3 Data Buses Flashcards
Name advantages that the star topology has over the bus topology.
- Multiple senders at same time
- Only one single point of failure
- No collisions
- No implicit broadcasts
The sublayers of the Data Link Layer (DLL are:)
Logic Link Control (LLC)
-Defines the frame format
-Defines Adresses / IDs
-Provides flow control1
-Provides error detection / correction
Media Access Control (MAC)
-Defines which participant may send with which
(Frequency / Code / Time)
-Defines how collisions are handled (if possible)
What topology uses I2C?
Bus Topology
What does Wired-AND mean?
A zero on the Bus is dominant.
What is the basic MAC concept of I2C? Why are there no collisions when multiple senders start at the same time?
The basic concept of Master-Slave is that the Master decides who can send at which time, while Slaves can only answer to read requests by Master. When there are multiple Masters the dominant 0 ”wins”, thus the Masters with a one at the first bit that differs between the senders stops transmitting.
What is the topology of Profibus and how is media access controlled?
Profibus uses a Bus Topology. Media Access is controlled through Master/Slave and Multiple Masters are managed using a Token Bus.
What are properties of the Nyquist-Shannon theorem?
► Any signal within a band of 0 Hz and fmax Hz must be sampled
with at least 2fmax Hz
► Signal can be reproduced exactly (with infinite effort)
► Signal can be approximated arbitrarily exact
► In practice 5fmax Hz to 10fmax Hz are common
Name advantages of the Bus topology:
- cheap
- simple
Name disadvantages of the Bus topology:
- multiple acces (Babbling idiot, security)
- Single point of failure
Name advantages of the Star topology:
- No multiple access
- Only central station is single point of failure
Name disadvantages of the star topology:
- expensive central station
- more wiring
Name advantages of the Ring topology:
- High quality of service
- No multiple access
Name disadvantages of the Ring topology:
- Complex (expensive)
- Single Point of failure
What are the properties of the physical layer of the ISO/OSI 7 layer architecture?
► Defines mechanical properties
▪ Medium: copper, optical fiber, air, EM waves
▪ Connectors: form and pin assignment
► Defines electrical / optical properties
▪ Voltage
▪ Frequencies
▪ Baud rate
▪ Bit encoding
► Hardware
▪ Cable, connector, terminator, antenna, amplifier
▪ Transceiver, repeater, hub
Which methods for bit encoding exist?
► Return to Zero (RZ) ► Non Return to Zero (NRZ) ► Differential NRZ ► Bit stuffing ► Manchester Code ► 4B/5B Code
Explain the synchronization problem and name a solution for it:
► Clocks are never perfectly synchronous ► Clock A ticks every 100μs ► Clock B ticks every 90μs ► Clock A sends nine ones →high level for 900μs ► Clock B interprets this as ten ones
Solution: Differential NRZ
What is Bit Stuffing and for what is it used for?
► Sender inserts a 0 after a sequence of n 1s (n=6 for USB)
► Receiver (checks and) removes inserted 0s
► Code violations (frame delimiters)
► Prevents long sequences of 1s
What are the properties of the 4B/5B code?
► Uses some form of NRZ
► 80% data rate
► Encoding table prevents long sequences (FDDI with NRZI)
What are the properties of the data link layer of the ISO/OSI 7 layer architecture?
► Encapsulates data (bits) into frames
► Frame formats/synchronization
► Logical link control
► Media access control
► Hardware: Switch, Bridge
► Two sublayers
▪ Logical Link Control (LLC)
▪ Media Access Control (MAC)How can Errors during the data transmission be detected?
► Parity bit
▪ Append parity bit such that the sum off all bits is
even / odd
▪ One bit error detection
► Cyclic Redundancy Check (CRC)
▪ Hash function based on polynomial division
▪ Detection of burst errors
► Hamming Code
▪ Set of parity bits
▪ Single error correction
▪ Double error detectionProcedure of succesful transmission:
▪ A sends frame to B
▪ B acknowledges frame
Procedure of unsuccesful transmission (transmission error):
▪ A send frame to B
▪ B detects error
▪ B sends negative acknowledgement (“NACK”)
▪ A resends frame to B
Procedure fo unsuccesful transmission (transmission lost)
▪ A sends frame to B
▪ Timeout occurs
▪ A resends frame to B
What is the purpose of Media Acces Control (MAC)?
Media Acces Control regulates access to a shared medium
