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Chapter One
Introduction to Computer Networks and Data Communications
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Introduction
• Who today has not used a computer network?• Mass transit, interstate highways, 24-hour bankers,
grocery stores, cable television, cellphones, businesses and schools, and retail outlets support some form of computer network
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The Language of Computer Networks
• Computer network – an interconnection of computers and computing equipment using either wires or radio waves over small or large geographic areas
• Local area network – networks that are small in geographic size spanning a room, floor, building, or campus
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The Language of Computer Networks
• Metropolitan area network – networks that serve an area of 1 to 30 miles, approximately the size of a typical city
• Wide area network – a large network that encompasses parts of states, multiple states, countries, and the world
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The Language of Computer Networks
• Personal area network – a network of a few meters, between wireless devices such as PDAs, laptops, and similar devices
• Voice network – a network that transmits telephone signals
• Data network – a network that transmits computer data
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The Language of Computer Networks
• Data communications – the transfer of digital or analog data using digital or analog signals
• Telecommunications – the study of telephones and the systems that transmit telephone signals
• Network management – the design, installation, and support of a network, including its hardware and software
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The Big Picture
• Networks are composed of many devices, including:– Workstations (computers, telephones)
– Servers
– Network hubs and switches (bridges)
– Routers (LAN to WAN and WAN to WAN)
– Telephone switching gear
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Computer Networks – Basic Connections
• Computer terminal / microcomputer to mainframe• Microcomputer to local area network• Microcomputer to Internet• Local area network to local area network• Personal area network to workstation
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Computer Networks – Basic Connections
• Local area network to metropolitan area network• Local area network to wide area network• Sensor to local area network• Satellite and microwave• Wireless telephone and wired telephone to network
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Basic Connections – Computer Terminal / Microcomputer to Mainframe Computer
• Predominant form in the 1960s and 1970s• Still used in many types of businesses for data entry
and data retrieval• Usually involves a low-speed connection
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Microcomputer to Local Area Network
• Highly common throughout business and academic environments, and now homes
• Typically a medium- to high-speed connection• Computer (device) requires a NIC (network interface
card)• NIC connects to a hub-like device
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Microcomputer to Internet
• Popular with home users and small businesses• Often a dial-up modem is used to connect user’s
microcomputer to an Internet service provider• Technologies such as DSL and cable modems are
replacing modems
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Local Area Network to Local Area Network
• Found in systems that have two or more LANs and a need for them to intercommunicate
• A bridge-like device (such as a switch) is typically used to interconnect LANs
• Switch can filter frames
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Personal Area Network to Workstation
• Interconnects wireless devices such as PDAs (personal
digital assistant ), laptops and notebooks, and music playback devices.
• Used over short distances such as a few meters
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Local Area Network to Metropolitan Area Network
• Used to interconnect companies (usually their local area networks) to networks that encompass a city
• High-speed networks with redundant circuits• Metro Ethernet is latest form of metropolitan LAN
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Local Area Network to Wide Area Network
• One of the most common ways to interconnect a user on a LAN workstation to the Internet (a wide area network)
• A router is the typical device that performs LAN to WAN connections
• Routers are more complex devices than switches
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Wide Area Network to Wide Area Network
• High-speed routers and switches are used to connect one wide area network to another
• Thousands of wide area networks across North America, many interconnected via these routers and switches
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Basic Connections – Sensor to Local Area Network
• Not all local area networks deal with microcomputer workstations
• Often found in industrial and laboratory environments
• Assembly lines and robotic controls depend heavily on sensor-based local area networks
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Satellite and Microwave
• Typically long distance wireless connections• Many types of applications including long distance
telephone, television, radio, long-haul data transfers, and wireless data services
• Typically expensive services but many companies offer competitive services and rates
• Newer shorter-distance services such as Wi-Max
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Chapter One - Introduction to ComputerNetworks And Data Communications
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Basic Connections – Wireless or Cellular Telephones
• Constantly expanding market across the U.S. and world
• Third generation services available in many areas and under many types of plans
• Newest generation includes higher speed data transfers (100s of kilobits per second)
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Chapter One - Introduction to ComputerNetworks And Data Communications
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An Additional Basic Connection – Telephone to Network
• Telephone systems are ubiquitous and now carry more data than voice
• Common configuration – telephone connected to POTS
• Newer configuration (VoIP) – telephone to LAN via gateway or telephone to gateway via DSL/cable
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Network Architectures
• A reference model that describes the layers of hardware and software necessary to transmit data between two points or for multiple devices / applications to interoperate
• Reference models are necessary to increase likelihood that different components from different manufacturers will converse
• Two models to learn: OSI model and TCP/IP protocol suite
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Network Architectures• The OSI model’s seven layers:
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Network Architectures• The TCP/IP protocol suite (DoD protocol suite, Internet
model):
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Network Architectures – TCP/IP
• Application layer – equivalent to OSI’s application and presentation layers
• Transport layer – equivalent to OSI’s transport layer• Network (Internet or internetwork) layer – equivalent
to OSI’s network layer• Network access (data link/physical) layer –
equivalent to OSI’s data link and physical layers
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Network Architectures
• Logical and physical connections – A logical connection is one that exists only in the software, while a physical connection is one that exists in the hardware
• Note that in a network architecture, only the lowest layer contains the physical connection, while are higher layers contain logical connections
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Chapter One - Introduction to ComputerNetworks And Data Communications
• Logical and physical connections
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Chapter One - Introduction to ComputerNetworks And Data Communications
• Example of data flow through layers
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Chapter One - Introduction to ComputerNetworks And Data Communications
• Network connections in action