Basically, any type of data. Data stored in computers is stored as 1's and 0's; such data ("digital data") can be encoded in such a way that it represent a wide variety of types of data, such as documents, images, sounds, videos, computer programs, and probably several other types of information. Any such data can be transmitted over a network. However, the network may impose a limit on how fast such data can be transmitted - or more accurately, with what bandwidth (measured in bits per second or some multiple, for example, Mbps). This may make it impractical, for example, to transmit high-quality movies over certain slower networks.
full-duplex and half-duplex
Data transmitted over the Internet is broken into Packets when transmitted over the Internet or other network.
packet sniffer
MD5
To access a network, some type of network card must be installed in the computer.
L2TP is a tunneling protocol for an IP network. L2 data is transmitted over the network but has no encryption or authentication abilities. This type of protocol is usually paired with IPSec to provide encryption and authentication.
The difference: With PSTN, the voice is transmitted through the network of cables. While with VoIP is transmitted through the internet. This is the main difference between the two communication systems.
Virtual Private Network (VPN)
D: md5
Data is commonly shared over the network by creating a network share. The network share is typically a shared folder that may or may not have password protection.
Bandwidth
frame
Power over ethernet (PoE)