Podcast
Questions and Answers
Considering the OSI model, which of the following is NOT a primary function of the application layer (Layer 7)?
Considering the OSI model, which of the following is NOT a primary function of the application layer (Layer 7)?
- Providing network transfer capabilities.
- Offering application-level services for user interaction with the computer.
- Enabling file sharing and email services.
- Defining data formatting and encryption standards. (correct)
Which of the following is NOT a characteristic of the Physical Layer (Layer 1) in the OSI model?
Which of the following is NOT a characteristic of the Physical Layer (Layer 1) in the OSI model?
- Involves the transmission of data as bits.
- Establishes the logical addressing scheme for routing. (correct)
- Concerns the physical and electrical characteristics of the network.
- Utilizes transition modulation to represent binary data.
Which of the following statements accurately contrasts TCP and UDP?
Which of the following statements accurately contrasts TCP and UDP?
- TCP is primarily used for audio and visual streaming due to its low overhead, unlike UDP.
- TCP is connectionless and unreliable, while UDP is connection-oriented and reliable.
- TCP includes sequencing and acknowledgment of segments, whereas UDP does not. (correct)
- TCP does not use a three-way handshake, while UDP relies on it for connection establishment.
In the OSI model, what is the primary role of the Session Layer (Layer 5)?
In the OSI model, what is the primary role of the Session Layer (Layer 5)?
Which of the following is NOT a typical function of the Data Link Layer (Layer 2)?
Which of the following is NOT a typical function of the Data Link Layer (Layer 2)?
What is the significance of the TCP three-way handshake?
What is the significance of the TCP three-way handshake?
How does Statistical Time Division Multiplexing (StatTDM) differ from Time Division Multiplexing (TDM)?
How does Statistical Time Division Multiplexing (StatTDM) differ from Time Division Multiplexing (TDM)?
Which of these is NOT a method of synchronization at Layer 2?
Which of these is NOT a method of synchronization at Layer 2?
Which of the following is NOT directly addressed by the Internet Control Message Protocol (ICMP)?
Which of the following is NOT directly addressed by the Internet Control Message Protocol (ICMP)?
What is the key function of 'windowing' at Layer 4?
What is the key function of 'windowing' at Layer 4?
Which of the following is NOT a typical device found at Layer 1 of the OSI model?
Which of the following is NOT a typical device found at Layer 1 of the OSI model?
In the context of data transmission and the OSI model, what does 'encapsulation' refer to?
In the context of data transmission and the OSI model, what does 'encapsulation' refer to?
Which of the following is NOT true about MAC addresses?
Which of the following is NOT true about MAC addresses?
Which of the following statements regarding broadband technology is most accurate?
Which of the following statements regarding broadband technology is most accurate?
Which of the following protocols operates at Layer 5 (Session Layer) of the OSI model?
Which of the following protocols operates at Layer 5 (Session Layer) of the OSI model?
Which statement is NOT correct regarding Layer 6 (Presentation Layer)?
Which statement is NOT correct regarding Layer 6 (Presentation Layer)?
Which of the following is NOT a typical component of an IP Header (Layer 3)?
Which of the following is NOT a typical component of an IP Header (Layer 3)?
Which of the following is NOT a file transfer protocol?
Which of the following is NOT a file transfer protocol?
Which statement about OSI model order is NOT correct?
Which statement about OSI model order is NOT correct?
Which of the following is valid example of IPv4 addresses?
Which of the following is valid example of IPv4 addresses?
Which of the following options are correct about the TIA/EIA-568A and TIA/EIA-568B standards? (Select all that apply)
Which of the following options are correct about the TIA/EIA-568A and TIA/EIA-568B standards? (Select all that apply)
Which of the following could cause packets to be reordered?
Which of the following could cause packets to be reordered?
Which of the following is not a WAN accelerator?
Which of the following is not a WAN accelerator?
Which of the following is the correct name for the data type in layer 4 for the UDP?
Which of the following is the correct name for the data type in layer 4 for the UDP?
What is the maximum size for payload, when using Ethernet?
What is the maximum size for payload, when using Ethernet?
What is the significance of the OSI model in modern networking?
What is the significance of the OSI model in modern networking?
Which of the following is an accurate definition of encapsulation in the context of the OSI model?
Which of the following is an accurate definition of encapsulation in the context of the OSI model?
Which layer of the OSI model is responsible for converting data into bits for transmission over a physical medium?
Which layer of the OSI model is responsible for converting data into bits for transmission over a physical medium?
Which OSI layer is primarily responsible for reliable data transport, including segmentation, acknowledgement, and windowing?
Which OSI layer is primarily responsible for reliable data transport, including segmentation, acknowledgement, and windowing?
Which of the following describes a key characteristic of 'asynchronous communication' at Layer 2?
Which of the following describes a key characteristic of 'asynchronous communication' at Layer 2?
What is the principal function of the session layer within the OSI model?
What is the principal function of the session layer within the OSI model?
Which layer in the OSI model is responsible for data formatting, encryption, and presentation?
Which layer in the OSI model is responsible for data formatting, encryption, and presentation?
In networking, what is the primary role of a 'MAC address'?
In networking, what is the primary role of a 'MAC address'?
What is the primary function of 'packet switching' at the network layer?
What is the primary function of 'packet switching' at the network layer?
Which of the following best describes the function of 'windowing' in TCP (Transmission Control Protocol)?
Which of the following best describes the function of 'windowing' in TCP (Transmission Control Protocol)?
What is the purpose of the Internet Control Message Protocol (ICMP)?
What is the purpose of the Internet Control Message Protocol (ICMP)?
Which OSI layer do 'routers' primarily operate at to forward traffic using logical addresses?
Which OSI layer do 'routers' primarily operate at to forward traffic using logical addresses?
Which of the following best describes the purpose of TIA/EIA-568A and TIA/EIA-568B standards in networking?
Which of the following best describes the purpose of TIA/EIA-568A and TIA/EIA-568B standards in networking?
What is the main difference between 'baseband' and 'broadband' in the context of bandwidth utilization?
What is the main difference between 'baseband' and 'broadband' in the context of bandwidth utilization?
Which layer of the OSI model is responsible for determining the best path for data to flow across a network, often utilizing dynamic routing protocols?
Which layer of the OSI model is responsible for determining the best path for data to flow across a network, often utilizing dynamic routing protocols?
What is the fundamental difference between TCP and UDP protocols in the transport layer?
What is the fundamental difference between TCP and UDP protocols in the transport layer?
Which of the following is a key function of the Application Layer (Layer 7) in the OSI model?
Which of the following is a key function of the Application Layer (Layer 7) in the OSI model?
In the context of OSI model, what does 'Statistical Time Division Multiplexing (StatTDM)' achieve?
In the context of OSI model, what does 'Statistical Time Division Multiplexing (StatTDM)' achieve?
Which of the following is NOT a standard image format handled by the presentation layer?
Which of the following is NOT a standard image format handled by the presentation layer?
Select all options that describe a characteristic of synchronous communication:
Select all options that describe a characteristic of synchronous communication:
Which options are the responsibility of the Physical Layer?
Which options are the responsibility of the Physical Layer?
What is the correct data type in layer 4 for the TCP and UDP, respectively?
What is the correct data type in layer 4 for the TCP and UDP, respectively?
Which of the following describe the main function of the Data Link Layer? (Select all that apply)
Which of the following describe the main function of the Data Link Layer? (Select all that apply)
What does the Ethernet header at Layer 2 include? (Select all that apply)
What does the Ethernet header at Layer 2 include? (Select all that apply)
Which statements are true regarding the TCP header? (Select all that apply)
Which statements are true regarding the TCP header? (Select all that apply)
Considering asynchronous communication, which of the following is the most accurate regarding its data transmission methodology within the physical layer?
Considering asynchronous communication, which of the following is the most accurate regarding its data transmission methodology within the physical layer?
In the context of Layer 1 of the OSI model, which statement accurately differentiates baseband and broadband technologies?
In the context of Layer 1 of the OSI model, which statement accurately differentiates baseband and broadband technologies?
Within the context of the OSI model's Physical Layer (Layer 1), what role does transition modulation play, and how does it achieve its function?
Within the context of the OSI model's Physical Layer (Layer 1), what role does transition modulation play, and how does it achieve its function?
In the labyrinthine domain of network synchronization at Layer 2, differentiate between isochronous and synchronous methods, emphasizing their intricacies.
In the labyrinthine domain of network synchronization at Layer 2, differentiate between isochronous and synchronous methods, emphasizing their intricacies.
Elaborate on the distinct roles of the Logical Link Control (LLC) sublayer within the Data Link Layer (Layer 2) of the OSI model.
Elaborate on the distinct roles of the Logical Link Control (LLC) sublayer within the Data Link Layer (Layer 2) of the OSI model.
Analyze the complexities involved in packet reordering at Layer 3, detailing possible causes and implications.
Analyze the complexities involved in packet reordering at Layer 3, detailing possible causes and implications.
In the context of Layer 4 of the OSI model, what differentiates TCP from UDP? (Select all that apply)
In the context of Layer 4 of the OSI model, what differentiates TCP from UDP? (Select all that apply)
Within the context of Layer 4 protocols, elaborate on the significance and mechanisms of 'windowing'.
Within the context of Layer 4 protocols, elaborate on the significance and mechanisms of 'windowing'.
Analyze the role and function of the Internet Control Message Protocol (ICMP) within the TCP/IP suite, detailing its operational scope.
Analyze the role and function of the Internet Control Message Protocol (ICMP) within the TCP/IP suite, detailing its operational scope.
Contrast the operational characteristics of multi-layer switches versus traditional Layer 2 switches, paying close attention to their respective functions within a network.
Contrast the operational characteristics of multi-layer switches versus traditional Layer 2 switches, paying close attention to their respective functions within a network.
In the context of Layer 5 (Session Layer) of the OSI model, what are the key functions?
In the context of Layer 5 (Session Layer) of the OSI model, what are the key functions?
Analyze the operational significance of the TIA/EIA-568A and TIA/EIA-568B standards in network cabling, highlighting both similarities and differences.
Analyze the operational significance of the TIA/EIA-568A and TIA/EIA-568B standards in network cabling, highlighting both similarities and differences.
Evaluate the role of the Presentation Layer(Layer 6) in the OSI model, especially in the context of data formatting and encryption.
Evaluate the role of the Presentation Layer(Layer 6) in the OSI model, especially in the context of data formatting and encryption.
Within the OSI reference model, what is the significance of Protocol Data Units (PDUs), how are they named, and what special considerations exist?
Within the OSI reference model, what is the significance of Protocol Data Units (PDUs), how are they named, and what special considerations exist?
Within the context of Layer 2 Ethernet frames, what is the purpose of the EtherType field, and which protocols can it indicate?
Within the context of Layer 2 Ethernet frames, what is the purpose of the EtherType field, and which protocols can it indicate?
Within the TCP header structure, which control flags are essential for managing connections, and what specific functions do they perform?
Within the TCP header structure, which control flags are essential for managing connections, and what specific functions do they perform?
How does Statistical Time Division Multiplexing (StatTDM) optimize bandwidth utilization compared to traditional Time Division Multiplexing (TDM)?
How does Statistical Time Division Multiplexing (StatTDM) optimize bandwidth utilization compared to traditional Time Division Multiplexing (TDM)?
Which of the following options accurately describe the process of encapsulation and decapsulation within the OSI model? (Select all that apply)
Which of the following options accurately describe the process of encapsulation and decapsulation within the OSI model? (Select all that apply)
What is the purpose of buffering at Layer 4, and how does it contribute to network performance and reliability?
What is the purpose of buffering at Layer 4, and how does it contribute to network performance and reliability?
In the context of Layer 5, what are the key characteristics and functions of the NetBIOS protocol? (Select all that apply)
In the context of Layer 5, what are the key characteristics and functions of the NetBIOS protocol? (Select all that apply)
In the context of Layer 6, how do standard text formats like ASCII, Unicode and EBCDIC differ in representing text?
In the context of Layer 6, how do standard text formats like ASCII, Unicode and EBCDIC differ in representing text?
Within the context of data transmission, what role do crossover cables play, and how are they specifically constructed according to TIA/EIA standards?
Within the context of data transmission, what role do crossover cables play, and how are they specifically constructed according to TIA/EIA standards?
Elaborate on the encryption algorithms utilized at Layer 6 emphasizing how they contribute to data transit security.
Elaborate on the encryption algorithms utilized at Layer 6 emphasizing how they contribute to data transit security.
How do devices at Layer 1 operate and how do their functionalities affect overall network performance?
How do devices at Layer 1 operate and how do their functionalities affect overall network performance?
What mechanisms does the Data Link Layer utilize to detect corrupted data frames?
What mechanisms does the Data Link Layer utilize to detect corrupted data frames?
Assuming a network packet is traversing from an application on one host to another, which of the following is the correct sequence of OSI layers that the packet's data will be encapsulated through?
Assuming a network packet is traversing from an application on one host to another, which of the following is the correct sequence of OSI layers that the packet's data will be encapsulated through?
During encapsulation within the OSI model, at which layer is the process responsible for adding source and destination MAC addresses to a data frame?
During encapsulation within the OSI model, at which layer is the process responsible for adding source and destination MAC addresses to a data frame?
In the context of OSI model encapsulation, which layer is responsible for adding source and destination port numbers?
In the context of OSI model encapsulation, which layer is responsible for adding source and destination port numbers?
During the decapsulation process, at what layer are headers removed and examined to route data based on IP addresses?
During the decapsulation process, at what layer are headers removed and examined to route data based on IP addresses?
Which of the following occurs at the Physical Layer during the encapsulation process?
Which of the following occurs at the Physical Layer during the encapsulation process?
What is the role of the Presentation Layer (Layer 6) during OSI model encapsulation?
What is the role of the Presentation Layer (Layer 6) during OSI model encapsulation?
When data is decapsulated, which layer is first to receive the data?
When data is decapsulated, which layer is first to receive the data?
Which header is added during encapsulation to ensure reliable transport between two hosts and includes sequence numbers?
Which header is added during encapsulation to ensure reliable transport between two hosts and includes sequence numbers?
At which layer of the OSI model does the addition of a trailer typically occur during encapsulation, and what is its primary function relate to?
At which layer of the OSI model does the addition of a trailer typically occur during encapsulation, and what is its primary function relate to?
In OSI model decapsulation, at which layer are session management protocols interpreted to maintain dialogue control?
In OSI model decapsulation, at which layer are session management protocols interpreted to maintain dialogue control?
During encapsulation, which layer determines the availability of communication partners and resources?
During encapsulation, which layer determines the availability of communication partners and resources?
Which layer's header, added during encapsulation, includes fields such as TTL, protocol type, and fragmented offset?
Which layer's header, added during encapsulation, includes fields such as TTL, protocol type, and fragmented offset?
A network administrator captures a packet and observes that it contains both a TCP header and an IP header. What is the correct order in which these headers were added during the encapsulation process?
A network administrator captures a packet and observes that it contains both a TCP header and an IP header. What is the correct order in which these headers were added during the encapsulation process?
In the process of decapsulation, at which layer would a network appliance inspect packet headers for Quality of Service (QoS) markings to prioritize traffic?
In the process of decapsulation, at which layer would a network appliance inspect packet headers for Quality of Service (QoS) markings to prioritize traffic?
Considering a scenario where an application is sending encrypted data, at which layer is the decryption process initiated during decapsulation?
Considering a scenario where an application is sending encrypted data, at which layer is the decryption process initiated during decapsulation?
If a network device is tasked with reassembling fragmented IP packets, at which layer of decapsulation does this process primarily occur?
If a network device is tasked with reassembling fragmented IP packets, at which layer of decapsulation does this process primarily occur?
During encapsulation, if a data packet exceeds the Maximum Transmission Unit (MTU) of a network, at which layer is the packet typically fragmented?
During encapsulation, if a data packet exceeds the Maximum Transmission Unit (MTU) of a network, at which layer is the packet typically fragmented?
Which layer in the OSI model is responsible for translating data into a format that the application layer can understand during decapsulation?
Which layer in the OSI model is responsible for translating data into a format that the application layer can understand during decapsulation?
In a network environment utilizing VLANs, at which layer is a VLAN tag added during encapsulation, and what does this tag primarily influence?
In a network environment utilizing VLANs, at which layer is a VLAN tag added during encapsulation, and what does this tag primarily influence?
During decapsulation, at which layer are TCP control flags (such as SYN, ACK, FIN) processed to manage connection states?
During decapsulation, at which layer are TCP control flags (such as SYN, ACK, FIN) processed to manage connection states?
In a network application that requires guaranteed delivery of data, which mechanism implemented at the transport layer relies on encapsulation to achieve reliability?
In a network application that requires guaranteed delivery of data, which mechanism implemented at the transport layer relies on encapsulation to achieve reliability?
If an application needs to ensure data is prioritized, such as in VoIP, which layer is responsible for setting the appropriate flags within the header during encapsulation?
If an application needs to ensure data is prioritized, such as in VoIP, which layer is responsible for setting the appropriate flags within the header during encapsulation?
Consider a situation where a network is experiencing high levels of packet loss. At which layer can devices use acknowledgments and retransmission requests (ARQ) during decapsulation to mitigate this?
Consider a situation where a network is experiencing high levels of packet loss. At which layer can devices use acknowledgments and retransmission requests (ARQ) during decapsulation to mitigate this?
What is the role of the Application Layer in initiating the encapsulation process, and how does it contribute to network communication?
What is the role of the Application Layer in initiating the encapsulation process, and how does it contribute to network communication?
Within the OSI model, which layer establishes, manages, and terminates connections between applications, ensuring a session remains active and coordinated?
Within the OSI model, which layer establishes, manages, and terminates connections between applications, ensuring a session remains active and coordinated?
Flashcards
OSI Model
OSI Model
A reference model developed in 1977 used to categorize network functions and for troubleshooting.
Physical Layer (Layer 1)
Physical Layer (Layer 1)
The first layer of the OSI model, responsible for transmitting bits across a network, and includes physical and electrical network characteristics.
Transition Modulation
Transition Modulation
Representing data by switching between levels (e.g., voltage or light) to signify 1s and 0s.
RJ-45 Connector
RJ-45 Connector
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Crossover Cables
Crossover Cables
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Straight-Through Cables
Straight-Through Cables
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Physical Topology
Physical Topology
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Asynchronous Communication
Asynchronous Communication
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Synchronous Communication
Synchronous Communication
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Broadband
Broadband
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Baseband
Baseband
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Multiplexing
Multiplexing
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Time Division Multiplexing (TDM)
Time Division Multiplexing (TDM)
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Statistical Time Division Multiplexing (StatTDM)
Statistical Time Division Multiplexing (StatTDM)
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Frequency Division Multiplexing (FDM)
Frequency Division Multiplexing (FDM)
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Layer 1 Device Characteristics
Layer 1 Device Characteristics
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Data Link Layer (Layer 2)
Data Link Layer (Layer 2)
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MAC Address (Media Access Control Address)
MAC Address (Media Access Control Address)
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Logical Link Control (LLC)
Logical Link Control (LLC)
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Isochronous Mode
Isochronous Mode
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Synchronous Method
Synchronous Method
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Asynchronous
Asynchronous
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Network Layer (Layer 3)
Network Layer (Layer 3)
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IP Variants
IP Variants
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Packet Switching (Routing)
Packet Switching (Routing)
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Bits (Layer 1)
Bits (Layer 1)
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Frames (Layer 2)
Frames (Layer 2)
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Packets (Layer 3)
Packets (Layer 3)
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Segments (Layer 4)
Segments (Layer 4)
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Copper Wire Voltage
Copper Wire Voltage
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Fiber Optic Light
Fiber Optic Light
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Infrastructure Devices
Infrastructure Devices
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Switch Operation
Switch Operation
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IPv4
IPv4
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Circuit Switching
Circuit Switching
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Message Switching
Message Switching
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Routing Tables
Routing Tables
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Dynamic Protocols
Dynamic Protocols
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ICMP (Internet Control Message Protocol)
ICMP (Internet Control Message Protocol)
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Multi-layer switches
Multi-layer switches
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Transport Layer
Transport Layer
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TCP (Transmission Control Protocol)
TCP (Transmission Control Protocol)
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Three-Way Handshake
Three-Way Handshake
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UDP (User Datagram Protocol)
UDP (User Datagram Protocol)
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Windowing
Windowing
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Buffering
Buffering
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Session Layer (Layer 5)
Session Layer (Layer 5)
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Presentation Layer (Layer 6)
Presentation Layer (Layer 6)
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Application Layer (Layer 7)
Application Layer (Layer 7)
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TCP/IP Mode
TCP/IP Mode
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Copper Wire
Copper Wire
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Bandwidth division
Bandwidth division
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Layer 1 Cables
Layer 1 Cables
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MAC Address Structure
MAC Address Structure
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Routing Protocols
Routing Protocols
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PING
PING
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Traceroute
Traceroute
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OSI Upper Layers
OSI Upper Layers
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Three-way Handshake Types
Three-way Handshake Types
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H.323
H.323
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Data Formatting
Data Formatting
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Transport Layer Security (TLS)
Transport Layer Security (TLS)
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Application Layer Focus
Application Layer Focus
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Application Services
Application Services
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Encapsulation
Encapsulation
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Decapsulation
Decapsulation
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Protocol Data Units (PDUs)
Protocol Data Units (PDUs)
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TCP Header (Layer 4)
TCP Header (Layer 4)
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RST (Reset)
RST (Reset)
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EtherType Field
EtherType Field
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Payload
Payload
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Wiring Standards
Wiring Standards
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Maximum Transmission Unit (MTU)
Maximum Transmission Unit (MTU)
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Jumbo Frames
Jumbo Frames
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Data (Layer 7)
Data (Layer 7)
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Packet Reordering
Packet Reordering
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Buffer
Buffer
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NetBIOS
NetBIOS
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ASCII
ASCII
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Email Applications (Layer 7)
Email Applications (Layer 7)
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SYN Flag
SYN Flag
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ACK Flag
ACK Flag
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FIN (Finished) Flag
FIN (Finished) Flag
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IP Header (Layer 3)
IP Header (Layer 3)
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MAC Address
MAC Address
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Maximum Transmission Unit (MTU)
Maximum Transmission Unit (MTU)
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Study Notes
OSI Model and TCP Model
- Objective 1.1 explains the concepts related to the Open Systems Interconnection (OSI) reference model
- The Open Systems Interconnect (OSI) model was developed in 1977 by the International Organization for Standardization
- OSI is a reference model used to categorize network functions and for troubleshooting
- Networks operate under the TCP/IP mode
- Networks are designed to make data flow across networks
OSI Layers
- Layer 1: Physical
- Layer 2: Data Link
- Layer 3: Network
- Layer 4: Transport
- Layer 5: Session
- Layer 6: Presentation
- Layer 7: Application
What Data is Called at Each Layer
- Bits - Layer 1
- Frames - Layer 2
- Packets - Layer 3
- Segments - Layer 4
- Data - Layer 5
- Data - Layer 6
- Data - Layer 7
Physical Layer (Layer 1)
- It is the first layer of the OSI model
- Transmission of bits across the network with physical and electrical network characteristics.
- Data type occurs as bits, where binary bits are represented as a series of 1s and 0s
Transition Modulation
- Switching between levels represents 1 or 0:
- Copper Wire (Cat5/Cat6) utilizes voltage (0V for 0, +5V/-5V for 1)
- Fiber Optic Cable uses light (on for 1, off for 0)
- Connector Standards incorporate the RJ-45 Connector used in CAT5/CAT6 cables and Wiring Standards.
- Cabling standards include TIA/EIA-568A and TIA/EIA-568B
- Crossover cables use TIA/EIA-568A on one end and TIA/EIA-568B on the other end where straight-through cables use TIA/EIA-568B on both ends.
Physical Topology
- Refers to different physical network layouts based on how cables are physically connected
- These include Bus, Ring, Star, Hub-and-Spoke, Full Mesh, and Partial Mesh
- Synchronization:
- Asynchronous Communication involves start and stop bits for out-of-sync data transmission
- Synchronous Communication is real-time communication using a common time source.
- Bandwidth Utilization:
- Broadband divides bandwidth into separate channels such as cable TV
- Baseband uses all the frequency of the cable all the time such as a telephone
Multiplexing
- Involves efficiently using a limited amount of resources
- Allows multiple people to use a baseband connection simultaneously
- Time Division Multiplexing (TDM) allocates dedicated time slots
- Statistical Time Division Multiplexing (StatTDM) dynamically allocates time slots based on when people need it
- Frequency Division Multiplexing (FDM) divides the medium into channels
Layer 1 Devices
- Cables include fiber optic, Ethernet, and coaxial
- Wireless Media includes Bluetooth, Wi-Fi, and near field communication
- Infrastructure Devices include hubs, access points, and media converters
- Layer 1 devices simply repeat what they receive, without logic or decision-making.
Data Link Layer (Layer 2)
- Responsible for packaging bits from Layer 1 into frames and transmitting these across the network
- Performs error detection and correction, identifying devices using MAC addresses, and provides flow control
MAC Address (Media Access Control Address)
- Means of physical device identification for operation on a logical topology.
- Every NIC has a unique 48-bit physical addressing system assigned
- Written in hexadecimal numbers
- First 24 bits identifies the manufacturer
- Remaining 24 bits identifies the specific device
- Crucial for logical topology to identify devices on the network
Logical Link Control (LLC)
- LLC provides connection services and acknowledges message receipt for controlled data flow
- It is the most basic form of flow control as it limits sender data and prevents receiver overwhelm
- Uses a checksum to detect corrupted data frames
Synchronization Methods at Layer 2
- Isochronous Mode uses a common reference clock with time slots for transmissions and less overhead
- Synchronous Method uses the same clock, with beginning and ending frames, and control characters for synchronization
- Asynchronous Method includes devices that reference their own clock cycles with no strict control over communication timing
Layer 2 Devices
- Network Interface Cards (NICs)
- Bridges
- Switches intelligently use logic to learn and send data to specific devices based on MAC addresses
Switch Operation
- Switches use CAM tables with MAC addresses to identify physical ports connected to devices, enabling selective data transmission to specific areas within the network
Network Layer (Layer 3)
- Concerned with routing and forwarding traffic with logical addresses
- Logical Addressing includes IP variants as common logical addressing schemes
- IPv4 is written in dotted octet notation as it uses four sets of numbers separated by dots (e.g., 172.16.254.1)
- Other protocols such as AppleTalk and IPX (Internetwork Packet Exchange) were replaced by IP (Internet Protocol)
Switching/Routing Methods
- Packet Switching (Routing) divides data into packets and then forwards them
- Circuit Switching establishes a dedicated link between two devices
- Message Switching divides data into messages stored and then forwarded
Route Discovery and Selection
- Routers maintain routing tables to determine the best path with dynamic protocols (e.g., RIP, OSPF) enabling sharing and updating of route information
- Routing protocols help decide how data flows across a network
Connection Services at Layer 3
- Augments Layer 2 services and includes flow control to prevent sender overwhelm and packet reordering to ensure correct data assembly.
- Internet Control Message Protocol (ICMP) sends error messages and operational information to an IP destination, used in PING as the most common ICMP
Troubleshooting
- Traceroute traces the route of a packet through the network
- Devices and Protocols are Routers, Multi-layer switches which have both Layer 2 switch and Layer 3 router features (A switch is always a Layer 2 device unless specified as multi-layer, then it is considered as a Layer 3 device)
- Layer 3 protocols include IPv4, IPv6, and ICMP.
- IP and routers are commonly encountered Layer 3 devices in exams
Transport Layer (Layer 4)
- Forms the dividing line between the upper and lower layers of the OSI model
- Upper Layers includes Transport, Session, Presentation and Application
Segments
- Data Type in Transport Layer
- Protocols in Layer 4
- TCP (Transmission Control Protocol) is a connection-oriented protocol that is a reliable way to transport segments across the network with acknowledgement
- Employs a Three-Way Handshake (SYN - synchronization, SYN-ACK – synchronization - acknowledgement, ACK - acknowledgement)
- TCP (Transmission Control Protocol) is a connection-oriented protocol that is a reliable way to transport segments across the network with acknowledgement
Windowing
- For flow control
- Used for all network data that needs assurance to get to its final destination
- UDP (User Datagram Protocol) is connectionless and transports segments unreliably (datagram)
- Used for audio and visual streaming, involves no three-way handshake, has less overhead, and has no acknowledgement or retransmission.
Layer 4 Examination
- Segment is the Data type for TCP, datagram is the data type for UDP.
- TCP is reliable, uses a Three-way Handshake, is connection-oriented, involves segment retransmission and flow control through windowing, sequencing, and acknowledgement of segments
- UDP is unreliable, uses No Three-way Handshake, is connectionless, involves no retransmission or windowing, sequencing, and no acknowledgment of datagrams
Windowing
- Allows clients to adjust the amount of data in segments during transmission
- Optimizes throughput and bandwidth
- Opens or closes window based on retransmissions.
- Buffering occurs when devices allocate memory to store segments if bandwidth is not readily available
Buffer
- Temporary memory storage for segments
- Prevents overflow by clearing segments
- Layer 4 Devices can use protocols such as TCP and UDP
- WAN accelerators, Load balancers and firewalls are devices used at Layer 4
Session Layer (Layer 5)
- Manages sessions, ensuring separate conversations to prevent data intermingling
- Setting Up Session involves checking user credentials and assigning numbers to sessions to help identify
- Maintaining Session requires continuous data transfer, and requires re-establishment if a connection breaks, acknowledges data
- Tearing Down a Session ends it when communication goals are achieved, and involves mutual agreement or one party disconnects
Layer 5 Examination
- Layer 5 issues involve protocols and software rather than specific devices
- H.323 is used for setting up, maintaining, and tearing down voice and video connections and operates over the real-time transport protocol (RTP)
- NetBIOS is utilized by computers for file sharing and commonly associated with Windows file sharing
Presentation Layer (Layer 6)
- Responsible for formatting data for exchange and securing it through encryption
- Data Formatting allows a computer to have compatibility between different devices
Formats
- American Standard Code for Information Interchange (ASCII) is text-based language to use,
- Ensures data is readable by receiving system, provides proper data structures, and negotiates data transfer syntax for the Application Layer (Layer 7)
- File types such as GIFs, JPEGs, and PNGs
- Formats enable compatibility between different devices
Encryption
- Used to scramble data in transit to keep it secure and provide data confidentiality
- Transport Layer Security (TLS) ensures secure data transfer and creates an encrypted tunnel, protecting sensitive information
- Scripting languages in Layer 6 control ASCII text display which include HTML, XML, PHP, and JavaScript
- Standard text formats include ASCII, Unicode, and EBCDIC
- Image formats includes GIFs, JPEGs, and TIFFs
Movie File Formats
- 1s and 0s formatted to create watchable videos and utilize MP4s, MPEGs and MOV
- Encryption Algorithms scrambles data to provide confidentiality and security during transit and storage with TLS and SSL (Secure Sockets Layer)
- Focus on Security
Application Layer (Layer 7)
- Provides application-level services where users communicate with the computer and focuses on lower-level applications involving file and network transfer
Application Services
- Unites components for more than one network application
- Application services may include file transfer, file sharing, email and low-level protocols include POP3 (Post Office Protocol 3), IMAP (Internet Message Access Protocol), and SMTP (Simple Mail Transfer Protocol)
- It includes remote access, network management, and client-server processes
- Service Advertisement requires applications to send announcements to other devices on the network and devices to advertise the services they offer
Layer 7 protocols
- Used for email applications using POP3, IMAP, and SMTP
- Used for Web Browsing via HTTP and HTTPS
- Used for Domain Name Service (DNS)
- Used for File Transfer Protocols via FTP, FTPS, and SFTP
- Remote Access uses Telnet, SSH, and SNMP
Encapsulation.
- The process of putting headers and trailers around data
Decapsulation
- The process of removing the encapsulation applied to access the original data
- In the OSI Model Layers, moving down from Layer 7 to 1 is encapsulation and moving up from Layer 1 to 7 is decapsulation
Protocol Data Units (PDUs)
- A single unit of information transmitted in a computer network
- Terminology for each layer is written as L(layer number) PDU: Example - L7 PDU for Layer 7
- Special names for the PDUs for layers 1, 2, 3, and 4:
- Layer 1 - Bits
- Layer 2 - Frames
- Layer 3 - Packets
- Layer 4 - Segments (TCP) or Datagrams (UDP)
TCP Header (Layer 4)
- The TCP Header has 10 mandatory fields, totaling 20 bytes, including source & destination ports, sequence & acknowlegment numbers, data offset, reserved data and control flags
- SYN synchronizes the connection in a three-way handshake
- ACK acknowledges the successful receipt of data
- FIN (Finished) tears down connections created by three-way handshake
TCP Header Control Flags
- RST (Reset) indicates an unexpected packet was received
- PSH (Push) ensures given data is prioritized
- URG (Urgent) identifies incoming data as urgent
- Window size
- TCP checksum and urgent pointer
- mTCP - optional
UDP Header (Layer 4)
- Uses an 8-byte header
- Includes source and destination port
- length is the total packet bytes
- a checksum that is not mandatory
IP Header (Layer 3)
- Contains various fields
- Version and length of IP header
- Type of service
- Total length of packet and header
- Identifier & Flags
- Fragmented offset
- Time to live & Protocol
- Header checksum
- Source and destination IP Addresses
- Options and Padding
- Ethernet Header (Layer 2)
- Destination and source MAC address
- Uses MAC Address- physical address to identity a network card
- Physical address to identity a network card on a local area network
- Processed by switches
- EtherType field indicates which protocol is encapsulated in the payload of a frame and can be IPv4 or IPv6
LAN
- VLAN Tag - optional
- IEEE 802.1Q
- IEEE 802.1AD
- A frame being sent at Layer 2 will include a payload containing:
- Data sent across the network
- 42 bytes - using VLANs
- 46 bytes - no VLANs
- Maximum Transmission Unit (MTU)
- Maximum size for payload (1500 bytes for Ethernet)
- Jumbo Frames can be larger than 1500 bytes, and may require reconfiguring MTU
Data Transmission
- Encapsulation adds a header at each layer:
- Layer 4 works with source/destination ports
- Layer 3 works with source/destination IP addresses
- Layer 2 works with source/destination MAC addresses
- Layer 1 transmits data as 1s/0s
- Decapsulation occurs at each intermediate device until the final host is reached, and the final host decapsulates up to Layer 7 for application understanding
Understanding the OSI Model: Practical Example
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