Transcript Chapter 2

Semester 1 Module 2
Networking Fundamentals
Andres, Wen-Yuan Liao
Department of Computer Science and
Engineering
De Lin Institute of Technology
[email protected]
http://www.cse.dlit.edu.tw/~andres
Overview
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Explain the importance of bandwidth in networking.
Use an analogy to explain bandwidth.
Identify bps, kbps, Mbps, and Gbps as units of
bandwidth.
Explain the difference between bandwidth and
throughput.
Calculate data transfer rates.
Explain why layered models are used to describe
data communication.
Explain the development of the OSI model.
List the advantages of a layered approach.
Identify each of the seven layers of the OSI model.
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Identify the four layers of the TCP/IP model.
Describe the similarities and differences between
the two models.
Briefly outline the history of networking.
Identify devices used in networking.
Understand the role of protocols in networking.
Define LAN, WAN, MAN, and SAN.
Explain VPNs and their advantages.
Describe the differences between intranets and
extranets.
Outline
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Networking Terminology
Bandwidth
Networking Models
Data networks
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There was no efficient way of sharing data among
multiple microcomputers
Floppy disks.
Sneakernet created multiple copies of the data.
If two people modified the file and then tried to share
it, what will happen?
Businesses needed a solution to address the
following problems:
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How to avoid duplication of equipment and resources?
How to communicate efficiently?
How to set up and manage a network?
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Networking technology could increase productivity
while saving money.
In the mid-1980s, each company that created
network hardware and software used its own
company standards.
Network technologies were incompatible with each
other.
Difficult to communicate with each other.
This often required the old network equipment to be
removed to implement the new equipment.
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LAN standards provided an open set of
guidelines for creating network hardware and
software, the equipment from different
companies could then become compatible.
In a LAN system, each department of the
company is a kind of electronic island.
WANs could connect user networks over
large geographic areas.
Network history
Networking devices
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Equipment that connects directly to a network
segment is referred to as a device.
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End-user devices : They include computers,
printers, scanners, and other devices that
provide services directly to the user.
Network devices : They include all the
devices that connect the end-user devices
together to allow them to communicate.
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End-user devices
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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.
A NIC is a printed circuit board that fits into the
expansion slot of a bus on a computer motherboard,
or it can be a peripheral device.
Each NIC is identified by a unique code called a
Media Access Control (MAC) address.
This address is used to control data communication
for the host on the network.
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Networking devices :
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Repeater :
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Repeaters regenerate analog or digital signals
distorted by transmission loss due to attenuation.
The purpose of a network repeater is to
regenerate and retime network signals at the bit
level.
This allows them to travel a longer distance on the
media.
A repeater does not perform intelligent routing like
a bridge or router.
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Hubs :
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They 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.
Multi-ported Repeater.
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Bridges :
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They provide connections between LANs.
Not only do bridges connect LANs, but they also
perform a check on the data to determine whether
it should cross the bridge or not.
This makes each part of the network more
efficient.
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Workgroup switches :
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They 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.
Multi-ported Bridge.
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Routers :
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They have all the capabilities listed above.
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.
None of the other devices can provide this type of
connection.
Network topology
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Network topology defines the structure of the
network.
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Physical topology, which is the actual layout of the
wire or media.
Logical topology, which defines how the media is
accessed by the hosts for sending data.
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Physical topologies :
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Bus topology
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It uses a single backbone cable that is
terminated at both ends.
All the hosts connect directly to this backbone.
Ring topology
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It connects one host to the next and the last
host to the first.
This creates a physical ring of cable.
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Star topology
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It connects all cables to a central point of
concentration.
Extended star topology
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It 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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Hierarchical topology
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It is similar to an extended star.
Instead of linking the hubs and/or switches
together, the system is linked to a computer that
controls the traffic on the topology.
Tree topology.
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Mesh topology
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Each host has its own connections to all other
hosts.
It provides much protection as possible from
interruption of service.
Although the Internet has multiple paths to any
one location, it does not adopt the full mesh
topology.
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The logical topology of a network is how
the hosts communicate across the
medium.
The two most common types of logical
topologies are :
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broadcast
token passing
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Broadcast topology
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It 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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Token passing
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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
 Fiber Distributed Data Interface (FDDI)
Network protocols
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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.
Without protocols, the computer cannot make or
rebuild the stream of incoming bits from another
computer into the original format.
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Protocols control all aspects of data
communication, which include the following:
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How the physical network is built.
How computers connect to the network.
How the data is formatted for transmission.
How that data is sent.
How to deal with errors.
Standard: IEEE, ANSI, TIA, EIA, ITU, CCITT.
Local-area networks (LANs)
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LANs consist of the following components:
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Computers
Network interface cards
Peripheral devices
Networking media
Network devices
Locally share files and printers efficiently.
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It makes internal communications possible.
They tie data, local communications, and
computing equipment together.
Some common LAN technologies are:
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Ethernet
Token Ring
FDDI
Wide-area networks (WANs)
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WANs connect user networks over a large
geographical area.
It allows computers, printers, and other devices on a
LAN to share and be shared with distant locations.
Allow access over serial interfaces operating at
lower speeds.
Provide full-time or part-time connectivity to local
services.
Provide e-mail, World Wide Web, file transfer, and ecommerce services.
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Some common WAN technologies are:
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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)
Metropolitan-area networks
(MANs)
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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.
Typically, a service provider is used to connect two
or more LAN sites using private communication lines
or optical services.
A MAN can also be created using wireless bridge
technology by beaming signals across public areas.
Storage-area networks (SANs)
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A SAN is a dedicated, high-performance network
used to move data between servers and storage
resources.
SAN technology allows high-speed server-tostorage, storage-to-storage, or server-to-server
connectivity.
Separate network infrastructure.
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SANs offer the following features:
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Performance – SANs enable concurrent access of
disk or tape arrays by two or more servers at high
speeds, providing enhanced system performance.
Availability – SANs have disaster tolerance built in,
because data can be mirrored using a SAN up to 10
kilometers (km) or 6.2 miles away.
Scalability – Like a LAN/WAN, it can use a variety of
technologies. This allows easy relocation of backup
data, operations, file migration, and data replication
between systems.
Virtual private network (VPN)
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A VPN is a private network that is constructed
within a public network infrastructure such as
the global Internet.
A secure tunnel between the telecommuter’s
PC and a VPN router in the headquarters.
Benefits of VPNs
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A VPN is a service that offers secure, reliable
connectivity over a shared public network
infrastructure such as the Internet.
The most cost-effective method of
establishing a point-to-point connection
between remote users and an enterprise
customer's network.
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The following are the three main types of
VPNs:
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Access VPNs – Access VPNs provide remote
access for 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, telecommuters,
and branch offices.
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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.
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.
Intranets and extranets
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Intranet
 One common configuration of a LAN is an intranet.
 Intranets are designed to permit users who have
access privileges to the internal LAN of the
organization.
 Browser technology is used as the common front end
to access information on servers such as financial,
graphical, or text-based data.
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Extranet
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Extranets refer to applications and services that are
Intranet based, and use extended, secure access to
external users or enterprises.
This access is usually accomplished through
passwords, user IDs, and other application-level
security.
Outline
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Networking Terminology
Bandwidth
Networking Models
Importance of bandwidth
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Why bandwidth is important :
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Bandwidth is finite
Bandwidth is not free
Bandwidth requirements are growing at a rapid
rate
Bandwidth is critical to network performance
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Bandwidth is finite
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Bandwidth is limited by the laws of physics and by
the technologies used to place information on the
media.
56 kbps modems with twisted-pair phone wires.
Newer technologies, DSL also use the same
twisted-pair phone wires, it provides much greater
bandwidth than conventional modems.
Optical fiber has the physical potential to provide
virtually limitless bandwidth.
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Bandwidth is not free
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It is possible to buy equipment for a LAN that will
provide nearly unlimited bandwidth over a long
period of time.
For WAN connections, it is almost always
necessary to buy bandwidth from a service
provider.
A network manager needs to make the right
decisions about the kinds of equipment and
services to buy.
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Bandwidth requirements are growing at a
rapid rate
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New network technologies and infrastructures are
built to provide greater bandwidth.
New applications are created to take advantage
of the greater capacity.
Streaming video and audio.
IP telephony systems.
The successful networking professional must
anticipate the need for increased bandwidth and
act accordingly.
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Bandwidth is critical to network performance
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It is a key factor in analyzing network performance,
designing new networks, and understanding the
Internet.
Information flows as a string of bits from computer
to computer throughout the world.
The Internet is bandwidth.
The desktop (Analogies)
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Bandwidth has been defined as the amount
of information that can flow through a network
in a given time.
There are two analogies that may make it
easier to visualize bandwidth in a network.
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Bandwidth is like the width of a pipe.
Bandwidth is like the number of lanes on a
highway.
Measurement
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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.
In digital systems, the basic unit of bandwidth is:
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bits per second (bps)
thousands of bits per second (kbps)
millions of bits per second (Mbps)
billions of bits per second (Gbps)
trillions of bits per second (Tbps)
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Bandwidth vs. Speed
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They are not exactly the same thing.
One may say, for example, that a T3 connection at
45Mbps operates at a higher speed than a T1
connection at 1.544Mbps ?
If only a small amount of their data-carrying capacity
is being used, each of these connection types will
carry data at roughly the same speed.
It is usually more accurate to say that a T3 connection
has greater bandwidth than a T1 connection.
This is because the T3 connection is able to carry
more information in the same period of time, not
because it has a higher speed.
Limitations
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Bandwidth varies depending upon the
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Type of media : twisted-pair copper wire, coaxial
cable, optical fiber, and air.
LAN and WAN technologies used.
The actual bandwidth is determined by the
signaling methods, network interface cards
(NICs), and other items of network equipment
that are chosen.
Throughput
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Bandwidth is the measure of the amount of
information that can move through the
network in a given period of time.
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.
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The factors that determine throughput
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Internetworking devices
Type of data being transferred
Network topology
Number of users on the network
Routing within the “Cloud”
Time of day
User computer
Server computer
Power conditions
Data transfer calculation
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transfer time = size of file / bandwidth
(T=S/BW)
Two important points should be considered
when doing this calculation:
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The result is an estimate only, because the file
size does not include any overhead added by
encapsulation.
A more accurate estimate can be attained if
throughput is substituted for bandwidth in the
equation.
Digital versus analog
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Analog bandwidth is measured by how much of
the electromagnetic spectrum is occupied by
each signal.
The basic unit of analog bandwidth is hertz (Hz),
or cycles per second.
The analog video signal that requires a wide
frequency range for transmission cannot be
squeezed into a smaller band.
Therefore, if the necessary analog bandwidth is
not available, the signal cannot be sent.
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In digital signaling all information is sent as
bits, regardless of the kind of information it is.
Voice, video, and data all become streams of
bits when they are prepared for transmission
over digital media.
Unlimited amounts of information can be sent
over the smallest or lowest bandwidth digital
channel.
Outline
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Networking Terminology
Bandwidth
Networking Models
Using layers to analyze
problems in a flow of materials
Using layers to describe data
communication
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A data communications protocol is a set of
rules or an agreement that determines the
format and transmission of data.
It is important that all the devices on the
network must speak the same language or
protocol on each layer.
OSI model
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The early development of networks was
disorganized in many ways.
International Organization for Standardization
(ISO) created the Open System
Interconnection (OSI) reference model in
1984.
It is considered the best tool available for
teaching people about sending and receiving
data on a network.
OSI layers
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The OSI reference model is a framework that is
used to understand how information travels
throughout a network.
Advantages
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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.
Peer-to-peer communications
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Peer-to-peer : 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.
Each layer of communication on the source computer
communicates with a layer-specific PDU (Protocol Data
Unit), and with its peer layer on the destination computer.
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.
Next, as the data moves down through the layers of the
OSI model, additional headers and trailers are added.
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The network layer
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Provides a service to the transport layer.
Move the data through the internetwork.
Encapsulate the data and attaching a header creating
a packet (the Layer 3 PDU).
The header contains information required to complete
the transfer, such as source and destination logical
addresses.
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The data link layer
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Provides a service to the network layer.
Encapsulates the network layer information in a frame
(the Layer 2 PDU).
The frame header contains information (for example,
physical addresses) required to complete the data link
functions.
The data link layer provides a service to the network
layer.
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Segments
Packets
Frames
Bits
: layer 4 PDU
: layer 3 PDU
: layer 2 PDU
: layer 1 PDU
TCP/IP model
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The U.S. Department of Defense (DoD) created the
TCP/IP reference model.
For military purposes.
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TCP
 The transport layer deals with the quality of
service issues of reliability, flow control, and error
correction.
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TCP is a connection-oriented protocol.
IP
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Best path determination and packet switching occur at
IP layer.
IP can be thought to point the way for the packets,
while TCP provides a reliable transport.
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Application layer protocols
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Transport layer protocols
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Transport Control Protocol (TCP)
User Datagram Protocol (UDP)
Internet layer
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File Transfer Protocol (FTP)
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Domain Name System (DNS)
Trivial File Transfer Protocol (TFTP)
Internet Protocol (IP)
Network access layer
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Refers to any particular technology used on a specific network.
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Similarities include:
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Both have layers.
Both have application layers, though they include very
different services.
Both have comparable transport and network layers.
Both models need to be known by networking
professionals.
Both assume packets are switched. This means that
individual packets may take different paths to reach the
same destination. This is contrasted with circuit-switched
networks where all the packets take the same path.
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Differences include:
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TCP/IP combines the presentation and session layer
issues into its application layer.
TCP/IP combines the OSI data link and physical layers into
the network access layer.
TCP/IP appears simpler because it has fewer layers.
TCP/IP protocols are the standards around which the
Internet developed, so the TCP/IP model gains credibility
just because of its protocols.
In contrast, networks are not usually built on the OSI
protocol, even though the OSI model is used as a guide. \
Detailed encapsulation
process
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Five conversion steps in order to encapsulate
data:
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Build the data.
Package the data for end-to-end transport.
Add the network IP address to the header.
Add the data link layer header and trailer.
Convert to bits for transmission.
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Build the data
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As a user sends an e-mail message, its
alphanumeric characters are converted to data
that can travel across the internetwork.
Package the data for end-to-end transport
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The data is packaged for internetwork transport.
By using segments, the transport function
ensures that the message hosts at both ends of
the e-mail system can reliably communicate.
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Add the network IP address to the header
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The data is put into a packet or datagram that
contains a packet header with source and
destination logical addresses.
These addresses help network devices send the
packets across the network along a chosen path.
Add the data link layer header and trailer
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Each network device must put the packet into a
frame.
The frame allows connection to the next directlyconnected network device on the link.
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Convert to bits for transmission
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The frame must be converted into a pattern of 1s
and 0s (bits) for transmission on the medium.
The medium on the physical internetwork can
vary along the path used.
For example, the e-mail message can originate on
a LAN, cross a campus backbone, and go out a
WAN link until it reaches its destination on
another remote LAN.
Good luck in your exams !