UART
UUCP
TFTP
VMTP
Frame
Datagram
Segment
Message
Disk space
Change keys
Modifier keys
Keyboard
A printer
A monitor
A telephone line
A scanner
Ping
E-mail
Web browsing
Internet chat
FTP
Telnet
Instant message
Storage device
Processing device
Input device
Output device
Modem
Repeater
Bridge
Router
DCE
DTE
DSE
DTE and DCE
Broadband channel
Narrowband channel
Voiceband channel
Wideband channel