Data Transmission

Data Transmission

Data communication is affected by several technical matters:

Voiceband - speed of standard telephone line
- 9,600 to 56,000 bps
Medium band - speed of special leased lines
- 56,000 to 264,000,000 bps
Broadband - speed of microwave, satellite, coaxial cable, and fiber-optics channels.
- 56,000 to 30,000,000,000 bps

Serial data transmission - bits flow in a continuous stream
- Example: data sent over telephone lines.
Parallel data transmission - bits flow through separate lines simultaneously.
- Example: data sent from the system unit to the printer.

Simplex communication
- Data travels in one direction only.
- Not used frequently in current communication systems
- Certain point-of-sales application may use this method.
Half-duplex communication
- Data flows in both directions, but not simultaneously.
- Frequently used to link microcomputers by telephone lines to other computer systems such as Bulletin Board Services.
Full-duplex communication
- Data can flow in both directions at the same time.
- Is the fastest method.
- Requires special equipments.
- Used primarily for mainframe communications.

Asynchronous transmission
- Data is sent and received one byte at a time
- Used frequently with microcomputers
- Often used for terminals with slow speeds
Synchronous transmission
- Data is sent and received several bytes (or a block) at a time.
- System requires a synchronized clock
- Sending and receiving of the blocks of bytes must occur at carefully timed intervals.

A protocol is a set of communication rules for the exchange of information.
Defines the speeds and modes for connecting with another computer.
Network protocols can become very complex and therefore must adhere to certain standards.
The first sets of standards was IBM System Network Architecture (SNA) which only works with IBM computers.
The Open Systems Interconnection (OSI) standard was developed by the International Standard Organization to:
- Identify functions provided by any network
- Separate each network functions into seven layers of communication rules.