Chapter 1 Flashcards
Why did they end all the different communication protocols?
People with different devices could not communicate with each other
What was the solution to the communication protocols?
Common elements were identified and called the OSI model
What does OSI mean?
Open System Intercommunication Model
In what layers does the TCP/IP model work at compared to the OSI model?
TCP works on the transport layer of the OSI model and IP works on the Network layer of the OSI model
What are the layers of the OSI model?
Layer 1 - Physical Layer 7-Application
Layer 2 - Data Link Layer 6-Presentation
Layer 3 - Network Layer 5- Session
Layer 4 - Transport Layer 4 - Transport
Layer 5 - Session Layer 3 - Network
Layer 6 - Presentation Layer 2 - Data Link
Layer 7- Application Layer 1 - Physical
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Which came first TCP/IP or OSI?
TCP/IP
What is the nickname given to the TCP/IP model?
The DoD model or the Deportment of Defense model (they made it)
What does PDU stand for?
product data unit
What are the names of the pdu in different layers of the OSI model?
layer 7-5 = data or pdu
layer 4 = segments
layer 3 = packets
layer 2 = frames
layer 1 = bits
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Why does data need to be split into segments in layer 4 (Transport)?
If we were to send larger data in one go, no one else would be able to communicate.
What does the physical layer define?
How to represent bits on the medium
Wiring standards for connectors and jacks
Physical topology
Synchronizing bits
Bandwidth usage
Multiplexing strategy
How are bits represented on the medium?
Data on a computer network is represented as a binary expression.
What are the two methods binary can be represented?
Current state modulation
State transition modulation
How are bits synchronized?
Asynchronous
Synchronous
Describe the asynchronous method of synchronizing bits
Sender states that it is about to start transmitting by sending a start bit to the receiver
receiver then starts its own internal clock to measure the next bits
sender transmits its data and then sends a stop bit to say that it has finished
Describe the synchronous method of synchronizing bits
internal clocks are synchronized to ensure that they agree on when bits begin and end
common approach is to use an external clock
What are the two methods of bandwidth usage? How are they different
Broadband - divides the bandwidth into different channels
Baseband - uses all the available frequencies on a medium to send data
What is multiplexing strategy?
Multiplexing allows multiple communications sessions to share the same physical medium
What is time-division multiplexing (TDM)?
Supports different communication sessions on the same physical medium by causing the sessions to take turns
Ex. Different phone conversations in a phone network
What is Statistical time-division multiplexing (StatTDM)?
StatTDM fixes an issue with TDM strategy. StatTDM dynamically assigns time slots to communications sessions on an as-needed basis.
What is Frequency-division multiplexing (FDM)?
Divides a medium’s frequency range into channels, and different communication sessions send their data over different channels.
What is Orthogonal frequency-division multiplexing (OFDM)?
OFDM encodes digital data onto multiple carrier frequencies. OFDM is very popular today and is used in wideband digital communication.
digital television, audio broadcasting, DSL Internet access, wireless networks, powerline networks, and 4G/5G mobile communications
The data link (layer 2) is concerned with what?
Packaging data into frames and transmitting those frames
Ensuring that frames do not exceed the maximum transmission unit (MTU)
Performing error detection/correction
Uniquely finding network devices with addresses
Handling flow control
What are the two sublayers of the Data Link layer (layer 2)?
MAC and LLC
Describe the MAC address
a 48-bit address assigned to a device’s network interface card (NIC)
MAC address are written in hexadecimal notation
First 24-bits of the 48-bit are the vendor code
The last 24-bits of a MAC are assigned by the manufacturer, and they act as a serial number for the device.
No two MAC addresses in the world should have the same value.
How does layer 2 (Data Link) devices view a network?
Layer 2 devices view a network as a logical topology.
Examples -bus and ring topologies
Why are acknowledgment messages important? (LLC data link sublayer)
they provide flow control and error control
The Data Link layer also does synchronization. How does the LLC (logical link control - data link sublayer) synchronize data frames?
Isochronous - Asynchronous - Synchronous
Describe the Isochronous method of synchronizing transmissions in layer 2
Network devices look to a common device in the network as a clock source, which created fixed-length time slots.
A time slot can accommodate more than one data frame.
Little overhead compared to asynchronous or synchronous transmission methods.