CST111 Networking Page 1

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1 CST Networking Page Networks and Telecommunications CST: Introduction to Information Technology A Network (Page ) A collection of computers and other devices that are connected together 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 A Network (Page ) 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 ( ), chat, social networks, etc. Enables device sharing Printers, scanners, fax machines, etc. Clients, Peers, and Servers (Page ) 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 Clients, Client/Server Peers, and Relationship Servers (Page ) 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 Typical Peer-to-Peer Peer-to-Peer Networking Network Advantages (Page ) 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 ) Needs no additional equipment or software beyond a suitable operating system Needs no dedicated administrator Works best for networks with 0 or fewer users

2 CST Networking Page Works best for networks with 0 or fewer users Peer-to-Peer Networking Disadvantages (Page ) 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 ) 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 0 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 Typical Client/Server Client/Server Networking Network Advantages (Page ) 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 ) A single password for network logon delivers access to all resources Appropriate for networks with 0 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 0 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 0 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

3 CST Networking Page 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.) Local Using Area Programs Network 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 ) 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 ) 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 Designing a Cable Network to a Layout NIC Topology the physical layout of the computers, cables, and other resources Also consider how the components communicate with 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 33

4 3 CST Networking Page Inherent weakness: a single cable break can halt the entire network Easy to install and troubleshoot Suited for small offices or temporary configurations Bus Star Topology (Page ) 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 (Page ) 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 Ring HubTopology (Page ) 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 Ring Topology (Page ) 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 ) The main communications technology 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 ) 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

5 43 CST Networking Page 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 T 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 5

6 CST Networking Page 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.5 Mbps (megabits per second) Advantages: Very fast and uses existing television cable Disadvantages: Slightly higher cost and not available everywhere T 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 signals at 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 T 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 00,000 s of networks Linked together to exchange data and distribute processing tasks The world s largest computer network covering the entire planet Internet Overview 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: 60

7 CST Networking Page In addition ISPs may provide: Internet 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 relationship with the server Once data has been sent, the temporary client/server relationship ends Server can form many relationships, so it can serve many clients at the same time Network Addresses (Page ) 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: IP addresses computers connected to the Internet are given a unique numerical address, four one-byte numeric values separated by dots (.) For example: four numbers in the range zero (0) to 55 Network Addresses (Page ) 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 ) 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 organization or its country of origin Domain Name System (Page ) Example : www3.sunysuffolk.edu www3 is the computer name sunysuffolk is the domain name edu is the TLD (top-level domain) Example : matisse.csc.villanova.edu matisse is the computer name csc.villanova is the domain name edu is the TLD (top-level domain) U.S. Top-Level Domain (TLD) Types

8 CST Networking Page 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 ) 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 ) 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 DNS Communications Servers 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 970 s Network Protocols (Page ) 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

9 CST Networking Page Must be common to any two computers that are currently communicating Network Protocols (Page ) 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 Data Link Layer Physical Layer TCP/IP Protocol (Transmission Control Protocol/Internet Protocol) (Page ) The TCP/IP protocol describes how information 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 ) 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 (Transmission Control Protocol/Internet Protocol) (Page 3)

10 CST Networking Page (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 TCP/IP Protocol (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 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 ( ) Software that: Maintains electronic mailboxes and sends messages from one computer to another Mail server software Network server software that controls flow Mail client software (including browser-based Client software that helps a user manage Electronic Internet Mail ( ) Addresses Format: user_id@computer_name.top_level_domain Example: struckc@sunysuffolk.edu MIME Types MIME type (Multipurpose Internet Mail Extension) a standard for defining the format of files that are included as attachments or on websites FTP (File Transfer Protocol) Method of uploading and downloading files from/to server to/from your local computer... Programs and data (anything from text, graphics, music, animations, video, etc.) Often requires a login... Login name may be anonymous if you have no account on the remote computer If so any password is possible but common convention is your address FTP Telnet (File Transfer Protocol) 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

11 CST Networking Page 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 Telnet Social Networks (Page ) 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 ) 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