How data is transferred between network devices using the OSI seven-layer model

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Application Layer

This provides applications with the means to access the services of the other layers and defines the protocols used by the applications to exchange data. The most widely known protocols are used for the exchange of user information are as follows:

HTTP - Hypertext transfer protocol
FTP - File transfer protocol 
TELNET - Used for logging on remotely to networks.
SMTP - Simple Mails Transfer Protocol

The following protocols are used to assist in the management and use of TCP/IP networks:

DNS - Domain Name System
RIP - Routing Information protocol (Used for example by routers to exchange routing information on an IP network)
SNMP - Simple Network Management Protocol (Used for example to collect and exchange network management information)

Transport Layer

This Layer is responsible for providing the application layer with session and datagram communication services. The main protocols are:
 
TCP - Transmission Control Protocol. This provides a one-to-one communication service and is responsible for the:
    Establishment of the TCP connection
    Sequences and acknowledgement of packets sent
    Recovery of packets lost during transmission
 
UDP - User datagram protocol. This provides a one-to-one or one-to-many communication service which is connection-less and unreliable. It is used when the amount of data to be transferred would fit into a single packet. It is used by network applications that want to save processing time.

Internet Layer

This layer is responsible for the addressing, packaging and routing functions. The main protocols. The main protocols are:

IP - Internet Protocol. Responsible for the IP addressing, routing and the fragmentation and re-assembly of packets.
ARP - Address Resolution Protocol. It ensures that the address of the internet layer can be linked to the network interface layer address, for example the hardware address.
IGMP - Internet Group Management Protocol is responsible for the management of IP groups
ICMP - Internet Control Message protocol provides the diagnostic functions and reporting errors when delivery of IP packets is unsuccessful

Network Interface Layer

This layer is responsible for placing TCP/IP packets on the network medium and receiving them off the network medium. TCP/IP can be used to connect different network medium. TCP/IP can be used to connect different network types for example LAN technologies such as token ring and WAN technologies such as frame relay. 
 
Contiguous data: data that is stored in a collection of adjacent locations
 
Time to live: the amount of time or 'hops' that a packet is set to exist inside a network before being discarded by the router. TTL is also used in Content Delivery Network caching and Domain Name System caching.
 
Hops: refers to the number of routers that a packet passes through from its source to its destination. A hop can also be counted when a packet passes through other hardware on a network such as switches, access points and repeaters. It is dependent on what role the devices have on the network and their configuration.

Test Yourself Questions

1. HyperText Transfer Protocol Secure is an application layer protocol. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can easily access, for example by a mouse click or by tapping the screen in a web browser
2.  This layer provides applications with the means to access the services of the other layers and defines the protocols used by the applications to exchange data.

 

 





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