MODULE 4: PHYSICAL LAYER PHYSICAL COMPONENTS

4.1 PURPOSE OF THE PHYSICAL LAYER • Physical Layer Standards address three
THE PHYSICAL CONNECTION functional areas:
• Before any network communications can ➢ Physical Components
occur, a physical connection to a local ➢ Encoding
network must be established. ➢ Signaling
• This connection could be wired or wireless, • The Physical Components are the hardware
depending on the setup of the network. devices, media, and other connectors that
• This generally applies whether you are transmit the signals that represent the bits.
considering a corporate office or a home. ➢ Hardware components like NICs,
• A Network Interface Card (NIC) connects a interfaces and connectors, cable
device to the network. materials, and cable designs are all
• Some devices may have just one NIC, while specified in standards associated with
others may have multiple NICs (Wired and/or the physical layer.
Wireless, for example). ENCODING
• Not all physical connections offer the same • Encoding converts the stream of bits into a
level of performance. format recognizable by the next device in the
• Transports bits across the network media network path.
• Accepts a complete frame from the Data Link • This ‘coding’ provides predictable patterns
Layer and encodes it as a series of signals that that can be recognized by the next device.
are transmitted to the local media • Examples of encoding methods include
• This is the last step in the encapsulation Manchester (shown in the figure), 4B/5B, and
process. 8B/10B.
• The next device in the path to the destination
receives the bits and re-encapsulates the
frame, then decides what to do with it.

SIGNALING
• The signaling method is how the bit values, “1”
4.2 PHYSICAL LAYER CHARACTERISTICS
and “0” are represented on the physical
PHYSICAL LAYER STANDARDS
medium.
• The method of signaling will vary based on the
type of medium being used.

Electrical Signals Over Copper Cable

 4.3 COPPING CABLING
CHARACTERISTICS OF COPPER CABLING
• Copper cabling is the most common type of
cabling used in networks today. It is
inexpensive, easy to install, and has low
Light Pulses Over Fiber-Optic Cable resistance to electrical current flow.
• Limitations:
➢ Attenuation – the longer the electrical
signals have to travel, the weaker they
get.
➢ The electrical signal is susceptible to
interference from two sources, which
can distort and corrupt the data
signals (Electromagnetic Interference
(EMI) and Radio Frequency
Interference (RFI) and Crosstalk).
• Mitigation:
➢ Strict adherence to cable length limits
will mitigate attenuation.
Microwave Signals Over Wireless ➢ Some kinds of copper cable mitigate
BANDWIDTH EMI and RFI by using metallic shielding
• Bandwidth is the capacity at which a medium and grounding.
can carry data. ➢ Some kinds of copper cable mitigate
• Digital bandwidth measures the amount of crosstalk by twisting opposing circuit
data that can flow from one place to another pair wires together.
in a given amount of time; how many bits can TYPES OF COPPER CABLING
be transmitted in a second.
• Physical media properties, current
technologies, and the laws of physics play a
role in determining available bandwidth.

BANDWIDTH TERMINOLOGY
• Latency
➢ Amount of time, including delays, for
data to travel from one given point to
another UNSHIELDED TWISTED PAIR (UTP)
• Throughput
➢ The measure of the transfer of bits
across the media over a given period of
time
• Goodput
➢ The measure of usable data
transferred over a given period of time
➢ Goodput = Throughput - traffic
overhead
 • UTP is the most common networking media. • There are different types of connectors used
• Terminated with RJ-45 connectors with coax cable.
• Interconnects hosts with intermediary • Commonly used in the following situations:
network devices. ➢ Wireless installations - attach
• Key Characteristics of UTP antennas to wireless devices
1. The outer jacket protects the copper ➢ Cable internet installations
wires from physical damage. - customer premises wiring
2. Twisted pairs protect the signal from
interference.
3. Color-coded plastic insulation
electrically isolates the wires from
each other and identifies each pair.
SHIELDED TWISTED PAIR (STP)

4.4 UTP CABLING

• Better noise protection than UTP
PROPERTIES OF UTP CABLING
• More expensive than UTP
• UTP has four pairs of color-coded copper
• Harder to install than UTP
wires twisted together and encased in a
• Terminated with RJ-45 connectors
flexible plastic sheath. No shielding is used.
• Interconnects hosts with intermediary
UTP relies on the following properties to limit
network devices
crosstalk:
• Key Characteristics of STP ➢ Cancellation - Each wire in a pair of
1. The outer jacket protects the copper wires uses opposite polarity. One wire
wires from physical damage is negative, the other wire is positive.
2. Braided or foil shield provides EMI/RFI They are twisted together and the
protection magnetic fields effectively cancel
3. Foil shield for each pair of wires each other and outside EMI/RFI.
provides EMI/RFI protection ➢ Variation in twists per foot in each wire
4. Color-coded plastic insulation - Each wire is twisted a different
electrically isolates the wires from amount, which helps prevent
each other and identifies each pair crosstalk amongst the wires in the
COAXIAL CABLE cable.
• Consists of the following:
1. Outer cable jacket to prevent minor
physical damage
2. A woven copper braid, or metallic foil,
acts as the second wire in the circuit
and as a shield for the inner conductor.
3. A layer of flexible plastic insulation
4. A copper conductor is used to
transmit the electronic signals.
UTP CABLING STANDARDS AND CONNECTORS 4.5 FIBER OPTIC CABLING
• Standards for UTP are established by the PROPERTIES OF FIBER-OPTIC CABLING
TIA/EIA. TIA/EIA-568 standardizes elements • Not as common as UTP because of the
like: expense involved
➢ Cable Types • Ideal for some networking scenarios
➢ Cable Lengths • Transmits data over longer distances at higher
➢ Connectors bandwidth than any other networking media
➢ Cable Termination • Less susceptible to attenuation, and
➢ Testing Methods completely immune to EMI/RFI
• Electrical standards for copper cabling are • Made of flexible, extremely thin strands of very
established by the IEEE, which rates cable pure glass
according to its performance. Examples • Uses a laser or LED to encode bits as pulses of
include: light
➢ Category 3 • The fiber-optic cable acts as a wave guide to
➢ Category 5 and 5e transmit light between the two ends with
➢ Category 6 minimal signal loss
TYPES OF FIBER MEDIA

• Dispersion refers to the spreading out of a light

pulse over time. Increased dispersion means
increased loss of signal strength. MMF has
greater dispersion than SMF, with a the
maximum cable distance for MMF is 550
meters.
UTP CABLING STANDARDS AND CONNECTORS
FIBER-OPTIC CABLING USAGE
(CONT.)
• Fiber-optic cabling is now being used in four
types of industry:
1. Enterprise Networks - Used for
backbone cabling applications and
interconnecting infrastructure devices
2. Fiber-to-the-Home (FTTH) - Used to
provide always-on broadband
services to homes and small
businesses
3. Long-Haul Networks - Used by
STRAIGHT-THROUGH AND CROSSOVER UTP service providers to connect countries
CABLES and cities
4. Submarine Cable Networks - Used to
provide reliable high-speed, high-
capacity solutions capable of
surviving in harsh undersea
environments at up to transoceanic
distances.
FIBER OPTIC CONNECTORS physical strand of media, so anyone
can gain access to the transmission.
➢ Shared medium - WLANs operate in
half-duplex, which means only one
device can send or receive at a time.
Many users accessing the WLAN
simultaneously results in reduced
bandwidth for each user.
TYPES OF WIRELESS MEDIA
FIBER PATCH CORDS • The IEEE and telecommunications industry
standards for wireless data communications
cover both the data link and physical layers. In
each of these standards, physical layer
specifications dictate:
➢ Data to radio signal encoding methods
➢ Frequency and power of transmission
• A yellow jacket is for single-mode fiber cables
➢ Signal reception and decoding
and orange (or aqua) for multimode fiber
requirements
cables.
➢ Antenna design and construction
FIBER VERSUS COPPER
• Wireless Standards:
• Optical fiber is primarily used as backbone
➢ Wi-Fi (IEEE 802.11) - Wireless LAN
cabling for high-traffic, point-to-point
(WLAN) technology
connections between data distribution
➢ Bluetooth (IEEE 802.15) - Wireless
facilities and for the interconnection of
Personal Area network (WPAN)
buildings in multi-building campuses.
standard
➢ WiMAX (IEEE 802.16) - Uses a point-
to-multipoint topology to provide
broadband wireless access
➢ Zigbee (IEEE 802.15.4) - Low data-
rate, low power-consumption
communications, primarily for
Internet of Things (IoT) applications
4.6 WIRELESS MEDIA WIRELESS LAN
PROPERTIES OF WIRELESS MEDIA
• In general, a Wireless LAN (WLAN) requires the
• It carries electromagnetic signals following devices:
representing binary digits using radio or ➢ Wireless Access Point (AP) -
microwave frequencies. This provides the Concentrate wireless signals from
greatest mobility option. Wireless connection users and connect to the existing
numbers continue to increase. copper-based network infrastructure
• Some of the limitations of wireless: ➢ Wireless NIC Adapters - Provide
➢ Coverage area - Effective coverage wireless communications capability
can be significantly impacted by the to network hosts
physical characteristics of the • There are a number of WLAN standards. When
deployment location. purchasing WLAN equipment, ensure
➢ Interference - Wireless is susceptible compatibility, and interoperability.
to interference and can be disrupted
• Network Administrators must develop and
by many common devices. apply stringent security policies and
➢ Security - Wireless communication
processes to protect WLANs from
coverage requires no access to a unauthorized access and damage.
 4.7 MODULE PRACTICE AND QUIZ
WHAT DID I LEARN IN THIS MODULE?
• Before any network communications can
occur, a physical connection to a local
network, either wired or wireless, must be
established.
• The physical layer consists of electronic
circuitry, media, and connectors developed by
engineers.
• The physical layer standards address three
functional areas: physical components,
encoding, and signaling.
• Three types of copper cabling are: UTP, STP,
and coaxial cable (coax).
• UTP cabling conforms to the standards
established jointly by the TIA/EIA. The
electrical characteristics of copper cabling
are defined by the Institute of Electrical and
Electronics Engineers (IEEE).
• The main cable types that are obtained by
using specific wiring conventions are Ethernet
Straight-through and Ethernet Crossover.
WHAT DID I LEARN IN THIS MODULE (CONT.)?
• Optical fiber cable transmits data over longer
distances and at higher bandwidths than any
other networking media.
• There are four types of fiber-optic connectors:
ST, SC, LC, and duplex multimode LC.
• Fiber-optic patch cords include SC-SC
multimode, LC-LC single-mode, ST-LC
multimode, and SC-ST single-mode.
• Wireless media carry electromagnetic signals
that represent the binary digits of data
communications using radio or microwave
frequencies. Wireless does have some
limitations, including coverage area,
interference, security, and the problems that
occur with any shared medium.
• Wireless standards include the following: Wi-
Fi (IEEE 802.11), Bluetooth (IEEE 802.15),
WiMAX (IEEE 802.16), and Zigbee (IEEE
802.15.4).
• Wireless LAN (WLAN) requires a wireless AP
and wireless NIC adapters.
 MODULE 5: NUMBER SYSTEMS DECIMAL TO BINARY CONVERSION
5.1 BINARY NUMBER SYSTEM • The binary positional value table is useful in
BINARY AND IPV4 ADDRESSES converting a dotted decimal iPv4 address to
• Binary numbering system consists of 1s and binary.
0s, called bits ➢ Start in the 128 position (the most
• Decimal numbering system consists of digits significant bit). Is the decimal number
0 through 9 of the octet (n) equal to or greater than
• Hosts, servers, and network equipment using 128?
binary addressing to identify each other. ➢ If no, record a binary 0 in the 128
• Each address is made up of a string of 32 bits, positional value and move to the 64
divided into four sections called octets. positional value.
• Each octet contains 8 bits (or 1 byte) ➢ If yes, record a binary 1 in the 128
separated by a dot. positional value, subtract 128 from the
• For ease of use by people, this dotted notation decimal number, and move to the 64
is converted to dotted decimal. positional value.
➢ Repeat these steps through the 1
positional value.

BINARY POSITIONAL NOTATION

• Positional notation means that a digit
represents different values depending on the
“position” the digit occupies in the sequence
of numbers.
• The decimal positional notation system
operates as shown in the tables below.
DECIMAL TO BINARY CONVERSION EXAMPLE
• Convert decimal 168 to binary

BINARY POSITIONAL NOTATION (CONT.)

• The binary positional notation system
operates as shown in the tables below.

IPv4 ADDRESSES
• Routers and computers only understand
binary, while humans work in decimal. It is
CONVERT BINARY TO DECIMAL important for you to gain a thorough
understanding of these two numbering
systems and how they are used in networking
 5.2 HEXADECIMAL NUMBER SYSTEM ➢ Convert the decimal number to 8-bi
HEXADECIMAL AND IPV6 ADDRESSES binary strings.
• To understand IPv6 addresses, you must be ➢ Divide the binary strings in groups of
able to convert hexadecimal to decimal and four starting from the rightmost
vice versa. position.
• Hexadecimal is a base sixteen numbering ➢ Convert each four binary numbers into
system, using the digits 0 through 9 and letters their equivalent hexadecimal digit.
A to F. • For example, 168 converted into hex using the
• It is easier to express a value as a single three-steps process.
hexadecimal digit than as four binary bit. ➢ 168 in binary is 10101000.
• Hexadecimal is used to represent IPv6 ➢ 10101000 in two groups of four binary
addresses and MAC addresses. digits is 1010 and 1000.
➢ 1010 is hex A and 1000 is hex 8, so 168
is A8 in hexadecimal.
HEXADECIMAL TO DECIMAL CONVERSIONS
• Follow the steps listed to convert hexadecimal
numbers to decimal values:
➢ Convert the hexadecimal number to 4-
bit binary strings.
➢ Create 8-bit binary grouping starting
from the rightmost position.
Convert each 8-bit binary grouping
into their equivalent decimal digit.
• For example, D2 converted into decimal using
HEXADECIMAL AND IPV6 ADDRESSES (CONT.)
the three-step process:
• IPv6 addresses are 128 bits in length. Every 4
➢ D2 in 4-bit binary strings is 1101 and
bits is represented by a single hexadecimal
0010.
digit. That makes the IPv6 address a total of 32
➢ 1101 and 0010 is 11010010 in an 8-bit
hexadecimal values.
grouping.
• The figure shows the preferred method of
➢ 11010010 in binary is equivalent to
writing out an IPv6 address, with each X
210 in decimal, so D2 is 210 is decimal
representing four hexadecimal values.
5.3 MODULE PRACTICE AND QUIZ
• Each four hexadecimal character group is WHAT DID I LEARN IN THIS MODULE?
referred to as a hextet.
• Binary is a base two numbering system that
consists of the numbers 0 and 1, called bits.
• Decimal is a base ten numbering system that
consists of the numbers 0 through 9.
• Binary is what hosts, servers, and networking
equipment uses to identify each other.
• Hexadecimal is a base sixteen numbering
system that consists of the numbers 0 through
9 and the letters A to F.
• Hexadecimal is used to represent IPv6
addresses and MAC addresses.
• IPv6 addresses are 128 bits long, and every 4
bits is represented by a hexadecimal digit for a
DECIMAL TO HEXADECIMAL CONVERSIONS total of 32 hexadecimal digits.
• Follow the steps listed to convert decimal
numbers to hexadecimal values:
• To convert hexadecimal to decimal, you must
first convert the hexadecimal to binary, then
convert the binary to decimal.
• To convert decimal to hexadecimal, you must
first convert the decimal to binary and then the
binary to hexadecimal.
 MODULE 6: DATA LINK LAYER PROVIDING ACCESS TO MEDIA
6.1 PURPOSE OF THE DATA LINK LAYER • Packets exchanged between nodes may
THE DATA LINK LAYER experience numerous data link layers and
1. The Data Link Layer is responsible for media transitions.
communications between end-device • At each hop along the path, a router performs
network interface cards or end to end delivery. four basic Layer 2 functions:
2. It allows upper layer protocols to access the 1. Accepts a frame from the network
physical layer and media and encapsulates medium.
Layer 3 packets (IPv4 and IPv6) into Layer 2 2. De-encapsulates the frame to expose the
Frames. encapsulated packet.
3. It also performs error detection and rejects 3. Re-encapsulates the packets into a new
corrupts frames. frame.
4. Forwards the new frame on the medium of
the next network segment.
DATA LINK LAYER STANDARDS
• Data link layer protocols are defined by
engineering organizations:
➢ Institute for Electrical and Electronic
Engineers (IEEE).
➢ International Telecommunications
Union (ITU).
➢ International Organizations for
IEEE 802 LAN/MAN DATA LINK SUBLAYERS Standardization (ISO).
• IEEE 802 LAN/MAN standards are specific to ➢ American National Standards Institute
the type of network (Ethernet, WLAN, WPAN, (ANSI).
etc.) 6.2 TOPOLOGIES
• The Data Link Layer consists of two sublayers. PHYSICAL AND LOGICAL TOPOLOGIES
Logical Link Control (LLC) and Media Access • The topology of a network is the arrangement
Control (MAC). and relationship of the network devices and
➢ The LLC sublayer communicates the interconnections between them.
between the networking software at • There are two types of topologies used when
the upper layers and the device describing networks:
hardware at the lower layers. ➢ Physical topology – shows physical
➢ The MAC sublayer is responsible for connections and how devices are
data encapsulation and media access interconnected.
control. ➢ Logical topology – identifies the
virtual connections between devices
using device interfaces and IP
addressing schemes.
WAN TOPOLOGIES
• There are three common physical WAN
topologies:
➢ Point-to-point – the simplest and
most common WAN topology.
Consists of a permanent link between
two endpoints.
➢ Hub and spoke – similar to a star
topology where a central site
 interconnects branch sites through ➢ Used on WLANs and legacy bus
point-to-point links. topologies with Ethernet hubs.
➢ Mesh – provides high availability but • Full-duplex communication
requires every end system to be ➢ Allows both devices to simultaneously
connected to every other end system. transmit and receive on a shred
POINT-TO-POINT WAN TOPOLOGY medium.
• Physical point-to-point topologies directly ➢ Ethernet switches operate in full-
connect two nodes. duplex mode.
• The nodes may not share the media with other ACCESS CONTROL METHODS
hosts. • Contention-based access
• Because all frames on the media can only • All nodes operating in half-duplex, competing
travel to of from the two nodes, Point-to-Point for use of the medium. Examples are:
WAN protocols can be very simple. ➢ Carrier sense multiple access with
collision detection (CSMA/CSD) as
used on legacy bus-topology Ethernet.
➢ Carrier sense multiple access with
LAN TOPOLOGIES
collision avoidance (CSMA/CA) as
• End devices on LANs are typically used on Wireless LANs.
interconnected using a star or extended star • Controlled access
topology. Star and extended star topologies ➢ Deterministic access where each
are easy to install, very scalable and easy to node has its own time on the medium.
troubleshoot. ➢ Used on legacy networks such as
• Early Ethernet and Legacy Token Ring Token Ring and ARCNET.
technologies provide two additional CONTENTION-BASED ACCESS – CSMA/CD
topologies: • CSMA/CD
➢ Bus – all end systems chained ➢ Used by legacy Ethernet LANs.
together and terminated on each end. ➢ Operates in half-duplex mode where
➢ Ring – each end system is connected only one device sends or receives at a
to its respective neighbors to form a time.
ring. ➢ Uses a collision detection process to
govern when a device can send and
what happens if multiple devices send
at the same time.
• CSMA/CD collision detection process:
➢ Devices transmitting simultaneously
will result in a signal collision on the
shared media.
➢ Devices detect the collision.
➢ Devices wait a random period of time
and retransmit data.
CONTENTION-BASED ACCESS – CSMA/CA
• CSMA/CA
➢ Used by IEEE 802.11 WLANs.
➢ Operates in half-duples mode where
HAIR AND FULL DUPLEX COMMUNICATION only one device sends or receives at a
• Half-duplex communication time.
➢ Only allows one device to send or ➢ Uses a collision avoidance process to
receive at a time on a shared medium. govern when a device can send and
 what happens if multiple devices send LAN AND WAN FRAMES
at the same time. • The logical topology and physical media
• CSMA/CA collision avoidance process: determine the data link protocol used:
➢ When transmitting, devices also ➢ Ethernet
include the time duration needed for ➢ 802.11 Wireless
the transmission. ➢ Point-to-Point (PPP)
➢ Other devices on the shared medium ➢ High-Level Data Link Control (HDLC)
receive the time duration information ➢ Frame-Relay
and know how long the medium will be • Each protocol performs media access control
unavailable. for specified logical topologies.
6.3 DATA LINK FRAME
THE FRAME
• Data is encapsulated by the data link layer
with a header and a trailer to form a frame. A
data link frame has three parts.
➢ Header
➢ Data
➢ Trailer
• The fields of the header and trailer vary
according to data link layer protocol.
• The amount of control information carried
with in the frame varies according to access
control information and logical topology.
FRAME FIELDS

LAYER 2 ADDRESSES

• Also referred to as a physical address.

• Contained in the frame header.
• Used only for local delivery of a frame on the
link.
• Updated by each device that forwards the
frame.