Data Transmission

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

Analog 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, whichconsists 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.

Bandwidth

• = 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

Serial vs Parallel Transmission

• 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 vs Parallel Transmission

• 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 – Data organised into blocks or groups and

transferred at regular specified interval

• 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

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.

Directions of Data Transmission

• Simplex

• Duplex

– Half Duplex

– Full Duplex

Simplex

• One way communications

• Data travels in single direction only i.e door bell

etc

• Relatively uncommon in computer communications

Half Duplex

• Data can travel in either direction but

only in one direction at a time.

• USB devices are half duplex

Full Duplex

• 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

• Circuit switched

– Data used dedicated path from sender to receiver

Packet‐Switched

• Data sent as individual packets, which are

assembled at the recipient’s destination

Broadcast Connections

• 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 compressed using MPEG‐2, and several file systems automatically compress files whenstored, 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.

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