Overview of Data Communications and Networking

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PART I
Overview of Data Communications and Networking
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Overview
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Definition of Data Communication

• Is the exchange of data between two devices via
  some form of transmission medium exp, wire cable.
• Communicating devices is a combination of
  hardware and software
• 3 fundamental characteristics needs for make sure
  the effectiveness of D.C
• Delivery deliver data to correct destination
• Accuracy The data must be delivered accurately
• Timelines the data must be sent in a timely
  manner.

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1.1 Data Communication
Components Data Representation Direction of
Data Flow
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Figure 1.1 Five components of data
communication
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• Message data- text,number,picture
• Sender-device that send the message-computer,
  workstation, handphone etc
• Receiver- device that accept the data
• Medium- the physical path by which a message
  travel from sender to receiver, wire, wireless
• Protocol- set of rules that governs D.C

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Data Representation

• Text
• Numbers
• Images
• Audio
• Video

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Direction of flow

• Communication between two devices can be
• Simplex
• Half-duplex
• Full-duplex

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Figure 1.2 Simplex
The communication is unidirectional-one way Exp
keyboards, traditional monitors
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Figure 1.3 Half-duplex
Each station can both transmit and receive but
not at the same time Exp walkie-talkies
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Figure 1.4 Full-duplex
Both stations can transmit and received at the
same time Exp telephone network
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Networks

• What is network?
• It is a set of devices (nodes) connected by
  communication links.
• Nodes?

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1.2 Networks

• Distributed Processing
• Task is divided among multiple computers
• Network Criteria
• Performance, Reliability, Security
• Physical Structures
• Type of connection, Physical Topology
• Categories of Networks
• LAN,WAN,MAN

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Figure 1.5 Point-to-point connection
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Figure 1.6 Multipoint connection
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Figure 1.7 Categories of topology

• The topology of a network is the geometric
  representation of the relationship of all the
  links and linking devices to one another

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Figure 1.8 Fully connected mesh topology (for
five devices)
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Mesh

• Every device has a dedicated point-to-point link
  to every other device
• The link carries traffic only when the two
  devices is connected
• A fully connected mesh network has n(n-1)/2
  physical channels to link n devices.

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Continue.. Advantages

• Use dedicated link- guarantees that each
  connection can carry its own data load, eliminate
  the traffic problems that can occur when links
  must be shared by multiple devices
• Robust-if one link becomes unusable, it does not
  incapacitate the entire system.
• Privacy/security-Only the intended recipient see
  the message
• Easy to detect faulty in the nodes since using
  point-to-point

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Continue..disadvantage

• Use many cable and i/o port
• Hard to install and reconfigure
• Expensive and bulky

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Figure 1.9 Star topology
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Star

• Each device has a dedicated point-to-point link
  only to a central controller/hub
• Devices are not directly linked to one another
• Does not allow direct traffic between devices
• Controller/hubs acts as an exchange

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Continue..advantages

• Less expensive compared to mesh
• Each device needs only one link and one i/o port
  to connect it to any number of others
• Easy to install and reconfigure
• Less cabling
• Robustness-if one fails, only that link is
  affected-thus easy to identified fault and
  isolate it

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Figure 1.10 Bus topology
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Bus

• Multipoint
• One cable acts as a backbone to link all the
  devices in a network
• Nodes are connected to the bus cable by drop
  lines and taps
• Drop lines-connection running between the device
  and the main cable
• Tap-a connector that either splices into the main
  cable or punctures the sheathing/covering of a
  cable to create a contact with the metallic core

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Continue

• Advantage
• Ease of installation

• Disadvantage
• Difficult reconnection and fault isolation
• Difficult to add new device
• Signal reflection at the taps can cause
  degradation in quality
• A fault in the bus cable stops all transmission
• The damaged area reflects signals back in the
  direction of origin, creating noise in both
  directions.

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Figure 1.11 Ring topology
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Ring

• Each device has a dedicate point-to point
  connection only with the two devices one either
  side of it.
• A signal is passes along the ring in one
  direction, from device to device until it reaches
  its destination
• Each device in ring incorporates a repeater
• When a device receives a signal intended for
  another device, its repeater regenerates the bits
  and passes them along

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Ring..continue..

• Easy to install and reconfigure
• Each device is linked only to its immediate
  neighbors
• To add/delete a device requires changing only two
  connections
• In a ring signal is circulating at all times, if
  one device does not receive a signal within a
  specified period, it can issue an alarm.
• The alarm alerts the network operator to the
  problem and its location

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Ring..continue

• Disadvantage-unidirectional traffic
• A break in a ring can disable the entire network
• Solves using a dual ring or a switch capable of
  closing the break.

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Figure 1.12 Categories of networks
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LAN

• Privately owned and links the devices in a single
  office,building or campus
• Designed to allow resources to be shared between
  pcs.
• Beside size, LAN are distinguished from other
  networks by their transmission media and topology
• Common topologies bus,ring,star
• Traditionally LAN data rates 4-16 Mbps
• Now up to 100Mbps

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Figure 1.13 LAN
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Figure 1.13 LAN (Continued)
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MAN

• Designed to extend over an entire city
• It can be a single network i.e cable tv network
  or connecting a number of LANS into a larger
  network,i.e a company use a MAN to connect the
  LANs in all its office throughout a city.
• It may be wholly owned and operated bya private
  company, service provided by a public company i.e
  local telephone company

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WAN

• Provides long-distance transmission of
  data,voice,image and video info over large
  geographic areas country continent, whole
  world.
• May utilize public,leased or private
  communication equipment
• WAN that is wholly owned and used by a single
  company known as enterprise network

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Figure 1.14 MAN
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Figure 1.15 WAN
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1.3 The Internet
A Brief History The Internet Today
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Figure 1.16 Internet today
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What is the Internet?

• Internet is a global network, which connecting
  millions of computers for the purpose of exchange
  data, news and opinions.
• It is made up of thousands of smaller commercial,
  academic, domestic and government networks
• Internet transmit data by packet switching using
  a standardized Internet Protocol (IP) and many
  other protocols
• It carries various information and services, such
  as electronic mail, online chat and the
  interlinked web pages and other documents of the
  World Wide Web.

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Internet(1)

• Internet is decentralized by design. Each
  Internet computer, called a host, is independent.
  
• Its operators can choose which Internet services
  to use and which local services to make available
  to the global Internet community.
• Internet was conceived by the Advanced Research
  Projects Agency (ARPA) of the U.S. government in
  1969 and was first known as the ARPANET.

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Internet(2)

• Today, the Internet is a public, cooperative, and
  self-sustaining facility accessible to hundreds
  of millions of people worldwide
• Physically, the Internet uses a portion of the
  total resources of the currently existing public
  telecommunication networks

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The Internet as mapped by The Opte
Project (http//opte.prolexic.com/) on 15.
January 2005
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1.4 Protocols and Standards
Protocols Standards Standards
Organizations Internet Standards
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Protocols

• Set of rules that governs D.C
• 3 Key elements
• Syntax-structure or format of the data, in order
  they were presented
• Semantics- the meaning of each section of bits
• Timing-when data should be sent and how fast it
  can be sent out

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Standards

• Need in creating and maintaining an open and
  competitive market for equipment manufacturers in
  making sure that devices make by different vendor
  able to be use/ work together
• Exp organizations creates standards
• ITU_T, ISO, CCITT,ANSI,IEEE

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NetworkModels
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2.1 Layered Tasks
Sender, Receiver, and Carrier Hierarchy Services
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Figure 2.1 Sending a letter
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2.2 Internet Model
Peer-to-Peer Processes Functions of
Layers Summary of Layers
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Figure 2.2 Internet layers
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Figure 2.3 Peer-to-peer processes
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Figure 2.4 An exchange using the Internet model
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Figure 2.5 Physical layer
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Note
The physical layer is responsible for
transmitting individual bits from one node to the
next.
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Figure 2.6 Data link layer
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Note
The data link layer is responsible for
transmitting frames from one node to the next.
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Figure 2.7 Node-to-node delivery
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Example 1
In Figure 2.8 a node with physical address 10
sends a frame to a node with physical address 87.
The two nodes are connected by a link. At the
data link level this frame contains physical
addresses in the header. These are the only
addresses needed. The rest of the header contains
other information needed at this level. The
trailer usually contains extra bits needed for
error detection
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Figure 2.8 Example 1
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Figure 2.9 Network layer
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Note
The network layer is responsible for the delivery
of packets from the original source to the final
destination.
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Figure 2.10 Source-to-destination delivery
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Example 2
In Figure 2.11 we want to send data from a node
with network address A and physical address 10,
located on one LAN, to a node with a network
address P and physical address 95, located on
another LAN. Because the two devices are located
on different networks, we cannot use physical
addresses only the physical addresses only have
local jurisdiction. What we need here are
universal addresses that can pass through the LAN
boundaries. The network (logical) addresses have
this characteristic.
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Figure 2.11 Example 2
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Figure 2.12 Transport layer
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Note
The transport layer is responsible for delivery
of a message from one process to another.
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Figure 2.12 Reliable process-to-process
delivery of a message
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Example 3
Figure 2.14 shows an example of transport layer
communication. Data coming from the upper layers
have port addresses j and k (j is the address of
the sending process, and k is the address of the
receiving process). Since the data size is larger
than the network layer can handle, the data are
split into two packets, each packet retaining the
port addresses (j and k). Then in the network
layer, network addresses (A and P) are added to
each packet.
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Figure 2.14 Example 3
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Figure 2.15 Application layer
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Note
The application layer is responsible for
providing services to the user.
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Figure 2.16 Summary of duties
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2.3 OSI Model
A comparison
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Figure 2.17 OSI model
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Note
The OSI model is briefly discussed in Appendix C.