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PowerPoint Presentation ITECH1102 Networking and Security Topic 3 – The Application Layer (Layer 5) 1 ITECH1102 Networking & Security 2 Last week Last week we looked at: The difference between Circuit Switched networks and Packet Switched networks. The origins of packet switched networks The Arpanet We saw how packet switching can lead to lost packets, duplicate packets and out of order network packets. The role of network interface cards How Hubs, Switches and Routers work We introduced 3 reference networks. Home network, Campus network & the Internet. Introduced the 5 layer Internet (TCP/IP) model of networking. Introduced the 7 layer OSI model of networking 2 ITECH1102 Networking & Security 3 This week – overview of content Introduction to the Application Layer of the Internet Model. Application architectures including: Client/Server Peer to peer Host based Cloud architectures How simple networked applications work (Web Browser & FTP client) Internet Services can be a source of considerable monetary value The role of Network protocols Common Application layer protocols How data travels through a network & protocol headers ITECH1102 Networking & Security 4 The Application Layer (User Applications) User applications give us the ability to interact with thousands of services and devices on the Internet and on our local network. These applications are enabled though their ability to use networks. Internet services include: Facebook Google search engine Google Maps FTP file download sites Domino’s pizza ordering online app There are thousands of others ITECH1102 Networking & Security 5 The Application Layer (Local user applications) At the local level networks allow: Access to printers Access to network faxes Access to Network attached storage Shared resources from other local machines Prior to the prevalence of computer networks users would transport data locally by carrying the data on removable media (Floppy disks) to the destination. This approach is commonly referred to as “sneaker net”, so called because everyone at the time wore a type of footwear called sneakers. ITECH1102 Networking & Security 6 Categories of interaction Client/Server Architecture In this type of network the user’s application is described as a client. Common clients include: email clients web clients FTP clients etc. Clients request services of Severs. For example a Web client will request web pages from web servers. Files are requested from File servers. Information from Database severs. ITECH1102 Networking & Security 7 Client/Server Architectures (continued) The role of Servers In client/server networks a server waits for client requests and responds to those requests. Some servers require authentication (Students J drive). Others do not (Eg. Most web servers). In client/server networks the server runs as a service (on Windows) or as a server Daemon (on Linux or Unix). In either case server processes listen for requests from client applications, and upon request respond to those requests. ITECH1102 Networking & Security 8 Strict distinction in roles In Client/Server networking there is a strict distinction between the roles of the client and the server. The client is a Consumer of services. The Server is a Provider of web, file, email or other services. The server program code is totally different from the client code. Example: Common web client software is Firefox, Chrome, Safari etc. Common web server software is IIS on Windows or Apache on Linux/Unix. ITECH1102 Networking & Security 9 Peer to Peer Architectures In peer-to-peer networking each machine in the network can act as both a server and a client (simultaneously if required). All machines (peers) can share resources (file and printers) and can also access any shared resource. Peer to peer networks do not require a dedicated server because the server role can be shared amongst many peers. Home networks that share files or printers to other computers on the network are a good example of a peer to peer network. ITECH1102 Networking & Security 10 Pro’s and cons of Client/server vs peer to peer. Peer to peer can work well in small networks like home network and small businesses. Administrative duties are distributed between the administrators of each peer, because any peer can act as a server. In larger networks (like Fed Uni campus network) network administration cannot be distributed as with peer to peer networks. Client/Server networking requires strong distinction between the roles of Network Administrators and network users. Network administrators control the network and its applications. Network users are only given the minimum access required to complete their day to day roles. ITECH1102 Networking & Security 11 Host based architectures Host based architectures were popular is the early days of computing and still have a strong presence today. Early system used a Mainframe with many attached dumb user terminals. The mainframe performed all the processing. Today Mainframes are used for high volume transaction processing functions like point or sale processing (Woolworths, Coles checkouts), Bank transactions, Airline transactions, Insurance company transactions etc. Some of the processing role has shifted to the point of sale or other terminals but the general processing architecture distinctions still exist. Microsoft Windows also supports a host based architecture to thin clients with its Citrix Metaframe product. (Most processing is done on the server). Users only require thin clients (low powered systems) because they are only required to render the graphical screen updates from the central Citrix server. ITECH1102 Networking & Security 12 Cloud based Architectures Cloud based Architectures are becoming increasingly important in modern computing. Cloud computing providers can supply a range of services to organisations including the computing platform, operating systems and software. This can be attractive to organisations because they no longer require in house hardware/software support for such systems or the associated costs of maintaining servers and associated infrastructure. Cloud services do come at considerable cost. ITECH1102 Networking & Security 13 Infrastructure as a Service (IAAS) The cloud provider manages all hardware, including servers, storage and networking components. The organisation is responsible for all software, including the Operating System/s, applications and associated data. The organisation is also responsible for virtualization software as required. Such architectures have the advantage that the organisation no longer has the responsibility of providing hardware, associated air conditioning of server rooms, power supply issues and associated uninterruptable power backup systems. ITECH1102 Networking & Security 14 Platform as a service (PaaS) The cloud provider offers the hardware, the operating system and base database or other software. The organisation’s programmers can code database or other applications in any language they like. They also have control over their own data. PaaS is not restricted to database infrastructure. This allows the organisation to build their own custom applications without the need to worry about the operating system, database system or hardware. ITECH1102 Networking & Security 15 Software as a Service (SaaS) Here the cloud provider provides everything including the software. User’s access the software from the Internet and are able to customise their user interface. Commonly email is outsourced by organisations to cloud providers. ITECH1102 Networking & Security 16 Common Internet Application Web Browser Allow us to view web pages Complete order forms over the Internet Pizza order Census online Download programs and other files from the web Search for information Run web applications from the browser (Eg. draw.io) Microsoft Office online ITECH1102 Networking & Security 17 Other network enabled applications Email client Compose and send email Read email File transfer services Many Internet sites allow downloading of all sorts of files Phone apps Weather forecasting applications Banking apps Considerable business value can be gained by developing popular web services (Examples: Facebook, Google, Twitter, Whatsapp etc.) ITECH1102 Networking & Security 18 A close look a some web applications Application 1: Web browser query to Google Open Browser to www.google.com (This is a request to display the Google search page dialog) Submit a query (outbound request) Web server replies with a list of suggested web sites (inbound) The browser renders the suggested links You select one of the options (outbound request) That web page is displayed on your browser screen ITECH1102 Networking & Security 19 File transfer from an FTP site Application 2 – Download a file using an FTP application Run the local FTP client program (Installed by default in Windows) The FTP program asks for the Internet address of the FTP server User enters the address (Eg ftp.novell.com) FTP client requests a connection to the FTP server Server requests a username User responds with valid credentials FTP server provides access to available downloadable files User requests file download ITECH1102 Networking & Security 20 Network protocols All networked applications, including those described above must adhere to a strict set of rules (called protocols) for network communication to succeed. For Web applications the application layer transfer protocol is HTTP (Hypertext Transfer Protocol). For FTP file transfers the FTP client and server applications must comply with the application layer File Transfer Protocol. ITECH1102 Networking & Security 21 Other Application Layer protocols There are many other Application Layer protocols in the TCP/IP protocol suite. Some familiar ones include: BitTorrent NTP(Network Time Protocol) POP(Post Office Protocol) SMB(Server Message Block) SSH(Secure Shell) Each of these protocols define the rules that applications and associated server programs must comply with for successful communications between one another. ITECH1102 Networking & Security 22 The role of application layer protocols Communications protocols do the following: Establish consistent rules between sender and receiver. Specify how data inside messages is structured and the types of messages that are sent between source and destination. Handle message dialogue, for instance which entity communicates first and how the response should be handled. ITECH1102 Networking & Security 23 Basic aim of networking As a rule one party in a network transaction makes a request of the other party according to the rules of the appropriate application protocol. We require the network to ensure that the data sent in either direction arrives intact. For instance in the FTP example above we require: The username and password entered at the client to arrive unchanged at the FTP server. We require client requested files sent from the server to be exactly the same at the client as they originated on the server. ITECH1102 Networking & Security 24 How do the client and server applications interact Lets start with an FTP client program on your PC and a remote FTP server User Program (FTP client Application) Application Layer Other layers FTP Server (FTP program) Application Layer Other layers Client’s Networking software Servers Networking software Login and other FTP protocol details are handled at the client and server application layers. The two application layers must exchange usernames, passwords etc. to implement the FTP protocol. Data Transfers occur between the FTP client application and the FTP server application. All transfers must use the physical network. ITECH1102 Networking & Security 25 Network data exchanges use all layers Client program data must pass through all underlying network layers to reach the Physical Network. So FTP data must traverse the following layers in turn: Transport layer Network Layer Data Link Layer Data being sent traverses down through the software layers of the protocol stack to the physical network. Received data rises up though the layers from the physical network. ITECH1102 Networking & Security 26 Protocol Headers As data passes through the protocol stack, Protocol headers