Chapter 10: Application Layer

Chapter 10: Application Layer

1. Application layer

   • the layer that provides the interface between the applications used for communication and the underlying network
     • used to exchange data between programs running on the source and destination hosts.
   • Presentation and session layers
     • Compress the data so that it can be decompressed by the target device
     • Encrypt data for transmission and decrypt upon receipt
     • create and maintain dialogues between source and destination applications
   • TCP / IP application layer protocols
     • specify the format and control information necessary for many common Internet communication functions
   • Client-server model
     • describes the format of requests and responses between clients and servers
   • Peer networks
     • Data from an even device is accessed without using a dedicated server.
     • Peer Applications
       • function as a client and as a server within the same communication
       • Common P2P Applications
         • eDonkey
         • G2
         • BitTorrent
         • Bitcoin
   • Web and email protocols
     • HTTP y HTTPS
       • GET: solicitud de datos por parte del cliente
       • POST: carga archivos de datos, como los datos de formulario, al servidor web
       • PUT: carga los recursos o el contenido
     • Email protocols
       • communicate with mail servers to send and receive emails
       • store, send and retrieve electronic messages through a network
       • SMTP
         • they need a header and a message body
         • you must have a recipient email address correctly
       • POP
         • is used by an application to retrieve email from a mail server
           • As POP does not store messages
       • IMAP
         • describes a method to retrieve emails
           • Original messages are kept on the server until they are manually deleted
       • Domain Name Service
         • they were created to convert numerical addresses into a simple and recognizable name
   • DNS message format
     • A: an IPv4 terminal address
     • NS: an authoritative name server
     • AAAA: a terminal IPv6 address
     • MX: a mail exchange record
   • DNS hierarchy
     • use domain names to form the hierarchy.
       • .com: a company or industry
       • org: a non-profit organization
       • .au: Australia
       • .co: Colombia
     • to create a database that provides name resolution
   • Dynamic Host Configuration Protocol
     • automates the assignment of IPv4 addresses, subnet masks, gateways and other network parameters
   • DHCP operation
     • starts or connects to the network, the client transmits a DHCP detection message
   • File Transfer Protocol
     • It was developed to allow data transfers between a client and a server
     • It is an application that runs on a client computer and is used to insert and extract data on an FTP server
   • Server Message Block
     • client / server file sharing protocol describing the structure of network resources
       • Start, authenticate and end sessions
       • Control access to files and printers
       • Authorize an application to send or receive messages to or from another device