The TCP/IP model has four layers

1.  Application  (OSI- application, presentation, session)
    ex.  FTP(21), TFTP(69), Telnet(23), SMTP(25), SNMP(162,162), DNS(53)

2.  Transport
End-to-End connectivit, allows application layer to do its job by ignoring network requests
    ex.  TCP, UDP

Ports- Identify or track applications running on a host, 65,535 total, 0-1,023 well known

3.  Internet
Path determination and packet switching
    ex.  ARP     known IP - unknown MAC
          RARP   unknown IP - known MAC

4.  Network Access
Provides access to a LAN
    ex.  Token Ring, FDDI, Ethernet

Sliding Windows, 3-way Handshake