Only reports error conditions to the original source, the source must relate error to individual application programs and take action to correct the problem
Provides communication between the Internet protocol software on one machine and the internet protocol software on another
Allows gateways to send error a control messages to other gateways or hosts
All of these
Peripheral
Expansion slot
Server
Network
ALU
CPU
Control unit
Register
Communication Protocol
Modem
DNS
Router
FDM
Synchronous TOM
Asynchronous TOM
Both a and b