Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Quiz 2: Networks
The Physical / Data Link Layer
| Question | Answer |
|---|---|
| At what altitude do GEO sats operate? | 35,000 kilometers + |
| What is the function of transponders? | Transponder listen to portions of the spectrum, amplify incoming signals, amplify them, and rebroadcast at a different frequency to avoid interference. |
| What is bent pipe? | Process of transponders rebroadcasting signals at different frequencies. |
| What does ITU do? | Allots time slots to sat users (countries) since a max of 180 can be in the sky at once. |
| What is station keeping? | The process of using rocket-motors to protect sats from celestial forces. Must be turned off if motors die. Helplessly float otherwise. |
| What is one issue with frequencies using GEO sats? | Downlink transmissions interfere with existing microwave users. So, ITU allocates frequencies bands to users. |
| What are the frequency ranges for bands? | lower range (downlink traffic/from sat) upper range (uplink/to sat) |
| Describe the Ku band | For commercial communication. Uncongested (for now), higher frequencies 1 degree spacing. Speeds at 500Mbps |
| What are the issues with the Ku band? | Rain absorbs short microwaves. Storms locational but extra resources required for extra towers and rapid switching. |
| How many transponders does a modern sat have? What is the average bandwidth? | 40 transponders with generally 36-Megahertz bandwidth. |
| What is FDM? | Frequency Division Multiplexing - Bandwidth is split into fixed frequency bands (pre-negotiated). Guard bands are placed between them to prevent interference. |
| What is TDM? | Time Division Multiplexing - Bandwidth is split into time slots. Users can use entire bandwidth for limited time. |
| What is a satellites footprint? | The area of Earth's surface its signal covers. |
| How do satellites support simultaneous multidirectional transmission? | Each satellite has multiple antennas and transponders that can be pointed at smaller geographic areas. (Elliptical shaped). Downward beams are called spot beams. |
| How big are VSAT antennas? | 1 meter or less |
| How do VSATs communicate with each other? | Through a ground station called a hub that relays information between micro stations. Longer latency but lower costs. |
| How long is a typical roundtrip? | 270 milliseconds |
| What are the characteristics of LEO sats? | Lower Earth Orbit sats offer higher bandwidth, low latency, strong signals, and high-speed internet. They operate at 5,000 km and are used for earth observation s and require thousands for full surface coverage. |
| What are the characteristics of MEO sats? | Medium Earth Coverage sats orbit in the 5,000 - 15,000 km range at about 6 hours, used for navigation systems (GPS), moderate latency, low signal strength due to distance, requires more tracking, and complex network management. |
| What are the characteristics of GEO sats? | Geostationary Earth Orbit sats orbit at 35,000 km, and are fixed position, spaced 2 degrees apart, covers about 1/3 earth's surface. |
| What is the purpose of the link layer in the overall stack? | Ensure that data is properly transferred over a physical medium. Defines how data is formatted into frames. |
| What is the difference between EDC and ECCs? | EDC - Detect errors without fixing ECC - detects and fixes errors |
| When is it practical to use EDCs? | When retransmission is fast and easy, low overhead important, errors are rare. |
| When is it practical to use ECCs? | Retransmission tedious, noisy channel, low latency required, data stored on first read. |
Created by:
n01602212