Modem: Modem combined with two words Modulator and Demodulator. A device that can convert a digital bit stream into an analog signal for transmission over some communication channel is called Modulation and can convert incoming analog signals back into digital signals known as Demodulation. Modems are used to connect digital devices across analog transmission lines .

Protocol: An entity is capable of sending or receiving information and a system is a physically distinct object that contains one or more entities. The key elements of Protocol are:

HDLC is an example of Protocol.The data to be exchanged must be sent in frames of a specific format.

Ethernet: The most commonly used medium access control techniques for bus/tree and star topologies is multiple access with collision detection or CSMA/CD. CSMA/CD can be termed random access or contention techniques.They are random access that there is no predictable or scheduled time for any station to transmit; station transmissions are ordered randomly. An important rule followed in CSMA/CD systems, Including the IEEE standard, is that frames should be long enough to allow collision detection prior to the end of transmission.

Broadband: Communication uses a modulation to apply a data signal to a transmission medium in analog form. Multiple signal can be present simultaneously using Frequency division multiplexing. Ethernet are inherently broadband in nature. Communication systems that use Broadband networking techniques on Coaxial cable. There are two classifications of Broadband Coaxial system. In one way system signal travel in only one direction in the cable. This kind of system is Cable TV systems. In two-way system signals can travel in both directions on the cable.Two-way systems fall into mid-split or sub-split categories .