Chapter 4 - The Physical Layer Flashcards
What are the Types of Transmission Media?
- Guided: channelled along a physical cable or fibre optic
- Unguided: propagated using radio or light signals
What is Latency?
The amount of time, including delays, for data to travel from one point to another.
What is Throughput?
The measure of the transfer of bits across the media over a given time period. This could be lower than the bandwidth stated due to the amount of traffic, the type of traffic or the latency
What are the Main Types of Interference in a Network?
- Crosstalk: a signal transmitted on one channel of a transmission system creates an undesired effect in another channel
- Radio Frequency Interference (RFI)
- Electrical Interference
How is Interference Reduced?
- Coaxial
- Unshielded Twisted Pair (UTP)
- Shielded Twisted Pair (STP)
What is UTP?
- consists of 2 balanced conductors
- wires surrounded by a protective jacket
- reduces noise and crosstalk
- terminated with RJ-45 connectors
- easy to install, industry standard, less costly
What is STP?
- twisted pair cable confined in foil or mesh shield
- guards the cable against electromagnetic interference
- provides better noise protection than UTP
- more expensive and difficult to install
What are Fibre Optics?
- a central glass core surrounded by a less dense cladding
- signals carried in the form of light rays
- much higher bandwidth than UTP or coaxial
- low signal attenuation so less frequent signal regeneration
How Does Propagation Work?
- Digital signals converted to laser or LED
- Enters the fibre if it falls within the acceptance cone
- Propagates along the fibre by Total Internal Reflection
- Optical transducers are used to convert the light signal back into a digital signal
What are the Transmission Modes?
- Single Mode: small core reducing pulse spreading, supports higher data rates, uses expensive lasers, more expensive to deploy
- Multimode: larger core with lower data rates to combat pulse spreading, allows coupling from inexpensive LED light sources
What Types of Fibre Connectors are There?
- ST
- SC
- LC Simplex
- Duplex Multimode LC
- Fibre Patch Cables
What are the Advantages of Fibre?
- higher bandwidth
- less signal attenuation
- immunity to electromagnetic interference
- no circulating ground currents
- lightweight
- improved security
What is Wireless Media?
A wireless transmission is where unguided media uses electromagnetic waves to transfer data/voice signals instead of a physical wire.
What are the Components of a WLAN?
- a Wireless Access Point (WAP)
- SOHO wireless routers
- wireless NIC adapters
What are the Main Wireless Standards?
- WLAN (WiFi)
- WPAN (Bluetooth)
- WiMax
- Zigbee
