1. Highcliffe ICT Department
Bus
Highcliffe ICT Department

2. Bus Bus = A linear transmission medium E.G. Coaxial Cable
Each PC on BUS has UNIQUE HARDWARE ADDRESS
Means each PC can be INDENTIFIED

3. BASEband bus systems Each Transmission = a series of VOLTAGE PULSES
Run the length of the BUS in BOTH DIRECTIONS
Can be received by ANY PC on the BUS
Voltage Pulses cease when they each the end of the BUS

4. Collisions When 2 PC’s transmit at the same time...
VOLTAGE PULSES COLLIDE
= Higher VOLTAGE SWINGS
= Transmission UNREADABLE
BUS = UNUSABLE until transmission ENDS

5. Frames System for reducing COLLISIONS uses FRAMES
FRAME = limited number of PULSES
Between a set MINIMUM & MAXIMUM to allow VOLTAGE RISE TO BE DETECTED

6. TRANSMISSION PROTOCOL
Aims to REDUCE collisions
CSMA/CD = popular protocol
Carrier Sensitive Multiple Access with Collision Detection

7. RULES FOR CSMA/CD If BUS QUIET = Transmit Frame
If BUS BUSY = wait for quiet then transmit immeadiately
While transmitting MONITOR for COLLISION
IF COLLISION - Transmit JAMMING signal & STOP
After TRANSMITTING JAMMING Signal - WAIT then start again