|
Protocols at this layer |
Function |
|
|
Application |
SMTP, HTTP, FTP, Telnet |
Deals with applications programs used by end user. |
|
Transport |
TCP |
Deal with the disassembly and reassembly of packets, error detection and correction, etc. |
|
Network |
IP |
Deals with the addressing of packets. |
|
Link |
PPP |
Handles the transmission of bits through the communications channel. |
The bottom layer – the Link – is responsible for communicating with the hardware that connects your machine to the Net If this is a dial-up access the hardware is the modem.
The next layer up – the Network layer – is responsible for figuring out how to get packets to their destination. This is where IP lives. It gives no guarantees about whether packets will get through; it just decides where they will be sent.
Above the Network layer is - the Transport layer – where TCP resides. Its job is to ensure the reliability and integrity of messages and process them to and from the Application layer above.
At the top of the stack is – the Application layer -. This is where the user interacts with the network. The protocols which reside at this level – SMTP, Telnet, FTP, HTTP – are embedded in the particular applications programs used to send and receive e-mail, log in to remote machines, transfer files or browse Web pages.
A TCP/IP stack works by passing packets up and down from layer to layer. Each layer does something to the packet in order to achieve its allotted purpose. Mostly this involves adding headers to, or stripping headers from, packets.