How many layers are in the OSI model?

The OSI 7 layer model descibes the theoretical levels of networking on a computer Layer 1 Physical Layer - actual network cable and connectors

Layer 2 Data Link Layer - network address (MAC) and packet switching

Layer 3 Network Layer - internet Protocol (IP) - addressing and packet routing

Layer 4 Transport Layer - Transmission Control Protocol (TCP) - packet sequencing & error correction

Layer 5 Session Layer - Connection control for repeated send/receive (a session)

Layer 6 Presentation Layer - presenting information to application in correct format

LAyer 7 Application Layer - actual display/control of information, layout etc. for two computers to communicate -example chat program the following would occur user types into a chat program on computer A (7)

application accepts input and decides what to do with it (6)

a connection is requested to send to computer B (5)

the message is broken into pieces and encpsulated within a packet (which includes the address to send to and the address from which it came) Packets are given a sequence number(4)(3)

Packet sent across the network using the addressing information to determine where to go to(3)(2)(1) on Computer B the revers happens - packet is put back together - addressing information is removed and eventually displayed on the screen.