DC 5 Flashcards
What is multiplexing?
A technique to share a single, high-speed telecommunications line among multiple transmission sources.
Why is multiplexing used in long-haul communications?
To optimize the utilization of high-capacity links like fiber optics, carrying multiple voice and data transmissions simultaneously.
What are the main types of multiplexing?
Frequency Division Multiplexing (FDM)
Time Division Multiplexing (TDM)
Statistical Time Division Multiplexing (STDM)
What is Frequency Division Multiplexing (FDM)?
A technique that transmits multiple analog signals simultaneously by allocating each signal a distinct frequency band.
How does FDM prevent interference?
Carrier frequencies are spaced far apart with guard bands to avoid significant overlap.
How does an FDM system work?
Multiple signals modulated onto different carrier frequencies.
Guard bands separate channels to prevent interference.
Composite analog signal transmitted.
What is Synchronous Time Division Multiplexing (TDM)?
A technique that allocates fixed time slots in repetitive frames to multiple sources, interleaving their data.
What does “synchronous” mean in TDM?
Time slots are preassigned and fixed, transmitted even if the source has no data to send.
What is Statistical Time Division Multiplexing (STDM)?
A dynamic TDM approach where time slots are not preassigned but allocated based on input buffer demands.
How does STDM handle varying input loads?
Uses buffers to store data during peak loads and adds overhead for address and data in each slot.
What are the efficiency improvements in STDM frame structure?
Packing multiple sources in one frame.
Relative addressing to reduce overhead.
Using bitmaps to indicate active sources.
What is a modem, and why is it important?
A device that converts digital signals to analog for transmission over ISP infrastructure and vice versa.
Name types of modems and their use cases.
Dial-up: Basic connectivity, slow (56 kbps).
DSL: Affordable, moderate speeds (up to 100 Mbps).
Cable: Faster, good for heavy use (up to 1 Gbps).
Fiber: Exceptional speeds (10 Gbps+), costly, business use.
LTE/5G: Portable, high-speed wireless.
What functions does a modern modem perform in a network?
Signal conversion (digital ↔ analog).
Data security via encryption.
Protocol handling (e.g., PPPoE).
Integration with routers.
Connection optimization (QoS settings).
What is Quality of Service (QoS) in modems?
A feature to prioritize bandwidth for critical applications like video calls or gaming.
