# 7. Application Layer

* Application
  * interface between the applications and user
  * data format, compression and encryption (presentation)
  * dialog between source and destination application (session)
* Hypertext Transfer Protocol (HTTP)
  * port 80
  * request/response protocol
  * HTTPS 443
* Email
  * Simple Mail Transfer Protocol (SMTP)
    * Sending email
    * port 25
  * Post Office Protocol (POP)
    * Receive email
    * port 110
  * Internet Message Access Protocol (IMAP)
    * Receive email
    * port 143
  * Mail User Agent     (MUA)
  * Mail Transfer Agent (MTA)
  * Mail Deliver Agent  (MDA)
* Domain Name System (DNS)
  * resolve name to IP
  * fully-qualified domain names 
  * distributed set of servers   
  * nslookup
* Dynamic Host Configuration Protocol (DHCP)
  * obtain IP automatically
* File Transfer Protocol (FTP)
  * data transfers between a client and a server
  * port 20 (data) and 21 (control)
* Server Message Block (SMB)
  * Sharing protocol