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Data Communications & Networking
Chapter 1
Introduction
2014/2015 ‫الثاني‬
Data Communication & Networking
 Communication
 Sharing information.
 Sharing can be local (face to face) or remote (over distance)
Tele communication
(telephone, television, telegraphy) means communication
at a distance remote communication. (tele: far)
Data communication:
exchange of data between two devices via transmission
medium (wire cable)
Communicating devices
made up of : H.W( physical equipments )and S.W
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Why Study Data Communication & Networking?
 Because Data Communication & Networking are changing the way we do
business and the way we live
Require immediate access to accurate information
Database, online shopping
Enable long distance communication
Internet, IP phone
Access variable of information (text, voice and image)
Email, messenger, video conference
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Networks
 Network
 is a collection of computers and devices (Nodes) connected by
communications channels that facilitates communications among
users and allows users to share resources with other users
 A node can be a computer, printer, or any other device can
capable of sending and/or receiving data generated by other
nodes on the network.
 Nodes attached to media through NIC (network interface card)
 Distributed Processing
 Most network uses distributed processing , in which a task is
divided among multiple computers. Instead of a single machine
responsible for all aspects of a process, separate
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Network Components
 Software components
Communication Protocols
Network Operating System- NOS
peer-to-peer (Windows Xp,Win7)
Client-server (Windows server 2003 ‫و‬Linux)
 Hardware components
 Server
 Workstations
 Connecting Devices
 Cabling system
 Shared resource & peripherals
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A Data Communication Model
 Protocol
 is a set of rules that governs data communications. It represents an
agreement between the communicating devices.
 Without a protocol two devices may be connected but not
communicating
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Protocols
 Protocols are set of rules that govern data communication to define
What is communicated?
How it communicated?
When it is communicated?
 Key elements
 Syntax
Structure or format of the data, meaning the order in which they are
presented
Example: A simple protocol might expect the first byte of data to be the
address of the sender, the second byte to be the address of the receiver and
the reset of the stream to be the message itself.
 Semantics
Refers to the meaning of each section of bits.
Example: does an address identify the route to be taken or the final
destination of the message
 Timing
When data to should be sent?
How fast they can be sent?
If a sender produces data at 100Mpbs but the receiver can process data at only 1Mpbs, transmission will overload7the
receiver and data will be largely lost
Standards
 Standard
provides a model for development
allows for interoperability
Types
De jure/Formal
legislated by an officially recognized body
De facto
Have been adopted as standers through widespread use
Established by manufacturers that define the functionality of a
new product or technology
Standards Organizations
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International Organization for Standardization (ISO)
International Telecommunication Union Telecommunication standard sector ( ITU-T)
American National Standards Institute (ANSI)
Institute of Electrical and Electronics Engineers (IEEE)
Electronic Industries Association (EIA)
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Data Representation
 Text
 represented as a bit pattern; codes often used
ASCII: 7-bit pattern (128 different symbols)
Extended ASCII: 8-bit pattern (with an extra 0 at left from
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00000000 to 0111111
Unicode:32 bits pattern (65,536,216) symbols, which is definitely
enough to represent any symbol in the world
ISO
Numbers
 represented by binary equivalent
Images
 represented by matrix of pixels, small dot.
 The size of pixel represent the resolution
 One method to represent color images is RGB
Audio represent sound by continuous (analog) signal
Video
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History of Internet
 Experimental work was funded by the U.S. DoD Advanced Research Projects
Agency (DARPA).
 The goal was to connect the major universities together to share computing
resources for improving the cooperation of scientists in joint projects & publications.
 ARPA contracted with BBN Corp. (formerly Bolt, Beranek and Newman) to
develop “ARPAnet”. This was the first ever network that was developed by DoD.
 The first e-mail program was created in 1972. NSF created a CNET connecting the
academic researchers together.
 In 1985 the defense withdraw from the network and it became funded by US
National Science Foundation. The network was called NSFNET with linked
many of the universities, Research labs, Libraries to access their super computers
thus establishing the communication. The network grew very rapidly.
 It was turned over to private Internet Service Providers (ISP) in 1995.
 In early 90’es a new information service, www was developed at CERN by
Timothy Berners-Lee. With the graphical browser it changed the whole picture as
multimedia capabilities became possible.
 Finally giving rise to INTERNET connecting millions of computers together 10
Effectiveness of data communication depends on
 Delivery
 System must deliver data to correct destination. Data
must be received by only intended device or user.
 Accuracy
 Data delivered accurately
 Altered data which left uncorrected are unusable.
 Timeliness
 Data delivered in timely manner without delay (real-time)
 Jitter
 variation in packet arrival time, It is the uneven delay in
the delivery of audio or video packets
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Direction of Data Flow
 Simplex
 communication is unidirectional. (one-way-street). Only one of the two devices
on a link can transmit; the other can only receive, As Keyboard and monitors
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 Half-duplex
 Each station can both transmit and receive , but not at the same time. When one
device is sending the other can receive and vice versa. one-lane road with two
direction)
 Full-duplex
 Both stations can transmit and receive simultaneously. ( telephone network)
 Like two way street with traffic flowing in both directions at the same time
 Signals going in either direction share the capacity of the link in two ways:
 Either the link must contain two physically separate transmission paths one for
sending and other for receiving.
 Capacity of the channel is divided between signals traveling in both direction
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Connecting devices
 Divided into 5 different categories based on the layer in
which they operate in a network
1.
2.
3.
4.
5.
Below the physical layer: passive hub
At the physical layer: repeater or active hub
At the physical and data link layers: bridge or two-layer switch
At the physical, data link, network layers: router or three-layer
switch
At all five layers: gateway
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Passive Hub
 Passive hub is just a connector.
 In a star-topology Ethernet LAN, it is just a point where
signals coming from different stations collide.
 The hub is the collision point.
 This type of hub is part of the media
 its location in the Internet model is below the physical
layer.
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Repeaters
 Operates only in the physical layers
 Can extend the physical length of a LAN
 Receive the signal before it becomes too weak or corrupted
and regenerates the original bit pattern
 Do not actually connect two LANs
 connects two segments of the same LAN
 Segments connected are still part of one single LAN
 A repeater cannot connect two LANs of different protocols
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Repeaters
 Operates only in the physical layers
 Can extend the physical length of a LAN
 Receive the signal before it becomes too weak or corrupted
and regenerates the original bit pattern
 While, Amplifiers, Cannot discriminate between the intended
signal and noise. It amplifies equally everything fed into I
 Do not actually connect two LANs
 connects two segments of the same LAN
 Segments connected are still part of one single LAN
 A repeater cannot connect two LANs of different protocols
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Example
 repeater can overcome 10Base5 Ethernet length restriction
 the length of the cable is limited to 500 m
 divide the cable into (500 m) sections and connect them with
repeaters
 The whole network is still considered one LAN
 Portions of the network separated by repeaters are called segments
 Repeaters acts as two-port node and has no filtering capability
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Active Hubs
 Actually a multiport repeater
 Used to create connections between stations in a physical
star topology
 Can also be used to create tree topology to removes the
length limitation of 10Base -T (100 m)
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Example
 repeater can overcome 10Base5 Ethernet length restriction
 the length of the cable is limited to 500 m
 divide the cable into (500 m) sections and connect them with
repeaters
 The whole network is still considered one LAN
 Portions of the network separated by repeaters are called segments
 Repeaters acts as two-port node and has no filtering capability
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Bridge
 device that connects two LAN segments together, which may be similar or
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dissimilar, such as Ethernet and Token Ring. A bridge is inserted in the
network to keep traffic contained within the segments to improve
performance
Operates in both the physical and the data link layer
Physical layer : regenerates the signal
Data link layer : check the physical (MAC) addresses (source & destination)
contained in the frame
Bridge has filtering capability, but repeaters has not.
Checks the MAC (physical) address of the destination when receives a
frame, and decide if the frame should be forwarded or dropped
forwards the new copy only to the segment (specific port) to which the
address belongs
Bridge has a table that maps addresses to the port.
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Bridge
Bridge has a table to
 Maps address to ports.
 Used in filtering decisions
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Transparent Bridges
 Bridges in which the stations are completely unaware of the bridge’s
existence. the stations does not reconfigured when a bridge is added or
deleted
 A system equipped with transparent bridges must meet three criteria:
 Frame must be forwarded correctly one station to another.
 The forwarding table is automatically made by learning frame movements in the
network.
 Loops in the system must be prevented.
 Learning:
 early bridges had static forwarding table
 Administrated manually enter each table entry
 simple, but not practical
 better solution
 dynamic table management that maps addresses to ports automatically
 bridge gradually learns from the frame movement
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Transparent Bridges
Destination physical address: used for the forwarding decision (table lookup).
Source physical address: used for adding entries to the table and for updating purposes.
• A sends frame to D:flooding
• E sends a frame to A: Forwarding
• B sends a frame to C :flooding
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Transparent Bridges
 Loop problem
 bridges are normally installed redundantly to make the system
more reliable
 Two LANs may be connected by more than one bridge
 they may create a loop packet may be going round and round
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Bridges: Spanning Tree
 Is graph in which there is no loop
 Create a topology in which each LAN can be reached from any other
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LAN through one path only (no loop)
Create a logical topology that overlays physical topology which can
not be changed
To find the spanning tree we need to Assign a cost (metric) to each
LAN
The interpretation of the cost is left up to network admin
It may be the path with :
 Minimum hops, (shortest distance)
 Minimum delay, or maximum bandwidth
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Spanning Tree with Minimum hops
 The hop count is normally 1 from a bridge to the LAN and 0 in the
reverse direction
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Connecting Devices
Network Interface cards
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Connecting Devices
 Wireless Bridge
 device that connects two LAN segments together via infrared or
microwave transmission. A wireless bridge is often used to span
buildings and provides a more economical method than laying cable or
leasing a private line
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Network Criteria
 Performance – depends on
 Number of user
 Type of transmission media,
 Capabilities of connected H.W and the efficiency of software
 Reliability – measured by
 Frequency of failure
 The time it takes to recover from failure
 Network’s robustness in a catastrophe
 Security
 Protection from unauthorized access and Viruses
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TYPE OF CONNECTION
 Point to point
 A dedicated link is provided between two devices
 Most of them uses an actual length of wire or cable
to connect the two ends but other options ,such as
microwave satellite are possible
Point – to – point connection
 Multipoint
 More than two devices share a single line.
 The capacity is shared either spatially or
temporally.
 Spatially: Several devices can use link simultaneously
 Temporally: Users take turns , it is a timeshared
Multipoint connection
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Topology
 Physical topology
 Is how the wires are run
 The way in which a network is laid out physically
 Logical topology is how the signal travels.
 A device can be wired to implement any logical topology.
 LANs are logical busses or rings, depending on how the hub is wired
 4 basic types: mesh, star, bus, ring
 The most common physical topology is the star.
 All the wires come back to a central point
 May often see hybrid
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Mesh Topology
 Every device has a dedicated point-to-point link to every other devices in
network
 Mesh topology often used in MANs and WANs
 A fully connected mesh network has n(n-1)/2 physical channels to link n
devices, Every device on the network must have n-1 I/O ports
 Advantage
 Privacy or security(every message travels along a dedicated line, only the intended
recipient sees it. Physical boundaries prevents other user from gaining access the
message
 eliminating the traffic problems. The use of dedicated links guarantees that each
connection can carry its own data load; that can occur when links must be shared
by multiple devices.
 A mesh is robust. If one link becomes unusable, it does not incapacitate the entire
system.
 Fault identification and fault isolation easy. This enables the network manager to
discover the precise location of fault and aids in finding its cause and solution.
 Disadvantage
 Need more resource (cable & ports)
 Expensive to implement
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Star Topology
 Each device has a dedicated point-to-point link only to a central device (hub,
switch, router)
 No direct traffic and link between devices
 Advantages of star topology
 Easy to install and reconfigure and less expensive
 Each device need only one link and I/O port to connect it to any other
devices.)
 Robustness, If one link fails, only that link affected and other links
remain active.
 Identification and fault isolation
 Disadvantages of star topology
 Failure of central device may cause network failure
 Requires more cable than (Ring ,bus)
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Tree topology
 Is a variation of star
 Not every device plugs directly into the central hub. The majority of devices
connect to secondary hub that in turn is connected to the central hub
 The advantages and disadvantages of tree topology are generally the same
as those of star.
 The addition of secondary hubs bring more advantage:
 Allow more devices to be attached to a single central hub, therefore increase the
distance a signal can travel between devices.
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Bus Topology
 A multipoint topology
 Consists of cables connecting PCs or file servers
 Terminator attached to each end of bus cable segment
 to absorb signal and prevent signal reflection back on to covered path
 Transmitting packet across bus
 Detected by all nodes on segment
 Given time limit to reach destination
 Advantages of bus design
 Requires less cable than other topologies
 Easy to install and extend bus with a workstation
 Disadvantages of bus topology
 Not secured
 Can become quickly congested with network traffic
 A fault in bus cable stops all transmissions even between devices on the same
side of the problem. The damaged area reflects signals back the direction of
origin, creating noise in both directions
 It can difficult to add new devices (adding more require modification of the
backbone).
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Ring Topology
 Each device is dedicated point-to-point connection only with the two
devices on either side of it
 Signal is passed from device to device until it reaches destination
 Each device functions as a repeater
 Advantage
 Relatively easy to install and reconfigure
 Fault isolation is simplified
 Disadvantage
 Unidirectional traffic
 A break in the ring can disable the entire network. This can be solved by use dual ring
 Hybrid topology
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Networks Categories
 Network category is determined by its size, ownership,
the distance it cover and its physical architecture
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LAN
 Privately owned and links the devices in a single office, building or campus
 LANs designed to allow resources to be shared between PCs or
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workstations. The resources may be H.W or S.W or data.
In LANs one of the computers has a large capacity drive and becomes a
server to other clients.
SW stored on server and used as needed by the whole group.
LAN size determined by licensing restrictions( No of users per copy of SW)
LAN use only one type of transmission medium.
The most common LAN topologies are bus, ring and star.
Today, LAN speed can be 100Mbps or 1000MBps(1G)
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MAN
 Owned by private company or it may be a service provided by public
company ( such as local tel.-company)
 Extended over an entire city.
 May be single network such as a cable television network, or it may be
connected number of LANs into a large network so that resources may be
shared LAN-TO-LAN.
 Examples:
 Company can use MAN to connect the LANs in all its offices throughout the
city.
 A part of the telephone line network that can provide DSL line to the customer
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WAN
 Provides long distance transmission of data, voice , image and video
information over large areas ( country or whole world)
 In contrast to LAN, WAN may utilize public or private
communication equipment's or combination
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Switched and a Point-to-point WAN
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Categories of Networks Based on Control
Peer-to-Peer Network
 No single computer controls the network.
 Each computer is the same (a peer) to all others
 It is suitable for small offices.
Server-Based Network
 The network is controlled by a special high-powered server.
 The server is dedicated to running the network.
 Print and file servers, application servers, communication servers, and
directory service servers are common.
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Interconnections of networks : internetwork
An internet (small i) is two or more networks that can
communicate with each other
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