Lecture 1. Lecture Overview. Intro to Networking. Intro to Networking. Motivation behind Networking. Computer / Data Networks

Transcription

1 Lecture 1 An Introduction to Networking Chapter 1, pages 1-22 Dave Novak BSAD 146, Introduction to Networking School of Business Administration University of Vermont Lecture Overview Brief introduction to networking Network Services LAN versus WAN Types of architectures Applications and programs Signals, protocols, and standards Internet and the WWW URL Sources: 1) Dean (2012), Network+ Guide to Networks, 6 th Edition Intro to Networking Although networks are widely used, few people understand basic networking technologies and terminology If you have any type of tech-related job, your employer will likely expect you to possess some basic understanding of computer / data networks How computer networks work Basic terminology Intro to Networking Growth in networking 20 years ago relatively few people had easy or high speed access to a data network from their desktop computer (at work or at home) Now it is hard to imagine not having reasonably high quality access to a network even when we travel What types of things brought about this growth? Computer / Data Networks A collection of computers and other networking devices that are connected by some type of telecommunications media Motivation behind Networking What was the initial motivation behind computer networking and how has this changed over the past several decades? 1

2 Network Services Network services (in general) are the specific functions/tasks/jobs provided by the network File sharing Printing Communication Mail Internet Management Common Network Services File and print services Allow sharing of data files and printers Communications services Such as mail services Coordination and storage of Internet services WWW, FTP, some security Access services Allow remote users to connect to network Login (authorization / authentication) Network Management Services Traffic monitoring, load balancing, diagnostics 3 General Categories of Networks We are focusing on the first two: 1) Local Area Network (LAN) 2) Wide Area Network (WAN) 3) Metropolitan Area Network (MAN) LAN versus WAN A LAN is a group of computers located in a relatively small geographical area (like a building or group of buildings) Typically owned by a single organization A WAN is used to connect host computers and sites (including other LANs) across a wide geographic area Collective, distributed ownership consisting of multiple organizations LAN versus WAN Local Area Network Data transfer rate Network technology Components Fault tolerance Ownership LAN High speed( 1000 mbps) Tend to primarily use Ethernet and WiFi, but also use Token Passing Generally consist of layer 2 devices like switches, bridges. To a lesser extent layer1 devices like hubs & repeaters LANs tend to have fewer problems associated with them, as there are a smaller number of systems to deal with. Typically owned, controlled, and managed by a single organization WAN Lower speed ( 155 mbps) WANs tend to use technology like MPLS and ATM, and to a lesser extent (Frame Relay & X.25) for connectivity over the longer distances Layer 3 (+) devices such as routers, multilayer switches and technology specific devices like ATM or Frame-relay Switches etc. WANs tend to be less fault tolerant. as they consist of a many different systems managed by different organizations. There is a lower amount of fault tolerance. WANs are typically not owned by any one organization but exist under collective or distributed ownership and management over long distances Costs Low High? PC PC PC Switch PC Printer 2

3 Wide Area Networks Architecture leased lines from a larger provider form part of the WAN Networked computers interact with each other in different ways Computers may have different roles on a network We refer to the ways in which computers interact with one another on the network and the organizational relationship between the computers as the Logical Architecture Some type of shared media A word of caution: you will hear architecture used in place of topology quite frequently. Also, there is not always a clear distinction between the two because modern software can do so much! For this class we will try to keep the terms distinct. Topology versus Architecture Architecture - specifies how functions are laid out between the various devices on the network which is independent of the networking technologies being used How do the devices on the network interact? Is there a designated server? What is the server s responsibility? What is the client s responsibility? Topology the physical arrangement of the devices on the network which is affected by the networking technologies being used Architecture 3 primary logical architectures (the book just refers to these as types of networks) 1. Host-based Traditional mainframe / central computer model 2. Client-based / Peer-to-Peer Historically most home-based and many small office networks 3. Client-server Microsoft model or what we commonly see today Fairly powerful clients interacting with some number of servers Model used on campus Four major device functions Data storage Where data are stored Data access logic Where software that interacts with the data source is located Application logic Where application that performs data processing is located Presentation logic (GUI) How information and data are displayed to the user Host-based architecture Host computer or server performs most functions Mainframe system Very large, powerful central computer Dumb terminals The clients (terminals) themselves have little or no processing power, they just provide a user interface to the server Client sends keystrokes and then accepts output 3

4 Host-based architecture Peer-to-Peer (P2P) Architecture Server Data storage Data access logic Application logic Client Presentation logic Dumb terminals basically provide a screen and keyboard No local processing or storage Distributed architecture where individual PCs have symmetric roles and can function as client and/or server Ad-hoc (no hierarchy) No centralized management or control Highly autonomous At the WAN level, may aggregate large numbers of computers that may join or leave the network on a frequent basis and may not use permanent IP addresses P2P architecture All 4 functions are responsibility of individual computers / nodes that partition various tasks among the peers P2P architectures are growing in popularity with respect to some services Individuals manage their own computer and share resources Security File sharing Backup No centralized server-based name resolution or authentication P2P architecture Client Data storage Data access logic Application logic Presentation logic all reside on individual peers or nodes Client / Server (CS) Client/Server architecture CS model distinguishes between client / server devices and applications Clients request specific services Servers respond to individual client requests for services Functionality implemented in software Depending on services the server provides, physical server computers can be different than other servers and client computers (i.e. more processing power, more memory, etc) Also see Fig 1-3 from book 4

5 Client/Server (CS) architecture Structured architecture with specific roles for specific devices using specific applications File server, printer server A managed network Unlike P2P will have a network admin CS is the most commonly observed architecture Most applications are designed to be used on CS architecture CS architecture Balance processing between clients and server(s) by dividing functions Client presentation and application logic Server Data access logic, data storage, application logic Why do this? Multi-Tier CS architecture Application versus Program Program set of instructions executed on a computer Application software that directly helps users perform specific tasks All applications are programs but the reverse is not true If it has a user interface, its generally considered an application Software drivers are programs Admin tools with nice GUIs are considered to be utility applications Applications versus Services File transfer protocol (FTP) Protocol that provides file transfer services between 2 or more computers over a network WS_FTP is an application (program with GUI written specifically to provide FTP functions to the end user) Applications versus Services Simple Mail Transfer Protocol (SMTP) Internet-based protocol for transmission over IP networks (a mail service) servers typically use SMTP for exchange Microsoft Outlook is a personal information management application (calendar, task manager, contact manager, and ) which provides mail services using SMTP 5

6 Signals Much of what occurs in the networking process does not concern the nature of the data passing over the network media The lower layers of the OSI model (the network transmission functionality, layers 1-4) don t know about or care about the type of data that are being transmitted Signals When data are transferred from one device to another, the data are reduced to signals (digital or analog) These signals must be compatible with the transmission channels associated with the specific medium being used Electrical voltage via copper cable Pulses of light via fiber optic cable Radio waves via WiFi Protocols A communications network could consist of identical devices all running the same system software and using the same application software OR more likely A variety of devices using different hardware components, made by different vendors, with different system software, running a wide variety of different applications using different data formats Protocols For a modern data/communications network to function in a way that most organizations consider to be acceptable: All devices on the network MUST be able to understand each other regardless of the hardware, manufacturer, system software, and applications being used While we may take this for granted, it is actually quite an amazing feat Protocols Protocol set of rules used to communicate Devices use MANY protocols even during simple data exchanges Protocols provide format, structure, and meaning to messages Protocols specify how communication occurs and the form it takes Protocols Enable communication between Different network devices Different hardware components within a single device Different software components within a single device Hardware and software within the device 6

7 Protocols Some of the things protocols do: Packet acknowledgment transmission of a return message by the recipient verifying receipt of a packet Segmentation division of a stream of data into segments suitable for transmission of a LAN Flow control balancing the rate at which the sending computer transmits compared to the rate at which the receiving computer accepts data Error detection special codes in a packet that are used to verify that the content of a packet was not damaged Data compression reducing the amount of data transmitted by eliminating redundant information A Protocol Stack When the transmitting computer generates a packet / message, it is passed down from the application to the topmost layer of the OSI model and then subsequently passed down to the lower layers one by one The protocols at each layer perform specific services or functions before passing the message down to the next layer Protocol Interaction Functions performed at a particular layer of the OSI model at the sending computer are also performed (or undone) at the corresponding layer of the receiving computer Protocols and standards Protocols are typically based on public standards developed by an independent committee - not on standards developed by a single manufacturer What are standards and why are they important in networking (or for technology use in general)? Protocols and standards Standards are needed because there are many different manufactures making similar (but not identical) products and/or different products that provide similar or identical services and there is a need to have some baseline for interoperability and technical guidelines How does one ensure that both a Dell and Apple computer can both work on a network with Cisco and IBM components? Segments and Backbones As a network grows, it is possible to begin connect devices and LANs together in a haphazard manner this is NOT a good thing Common to connect a number of segment LANs together using a backbone LAN Segment LAN Backbone LAN 7

8 Backbone Network The Internet The backbone LAN consists of the three routers and their media The segments consist of five PCs connected to hubs at each floor It is more common to see switches used on this particular LAN design than routers This would represent a modern switched Ethernet design The Internet is a global WAN A very large WAN that spans the globe Connects many smaller WANs and MANs each of which, in turn, connect many LANs The Internet includes the SBA LAN (the physical computer network that exists in this building) SBA has some type of connection to the larger UVM network, which has some connection to the outside leased from some long distance carrier History of the Internet U.S. Department of Defense Advanced Research Projects Agency (DARPA) pioneered research that led to the modern Internet ARPANET 1970s Nuclear attack by former Warsaw Pact members, when central command and control structures are taken out, data communications can still occur via packetswitched routing systems When links and nodes are destroyed, packets will re-route to other links and nodes World Wide Web (WWW) World Wide Web (WWW) WWW is NOT synonymous with the Internet You (as a client) are typically exposed to the Web via a graphical browser such as IE or Firefox Web browsers allow one to open a Uniform Resource Locator (URL). The URL provides information about the location of things on the Web. For example When this hypertext link is clicked, we are actually retrieving a file that is stored on another computer that is located in the SBA building The URL is local, what happens if we click on World Wide Web (WWW) WWW continued A URL is an address to another computer on a communication network. It consists of 3 parts method://host/path Method (or protocol) indicates how information should be retrieved. Examples: ftp, gopher, http Host specifies the computer or group to access Path specifies the directory and file to read Example: course Web site breakdown Internet vs- WWW (general) The internet is a proper name that describes a specific network the one and only global network that connects most other networks around the world An internetwork is a generic term that describes some arbitrary collection of networks that are interconnected via routers and operate as one WWW can be viewed as a technology because it involves devices communicating specifically using HTTP 8

9 Summary Brief introduction to networking Network Services LAN versus WAN Types of architectures Applications and programs Signals, protocols, and standards Internet and the WWW URL 9