Chapter 5
Chapter 5
Ethernet Basics
Physical Layer Ethernet Standards
Data Link Layer Ethernet Standards
Ethernet Security
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
Four Introductory Chapters
◦ Gave you the concepts and principles to apply for
the rest of the term
◦ Chapter 1: Core concepts
◦ Chapter 2: Standards concepts
◦ Chapter 3: Security principles
◦ Chapter 4: Network management
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Three Chapters on Local Area Networks
◦ Chapter 5: Wired Ethernet LANs
◦ Chapters 6 and 7: Wireless LANs
◦ Governed by Layer 1 and Layer 2 Standards

Remaining Chapters
◦ Chapters 8 and 9: TCP/IP Internetworking
◦ Chapter 10: Wide Area Networks
◦ Chapter 11: Applications
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Characteristic
Location
Consequence
of Location
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Local Area
Network (LAN)
Located entirely
on customer’s
premises
Owning
company
operates the
LAN
Wide Area Network
(WAN)
Must carry
transmissions
beyond customer’s
premises
User must contract
with a carrier that
has rights of way to
carry wires between
premises
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Characteristic
Technology
and Service
Consequence
of Corporate
versus Carrier
Ownership
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Local Area
Network (LAN)
Owner can use
any technology
and service
options it wishes
Wide Area Network
(WAN)
Customer is limited
to technologies and
service options
offered by available
carriers
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Local Area
Network (LAN)
Labor
Owner must do
Consequences all operation and
of Corporate
maintenance
versus Carrier work
Ownership
Characteristic
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Wide Area Network
(WAN)
Operational and
maintenance work is
done by the carrier
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Characteristic
Economics
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Local Area
Network (LAN)
Transmission
distances are
short, so the
cost per bit
carried is low
Wide Area Network
(WAN)
Transmission
distances are long,
so the cost per bit
carried is high
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Characteristic
Local Area
Network (LAN)
Wide Area Network
(WAN)
Speed
Very high
Consequences speeds are
of Economics affordable
Customers are
content with lower
speeds
Design
Optimization of
Consequences transmission
of Economics capacity is not
pressing
Optimization of
transmission
capacity is critical
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Workgroup Switches Connect Hosts to
the Network
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Core Switches Connect Switches
to Other Switches
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Hosts Normally Connect to Workgroup
Switches Through UTP Copper Wiring
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Switches Often Connect to Other Switches
Through Optical Fiber
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Characteristic
Unshielded
Twisted Pair
Optical Fiber
Medium
Copper wire
Glass
Signal
Electrical
Light
Maximum
Usually 100
Distance in LANs meters
Usually 200 to
500 meters
Speed
Similar
Similar
Cost
Lower
Higher
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Ethernet Basics
Physical Layer Ethernet Standards
Data Link Layer Ethernet Standards
Ethernet Security
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NOT just 4 pairs!
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Propagation
Effect(s)
Impact
Installation
Discipline
Attenuation
Signal may become too low to
be received properly.
Limit cord distance
to 100 m
Noise
Random electromagnet energy
in the wire (noise) adds to the
signal and may produce errors.
Terminal
crosstalk
interference
Interference by other wire pairs Limit untwisting of
in the cord is crosstalk
the wires to
interference.
1.25 cm (0.5 in)
Crosstalk interference at the
two ends where the wires are
untwisted is terminal crosstalk
interference. Major problem
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Ethernet
Signaling
Standard
Transmission
Speed
UTP Quality
Category
Maximum
Cord Length
100BASE-TX
100 Mbps
Category 5e,
6, or higher
100 meters
1000BASE-T
1 Gbps
Category 5e,
6, or higher
100 meters
10GBASE-T
10 Gbps
Category 6
55 meters
10GBASE-T
10 Gbps
Category 6A
100 meters
Category is a measure of UTP QUALITY
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When modes arrive at different times, this is
called modal dispersion.
If light rays from different clock cycles
overlap, modal dispersion may make the
signal unreadable.
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Wavelength
Core
Diameter
850 nm
62.5 microns 160 MHz-km 220 m
850 nm
62.5 microns 200 MHz-km 270 m
850 nm
50 microns
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Modal
Bandwidth
Maximum
Propagation
Distance
500 MHz-km 500 m
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UTP

Optical Fiber
UTP wire quality is
indicated by a
cord’s category
number (5e, 6,
etc.).
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Multimode optical
fiber quality is
indicated by a
cord’s modal
bandwidth.
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

Wavelength is the physical distance between
comparable points on adjacent cycles.
Optical fiber transmission is described in
terms of wavelength.
Wavelengths for optical fiber are measured
in nanometers (nm).
For LANs, 850 nm light is used almost
exclusively.
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Characteristic
LAN Fiber
Carrier WAN
Fiber
Required
Distance Span
200 to 300 m
1 to 40 m
Light Wavelength 850 nm
1,310 or 1,550
nm
Type of Fiber
Multimode
(Thick Core)
Single-Mode
(Thin Core)
Core Diameter
50 or 62.5
microns
8.3 microns
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Characteristic
LAN Fiber
Primary Distance Modal
Limitation
Dispersion
Quality Metric
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Carrier WAN
Fiber
Absorptive
Attenuation
Modal Bandwidth Not Applicable
(MHz-km)
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The first physical link is 100BASE-TX,
so the maximum physical span is 100 meters.
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The switch regenerates the received signal.
On a 1000BASE-SX link, the clean new signal
can travel up to another 220 meters.
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The second switch also regenerates the signal.
The clean regenerated signal goes on.
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Ethernet Basics
Physical Layer Ethernet Standards
Data Link Layer Ethernet Standards
Ethernet Security
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4 Bits
0000
0001
0010
0011
0100
0101
0110
0111
Decimal
(Base 10)
0
1
2
3
4
5
6
7
Hexadecimal
(Base 16)
0 hex
1 hex
2 hex
3 hex
4 hex
5 hex
6 hex
7 hex
What is 0101 in hex?
What is 0000 in hex?
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4 Bits*
1000
1001
1010
1011
1100
1101
1110
1111
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Decimal
(Base 10)
8
9
10
11
12
13
14
15
Hexadecimal
(Base 16)
8 hex
9 hex
A hex
B hex
C hex
D hex
E hex
F hex
What is 1001 in hex?
What is 1111 in hex?
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Converting a 48-bit MAC address to hex
◦ Write down the 48-bit address in 12 four-bit
nibbles.
◦ Represent each nibble as a hex symbol.
◦ Pair the hex symbols and put a dash between the
6 pairs.
◦ Try these four nibbles: 0000111101011010
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A packet from A1… to
E5… must pass through
Switches 1, 2, and 3.
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Switch 1 sees
that it should
send the
frame to E5
out Port 5.
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Switch 2 sees
that it should
send the
frame to E5
out Port 7.
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Switch 3 sees that it
should send the frame to
E5 out Port 6.
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Loops are not allowed in Ethernet.
A strict hierarchy is required.
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Tag Control Information (TCI) Field
◦ There are 12 bits for VLAN addresses.
◦ There are 3 bits for frame priority.
◦ This permits 23 = 8 different priority values.
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Ethernet Basics
Physical Layer Ethernet Standards
Data Link Layer Ethernet Standards
Ethernet Security
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Power over Ethernet (POE)
◦ Switches can supply power to devices via UTP.
◦ (Wired telephone systems and USB ports already
do this.)
◦ Less expensive than
supplying power
separately.
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Latest POE Standard
◦ Provides up to 25 Watts to attached devices
◦ Sufficient for most wireless access points
◦ Sufficient for VoIP phones
◦ Sufficient for surveillance cameras
◦ Sufficient for tablets

Not sufficient for desktop or notebook PCs
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The Future
◦ Nonstandard products now supply 60 Watts of power.
◦ May become a future standard.
◦ Still will not be enough for desktop or notebook PCs.

POE switches
◦ New switches can be purchased with POE.
◦ Companies can also add POE equipment to an existing
non-POE switch.
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The Problem
◦ Anyone can enter the building and plug their
computer into a switch or into a wall RJ-45 port,
which connects to a switch.
 This usually gives the attacker access to the
network without going through a firewall.

Solution: access control at switch ports.
◦ 802.1X Port Based Access Control can do this.
◦ Created by the 802.1 WG, not the 802.3 WG.
◦ 802.1 WG creates general standards, such as
security standards.
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Advantages of a Central Authentication
Server
◦ Consistency: Attacker cannot find a
misconfigured switch.
◦ Rapid changes: When someone leaves, is hired, or
needs credential changes.
◦ Switch cost: Authentication server does heavy
work.
◦ Reduced management cost: Only one
authentication database to maintain.
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Box


802.3ba governs Ethernet for both 40 Gbps
and 100 Gbps
Virtual Lane
◦ Entire 40 Gbps or 100 Gbps

Media Lane
◦ Physical connection
◦ There may be several per virtual lane
◦ Essentially, built-in bonding
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Box

Example: 100GBASE-SR10
◦
◦
◦
◦

100 Gbps virtual lane
S = 850 nm light
R = How bits are processed
10 = 10 Gbps media lane
Media Lanes
◦ 10 Mbps optical fiber pairs
◦ 2 extra pairs
◦ 24 optical fiber strands in total
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