1. TRANSLATION
   1. accept APPLICATION LAYER's data => format in one type of data
   2. TEXT ENCODING
      1. US-ASCII
         1. ASCII
      2. Unicode
   3. BYTE ORDER
   4. BIT ORDER
      1. look at actual data stream
   5. FILE SYNTAX
2. ENCRYPTION
   1. clear text
      1. unencrypted files
   2. cipher text
      1. encrypted files
   3. PUBLIC KEY
   4. PRIVATE KEY