Punctuality
That's why Dr. Dayang angry about.
Today, we were taught to define data communication technology.
Simple definition of data communication :
- collection &b distribution of the electronic represenred of information FROM & TO remote facilities by means of electrical transmission system such as telephone lines, satellites or coaxial cable.
- Data, text, voice, still pics, graphics & video. (RAW,DATA/INFORMATION=must be DIGITIZED)
Types of signal
- All this type of info needs to be converted.
(i) Digital Signal
- transmission of binary electrical/light pulses that only have to possible states 0 and 1. (this is language of computerswhich represented of a squre wave).
- digital signal need changed into analogue signal to transmitted through PSTN line.
- analogue → digital signal = modulation
- digital → analogue = demodulation
- e.g of hardware that used in computer to do thus process : MoDem
(ii) Analogue Signal
- like human voice
- formed by continuously varying voltage levels that create a wave that can be grasped by an analogue transmitter like microphone.
- Frequency is a number of completed wave is cycles & measured in Hertz(Hz) which is cycle per second.
- Analogue signal is transmit through PSTN line known commonly as phone line.
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 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
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.
e.g : 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.
0 comments:
Post a Comment