4.
1 Physical Layer Protocols
Physical Layer Connection
Types of Connections
Before network
communications can occur, a
physical connection to a local
network must be established.
A physical connection can be a
wired connection using a cable
or a wireless connection using
radio waves.
Physical Layer Connection
Network Interface Cards Network Interface Cards (NICs) connect a device to a network.
Used for a wired connection.
Wireless Local Area Network (WLAN) NICs are
used for wireless connections.
Purpose of the Physical Layer
The Physical Layer
• Provides the means to transport
the bits that make up a data
link layer frame across the
network media.
• Accepts a complete frame from
the data link layer and encodes
it as a series of signals that are
transmitted onto the local
media.
• Encoded bits that comprise a
frame are received by either
an end device or an
intermediate device.
Purpose of the Physical
Layer
Physical Layer Media
Three basic
forms of
network media
Purpose of the Physical Layer
Physical Layer Standards
International
Organization for
Standardization (ISO)
Telecommunications
Industry
Association/Electronic
Industries Association
(TIA/EIA)
International
Telecommunication
Union (ITU)
American National
Standards Institute
(ANSI)
Institute of Electrical and
Electronics Engineers
Physical Layer Characteristics
Functions The transition occurs at
the
middle of each bit
Encoding period.
• Method of converting a stream of data bits into a
predefined "code”.
Signaling Method
• Method of representing the bits. Modulation is
• Physical layer standards must define what type of
signal represents a "1" and what type of signal
the process
represents a "0”. by which the
• Long pulse might represent a 1 whereas a short characteristic
pulse represents a 0.
of one wave
(the signal)
modifies
another wave
(the carrier).
Physical Layer Characteristics
Bandwidth
Capacity of a medium to carry data.
Digital bandwidth measures the amount of data that can flow from one place to another in a given
amount of time.
Bandwidth is sometimes thought of as the speed that bits travel, however this is not accurate. In both 10Mb/s and
100Mb/s Ethernet, the bits are sent at the speed of electricity. The difference is the number of bits that are
transmitted per second.
11
Physical Layer Characteristics
Throughput
Measure of the transfer of bits across the media
over a given period of time.
Usually does not match the specified bandwidth
in physical layer implementations due to many
factors.
• Amount of traffic
• Type of traffic
• Latency created by network devices
encountered between source and
destination
Goodput is throughput minus traffic overhead for
establishing sessions, acknowledgments, and
encapsulation.
12
Physical Layer Characteristics
Types of Physical
Media
The figure shows different types of interfaces and ports available on a 1941 router.
13
4.2 Network Media
Copper Cabling
Characteristics of Copper Media
Transmitted on copper cables as electrical pulses.
Attenuation - the longer the signal travels, the more
it deteriorates.
All copper media must follow strict distance
limitations.
Electromagnetic interference (EMI) or radio frequency
interference (RFI) - distorts and corrupts the data signals
being carried by copper media.
• To counter copper cables wrapped in shielding.
Crosstalk - disturbance caused by the electric or magnetic
fields of a signal on one wire to the signal in an adjacent wire.
• To cancel crosstalk opposing circuit wire pairs
twisted together.
14
Copper
Cabling
Copper
Media There are three main types of copper media used in
networking.
15
Copper Cabling
Unshielded Twisted-Pair Cable
UTP cabling is the most common networking media.
• Terminated with RJ-45 connectors.
• Used for interconnecting network hosts with networking devices such as switches.
• Consists of four pairs of color-coded wires that have been twisted together to help protect
against signal
interference from other wires.
• Color codes aid in cable termination.
16
Copper Cabling
Shielded Twisted-Pair (STP) Cable
STP provides better noise protection than UTP.
STP cable is significantly more expensive and difficult
to install.
Uses an RJ-45 connector.
Combines the techniques of shielding to counter EMI
and RFI, and wire twisting to counter crosstalk.
Uses four pairs of wires, each wrapped in a foil shield,
which are then wrapped in an overall metallic braid or
foil.
17
Copper Cabling
Coaxial Cable
Coax consists of:
• A copper conductor used to transmit the electronic signals.
• A layer of flexible plastic insulation surrounding a copper conductor.
• The insulating material is surrounded in a woven copper braid, or
metallic foil, that acts as the second wire in the circuit and as a
shield for the inner conductor.
• The entire cable is covered with a cable jacket to prevent minor
physical damage.
UTP cable has essentially replaced coaxial cable in modern
Ethernet installations but is used in:
• Wireless installations: Coaxial cables attach antennas to wireless
devices.
• Cable Internet installations
18
Copper Cabling
Copper Media
Safety Copper media are susceptible to fire and electrical hazards.
19
UTP
Cabling
Properties of UTP Cabling
Consists of four pairs of color-coded copper wires that
have been twisted together and then encased in a
flexible plastic sheath.
Notice that the
Small size can be advantageous during installation.
orange/orange white
UTP cable does not use shielding to counter pair is twisted less
the effects of EMI and RFI.
than the blue/blue
• Cancellation: When two wires in an electrical circuit are
placed close together, their magnetic fields are the exact white pair.
opposite of each other and cancel out any outside EMI Each colored pair
and RFI signals.
• Varies the number of twists per wire pair to further
is twisted a
enhance the cancellation effect of a paired circuit. different number
of times.
20
UTP Cabling
UTP Cabling Standards
UTP cabling conforms to the standards established by TIA/EIA.
• TIA/EIA-568 stipulates the cabling standards for LAN
installations
Cat 3 Cable
• Used for voice communication
• Most often used for phone lines
Cat 5 and 5e Cable
• Used for data transmission
• Cat5 supports 100 Mb/s and can support 1000Mb/s, but it is not
recommended
• Cat5e supports 1000 Mb/s
Cat 6 Cable
• Used for data transmission
• An added separator is between each pair of wires
allowing it to function at higher speeds
• Support 1000 Mb/s – 10 Gb/s, though 10 Gb/s is not recommended
21
UTP
Cabling
UTP Connectors
UTP cable terminated with an RJ-45
connector.
TIA/EIA-568 standard describes the wire color
codes to pin assignments (pinouts) for Ethernet
cables.
RJ-45 connector is the male component,
crimped at the end of the cable.
Socket is the female component of a network
device, wall, cubicle partition outlet, or patch
panel.
Essential that all copper media terminations be of
high quality to ensure optimum performance with
current and future network technologies.
22
UTP
Cabling
Types of UTP Cable
23
UTP Cabling
Testing UTP Cables
UTP Testing Parameters:
Wire map
Cable length
Signal loss due to
attenuation
Crosstalk
24
Fiber Optic
Cabling
Properties of Fiber Optic Cabling Transmits data over longer distances
and at higher bandwidths.
Transmit signals with less attenuation
and is
completely immune to EMI and RFI.
Used to interconnect network devices.
Flexible, but glass,
of very pure extremely thin, bigger
not much
Fiber-optic cabling is now transparent
than a strand
being human hair.
used in four types
Enterprise of
Networks
industry:
• Fiber-to-the-Home Bits are encoded on the fiber as light
(FTTH) pulses.
• Long-Haul Networks
• Submarine Cable
Networks 25
Fiber Optic Jacket
Cabling Protects the fiber against abrasion, moisture, and
Fiber Media Cable Design other contaminants. Composition can vary
depending on the cable usage.
Strengthening Material
Surrounds the buffer, prevents the fiber cable from
being stretched when it is being pulled. Often the
same material used to produce bulletproof vests.
Buffer
Used to help shield the core and cladding from
damage.
Cladding
Tends to act like a mirror by reflecting light back in
the core of the fiber. Keeps light in the core as it
travels down the fiber.
Core
Light transmission element at the center of the
optical fiber. Core is typically silica or glass. Light
pulses travel through the fiber core.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 27
26
Fiber Optic
Cabling
Types of Fiber Media
27
Fiber Optic Cabling
Fiber-Optic
Light can only travel in one direction over optical fiber,
two fibers are required to support the full duplex
operation.
Connectors Straight-Tip (ST) Connectors
• One of the first connector types used.
• Locks securely with a “twist-on/twist-off”.
Subscriber Connector (SC) Connectors
• Referred to as square or standard connector.
• Uses a push-pull mechanism to ensure positive insertion.
• Used with multimode and single-mode fiber.
Lucent Connector (LC) Simplex Connectors
• Smaller version of SC and popular due to size.
Duplex Multimode LC Connectors
• Similar to LC but using a duplex connector.
28
Fiber Optic
Cabling
Fiber-Optic Connectors (Cont.)
Fiber patch cords are required for
interconnecting infrastructure
devices.
Yellow jacket is for single-mode
fiber cables
Orange (or aqua) for multimode
fiber cables.
Fiber cables should be protected
with a
small plastic cap when not in
use. 29
Fiber Optic Cabling
Testing Fiber Cables
Terminating and splicing fiber-optic
cabling requires special training and
equipment.
Three common types of fiber-optic
termination and splicing errors are:
• Misalignment: The fiber-optic media are
not precisely aligned to one another
when joined.
• End gap: The media does not completely
touch at the splice or connection.
• End finish: The media ends are not well
polished, or dirt is present at the
Can be field tested by shining a bright
termination.
flashlight into one end of the fiber while
Optical Time Domain observing the other end.
Reflectometer (OTDR) can be
used to test each fiber- optic
cable segment
30
Fiber Optic
Cabling
Fiber versus Copper
31
Wireless Media
Properties of Wireless Media
Wireless media carry electromagnetic signals that represent
the binary digits of data communications using radio or
microwave frequencies.
Wireless areas of concern:
• Coverage area: Construction materials used in buildings and
structures, and the local terrain, will limit the coverage.
• Interference: Disrupted by such common devices as
fluorescent lights, microwave ovens, and other wireless
communications.
• Security: Devices and users, not authorized for access to the
network, can gain access to the transmission.
• Shared medium: Only one device can send or receive at a
time and the wireless medium is shared amongst all wireless
users.
32
Wireless Media
Types of Wireless Media
Wi-Fi: Standard IEEE 802.11
• Uses Carrier/Sense Multiple Access/Collision Avoidance
(CSMA/CA).
• Wireless NIC must wait till channel is clear.
Bluetooth: Standard IEEE 802.15
• Wireless Personal Area Network (WPAN)
• Uses a device pairing process for distances 1 to 100 meters
WiMAX: Standard IEEE 802.16
• Worldwide Interoperability for Microwave Access
• Wireless broadband access.
33
Wireless Media
Wireless LAN
Wireless LAN requires the
following network devices:
• Wireless Access Point (AP):
Concentrates the wireless signals
from users and connects to the
existing copper-based network
infrastructure, such as Ethernet.
• Wireless NIC adapters: Provide
wireless communication capability
to each network host.
Home and small business wireless
routers integrate the functions of a
router, switch, and access point into
one device.
34
