DATA TRANSMISSION
Data travel over a network in various characteristics: form, amount of data : type, direction and timing:
- Analog vs digital.
- Bandwidth.
- Serials Vs Parallel.
- Transmission timing.
- Transmission directions.
- Circuit switched, Packet‐Switched, and Broadcast Connections
Analogs VS Digital
Analog transmission uses signals that are exact replicas of a sound wave or image. Signals of varying frequency or amplitude are added to carrier waves with a given frequency of electromagnetic current to produce a continuous electric wave
E.g standard phones, fax machines, and modems.
Digital transmission the signals are converted into a binary code, which consists of two elements.Digital format is ideal for electronic communication as the string of 1s and 0s can be transmitted by a series of "on/off" signals represented by pulses of electricity or light.
Bandwith
- The amount of data that can be transmitted in a fixed amount of time.
- For digital devices, the bandwidth is usually measured in bits per second(bps), Megabits persecond (Mbps) etc.
- Medium with higher bandwidth deliver data faster.
Serials VS Parallel
- Serial transmission : data sent one bit at a time, one after another a long a single path.
- Parallel transmission : data is sent at least one byte at a time, each bit in the byte taking separate path.
- Serial transmission : used for short communication e.g between computer to printer.
- Parallel transmission used within computer component e.g buses.
Transmission Timing
- Synchronous transmission.
- Asynchronous transmission.
- Isochronous transmission.
1.Synchonous transmission - Data organised into blocks or groups and transferred at regular specified interval
2.Asynchronous transmission - the process where transmitted data is encoded with start and stop bits, specifying the beginning and end of each character.Data sent without being synchronised.
3.Isochronous transmission - data is sent at the same time as other related data to support certain types of real time applications e.g streaming voice, video and music.
Direction of Data Transmission
1.Simplex
- One way communications.
- Data travels in single direction only i.e door bell etc.
- Relatively uncommon in computer communication.
2.Half Duplex
- Data can travel in either direction but only in one direction at a time.
- USB devices are half duplex.
3.Full Duple
- Data can moves in both directions at he same time, such as with a telephones.
- Ideal for hardware devices that need to pass large amount of data between each other.
- Many networks and most internet connections are full duplex.
Circuit switched, Packet-Switched, and Broadcast Connections
1.circuit switched - Data used dedicated path from sender to receiver.
2.packet switched - Data sent as individual packets, which are assembled at the recipient’s destination.
3.broadcast connection - Data broadcast to all nodes within range.
Data Compression
- Data compression encoding information using fewer bits than the original representation.
- Compression is used just about everywhere. All the images you get on the web are compressed, typically in the JPEG or GIF formats, most modems use compression, HDTV will be compressedusing MPEG‐2, and several file systems automatically compress files when stored, and the rest of us do it by hand.
- Data compression is particularly useful in communications because it enables devices to transmit or store the same amount of data in fewer bits.
- In addition, there are file compression formats, such as ARC and ZIP.
WEEK 3
24 March 2012 at 00:59
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