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Networking Basics CCNA 1
Chapter 2
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Networking Basics and Terminology
A Brief History of the Networking Universe
• Earliest commercial computers were large
mainframes, run by computer scientists
• Terminals were invented, allowing users to
interact with the computers
• Eventually (1960s), some terminals were
located to allow remote access
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Networking Basics and Terminology
A Brief History of the Networking Universe
• By late 1960s minicomputers entered
marketplace
• “Mini’s” were smaller, less powerful and
less expensive than mainframes
• Mid 1970s – First personal computers
(PCs) built by researchers
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Networking Basics and Terminology
A Brief History of the Networking Universe
• 1977 – Apple introduces the Apple-II
• 1981 – IBM introduces its first PC
• Mid 1980s – Computer users with
standalone computers start sharing data
through the use of modems connecting to
another computer (dialup, point-to-point)
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Networking Basics and Terminology
The Need for Networking Protocols and Standards
• 1960s to 1980s – Each vendor set its own
proprietary protocols and standards
• Equipment from different vendors would not
interoperate
• Eventually, open standards were agreed upon
• Open standards allow more competition, which
increases speed of development
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Networking Basics and Terminology
Popular Network Standards Organizations
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Networking Basics and Terminology
Ethernet LANs and LAN Devices
• Ethernet LANs originally used coaxial cable
(similar to Cable TV cable)
• Network Interface Cards (NICs) would attach to
a length of cable called a segment
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Networking Basics and Terminology
Ethernet LANs and LAN Devices
• In early Ethernet LANs, all devices sent their
data on one wire
• All other devices on the segment received the
signal
• These types of Ethernet are said to be
“broadcast” media, because any signal sent by
one device is received by all other devices
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Networking Basics and Terminology
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Characteristics of Early Ethernet LANs
Limited to a relatively small geographic area
Allows multiple devices access to high-speed
media
Administrative control rests within a single
company
Provides full-time connectivity
Typically connects devices that are close
together
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Networking Basics and Terminology
Cisco Networking Device Icons
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Networking Basics and Terminology
Ethernet Repeaters
• When a signal is sent over a wire, it degrades
• 10BASE5 limited a single segment to 500
meters; 10BASE2 to a little less than 200 meters
(185 meters) – hence their names (the 5 and the
2; the 10 is for 10Mbps)
• To extend the distance of LANs, repeaters were
developed
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Networking Basics and Terminology
Features of Ethernet Repeaters
• Typically had two ports connecting two
different Ethernet segments
• Interpreted the incoming signal on one
port as 1’s and 0’s
• Sent a regenerated clean signal out the
other port
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Networking Basics and Terminology
Repeated Ethernet Signal
See Conceptual View on next slide
• Betty sends a clean signal
• The signal degrades by the time it reaches
the repeater
• The repeater regenerates a new, clean
signal and sends it out its other port
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Networking Basics and Terminology
Repeated Ethernet Signal
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Networking Basics and Terminology
Ethernet Hubs and 10BASE-T
• Coax cables were expensive and difficult
to work with
• If the cable broke, everyone on the LAN
had problems
• Lead to the creation of 10BASE-T
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Networking Basics and Terminology
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Ethernet Hubs and 10BASE-T
The 10 means it runs at 10Mbps
The T means that it uses twisted-pair cable
The cable is Unshielded Twisted-Pair (UTP),
which is cheaper than coax cable
Smaller diameter than coax cable
Terminated with RJ-45 connectors
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Networking Basics and Terminology
10BASE-T with a Hub – Star Topology
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Networking Basics and Terminology
Functions of a Hub
• Provides RJ-45 jacks so cables with RJ-45
connectors can be attached
• Repeats any incoming signal out all other
ports
• Was originally called a “multiport repeater”
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Networking Basics and Terminology
Ethernet Bridges
• Examine incoming signal, interpret signal as 0’s
and 1’s, find the destination MAC address listed
in the frame
• If destination MAC address is reachable via a
different interface than the one on which it was
received, then clean, regenerate and forward the
frame out that interface
• If the destination is reachable on the same
interface on which it was received, discard the
frame (this is called “filtering”)
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Networking Basics and Terminology
A Bridge Making a Filtering Decision
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Networking Basics and Terminology
A Bridge Making a Forwarding Decision
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Networking Basics and Terminology
Ethernet Frames
• An Ethernet frame is the data sent by an
Ethernet NIC or interface
• The first bits sent are the header; contains
info such as the destination and source
MAC addresses
• Includes headers from other protocols,
such as IP
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Networking Basics and Terminology
Conceptual View of an Ethernet Frame
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Networking Basics and Terminology
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Unicast and Broadcast Ethernet Frames and
Addresses
Before the introduction of bridges, the LAN acted
as a broadcast medium
The term unicast MAC address identifies a single
NIC or Ethernet interface
Sometimes a computer needs to send a frame that
will reach all devices on the LAN; it uses a
broadcast address: FFFF.FFFF.FFFF
All devices must process data sent to this address
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Networking Basics and Terminology
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LAN Switches
Like a hub, a switch provides a large
number of ports/jacks to plug in cables
Forms a physical star topology
When forwarding a frame, the switch
regenerates a clean signal
Like bridges, switches use the same
filtering/forwarding logic on a per-port basis
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Networking Basics and Terminology
A Switch Making a
Forwarding Decision
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Networking Basics and Terminology
Wide-Area Networks (WANs)
• Cover a large geographic area
• WAN Technologies:
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Modems
Integrated Services Digital Network (ISDN)
Digital Subscribe Line (DSL)
Frame Relay
T1 or E1 leased lines – T1, E1, T3, E3, etc.
Synchronous Optical Network (SONET) – synchronous
transport Level 1(STS-1) optical carrier [OC]-1, STS-3
(OC-3), etc.
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Networking Basics and Terminology
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Point-to-Point Leased Lines
A point-to-point leased line extends
between two locations
The line is not owned by the user; it is
leased from a service provider
The service provider is often a telephone
company (telco)
Often, the term link is used to describe a
point-to-point leased line
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Networking Basics and Terminology
Point-to-Point
Leased Lines:
Leased lines
are drawn like
lightning bolts
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Networking Basics and Terminology
Routers and Their Use with LANs
• Routers perform a basic but very important
forwarding process in which they receive data
packets and then forward the packets toward
the destination
• Routers can send and receive traffic on most
any kind of physical networking media
• Routers are the perfect device to connect a
LAN to a WAN
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Networking Basics and Terminology
Metropolitan Area Networks (MANs)
• A medium-sized network geography,
perhaps city-wide
• Usually very high speed
• Optical media used between routers can
move data at 10 Gbps or even 40 Gbps
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Networking Basics and Terminology
High-Speed City-Wide MAN
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Networking Basics and Terminology
Storage-Area Networks (SANs)
• Allow computers to communicate with storage
devices
• Features of SANs:
– Performance: concurrent access of disk or tape
arrays
– Availability: used to back up data to offsite locations
– Scalability: easy relocation of backup data,
operations, file migration, and data replication
between systems
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Networking Basics and Terminology
Typical SAN Used
by a Server Farm
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Networking Basics and Terminology
Virtual Private Networks (VPNs)
• Companies can use the Internet to send
data between sites, instead of using
leased lines
• Often less expensive than leased lines
• Can be less secure than leased lines
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Networking Basics and Terminology
Virtual
Private
Networks
(VPNs)
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Networking Basics and Terminology
Intranet VPNs
• Packets are encrypted before they
leave for the Internet
• Not practical for a hacker to break the
encryption
• Intranet VPNs are used inside a single
organization
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Networking Basics and Terminology
Intranet VPN
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Networking Basics and Terminology
Comparing Intranet VPNs to Extranet
and Access VPNs
• Intranet VPN – A VPN between sites of a single
organization
• Extranet VPN – A VPN between sites of
different organizations
• Access VPN – A VPN between individual users
and an enterprise network, allowing access
while working from home or traveling
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Networking Basics and Terminology
Extranet and Access VPNs
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Networking Basics and Terminology
Physical Network Topologies
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Networking Basics and Terminology
Physical Bus Topology
• 10BASE2 and 10BASE5 use a bus
topology
• Looks like a city street where each of the
computers is a bus stop
• A frame sent by one device is received
by all other devices
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Networking Basics and Terminology
Physical Star Topology
• 10BASE-T Ethernet connects with a hub
• The hub is the device at the center, so it
resembles a start
• The actual physical layout of the cable
may not be in a star pattern
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Networking Basics and Terminology
Logical Bus Topology
• “Logical” refers to how the network
operates, not where the cables run
• 10BASE-T is a logical bus, because all
devices see any signal sent by other
devices on the network
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Networking Basics and Terminology
Physical versus Logical Topology
• Physical Topology – The topology is
determined by the physical layout of the
cabling and transmission media
• Logical Topology – The topology is
determined by the media access control
logic and how the devices collectively
send traffic over the network
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Networking Basics and Terminology
Typical
Modern
LAN and Its
Similarities
to a Star
Topology
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Networking Basics and Terminology
Typical
Modern
LAN Design
for a Single
Building
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Networking Basics and Terminology
Ring Topologies
• Cable is installed from first device to
second device, second device to third
device, and so on, until the last device
connects to the first device
• Each device cleans up the signal, so
fewer repeaters are needed
• Can have single or dual rings
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Networking Basics and Terminology
Ring Topology
• R1 and R2 detect that
cable between them
is cut
• R1 and R2 loop the
primary ring to the
backup ring using
circuitry in the routers
• One ring still works,
assuring connectivity
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Networking Basics and Terminology
Hierarchical and Extended Star Topologies
• A central device or site connects to several
other sites
• Much like a star topology
• The other sites then connect to still more sites
• Extended star topologies have the same
features as a hierarchical topology, but are not
drawn in a hierarchy
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Networking Basics and Terminology
Hierarchical Network Design
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Networking Basics and Terminology
Mesh: Full and Partial
• Most often refers to WAN topologies
• Full mesh: all devices connect to all other
devices – highly reliable – Frame Relay is an
example
• Partial mesh: Each device connects to many,
but not all, other devices
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Networking Basics and Terminology
Mesh: Full and Partial
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Bandwidth
Bandwidth: Number of bits per second that can be sent
by a device across a particular transmission medium
Names and Units of Digital bandwidth:
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Bandwidth
LAN and WAN Bandwidth
• Actual speed is limited by 3 factors: cabling,
cable length, and the speed at which the
devices on the end of the cable try to send data
• Ethernet standards call for Category 5 (Cat 5)
UTP cabling, for speeds of 10, 100 and even
1000 Mbps
• The cable can handle higher speeds, but is
hardware limited
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Bandwidth
Bandwidths for Various Ethernet Standards and Cables
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Bandwidth
WAN Bandwidths
• Vary significantly, as do LAN bandwidths
• Engineers need to worry about details such as
cable length restrictions and required equipment
• Customers need to worry about how fast the
WAN link is, how much it costs, and the type of
technology used
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Bandwidth
WAN Bandwidth Standards
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Bandwidth
WAN Bandwidth Standards (continued)
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Bandwidth
Throughput Versus Bandwidth
• Throughput is how many bits are actually
transferred between two computers in a given
time
• Two points to consider when comparing
throughput to bandwidth:
– Throughput rate may vary over time due to network
conditions; bandwidth does not vary over time
– Bandwidth defines the speed of a single link;
throughput measures the speed of the end-to-end
connection
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Bandwidth
Two Examples
of Throughput
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Bandwidth is What You Pay for,
Throughput is What You Get
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Factors That Affect Throughput
Networking devices in the route being used
Type of data being transferred
Protocols used to transfer the data
Topology of the network
Congestion level in the network
Speed and current workload of the computers
Time of day (# of active concurrent users)
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Bandwidth
Calculating Data Transfer Time: Two Methods
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Bandwidth
Calculating Data Transfer Time:
Four Examples from the “Two Examples of Throughput” Slide
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Bandwidth
Analog Bandwidth
• In the analog world, a number of consecutive
frequencies (a “band of frequencies”) defined how
much information could be sent with an analog signal
• The wider the band of frequencies, the more
information could be sent
• With digital transmission, the range of frequencies
does not affect the speed, but the term “bandwidth” is
still used to describe the speed of the bits across a link
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Bandwidth
Analog Bandwidth (continued)
• Analog transmission requires a set frequency band to
work
• The figure below shows a 3-hertz signal
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Bandwidth
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Planning for Bandwidth
Neither LAN nor WAN bandwidth is free
On enterprise networks, WAN costs can be
30-40% of the total budget
LAN links cost money, due to wiring costs and
the costs of networking devices such as
switches
Bandwidth is not infinite, and it costs money to
upgrade
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Bandwidth
Planning for Bandwidth (continued)
Four reasons why bandwidth is important:
• Bandwidth is finite
• Bandwidth is not free
• Network engineers need to plan for bandwidth
• Bandwidth demand is ever-increasing
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The OSI and TCP/IP Networking
Models
• Networking models define a related set of
standards and protocols
• When used together, these protocols and
standards allow the creation of a working
network
• The two most commonly used models are the
Open Systems Interconnection (OSI) model
and the Transmission Control Protocol/Internet
Protocol (TCP/IP) model
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The OSI and TCP/IP Networking
Models
• In the 1960s, vendors each used their own set
of standards and protocols
• These proprietary networking models would
not allow equipment from one company to
work with equipment from another company
• To overcome this problem, the OSI model was
developed beginning in 1984
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The OSI and TCP/IP Networking
Models
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The OSI Model
Goal was to be the one open networking model that all
vendors would implement
The term “open” means that all vendors have access
to the protocols and rules for building products
Most vendors worked toward adopting the OSI model
in the late 1980s and early 1990s
Many vendors and networking professionals adopted
the OSI terminology to hold meaningful conversations
about different networking models, making those
conversations a little easier
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The OSI and TCP/IP Networking
Models
The OSI Model (continued)
• The OSI model might have been the final
standard for networking, but TCP/IP proved to
be more widely accepted
• Computers today rarely implement the OSI
model as their model for networking
• Why use OSI? The terminology is still used,
and it is useful in troubleshooting networking
problems
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The OSI and TCP/IP Networking
Models
The OSI Layers
General networking functions are defined in layers:
• Allows better standardization of different components
• Opens up competition in marketplace
• Standardizes components
• Standardizes interfaces between different layers,
allowing companies to focus on one layer
• Prevents changes in one layer from affecting other
layers
• Breaks network communication into smaller
components
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The OSI and TCP/IP Networking
Models
The OSI Layers
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The OSI and TCP/IP Networking
Models
Memorizing the Order of the OSI Layers
• Starting with Layer 1:
– Please Do Not Take Sausage Pizza Away
– Pew! Dead Ninja Turtles Smell Pretty Awful
• Starting with Layer 7:
– All People Seem To Need Data Processing
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The OSI and TCP/IP Networking
Models
Functions of the OSI Layers
• Layer 7 (application layer)
– Provides services to end user’s applications
– Does not provide services to any other OSI layer
• Layer 6 (presentation layer)
– Ensures info from one system’s application layer can be read
by another system
– Translates among multiple data formats
– Does encryption and decryption
– Handles graphics standards such as PICT, TIFF, JPEG, MIDI
and MPEG
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The OSI and TCP/IP Networking
Models
Functions of the OSI Layers (continued)
• Layer 5 (session layer)
– Establishes, manages and terminates sessions
between two hosts
• Layer 4 (transport layer)
– Segments data given to it by the session layer into
smaller chunks
– Defines error-recovery services
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The OSI and TCP/IP Networking
Models
Functions of the OSI Layers (continued)
• Layer 3 (network layer)
– Provides connectivity and path selection between two host
systems
– Concerned with logical addressing
• Layer 2 (data link layer)
– Provides transit of data across a physical link by defining the
rules about how the link is used
– Concerned with physical addressing
• Layer 1 (physical layer)
– Defines electrical, mechanical, procedural, and functional
specifications for activating, maintaining, and deactivating the
physical link between end systems
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The OSI and TCP/IP Networking
Models
Relationship of OSI Layers and Devices
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The OSI and TCP/IP Networking
Models
The TCP/IP Networking Model
• Began as part of a research project for the US
Dept. of Defense (DoD) in the 1970s.
• The structure remains the same today, but
many new protocols have been added
• Can be easily compared to the OSI model;
uses 4 layers instead of 7
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The OSI and TCP/IP Networking
Models
The TCP/IP Reference Model Layers
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The OSI and TCP/IP Networking
Models
Encapsulation
1.
2.
3.
4.
5.
Application
headers are
added
Data is
segmented
IP address
information is
added
Data link header
and trailer are
added
Bits are
transmitted
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The OSI and TCP/IP Networking
Models
Segments, Packets, Frames, and PDUs
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Important to know the terminology for the group
of bytes at each layer
The generic term is protocol data unit (PDU)
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The OSI and TCP/IP Networking
Models
De-encapsulation
1.
2.
3.
4.
5.
Physical layer interprets
incoming electrical signal
Contents of Ethernet
header and trailer
analyzed; IP packet
extracted
Network layer verifies IP
header is okay, extracts
contents of data field
Segments are
reassembled and error
recovery performed
Data is given to
application
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The OSI and TCP/IP Networking
Models
Layer Interactions
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Same layer interaction – creation of headers, and
possibly trailers, by a protocol at one networking
layer on one computer, with the goal of
communicating to the same layer and protocol on
another computer
Adjacent layer interaction – On a single computer,
the interaction of protocols that sit at adjacent layers
of their networking model. Includes exchange of
data during encapsulation and de-encapsulation,
and how a lower layer protocol provides service to
an upper layer protocol
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Networking Fundamentals
Summary
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Network devices (hubs, repeaters, bridges, switches, routers)
connect host devices to allow them to communicate
Protocols provide sets of rules for communication
The physical topology is the actual layout of the wire or media
Common physical topologies are bus, ring, star,extended star,
hierarchical, and mesh
A LAN is designed to work in a limited geographical area,
providing multi-access to high-bandwidth media
LANs are controlled privately under local administration
LANs provide full-time connectivity to services and connect
physically adjacent devices
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Networking Fundamentals
Summary
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WANs operate over large geographical areas
WANs allow access serial interfaces that operate at lower
speeds, provide full- and part-time connectivity to local services
and connect devices separated over large areas
A MAN is a network that spans a metropolitan area such as a
city
A SAN is a dedicated, high performance network used to move
data between servers and storage resources
SANs are scalable and have disaster tolerance built it
A VPN is a private network constructed with a public network
infrastructure such as the Internet
The three main types of VPNs are access, intranet and
extranet
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Networking Fundamentals
Summary
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Access VPNs provide mobile workers connectivity
Intranet VPNs are only available to users who have access
privileges to the internal network of an organization
Extranet VPNs are design to provide applications and services
to external users or enterprises
Bandwidth equals number of bits per second (bps) that can
theoretically be sent through a network connection
Throughput is the amount of data that actually passes through
a connection in a give time, and is constrained by the slowest
link between the two end devices
Analog bandwidth is a measure of how much of the
electromagnetic spectrum is occupied by each signal
Digital bandwidth is measured in bits per second
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Networking Fundamentals
Summary
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Layers are used to describe communication from one computer
to another because it:
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Reduces complexity
Standardizes interfaces
Facilitates modular engineering
Ensures interoperability
Accelerates evolution
Simplifies teaching and learning
Two models are the OSI model and the TCP/IP model
The OSI model has seven layers; the TCP/IP model has four –
some layers have the same name but do not correspond
exactly
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Networking Fundamentals
Summary
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Data is encapsulated with these steps:
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Images and text are converted to data
Data is packaged into segments
Each data segment is encapsulated in a packet with source
and destination addresses
Each packet is encapsulated in a frame with the MAC
address of the next directly connected device
Each frame is converted to a pattern of 1s and 0s and
transmitted on the media
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