450 Flashcards
NRZ encoding
Transmission is high on 1 and low on 0. Signal shifts between numbers, sustaining between repeating numbers.
NRZI encoding
Transmission shifts on 1’s and sustains on 0’s. Transitions ocour during numbers / in the middle of the clock cycle.
Manchester encoding
Transmission shifts to high on 0’s and shifts to low on 1’s. Transitions occur during numbers / in the middle of the clock cycle.
What can occur if there is a long sequence of either ones or zeroes in a transmission?
What impact might this have?
A long sequence of 1’s and 0’s keep the signal high or low for too long. This can cause the
baseline signal of the receiver to change. This can also cause the clock signal to drift.
Why is Manchester encoding only 50% efficient? What is the efficiency measured
against?
Manchester encoding has a 50% efficiency, due it’s doubled rate of signal transitions, as NRZ and
NRZ can transmit twice the bits. It is NRZI and NRZ that Manchester is measured against.
Does NRZI with 4B/5B encoding have the same efficiency as Manchester encoding?
Explain.
NRZI 4B/5B encoding has an 80% efficiency. 4b/b encoding lessens the amount of consecutive.
1’s and caps the amount of 0 at 3. NRZI also deals with consecutive 1’s by switching upon 1’s.
Manchester encoding has a 50% efficiency.
What are the 2 interfaces of a protocol
Service interface and peer interface
What is a service interface
- the interface to the other network layers
- defines the operations that local objects can preform on the protocol.
What is a peer interface
- Interface between different peers on a network.
- the format of message headers and trailers.
- defines the form and meaning of messages exchanged between protocol peers to implement the communication service.
What type of address would a wifi distribution system use?
MAC address as it operates at the link layer.
fully explain how 802.11 achieves collision avoidance, include the optional mechanism described in the book.
Carrier Sense and RTS-CTS
what is RTS
request to send
What is CTS
clear to send
Whats a checksum?
Check + Sum.
what happens in binary addition when you extant by 1
remove the extant 1, and add 1 to remainder.
What is XOR
00 = 0
01 = 1
10 = 1
11 = 0
how is a checksum performed
Divide binary string into 4 nibble chunks. Add the 1st 2 chunks (wrap around extant 1’s) add the 3rd chunk to the sum, add the 4th to that sum etc. when finished find the binary compliment.
how do i
what is the CRC polynomial
a based ass number that we dont need to find the origin to.
