This document discusses the seven layers of the OSI model from application to physical layer. It provides brief descriptions of functions for each layer such as presentation layer handling text formatting, transport layer providing host-to-host communication, and physical layer dealing with signal and hardware specifications.

2. Application layer
- OSI
-
-
-
- header
-

3. Presention layer
- text
-
-

4. Session layer
-
-
- header

5. Transport layer
- host-to-host
-
End-to-End
-
-

6. Network layer
-
-
-
-
-
-

7. Data link layer
-
Checksum
-
-
ACK Acknowledge
- ACK
-

8. Physical layer
-
- -
-
RS-323-C PIN
-