper layers
• Ethernet separates the functions of the Data Link layer into two
distinct sublayers, LLC and MAC.
• LLC has the following characteristics
 IEEE 802.2.
 is implemented in software.
 can be considered the driver software for the NIC.

MAC – Getting data to the media
• IEEE 802.3.
• MAC is implemented in hardware.
• Typically in the computer NIC.
• The underlying logical topology of Ethernet is a multi-access bus.

Historic Ethernet
• The foundation for Ethernet technology in 1970 was Alohanet.
• Alohanet was a digital radio network that transmits information over a shared
radio frequency between the Hawaiian Islands.
• The techniques for using a shared medium were later applied to wired
technology in the form of Ethernet.

Early Ethernet Media
• Used coaxial cable to connect computers in a bus topology.
• It was known as Thicknet (10BASE5) and Thinnet (10BASE2).

Ethernet Collision Management
• Legacy Ethernet
 Based on hubs.
 10BASE-T networks.
 half-duplex communication.
 Uses CSMA/CD.
• Current Ethernet
 Based on switches.
 100BASE-TX.
 Full-duplex communication.
 Gigabit Ethernet.

The Frame – Encapsulating the packet
• There are two styles of Ethernet framing: IEEE 802.3 (original)
and the revised IEEE 802.3 (Ethernet).
• The IEEE 802.3ac standard, released in 1998, extended the
maximum allowable frame size to 1522 bytes.

The Ethernet MAC
• The MAC address (BIA) because it is burned into ROM on the NIC.
• IEEE requires a vendor to follow two simple rules:
1. All MAC addresses must use vendor's OUI as the first 3 bytes.
2. All MAC addresses with the same OUI must be assigned a
unique value (vendor code) in the last 3 bytes.

The Ethernet MAC
• The OUI and the vendor assigned number ensure that the
assigned MAC addresses remains unique.
• You will see them expressed in different ways.
Cisco MAC Address
00-60-2F-3A-07-BC
00:60:2F:3A:07:BC
0060.2F3A.07BC
Intel MAC Address
00-20-E0-6B-17-62
00:20:E0:6B:17:62
0020.E06B.1762

Another layer of Addressing
• The Network layer address enables the packet to be forwarded toward its
destination.
• The Data Link layer address enables the packet to be carried by the local
media across each segment.

Ethernet Unicast

Ethernet Broadcast

Ethernet Multicast

Ethernet Multicast
• The multicast MAC address begins with 01-00-5E in hexadecimal.
• The value ends by converting the lower 23 bits of the IP multicast
group address into the remaining 6 hexadecimal characters of
the Ethernet address. The remaining bit is always a "0".

Media Access Control in Ethernet

CSMA/CD – The process

Carrier Sense
Multiple Access
Collision Detection
JAM Signal
Random Backoff

• Hubs, multi-port repeaters, and repeaters are intermediary
devices that extend the distance that Ethernet cables can reach.
• Collision domain: The area of a network where collisions can
occur.

Ethernet Timing
• Latency
 The electrical signal that is transmitted takes a certain amount
of time (latency) to propagate (travel) down the cable.
 Each hub or repeater in the signal's path adds latency as it
forwards the bits from one port to the next.
 This delay increases the likelihood that collisions will occur
because a listening node may transition into transmitting
signals while the hub or repeater is processing the message.

Ethernet Timing
• Timing and Synchronization
 Ethernet with throughput speeds of 10 Mbps and slower are
asynchronous.
 Ethernet implementations with throughput of 100 Mbps and
higher are synchronous.

Ethernet Timing
• Bit Time: The period of time required for a bit to be placed and sensed on the
media.
• Slot Time: is the time it takes for an electronic pulse to travel the length of the
maximum theoretical distance between two nodes.
 It is also the time that a transmitting station waits before attempting to
retransmit following a collision

Interframe Spacing
• The minimum interval, in bit-times, that a station has to wait
before sending another frame
• Allows slower stations to process the frame and “get ready” for
the next frame.

Types of Ethernet
Ethernet Type Bandwidth Cable Type Maximum Distance (m)
10BASE5 10 Mbps Thick Coax 500
10BASE2 10 Mbps Thin Coax 185
10BASE-T 10 Mbps Cat3/Cat5 UTP 100
100BASE-TX 100 Mbps Cat5 UTP 100
100BASE-FX 100 Mbps MM or SM Fiber 400/2000
1000BASE-T 1 Gbps Cat5e UTP 100
1000BASE-TX 1 Gbps Cat6 UTP 100
1000BASE-SX 1 Gbps MM Fiber 550
1000BASE-LX 1 Gbps SM Fiber 2000
10GBASE-T 10 Gbps Cat6a/Cat7 UTP 100
10GBASE-LX4 10 Gbps MM Fiber 300
10GBASE-LX4 10Gbps SM Fiber 10,000

10 Mbps Ethernet
• The principal 10 Mbps implementations of Ethernet include:
1. 10BASE5 using Thicknet coaxial cable
2. 10BASE2 using Thinnet coaxial cable
3. 10BASE-T using Cat3/Cat5 unshielded twisted-pair cable
• 10BASE5, and 10BASE2 used coaxial cable in a physical bus, no longer used.
• 10BASE-T uses Manchester-encoding over 2 UTP cables. Early used Cat3, Now
Cat5. Physical star using hub, up to 100 m.

100 Mbps Ethernet (FastEthernet)
• The popular implementations of 100 Mbps Ethernet are:
1. 100BASE-TX using Cat5 or later UTP
2. 100BASE-FX using fiber-optic cable
• 100BASE-TX support transmission over two pairs of Cat 5 UTP copper, Uses
4B/5B encoding, Physical star using switch.
• The 100BASE-FX standard uses the same signaling procedure as 100BASE-
TX, but over optical fiber media rather than UTP copper.
• 100BASE-FX uses SC connector.

1000 Mbps Ethernet (GigabitEthernet)
• 1000BASE-T Ethernet provides full-duplex transmission using all four pairs in
Category 5 or later UTP cable.
• 1000BASE-T uses 4D-PAM5 line encoding to obtain 1 Gbps data throughput.
• 1000BASE-SX and 1000BASE-LX Ethernet Using Fiber-Optics.
• 1000BASE-SX and 1000BASE-LX - offer the following advantages over UTP:
noise immunity, small physical size, and increased unrepeated distances and
bandwidth.
• The transmission coding is based on the 8B/10B encoding scheme.

Ethernet – Future Options
• The IEEE 802.3ae standard was adapted to include 10 Gbps, full-duplex
transmission over fiber-optic cable.
• 10GbE is evolving for use not only in LANs, but also for use in WANs and
MANs.
• With 10Gbps Ethernet, flexible, efficient, reliable, relatively low cost end-to-
end Ethernet networks become possible.

Layer 1 Devices
• Repeater: is a network device used to regenerate a signal.
• Repeaters regenerate signals distorted by transmission loss due
to attenuation.
• Rule: no more than four repeaters can be used between hosts on
a LAN.

Layer 1 Devices
• A Hub: is a multi-port Repeater.
• Hubs takes data bits from input port and floods it to all other
ports (logically bus).
• Repeater and hub work in half duplex mode.
• All ports of the Repeaters and Hubs are members in a single
collision domain, and single broadcast domain
• Rule: no more than four hubs can be used between hosts on a
LAN.

Layer 2 devices
• A layer 2 device is a device that understand MAC, for example:
• NIC (Network Interface Card)
• Bridge:
 address learning
 forwarding decisions are based on software
 bridge is used for LAN segmentation
 max. 16 port.
• Switch:
a multi-port bridge up to 256 port
forwarding decisions are based on hardware ASIC
faster than bridge

Network Fundamentals: Ch9 - Ethernet

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