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Module 2
Networking
Fundamentals
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Data Networks
• Data networks developed as a result of business applications
that were written for microcomputers.
• Businesses needed a solution that would successfully address
the following three problems:
– How to avoid duplication of equipment and resources
– How to communicate efficiently / reduce duplicate copies of files
– How to set up and manage a network
• Businesses realized that networking technology could increase
productivity while saving money.
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Data Networks
• In the mid-1980s, the network technologies that had emerged
had been created with a variety of different hardware and
software implementations.
• Each company that created network hardware and software
used its own company standards.
• These individual standards were developed because of
competition with other companies.
• Consequently, many of the new network technologies were
incompatible with each other.
• This often required the old network equipment to be removed to
implement the new equipment.
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Data Networks
• One early solution was the creation of local-area network (LAN)
standards.
• Because LAN standards provided an open set of guidelines for
creating network hardware and software, the equipment from
different companies could then become compatible.
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Networking Devices
• Network devices include all the devices that connect the enduser devices together to allow them to communicate.
• End-user devices include computers, printers, scanners, and
other devices that provide services directly to the user.
• End-user devices that provide users with a connection to the
network are also referred to as hosts.
• The host devices can exist without a network, but without the
network the host capabilities are greatly reduced.
• Host devices are physically connected to the network media
using a network interface card (NIC).
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Networking Devices
• Network devices provide transport for the data that needs to be
transferred between end-user devices.
• Network devices provide extension of cable connections,
concentration of connections, conversion of data formats, and
management of data transfers.
• Examples of devices that perform these functions are
repeaters, hubs, bridges, switches, and routers.
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Networking Devices
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Networking Devices
Repeaters
• A repeater is a network device used to regenerate a signal.
• Repeaters regenerate analog or digital signals distorted by
transmission loss due to attenuation.
• A repeater does not perform intelligent routing.
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Networking Devices
Hubs
• Hubs concentrate connections.
• In other words, they take a group of hosts and allow the
network to see them as a single unit.
• This is done passively, without any other effect on the data
transmission.
• Active hubs not only concentrate hosts, but they also
regenerate signals.
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Networking Devices
Bridges
• Bridges convert network transmission data formats as well as
perform basic data transmission management.
• Bridges provide connections between LANs.
• Bridges also perform a check on the data to determine whether
it should cross the bridge or not.
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Networking Devices
Workgroup Switches
• Workgroup switches add more intelligence to data transfer
management.
• Not only can they determine whether data should remain on a
LAN or not, but they can transfer the data only to the
connection that needs that data.
• Another difference between a bridge and switch is that a switch
does not convert data transmission formats.
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Networking Devices
Routers
• Routers can regenerate signals, concentrate multiple
connections, convert data transmission formats, and manage
data transfers.
• They can also connect to a WAN, which allows them to connect
LANs that are separated by great distances.
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Network Topologies
• Network topology defines the structure of the network.
• One part of the topology definition is the physical topology,
which is the actual layout of the wire or media.
• The other part is the logical topology, which defines how the
media is accessed by the hosts for sending data.
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Physical Topologies
• Commonly used physical topologies
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Physical Topologies
Bus
• A bus topology uses a single backbone cable that is terminated
at both ends.
• All the hosts connect directly to this backbone.
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Physical Topologies
Ring
• A ring topology connects one host to the next and the last host
to the first.
• This creates a physical ring of cable.
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Physical Topologies
Star
• A star topology connects all cables to a central point of
concentration.
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Physical Topologies
Extended Star
• An extended star topology links individual stars together by
connecting the hubs and/or switches.
• This topology can extend the scope and coverage of the
network.
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Physical Topologies
Hierarchical
• A hierarchical topology is similar to an extended star.
• However, instead of linking the hubs and/or switches together,
the system is linked to a computer that controls the traffic on
the topology.
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Physical Topologies
Mesh
• A mesh topology is implemented to provide as much protection
as possible from interruption of service.
• Each host has its own connections to all other hosts.
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Logical Topologies
• The logical topology of a network is how the hosts
communicate across the medium.
• The two most common types of logical topologies are broadcast
and token passing.
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Logical Topologies
Broadcast
• Broadcast topology simply means that each host sends its data
to all other hosts on the network medium.
• There is no order that the stations must follow to use the
network.
• It is first come, first serve.
• Ethernet works this way.
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Logical Topologies
Token Passing
• Token passing controls network access by passing an
electronic token sequentially to each host.
• When a host receives the token, that host can send data on the
network.
• If the host has no data to send, it passes the token to the next
host and the process repeats itself.
• Two examples of networks that use token passing are Token
Ring and Fiber Distributed Data Interface (FDDI).
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Network Protocols
• Protocol suites are collections of protocols that enable network
communication from one host through the network to another
host.
• A protocol is a formal description of a set of rules and
conventions that govern a particular aspect of how devices on a
network communicate.
• Protocols determine the format, timing, sequencing, and error
control in data communication.
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Local-area Networks (LANs)
• LANs are designed to:
– Operate within a limited geographic area
– All multi-access to high-bandwidth media
– Control the network privately under local administration
– Provide full-time connectivity to local services
– Connect physically adjacent devices
• LANs make it possible for businesses that use computer
technology to locally share files and printers efficiently, and
make internal communications possible.
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Local-area Networks (LANs)
• LANs consist of the following components:
– Computers
– Network interface cards
– Peripheral devices
– Networking media
– Network devices
• Some common LAN technologies are:
– Ethernet
– Token Ring
– FDDI
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Wide-area Networks (WANs)
• WANs interconnect LANs, which then provide access to
computers or file servers in other locations.
• WANs are designed to:
– Operate over a large geographical area
– Allow access over serial interfaces operating at lower speeds
– Provide full-time and part-time connectivity
– Connect devices separated over wide, even global areas
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Wide-area Networks (WANs)
• Some common WAN technologies are:
– Modems
– Integrated Services Digital Network (ISDN)
– Digital Subscriber Line (DSL)
– Frame Relay
– US (T) and Europe (E) Carrier Series – T1, E1, T3, E3
– Synchronous Optical Network (SONET)
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Metropolitan-area Networks (MANs)
• A MAN is a network that spans a metropolitan area such as a
city or suburban area.
• A MAN usually consists of two or more LANs in a common
geographic area.
• For example, a bank with multiple branches may utilize a MAN.
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Storage-area Networks (SANs)
• A SAN is a dedicated, high-performance network used to move
data between servers and storage resources.
• Because it is a separate, dedicated network, it avoids any traffic
conflict between clients and servers.
• SANs offer the following features:
– Performance
– Availability
– Scalability
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Virtual Private Network (VPN)
• A VPN is a service that offers secure, reliable connectivity over
a shared public network infrastructure such as the Internet.
•
VPNs maintain the same security and management policies as
a private network.
• They are the most cost-effective method of establishing a pointto-point connection between remote users and an enterprise
customer's network.
• The three main types of VPNs are:
– Access VPNs
– Intranet VPNs
– Extranet VPNs
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Access VPNs
• Access VPNs provide remote access to a mobile worker and
small office/home office (SOHO) to the headquarters of the
Intranet or Extranet over a shared infrastructure.
• Access VPNs use analog, dialup, ISDN, digital subscriber line
(DSL), mobile IP, and cable technologies to securely connect
mobile users
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Intranet VPNs
• Intranet VPNs link regional and remote offices to the
headquarters of the internal network over a shared
infrastructure using dedicated connections.
• Intranet VPNs differ from Extranet VPNs in that they allow
access only to the employees of the enterprise.
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Extranet VPNs
• Extranet VPNs link business partners to the headquarters of the
network over a shared infrastructure using dedicated
connections.
• Extranet VPNs differ from Intranet VPNs in that they allow
access to users outside the enterprise.
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Intranet and Extranets
• Intranets are designed to permit access by users who have
access privileges to the internal LAN of the organization.
•
Intranet Web servers differ from public Web servers in that the
public must have the proper permissions and passwords to
access the Intranet of an organization.
• Extranets refer to applications and services that are Intranet
based, and use extended, secure access to external users or
enterprises.
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Bandwidth
• Bandwidth is defined as the amount of information that can flow
through a network connection in a given period of time.
• Why bandwidth is important:
– Bandwidth is limited by physics and technology (it is finite)
– Bandwidth is not free
– Bandwidth requirement are growing at a rapid rate
– Bandwidth is critical to network performance
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Bandwidth Analogy
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Bandwidth Measurements
• In digital systems, the basic unit of bandwidth is bits per second
(bps).
• Bandwidth is the measure of how much information, or bits, can
flow from one place to another in a given amount of time, or
seconds.
Most common measurements
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Bandwidth Limitations
• Bandwidth varies depending upon the type of media as well as
the LAN and WAN technologies used.
• The actual bandwidth of a network is determined by a
combination of the physical media and the technologies chosen
for signaling and detecting network signals.
• In other words, the actual bandwidth is determined by the
signaling methods, network interface cards (NICs), and other
items of network equipment that are chosen.
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Throughput
• Throughput refers to actual measured bandwidth, at a specific
time of day, using specific Internet routes, and while a specific
set of data is transmitted on the network.
• Throughput is often far less than the maximum possible digital
bandwidth of the medium that is being used.
• Factors that determine throughput:
–
–
–
–
–
–
–
Internetworking devices
Type of data being transferred
Network topology
Number of users on the network
User computer
Server computer
Power conditions
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Data Transfer Calculation
• Using the formula transfer time = size of file / bandwidth
(T=S/BW) allows a network administrator to estimate several of
the important components of network performance.
• If the typical file size for a given application is known, dividing
the file size by the network bandwidth yields an estimate of the
fastest time that the file can be transferred.
• Two important points should be considered when doing this
calculation.
1. The result is an estimate only, because the file size does not
include any overhead added by encapsulation.
2. The result is likely to be a best-case transfer time, because
available bandwidth is almost never at the theoretical maximum for
the network type. A more accurate estimate can be attained if
throughput is substituted for bandwidth in the equation.
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Data Transfer Calculation
• Although the data transfer calculation is quite simple, one must
be careful to use the same units throughout the equation.
• In other words, if the bandwidth is measured in megabits per
second (Mbps), the file size must be in megabits (Mb), not
megabytes (MB).
• Since file sizes are typically given in megabytes, it may be
necessary to multiply the number of megabytes by eight to
convert to megabits.
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Data Transfer Calculation
• Formula
T=
S
BW
transfer time = size of file / bandwidth
• Example – Approximately how long would it take to transfer a
10 Mb file over a T1 line?
10 Mb = 10,000,000 bits
T1 = 1.544 Mbps or 1,544,000 bits per second
10,000,000 / 1,544,000 = 6.477 Mbps
OR
10 / 1.544 = 6.477 seconds
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Data Transfer Calculation
• Formula
T=
S
BW
transfer time = size of file / bandwidth
• Example – Approximately how long would it take to transfer a
10 MB file over a T1 line?
10 MB = 10,000,000 bytes
T1 = 1.544 Mbps or 1,544,000 bits per second
Convert the bytes to bits  10,000,000 X 8 = 80,000,000 bits
80,000,000 / 1,544,000 = 51.81 Mbps
OR
80 / 1.544 = 51.81 seconds
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Data Transfer Calculation
• Formula
T=
S
BW
transfer time = size of file / bandwidth
• Problem – Approximately how long would it take to transfer a
18.9 MB file over a T1 line?
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Layered Communication Model
• The information that travels on a network is generally referred
to as data or a packet.
• A packet is a logically grouped unit of information that moves
between computer systems.
• In order for data packets to travel from a source to a destination
on a network, it is important that all the devices on the network
speak the same language or protocol.
• A protocol is a set of rules that make communication on a
network more efficient.
• A data communications protocol is a set of rules or an
agreement that determines the format and transmission of data.
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Layered Communication Model
• Layer 4 on the source computer communicates with Layer 4 on
the destination computer.
• The rules and conventions used for this layer are known as
Layer 4 protocols.
• It is important to remember that protocols prepare data in a
linear fashion.
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OSI Model
• To address the problem of network incompatibility, the
International Organization for Standardization (ISO) researched
networking models in order to find a generally applicable set of
rules for all networks.
• Using this research, the ISO created a network model that
helps vendors create networks that are compatible with other
networks.
• The Open System Interconnection (OSI) reference model
released in 1984 was the descriptive network model that the
ISO created.
• It provided vendors with a set of standards that ensured greater
compatibility and interoperability among various network
technologies.
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OSI Model
• The OSI reference model has become the primary model for
network communications.
• Although there are other models in existence, most network
vendors relate their products to the OSI reference model.
• Benefits of the OSI Model:
– Reduces complexity
– Standardizes interfaces
– Facilitates modular engineering
– Ensures interoperable technology
– Accelerates evolution
– Simplifies teaching and learning
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OSI Model
• The OSI reference model is a framework that is used to
understand how information travels throughout a network.
• The OSI reference model explains how packets travel through
the various layers to another device on a network, even if the
sender and destination have different types of network media.
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OSI Model
• Dividing the network into seven layers provides the following
advantages:
– It breaks network communication into smaller, more manageable
parts.
– It standardizes network components to allow multiple vendor
development and support.
– It allows different types of network hardware and software to
communicate with each other.
– It prevents changes in one layer from affecting other layers.
– It divides network communication into smaller parts to make
learning it easier to understand.
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OSI Model
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OSI Model
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OSI Model
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OSI Model
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OSI Model
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OSI Model
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OSI Model
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OSI Model
• In order for data to travel from the source to the destination,
each layer of the OSI model at the source must communicate
with its peer layer at the destination.
• This form of communication is referred to as peer-to-peer.
• During this process, the protocols of each layer exchange
information, called protocol data units (PDUs).
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OSI Model
• Data packets on a network originate at a source and then travel
to a destination.
• Each layer depends on the service function of the OSI layer
below it.
• To provide this service, the lower layer uses encapsulation to
put the PDU from the upper layer into its data field; then it adds
whatever headers and trailers the layer needs to perform its
function.
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OSI Model
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TCP/IP Model
• The U.S. Department of Defense (DoD) created the TCP/IP
reference model, because it wanted to design a network that
could survive any conditions, including a nuclear war.
• TCP/IP was developed as an open standard.
• This meant that anyone was free to use TCP/IP.
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TCP/IP Model
• The TCP/IP model has the following four layers:
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TCP/IP Model
• Although some of the layers in the TCP/IP model have the
same name as layers in the OSI model, the layers of the two
models do not correspond exactly.
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TCP/IP Model
• The figure illustrates some of the common protocols specified
by the TCP/IP reference model layers.
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Encapsulation
• All communications on a network originate at a source, and are
sent to a destination.
• The information sent on a network is referred to as data or data
packets.
• If one computer (host A) wants to send data to another
computer (host B), the data must first be packaged through a
process called encapsulation.
• Encapsulation wraps data with the necessary protocol
information before network transit.
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Encapsulation
•
Five conversion steps in order to encapsulate data:
1. Build the data – Layers 7 - 5
2. Package the data for end-to-end transport – Layer 4
3. Add the network IP address to the header – Layer 3
4. Add the data link layer header and trailer – Layer 2
5. Convert to bits for transmission – Layer 1
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Encapsulation
Source
Destination
Segments
Packets
IP Aderess
Frames
MAC Address
Bits
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