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.
Describe the Asynchronous method of synchronizing transmissions in layer 2
Network devices reference their own internal clocks, and network devices do not need to synchronize their clocks.
Describe the Synchronous method of synchronizing transmissions in layer 2
two network devices that want to communicate between themselves must agree on a clocking method to show the beginning and ending of data frames.
How does asynchronous and synchronous perform error detection (layer 2)?
asynchronous - parity bits
synchronous - cyclic redundancy check (CRC)
The network layer is primarily concerned with what?
forwarding data based on logical addresses
What are some of the task the network layer (layer 3) is responsible for?
logical addressing
switching
route discovery and selection
connection services
bandwidth usage
multiplexing strategy
Whereas the data link layer (layer 2) uses physical address (MAC) to make forwarding decisions, the network layer uses what?
Logical addressing
most widely deployed routed protocol is Internet Protocol (IP)
The term switching is commonly associated with layer 2 (Data Link); however, the concept of switching also exist at Layer 3 (network). What are the three common switching techniques in layer 3?
Packet Switching
Circuit Switching
Message Switching
What is Packet Switching?
A data stream is divides into packets. Each packet has a layer 3 header that includes source and destination Layer 3 addresses.
What is another term for packet switching?
routing
What is Circuit Switching
circuit switching dynamically brings up a dedicated communication link between two parties for those parties to communicate.
Think phone calls (the connection only exist for the duration of the phone call)
What is Message Switching?
data stream is divided into messages
sometimes called a store-and-forward
not suited for real-time applications because of delay
think of an email
Just as the data link layer (2) offers connection services for flow control and error control, connection services also exist at the network layer. Why?
If the data link’s LLC sublayer is not preforming connection services, connection services at the network layer can improve the communication reliability.
Flow control and packet reordering
What is the most common Layer 3 protocol?
IPv4 but IPv6 is starting to gain popularity
The transport layer act as what?
the dividing line between the upper layers and the lower layers
Specifically, messages are taken from upper layers (5-7) and are encapsulated into segments for transmission to the lower layers (1-3)
decapsulation
What are the two common transport layer protocols?
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol)
Describe the TCP (transmission control protocol)
TCP is a connection-oriented transport protocol.
It offers reliable transport, if a segment is dropped, the sender can detect the drop and retransmit the dropped segment.
Describe the UDP (user datagram protocol)
UDP is a connectionless transport protocol.
Connectionless transport protocols offer unreliable transport,
in that if a segment is dropped, the sender is unaware of the drop, and
no retransmission occurs.
Just like layer 2(Data Link) and layer 3 (network) layer 4 (Transport) also offer flow control services. What are the two common flow control approaches at layer 4(transport)?
Windowing and buffering
Describe the layer 4 (transport) flow control approach – windowing
TCP communication uses windowing
One or more segments are sent at one time, and a receiver can attest to the receipt of all the segments in a window with a single acknowledgment.
Describe how sliding windowing works
window size begins with one segment, if there is a successful acknowledgment of that one segment the window size doubles
This exponential increase in window size continues until the receiver does not acknowledge successful receipt of all segments within a certain amount of time (round-trip time RTT) or until a configured maximum window size is reached
describe the layer 4 (transport) flow control protocol - buffering
a device uses a chunk of memory to store segments if bandwidth is not available to send those segments
The session layer (layer 5) is responsible for what?
setting up a session
maintaining a session
tearing down a session
Describe what the session layer (5) does in the setting up of a session
*Check uses credentials (username password)
*Assigning numbers to a session’s communication flows to uniquely find each one
*Negotiating services needed during the session
*Negotiating which device begins sending data
describe what the session layer (5) does when maintaining a session
*Transferring data
*Reestablishing a disconnected session
*Acknowledging receipt of data
How does the session layer (5) tear down a session? Why?
A session can be disconnected based on agreement of the devices in the session. A session might be torn down because one party disconnects.
What is SIP?
Session Initiation Protocol (SIP) is an example of a session layer protocol (layer 5), which can help set up, support and tear down a voice or video connection.
What is the presentation layer (layer 6) responsible for?
Data formatting and Encryption
Why is data formatting necessary?
compatibility between communicating devices
Whys is encryption needed?
To add a layer of security, encryption can be used to scramble (encrypt) the data in such a way that if the data were intercepted, a third party would not be able to unscramble (decrypt) it.
the intended recipient would be able to decrypt the transmission
What does the application layer (layer 7) do?
gives application services to a network
service advertisement
What is an often-misunderstood concept of the application layer (layer 7)
that end-user application (such as Microsoft Word) live at the application layer
the application layer supports services used by the end-user
What are some application services that live at the application layer?
email and file sharing
How does service advertisement work?
some applications’ services periodically send out advertisements, making their availability known to other devices on the network.
other services register themselves and their services with a centralized directory, which can be queried by other network devices seeking such services.
Most of the traffic on the Internet is based on the ___ protocol suit.
TCP/IP
How many layers does the TCP/IP stack have?
4
What are the layers of the TCP/IP stack?
Application Transport Internet Network Interface
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How does the TCP/IP layer compare to the OSI model?
TCP/IP - Application layer works in the layers 7-5 of the OSI
TCP/IP -Transport layer works in the OSI transport layer
TCP/IP - Internet layer works in the Network layer of the OSI model
TCP/IP- Network Interface layer works in layers 2-1 of the OSI model
What is the network interface layer sometimes called instead?
Network access layer
What does the internet layer of the TCP/IP focuses on?
IP as the protocol to be routed through a network
What are the two primary protocol found at the TCP/IP stack’s transport layer?
TCP AND UDP
What is noticeably different from the TCP segment format compared to the UDP segment format? Why?
The TCP is much more detailed and has way more than just the destination and sender address. This is because TCP is a connection orientated protocol and UDP is more concerned with speed.
What is the biggest difference between the TCP/IP stack and the OSI model is at the TCP/IP stack’s ________ layer.
application layer
Port numbers 1023 and below are called what?
well-known ports
Ports above 1023 are called what?
ephemeral ports
What is the maximum value of a port?
65,535
