Flashcards
Data Link Layer
Flashcards do conjunto (13)
- 1What layer of the ISO OSI is Data Link?2nd (just above physical)
- 2What does the Data Link layer do?Provides services by encapsulating data in frames
- This introduces overheads reducing channel efficiency - 3What is the framing process?1. Split data into frames
2. Add header data to frames
3. Transmit frames
4. Receive frames
5. Check header
6. Strip header and reconstruct message - 4What does IEEE 802 do?Encapsulates standards for a range of network types:
- IEEE 802.3 - Wired Ethernet
- IEEE 802.11 - Wireless ethernet
- IEEE 802.15 - Bluetooth - 5IEEE 802 divides the data link layer into 2 sub layers, what are they?1. Logical Link Control (LLC):
- Multiplexing protocols (encode and decode)
- Flow and error control
2. Media Access Control (MAC)
- Physical Addressing
- Co-ord. access to the medium (channel access) - 6How long is a mac address?6 byte (48 bits)
- 7What are the 2 protocols used to counteract the effect of collisions?- Random Access
- Scheduled (Controlled) Access - 8What is ALOHA and what are the two versions of it?ALOHA - Random Access Protocol
1. Pure
2. Slotted - 9What is Pure ALOHA?If you have data send it!
- Collision detection by waiting for ACK response
- If collision: resend original data later - 10What is the vulnerable period?The length of time where there is a possibility of collision
- 11How does pure ALOHA detect collisions?Reliance upon ACK or lack of ACK to detect collisions
- 12What is back off time?A random amount of time a station waits before trying to resend data so as to avoid a collision
- 13What is the purpose of Slotted ALOHA?Improves on the efficiency of Pure ALOHA by diving time into slots of T(frame) seconds and only allowing transmission at beginning of each slot