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SEMESTER 1 Chapter 9
Ethernet
V 4.0
9.1.1
9.1.2
9.1.3
9.1.4
9.1.5
Who originally published the
Ethernet standard and when
was that?
Who and when published
LAN standards?
What is the number for the
Ethernet LAN standard?
What layers of the OSI
model do Ethernet
standards operate at?
What does Ethernet Layer 1
involve?
140 Points
published in 1980 by a consortium of Digital
Equipment Corporation, Intel, and Xerox (DIX).
1985, the Institute of Electrical and Electronics
Engineers (IEEE)
802.3
1 and 2
signals, bit streams that travel on the media,
physical components that put signals on
media, and various topologies
What are the Ethernet Layer Connects to the upper layers via the LLC
2 functions that overcome
Uses addressing schemes to identify devices
the limitations of Ethernet
Uses frames to organize bits into groups
Layer 1?
Uses MAC to identify transmission sources
What are the two sublayers the Logical Link Control (LLC) sublayer and
of the Data Link Layer?
the Media Access Control (MAC) sublayer.
What are the 4 functions of
Makes connection with the upper layers
the LLC?
Frames the network layer packet
Identifies the network layer protocol
Remains relatively independent of the physical
layer
What type of environment is Software
LLC implemented in?
Where is the MAC sublayer NIC
implemented?
What are the 2 primary
Data Encapsulation
functions of the MAC
Media Access Control
sublayer?
What are the 3 primary
Frame delimiting
functions of data
Addressing
encapsulation?
Error detection
What are the two main
Control of frame placement on and off the
functions of the media
media
access control?
Media recovery
What is the underlying
Mulit-access bus
topology of Ethernet?
What is the media access
CSMA/CD Carrier Sense Multiple Access with
control method for
Collision Detection
Ethernet?
What are the four factors
Simplicity and ease of maintenance
that have made Ethernet a
Ability to incorporate new technologies
success?
What part of the Ethernet
standard remains consistent
across all of its physical
implementations?
9.2.1
What was the historic
network that Ethernet was
based on called?
9.2.1.2 Describe the method of
transmission on a hub?
9.2.2
What is legacy Ethernet?
What is the current standard
for Ethernet?
What is full duplex?
What is the difference when
forwarding a frame from a
switch vs. hub?
9.2.3
What two new uses are
requiring the move to
Gigabit Ethernet?
9.2.3.2 Define a MAN?
9.3.1
What is the most significant
difference between the
IEEE 802.3 (original) and
the revised IEEE 802.3?
What were the minimum
and maximum sizes of
Ethernet frames originally?
What is the new maximum
size for a frame?
What happens if the size of
a transmitted frame is less
than the minimum or greater
than the maximum?
9.3.1.2 What are the six portions of
an Ethernet frame
discussed?
9.3.1.3 What is the Frame Check
Sequence (FCS)?
What is the algorithm used
in determining the value of
the FCS?
What happens if the FCS
values do not match?
9.3.2
What was created to assist
in determining the source
and destination address?
Reliability
Low cost of installation and upgrade
Frame structure
Alohanet
A frame received in one port is transmitted out
all other ports
10Base-T network with a hub at its center
100Base-T network with switches
a connection that can carry both transmitted
and received signals at the same time
Hub always send the signal out all ports and
switch sends directly to device if it’s address is
known
Voice over IP (VoIP) and multimedia services
Ethernet connection across an entire city
the addition of a Start Frame Delimiter (SFD)
and a small change to the Type field to include
the Length
the minimum frame size as 64 bytes and the
maximum as 1518 bytes
1522 bytes
It is dropped
Preamble, start frame delimiter, destination
address, source address, length/type, 802.2
header and data, frame check sequence
(4 bytes) used to detect errors in a frame
Cyclical redundancy check
The frame is dropped
Media Access Control (MAC) address
How is an Ethernet MAC
address represented?
9.3.2.2 Define the two parts of an
Ethernet MAC address?
What is another name for
the MAC address?
As an Ethernet frame
passes through a network
what happens if that
devices MAC address
matches the destination
MAC address?
As an Ethernet frame
passes through a network
what happens if that
devices MAC address does
not match the destination
MAC address?
9.3.3.2 Where can you find your
computer’s MAC address?
9.3.4
What is the problem with
physical addressing?
What is the difference
between physical (Network
Layer) and logical (Data
Link Layer) addressing?
9.3.5
When a unicast
transmission used?
9.3.5.2 When is a broadcast
transmission used?
How is a broadcast IP
address represented?
How is a broadcast MAC
address represented?
9.3.5.3 When is a multicast
transmission used?
How can a multicast packet
only be used?
What type of address does
the source have?
What is the multicast MAC
address?
a 48-bit binary value expressed as 12
hexadecimal digits
All MAC addresses assigned to a NIC or other
Ethernet device must use that vendor's
assigned OUI as the first 3 bytes.
All MAC addresses with the same OUI must be
assigned a unique value (vendor code or serial
number) in the last 3 bytes.
Burned-in address
the NIC passes the frame up the OSI layers,
where the decapsulation process take place
The frame is discarded
Ipconfig/all or ipconfig
No meaning outside the local network
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.
when a frame is sent from a single transmitting
device to single destination device
all hosts on that local network (broadcast
domain) will receive and process the packet
All 1’s in the host portion of the IP address
FF-FF-FF-FF-FF-FF
When a frame is sent to a group of computers
as the destination of a packet
Unicast
Begins with 01-00-5E The value ends by
converting the lower 23 bits of the IP multicast
group address into the remaining 6
hexadecimal characters of the Ethernet
9.4.1
9.4.2
How does a shared media
environment operate?
When does a device on a
shared environment
transmit?
Define latency.
Define collision.
How does collision
detection occur?
What happens when all
devices on a shared
medium detect a collision?
What is invoked after a
device receives a jamming
signal?
How does a backoff
algorithm work?
What mode does a device
return to after the backoff
algorithm has expired?
9.4.2.2 What are the three reasons
given that the growth of the
Internet has resulted in
more collisions?
Define a collision domain?
What does the connection
of hubs and repeaters do to
collision domains?
What happens when the
number of collisions
increases significantly?
9.4.3
Which devices extend the
latency in the medium?
Why would an increased
latency cause more
collisions?
9.4.3.2 What is sent before an
entire Ethernet frame is
sent?
address. The remaining bit in the MAC
address is always a "0".
all devices have guaranteed access to the
medium, but they have no prioritized claim on
it. If more than one device transmits
simultaneously, the physical signals collide
and the network must recover in order for
communication to continue.
When it detects that no other computer is
sending a frame, or carrier signal
The time delay between when a process is
started and that same process is detected
When two stations transmit at the same time
When a device is in listening mode it can
detect an increase in amplitude of the signal
above the normal level
they send out a jamming signal
The backoff algorithm
All devices stop transmitting for a random
amount of time
Listening
More devices are being connected to the
network.
Devices access the network media more
frequently.
Distances between devices are increasing.
The media within a network where collsions
can occur
They increase the collision domain size
reduces the network's efficiency and
effectiveness until the collisions become a
nuisance to the user
Hubs and repeaters
The other device may not hear the signal
before it begins to transmit
The preamble
What does asynchronous
communication mean?
What does synchronous
communication mean?
9.4.3.3 What is a bit time?
What is the slot time?
9.4.4
What is interframe spacing?
What happens to interframe
spacing as the network
speed increases?
9.4.4.3 What happens when the
MAC layer is unable to send
a frame after 16 attempts?
9.5.1
What are the four data rates
are currently defined for
operation over optical fiber
and twisted-pair cables?
9.5.2
What are the three principal
10 Mbps implementations of
Ethernet?
9.5.2.2 What are the most popular
implementations of 100
Mbps Ethernet?
9.5.3
What is Gigabit Ethernet
more susceptible to
because of its speed?
What type of transmission
does 1000Base-T allow for?
9.5.4
What is the maximum
number of voltages used on
the media at the same
during transmission?
What are the two main
causes of noise on the line?
What are the ways that
10Gbps can be compared
to other varieties of
Ethernet?
each receiving device will use the 8 bytes of
timing information to synchronize the receive
circuit to the incoming data and then discard
the 8 bytes
the timing information is not required
a period of time is required for a bit to be
placed and sensed on the media
The time it takes for an electronic pulse to
travel the length of the maximum theoretical
distance between two nodes.
time measured from the last bit of the FCS
field of one frame to the first bit of the
Preamble of the next frame
The time reduces
it gives up and generates an error to the
Network layer
10 Mbps - 10Base-T Ethernet
100 Mbps - Fast Ethernet
1000 Mbps - Gigabit Ethernet
10 Gbps - 10 Gigabit Ethernet
10BASE5 using Thicknet coaxial cable
10BASE2 using Thinnet coaxial cable
10BASE-T using Cat3/Cat5 unshielded
twisted-pair cable
100BASE-TX using Cat5 or later UTP
100BASE-FX using fiber-optic cable
Noise
the transmission and reception of data in both
directions - on the same wire and at the same
time
17
cable and termination problems
Frame format is the same, allowing
interoperability between all varieties of legacy,
fast, gigabit, and 10 gigabit Ethernet, with no
reframing or protocol conversions necessary.
Bit time is now 0.1 nS. All other time variables
scale accordingly.
Because only full-duplex fiber connections are
9.6.1
What is the problem
associate with the classic
Ethernet implementation
using hubs?
List the four problems
related to the
implementation of classic
Ethernet?
9.6.2
How do switches segment a
LAN?
What does the separation of
collision domains mean for
the bandwidth to the
device?
9.6.2.2 What are the three reasons
that bandwidth increases
dramatically when each
device is connected to a
switch port?
What are the three reasons
that hubs are still being
used?
9.6.3
Describe selective
forwarding?
What is the process called
when the switch holds the
frame until the receiving
node is available called?
Describe the store-andforward operation mode of a
switch?
How does a switch use a
MAC table?
9.6.3.2 What are the five basic
operations of a switch?
How does a switch learn a
MAC address?
What happens when an
used, there is no media contention and
CSMA/CD is not necessary.
The IEEE 802.3 sublayers within OSI Layers 1
and 2 are mostly preserved, with a few
additions to accommodate 40 km fiber links
and interoperability with other fiber
technologies.
high levels of collisions on the LAN
Scalability, Latency, Network Failure, and
Collisions
Separate collision domains
Full media bandwidth to each device
Dedicated bandwidth to each port
Collision-free environment
Full-duplex operation
Availability, Economics, and Requirements
establishing a momentary point-to-point
connection between the transmitting and
receiving nodes
Store-and-forward
The switch receives the entire frame and
checks the FCS before forwarding the frame
The incoming frame destination MAC address
is compared to the MAC table to decide which
port to forward the frame to
Learning
Aging
Flooding
Selective Forwarding
Filtering
The source address of the incoming frame
The address is removed from the MAC table
addresses countdown
reaches 0?
What happens when a
switch does not know the
destination address?
What type of frames will not
be forwarded?
9.7.1
What are the two basic
functions of ARP?
What are the names of the
tables that store the list of
MAC addresses with the
network address?
What are the two ways a
computer can gather MAC
addresses?
What are the 2 destination
addresses in an ARP
Request?
9.7.2
If the destination is on the
local network segment,
what MAC address is used?
If the destination is on a
remote network, what MAC
address is used?
If the MAC address of the
gateway is unknown, what
process is used?
9.7.2.2 What is the most common
reason for using a proxy
ARP?
9.7.3
How long are addresses
held in the ARP table?
9.7.4
How could ARP requests
impact performance on a
network?
What is another problem
that may be associated with
ARP?
The frame is flooded out all but the incoming
port
A frame with a destination of the same port, a
corrupt frame, and security reasons
Resolving IPv4 addresses to MAC addresses
Maintaining a cache of mappings
ARP table or ARP Cache
From an incoming frame or using an ARP
request
Broadcast MAC address and the destination
MAC address
The device MAC address
The gateway MAC address
ARP Request
When the device can not determine if the host
is on the same network or not
2 minutes unless used again in those 2
minutes and then 10 minutes
Too many broadcasts at once that each host
receives and processes therefore slowing
down the network
Security- ARP spoofing which causes errors
on the network
* 3 Ethernet media types:
– Coaxial cable - bus topology (old technology)
– Copper cable (UTP) - star topology
– Optical fiber cable - star topology
* You need to be able to do Hexadecimal Number conversion.
 For example, the binary value 0000 1010 is shown in hexadecimal as 0A.
* Ethernet operates in the lower two layers of the OSI model: the Data Link layer and
the Physical layer.
•
IEEE 802.2 standard describes the LLC sublayer
•
•
LLC handles the communication to the upper layers
LLC takes the network protocol data, and adds control information to help deliver the
packet to the destination node.
•
IEEE 802.3 standard describes the MAC sublayer and the Physical layer functions.
• Data Encapsulation
• Frame delimiting
• Addressing
• Error detection
• Media Access Control
• The MAC sublayer controls the placement of frames on the media and
the removal of frames from the media
• CSMA/CD.
•
Make sure you also remember the name mapping between OSI and TCP/IP model.
* The Frame – Encapsulating the Packet.
–
The Ethernet frame structure adds headers and trailers around the Layer 3 PDU.
* MAC address:
 The MAC address is often referred to as a burned-in address (BIA) because it is
burned into ROM (Read-Only Memory) on the NIC.
 All MAC addresses assigned to a NIC must use that vendor's assigned OUI as
the first 3 bytes.
 All MAC addresses with the same OUI must be assigned a unique value in the
last 3 bytes.
* Make sure you still remember this:
– IP address global
– Mac address local
* What is the definition of “Interframe Spacing”? How does it work?
 The Ethernet standards require a minimum spacing between two non-colliding
frames.
 This gives the media time to stabilize after the transmission of the previous frame
and time for the devices to process the frame.
* What is the “random backoff” in CSMA/CD? How does it work?
 After a collision occurs and all devices allow the cable to become idle (each waits
the full interframe spacing), the devices whose transmissions collided must wait
an additional - and potentially progressively longer - period of time before
attempting to retransmit the collided frame.
 The waiting period is intentionally designed to be random so that two
stations do not delay for the same amount of time, which would result in
more collisions.
 Among the groups of devices that received the jam signals and starts the
backoff timer, the station that will 1st try to resend the frame is the station
whose timer expired first. (ADD this to the PPT)
* CSMA/CD: Collisions will occur in any shared media topology.
– Collisions are the cost that Ethernet pays to get the low overhead associated with
each transmission.
– Every time a collision happens on a network, all transmission stops for a period
of time.
– Collisions are the cost that Ethernet pays to get the low overhead associated with
each transmission.
– Using hubs to provide network access to more users reduces the performance
because the fixed capacity of the media has to be shared between more devices.
* These are all CSMA/CD LAN access protocols:
* Full Duplex (typically on a switch):
– In a network that uses twisted-pair cabling, one pair is used to carry the
transmitted signal. A separate pair is used for the return or received signal. It is
possible for signals to pass through both pairs simultaneously.
– In full duplex mode, there is no contention for the media (no collision). Thus, a
collision domain no longer exists.
* Legacy Ethernet (Hub and half-duplex)
– In 10BASE-T networks, typically the central point of the network segment was a
hub. This created a shared media.
– Because the media is shared, only one station could successfully transmit at a
time. .
– As more devices were added to an Ethernet network, the amount of frame
collisions increased significantly.
* Using switch instead of hub:
– Dedicated bandwidth to each port
– Collision-free environment
– Full-duplex operation
– Increase throughput
* What is ARP?
 For a frame to be placed on the LAN media, it must have a destination MAC
address. The ARP protocol provides two basic functions:
 Resolving IPv4 Addresses (known) to MAC Addresses (unknown)
 Maintaining the ARP Table
 When the destination device is on the same LAN (subnet)
 ARP sends a Layer 2 broadcast to all devices on the Ethernet LAN. The
frame contains an ARP request packet with the IP address of the
destination host.
 The node receiving the frame that identifies the IP address as its own
responds by sending an ARP reply packet back to the sender as a unicast
frame. This response is then used to make a new entry in the ARP table.
 If the destination IPv4 host is not on the local network,
 The source node will use the MAC address of the gateway as the
destination address for frames containing an IPv4 packet addressed to
hosts on other networks.
 In the event that the gateway entry is not in the table, the normal ARP
process will send an ARP request to retrieve the MAC address associated
with the IP address of the router interface