The OSI model

    L7 - Application layer. Data. HTTP, FTP, DNS, Telnet
    L6 - Presentation layer. Data. SSL or TLS, JPEG, GIF
    L5 - Session. Data. NetBIOS, PPTP
    L4 - Transport. Segments. TCP, UDP
    L3 - Network. Packets. IP, ICMP - ping, ARP
    L2 - Data link. Frames. MAC address level. Router / Switch level
    L1 - Physical. Bits. ethernet cable connection

The TCP/ICP model

    L4 - Application, HTTP, FTP, SMTP, DHCP, Telnet
    L3 - Transport, TCP, UDP
    L2 - Internet layer
    L1 - Network layer