Networks and Telecommunications
CST111: Introduction to Information Technology
A Network (Page 1)
A collection of computers and other devices that are connectedtogether in order to communicate and share resources
They use communication channels to share hardware, software and data Connections between computing devices can be physical using wires or cables or
wireless using radio waves or infrared signals
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A Network (Page 2)
Node (host)—any device on a network
Data transfer rate (bandwidth)—the speed with which data is moved from one place to another on a network
Primary Benefits of Networking
Permits groups of users to exchange information and to route data from one individual to another
Single consistent master copy of data files Improves human communication
Electronic mail (e-mail), chat, social networks, etc. Enables device sharing
Printers, scanners, fax machines, etc.
Clients, Peers, and Servers (Page 1)
Server—computer that shares its resources across network responding to client requests for information by providing the requested information
File server—a computer that stores and manages files for multiple users on a network
Web server—a computer dedicated to responding to requests (from the browser client) for web pages
Client—computer that accesses shared resources, i.e. requests information
The Client/Server Relationship 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 1 2 68 1 2 69 70 71 72 73 74 75 76 77 1 2 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 1 2 145 1 2 146 1 2 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169
Clients, Peers, and Servers (Page 2)
Client/server network—certain computers take specialized roles and function mostly as servers
Ordinary users’ machines tend to function mostly as clients
Peer-to-peer network—each computer can be a client to other computers and can act as a server as well
Peer-to-Peer Networking
A distributed network in which a non-dedicated server (peer-to-peer network) All workstations can function in the dual role of server and client
There is no central control
No one computer has any higher priority to access, or heightened responsibility to provide, shared resources on the network
Every user must act as system administrator
Controls whether each user has unlimited or restricted access
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Peer-to-Peer Networking Advantages (Page 1)
Easy to install and configure
Not dependent on a dedicated server
Individual users control their own shared resources
Inexpensive to purchase and operate for smaller organizations
Peer-to-Peer Networking Advantages (Page 2)
Needs no additional equipment or software beyond a suitable operating system Needs no dedicated administrator
Works best for networks with 10 or fewer users
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CST111—Networking
Page 2
Works best for networks with 10 or fewer users
Peer-to-Peer Networking Disadvantages (Page 1)
Network security applies only to a single resource at a time, not network-wide Users may be forced to use as many passwords as there are shared resources Each machine must be backed up individually to protect all shared data
Peer-to-Peer Networking Disadvantages (Page 2)
Every time a user accesses a shared resource, the user at the machine where the resource resides suffers reduced performance
No centralized organizational scheme to locate or control access to data Does not usually work well with more than 10 users
Client/Server Networks
Centralized network with a server that exclusively delivers programs, data files and other services to workstations (the clients)
The only job of the server (or even multiple linked servers) is to provided services for the clients
The server generally does not run applications
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Client/Server Networking Advantages (Page 1)
Simplified network administration: centralized user accounts, security, and access controls
Administration may even take place from one or more client workstations Centralized data for control and backup
More powerful equipment means more efficient access to network resources
Client/Server Networking Advantages (Page 2)
A single password for network logon delivers access to all resources
Appropriate for networks with 10 or more users or any networks where resources are used heavily
Easier to scale up to any size needed
Client/Server Networking Disadvantages
Server failure may render network unusable; at best, it results in loss of network resources
Single point of failure
There must be a plan for mission critical services
Complex, special-purpose server software requires allocation of expert staff, which increases expenses
Dedicated hardware and specialized software add to the cost
Choose Peer-to-Peer When …
Network includes no more than 10 users (preferably no more than 5)
All networked machines are close enough to fit within the span of a single LAN Budget considerations are paramount
No specialized servers are needed
Use Client/Server When One or More Is True…
More than 10 users must share network access
Centralized control, security, resource management, or backup is desirable Users need access to specialized servers, or place heavy demands for network
resources
An internetwork is in use, or WAN access is required
Local Area Network (LAN)
Network consisting of a relatively small number of machines located in a well-defined (close geographical) area
The same room, building or a group of buildings
Connected computers are close enough to be linked by a single cable or wire pair
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CST111—Networking
Page 3
Connected computers are close enough to be linked by a single cable or wire pair Designed for sharing programs, data and devices (i.e. printers, scanners, fax
machines, etc.)
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Using Programs
On a workstation:
Program loaded from the hard drive of the workstation into RAM of the workstation Must be stored on every computer individually
In a network:
Program is loaded from the hard drive of the server into RAM of the workstation Alternately programs can be installed onto individual hard drives from the network
server
Using Data Files (Page 1)
On a workstation:
Only the local user has access to documents, data-bases and other files In a network:
Data files can be created by one user and shared (accessed by other users)
Using Data Files (Page 2)
File locking:
Documents, spreadsheets, graphics and other files can be used by only one user at a time
Record locking:
Multiple users can access different records from the same database at the same time
Using Printers
On a workstation:
Print data is sent to the parallel port through a cable to a local printer In a network:
The network operating system (NOS) captures print job and redirects it to a network printer
The job is placed into a print queue until the printer is ready for it One high quality printer shared by several users
The Network Interface Card (NIC)
Also called the LAN card
Installed in every workstation and the server ...
Plugs into a main board (motherboard) expansion slot inside computer Attached to network cabling
Uses electronic circuitry to send and receive network messages
Connecting Cable to a NIC 2
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Designing a Network Layout
Topology—the physical layout of the computers, cables, and other resources Also consider how the components communicatewith each other
Both of these factors:
Have a significant effect on performance and growth potential
Impact the type of equipment to purchase and approach to network management
Standard Topologies
Bus (or linear bus)—a series of computers connected along a single cable segment Star—computers connected via a central concentration point called a hub
Ring—computers connected to form a loop
Bus Topology
Most basic in which all components connect via a backbone, a single cable segment that interconnects all the computers in a straight line
Inherent weakness: a single cable break can halt the entire network
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CST111—Networking
Page 4
Inherent weakness: a single cable break can halt the entire network Easy to install and troubleshoot
Suited for small offices or temporary configurations
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Star Topology (Page 1)
Computers are connected by cable segments to a central hub
Hub receives and retransmits signals down every cable segment to all other computers/devices
Only the computers that such signals address directly pay attention to or act upon that data Star Topology 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 1 2 68 1 2 69 70 71 72 73 74 75 76 77 1 2 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 1 2 145 1 2 146 1 2 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169
Star Topology (Page 2)
Benefits
Inherent centralization of resources
Higher degree of fault tolerance; if one computer or cable fails, it has no effect on the rest of the network
Drawbacks
Requires more intricate cable installation
If the hub fails, all other attached computers/devices lose network access
Hubs
Central point of concentration for a star network Pass electronic signals to the network
Duplicates data packets received via one port, and makes them available to all ports allowing data sharing between all devices connected to the hub
A Hub 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 1 2 68 1 2 69 70 71 72 73 74 75 76 77 1 2 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 1 2 145 1 2 146 1 2 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169
Ring Topology (Page 1)
As a computer receives a signal called a token , it either acts on it or regenerates it and passes it along
Called token passing
Node that has the token is authorized to transmit
Signals travel in only one direction around the ring (no termination required)
An active topology since every computer in a ring is responsible for retransmitting the token or data
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Ring Topology (Page 2)
Advantages: Very fast
Can recognize a single computer’s failure and automatically remove the computer from the ring
Able to share network resources fairly Drawback:
Adding computers consistently degrades the network performance
Ethernet (Page 1)
The main communicationstechnology for LANs configured in bus and star topologies Communication channel (wire, wire pair, or fiber optic) connected to or winds past a
set of computers and devices
Each device is connected to a channel
Allows it to send a signal that can be detected by all computers connected to the channel
Ethernet (Page 2)
Decentralized scheme:
Each computer listens to the channel, and if it is quiet, it is free
Computer transmits unless another starts at the same time, in which case a collision occurs
In that case, both stop for a random amount of time and then try again
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CST111—Networking
Page 5
In that case, both stop for a random amount of time and then try again
Only computers that signals address directly pay attention to or act upon the data
Designing a Network Layout
Deciding how to best situate components in a topology Understand uses and limitations of various topologies Provide room for growth
Meet defined security requirements
MAN (Metropolitan Area Network)
A large computer network that usually spans a city or a large campus ranging from several blocks of buildings to entire cities
Its geographic scope falls between a LAN and WAN (wide area network) Usually interconnects several local area networks using a high-capacity backbone
technology such as fiber-optical links
Provides up-link services to wide area networks and/or the Internet
WAN (Wide Area Network)
Network covering a broad area (across metropolitan, regional, national or even international boundaries)
Used to connect LANs and other types of networks together over a potentially large geographic distance
As a result computers in one location are able to communicate with computers in other locations
The Internet is a collection of wide area networks
Constructing a Network Layout
Evaluate underlying requirements
Number of client computers to be attached Number of servers to be attached
Kind of applications that will run Peer-to-peer or server-based network?
Amount of fault tolerance required by applications Budget
Sketch network layout (third party tools are available) Put your network map into a computer
Comparison of Lines and Services
Different types of telecommunication services: Standard phone service (modem)
ISDN (Integrated Services Digital Network) DSL (Digital Subscriber Line)
Cable modem T1 and T3
Modems
A telecommunications device that converts messages between: Digital signals of computers
Analog signals of telephone lines and other communications media The term mo-dem represents:
Modulate—convert from digital to analog Demodulate—convert from analog to digital
Standard Phone Service
A “dial-up” service called a switched line— Multiple users share the line one at a time
Converts computer data to an analog audio signal for transfer over a telephone line, and then modem at the destination converts it back again into data
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CST111—Networking
Page 6
and then modem at the destination converts it back again into data Advantages: Low cost and still widely available; uses standard modem Disadvantages: Slow for video and large file downloads
ISDN
ISDN (Integrated Services Digital Network) is a dedicated phone line with constant connection
Leased line with no switching or dialing
Outdated but still widely used for professional audio and broadcast applications Advantages: Faster for video and other applications; highly secure
Disadvantages: Higher cost and not available everywhere
DSL
DSL (Digital Subscriber Service) uses a standard switched phone line which is available even if being using by a voice call at the same time
Advantages: Comes over a standard phone line but many times faster than regular dial-up
Disadvantages: Slightly higher cost and not available everywhere
Cable Modem
A device that enables PCs to be hooked up to a local cable TV line and receive data at about 1.5 Mbps (megabits per second)
Advantages: Very fast and uses existing television cable
Disadvantages: Slightly higher cost and not available everywhere
T1 and T3
Dedicated high capacity cable (not phone line) services that are most often used in business to support a WAN
Advantages: Fastest uploads and downloads, and can handle multiple signalsat the same time
Disadvantages: Very expensive, fee based on distance; typically used by corporations and other large organizations
Broadband
A connection in which transfer speeds are faster than 768 Kbps (kilobits per second) DSL connections, cable modems, and T1 and T3 lines are broadband connections Download speeds may not be the same as uploads
Downloads—getting data from the Internet to a home computer Uploads—sending data a from home computer to the Internet
The Internet
A WAN (wide area network) consisting of 100,000’s of networks Linked together to exchange data and distribute processing tasks The world’s largest computer network covering the entire planet
Internet Overview
http://video.google.com/videoplay?docid=595627119527730575#
Internet Backbone
A set of high-speed networks that carry traffic on the Internet over fiber optic and other lines
The principal data routes between large, strategically interconnected networks and core routers
The routes are hosted by commercial, government, academic and other high-capacity network centers
Provided by companies such as AT&T, Verizon, GTE, British Telecom, and IBM
Internet Service Provider (ISP)
A company that provides other companies and/or individuals access to the Internet In addition ISPs may provide:
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In addition ISPs may provide: Internet e-mail accounts to users
Services such as remotely storing data files on behalf of their customers A wide variety of other features
Gateway
A network point set up to handle all communication going between a LAN and other networks
Computers that control traffic within a company’s network or at your local Internet service provider are gateway nodes
In most homes a gateway is the device provided by the ISP that connects users to the Internet
Firewalls
Firewall—gateway machine and its software that protects a network by filtering the traffic it allows
Access control policy—used by the firewall to set rules established to specify the permitted and denied types of network communication
The Client/Server Structure on the Internet
Server—the computer that stores the data Web server, file server, mail server Client—computer that accesses the data
When a client requests services, enters client/server relationshipwith the server Once data has been sent, the temporaryclient/server relationship ends
Server can form many relationships, so it can serve many clients at the same time
Network Addresses (Page 1)
Hostnames—human-readable symbolic word names, based on domain hierarchy that uniquely identify a computer on the Internet
Easier to read and remember For example: www.sunysuffolk.edu
IP addresses—computers connected to the Internet are given a unique numerical address, four one-byte numeric values separated by dots (.)
For example: 148.78.250.12—four numbers in the range zero (0) to 255
Network Addresses (Page 2)
Host number—the part of the IP address that specifies a particular host (machine) on the network
Class A: first byte for network address and three remaining bytes for host number Class B: first two bytes for network address and the last two bytes for host number Class C: first three bytes for network address and the last byte for host number
Domain Name System (Page 1)
Domain name—the part of the hostname that specifies a specific organization or group Top-level domain (TLD)—the last section of a domain name that specifies type of
organizationor its country of origin
Domain Name System (Page 2)
Example 1: www3.sunysuffolk.edu “www3” is the computer name “sunysuffolk” is the domain name “edu” is the TLD(top-level domain) Example 2: matisse.csc.villanova.edu
“matisse” is the computer name “csc.villanova” is the domain name “edu” is the TLD(top-level domain)
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U.S. Top-Level Domain (TLD) Types
.aero—Air transport industry .biz—Alternative to .com .com—Business organization .coop—Non-profit cooperatives .edu—Educational
.firm—Businesses and firms .gov—Government
.info—Unrestricted use
.int—International organizations .jobs—Employment
.mil—Military
.museum—Museums .name—Individuals
.net—Networking organizations .org—Non-profit organizations
.pro—Accountants, lawyers, physicians
Foreign Top-Level Domain (TLD) Types
Organizations based in countries other than the United States use a top-level domain that corresponds to a two-letter country code
.au—Australia .br—Brazil .ca—Canada .gr—Greece .in—India
.ru—Russian Federation .uk—United Kingdom
DNS (Domain Name System) Servers (Page 1)
Domain name system (DNS)—a distributed system for managing hostname resolution A domain name server is the computer that attempts to translate human-readable
hostnames into IP addresses
The Internet host to which computer is connected knows the IP address of its nearest DNS server
The DNS server is a computer that keeps a list of host/domain names and corresponding IP addresses
DNS (Domain Name System) Servers (Page 2)
If a DNS server does not know the IP address, it asks a root name server, which keeps a master list of name-to-address relationships
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Communications Protocols
Ethernet—popular communications protocol often used in local area networks that ensures compatibility among devices so that many people can attach to a common cable to share network facilities and resources
Open Systems Interconnection (OSI model)—this protocol divides data
communications functions into seven distinct layers to simplify the development, operation and maintenance of complex telecommunications networks
Transport control protocol/Internet protocol (TCP/IP)—the primary communications protocol of the Internet, developed in the 1970’s
Network Protocols (Page 1)
Protocols are sets of agreed-upon rules for computers to communicate across a network so they can understand each other
Must be common to any two computers that are currently communicating
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Must be common to any two computers that are currently communicating
Network Protocols (Page 2)
Defines how data is formatted and processed on a network I.e. rules that allow client/server interaction
These rules include:
How to interpret each others’ signals How to identify one’s self to the other How to initiate and end communication How information on the medium is managed
Network Protocols (Page 3)
Network protocols are layered such that each one relies on the protocols that underlie it
Sometimes referred to as a protocol stack
Open Systems
A logical progression …
Proprietary system—system that uses technologies kept private by a particular commercial vendor
Interoperability—the ability of software and hardware on multiple machines and from multiple commercial vendors to communicate
Open systems—systems based on a common model of network architecture and a suite of protocols used in its implementation
Open Systems
Open Systems Interconnection (OSI) Reference Model—a seven-layer logical break down of network interaction to facilitate communication standards
Each layer deals with a particular aspect of network communication Number Layer
7 Application Layer 6 Presentation Layer 5 Session Layer 4 Transport Layer 3 Network Layer 2 Data Link Layer 1 Physical Layer
TCP/IP Protocol
(Transmission Control Protocol/Internet Protocol) (Page 1)
The TCP/IP protocol describes howinformation is actually sent on the Internet Transport Control Protocol (TCP)—the rules that computers on a network use to
establish and break connections
Software that breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination
TCP/IP Protocol
(Transmission Control Protocol/Internet Protocol) (Page 2)
Internet Protocol (IP)—software that deals with the routing of packets through maze of interconnected networks to their final destination
Information is broken into a sequence of small fixed-sized units called IP packets The packets are units of data sent across a network—perhaps hundreds or
thousands of packets per transmission
Each packet has space for the unit of data, the source and destination IP addresses, and a sequence number
TCP/IP Protocol
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(Transmission Control Protocol/Internet Protocol) (Page 3)
The packets are sent over the Internet one at a time using whatever route is available A router, the network device that directs packets between networks toward their
final destination, may send each packet over a different route
As a result, congestion and service interruptions do not delay transmissions Packets are reassembled at the delivery point using sequence numbers
TCP/IP Protocol
(Transmission Control Protocol/Internet Protocol) (Page 4)
This process of dividing data into packets, routing them individually routed to their destination, and reassembling them is called packet switching
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(Transmission Control Protocol/Internet Protocol) (Page 5)
User Datagram Protocol (UDP)—an alternative to TCP that is faster but less reliable Ping—a program used to test whether a particular network computer is active and
reachable
Traceroute—a program that shows the route a packet takes across the Internet
Warriors of the Net
http://www.youtube.com/watch?v=LGnJw9rtjas
High-Level Protocols
Other protocols build on the TCP/IP protocol suite:
Simple Mail Transfer Protocol (SMTP)—used to specify transfer of electronic mail File Transfer Protocol (FTP)—allows a user to transfer files to and from another
computer
Telnet—used to log onto one computer from another
Hyper Text Transfer Protocol (http)—allows exchange of Web documents (next chapter)
Electronic Mail (E-mail)
Software that:
Maintains electronic mailboxes and sends messages from one computer to another Mail server software
Network server software that controls e-mail flow Mail client software (including browser-based
Client software that helps a user manage e-mail
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Internet E-mail Addresses
Format:
user_ID@computer_name.top_level_domain Example:
MIME Types
MIME type (Multipurpose Internet Mail Extension)—a standard for defining the format of files that are included as email attachments or on websites
FTP (File Transfer Protocol)
Method of uploading and downloading files from/to serverto/from your local computer ...
Programs and data (anything from text, graphics, music, animations, video, etc.) Often requires a login ...
Login name may be anonymousif you have no account on the remote computer • If so any password is possible but common convention is your e-mail address
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Establishes a connection between your computer and a remote host (i.e. a mainframe) The local computer becomes a terminal running programs on the host ...
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The local computer becomes a terminal running programs on the host ... Literally becomes a part of the host network
A command line (text-based) interface
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Social Networks (Page 1)
Social networks are a model (simulation) of how objects (individuals and organizations) interact
A social structure made up of individuals called "nodes", which are tied by one or more specific types of interdependency
I.e. friendship, kinship, common interest, financial exchange, dislike, sexual relationships, beliefs or knowledge, etc.
Social Networks (Page 2)
Types:
Internal: Participants are within a closed or private community, i.e. company, association, or organization
External: No restrictions on membership
Social Networks (Page 3)
Participants can … Describe themselves Set privacy settings Block unwanted members
Have personal pages of pictures and/or blogs
Form or be a member of a community within the larger community
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