Cisco – Chapter 15 Application Layer closest to you as an end-user, when you are interacting with software

Layer 7 Responsibilities Identifying and establishing the availability of intended communication partners Synchronizing cooperating applications Establishing agreement on procedures for error recovery Controlling data integrity

Layer 7 Protocols Client-Server Redirectors Domain Name System Telnet FTP HTTP

Protocols Explained The World Wide Web uses the HTTP protocol. Remote access programs use the Telnet protocol for directly connecting to remote resources. programs support the POP3 application layer protocol for electronic mail. File utility programs use the FTP protocol for copying and moving files between remote sites. Network data gathering and monitoring use the SNMP protocol.

Telnet Explained When the data reaches the remote host computer, the data link, network, and transport layers, reassemble the original data commands. The remote host computer executes the commands and transmits the results back to the local client computer by using the same process of encapsulation All work done by remote host

FTP Explained FTP session is established the same way in which a Telnet session is established. Just like Telnet, the FTP session is maintained until the client terminates it, or there is some sort of communication error. Uploads and downloads files Requires login id and password –Anonymous is login id and address is password

HTTP Explained tells the browser which protocol to use. The second part, "www", tells the browser what type of resource it wishes to contact. The third part, "cisco.com," identifies the domain of the Web server IP address. The last part, "edu" identifies the specific folder location (on the server) that contains the Web page.

Layer 6 Protocols POP Usenet FTP HTTP Telnet DNS SNMP, NFS

Relationship to Other Layers Does not provide services to any other OSI layer. It does provide services to application processes lying outside the scope of the OSI model –Spreadsheets, databases, etc

Client-Server Environment Most applications that work in a networked environment –FTP, web browsers, and –Client side and server side Web browser is probably the most commonly used network applications –accesses a web page by requesting a uniform resource locator (URL), or web address, on a remote web server.

Redirector Protocol that works with computer operating systems and network clients instead of specific application programs –Apple File Protocol, NetBIOS Extended User Interface (NetBEUI), Novell IPX/SPX protocols, Network File System (NSF) of the TCP/IP protocol suite Applications on the client never have to recognize the network Allow users to share documents, templates, databases, printers, and many other resource types

Two Types of Connection FTP and Telnet Establish and maintain until all communication is complete Network Services Make/Break, Make/Break, Make/Break

DNS Domains Edu Gov Com Org Net Int Mil

DNS Server and Resolves (translates) DNS name to IP address Address It consists of two parts: the recipient’s name (located before sign); and the recipient’s post office address (after sign).