The OSI Model and Encapsulation

Question 1

Open Systems Interconnection (OSI) reference Model

Answer 1

A seven layer model that categorizes various network technologies. It is commonly referred to as the OSI model or the OSI stack

Question 2

What are the 7 Layers

Answer 2

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7-Application, 6-Presentation, 5-Session, 4-Transport, 3-Network, 2-Data Link, 1-Physical.

Question 3

protocol data unit (PUD)

Answer 3

Data at different layers of the OSI model. Specifically, a Layer 4 PDU is a segment, Layer 3 PDU is a packet, a Layer 2 PDU is a frame, and a Layer 1 PDU is a bit.

Question 4

IP (Internet Protocol) header

Answer 4

Information at the beginning of an Internet Protocol (IP) packet that enables proper addressing and routing

Question 5

TCP (Transmission Control Protocol) header

Answer 5

a data packet header that contains 10 mandatory fields totaling 20 bytes (or octets). the header holds information about the connection and data currently being sent.

Question 6

UDP (User Datagram Protocol) header

Answer 6

In a UDP datagram, a header that contains four fields (source port, destination port, length, and checksum) totaling 8 bytes.

Question 7

TCP flag

Answer 7

A field in a TCP header that is used to indicate a particular connection state or provide additional information. It is often used for troubleshooting purposes or to control how a particular connection is handled.

Question 8

Payload

Answer 8

Way to describe data itself, which is separate and distinct from any of the other information required for proper transmission.

Question 9

(MTU)- Maximum transmission unit

Answer 9

The largest packet size supported on an interface.

Question 10

Current state modulation

Answer 10

A way to electrically or optically represent binary digits by using a binary 1 for the presence of voltage on a copper cable or the presence of light on a fiber-optic cable and using a binary 0 for the absence of light or voltage.

Question 11

State transition modulation

Answer 11

An approach of representing binary digits in which the transition between a voltage level (for example, going from a state of no voltage to a state of voltage, or vice versa, on a copper cable) or the transition of having light or no light on a fiber-optic cable is represented as a binary 1; having no transition in a voltage level or light level from one time period to the next is represented as a binary 0.

Question 12

Cyclic redundancy check (CRC)

Answer 12

A mathematical algorithm that is executed on a data string by both the sender and the receiver of the data string. If the calculated CRC values match, the receiver can conclude that the data string was not corrupted during transmission.

Question 13

Physical Layer

Answer 13

Layer 1- of the OSI model, Which is concerned with the transmission of bits on a network.

Question 14

Data Link Layer

Answer 14

Layer 2 of the OSI model, which is packaging data into frames and transmitting those frames on a network, performing error detection/correction, uniquely identifying network devices with an address, and handling flow control.

Question 15

Network Layer

Answer 15

Layer 3 of the OSI model, which is forwarding data based on logical addresses.

Question 16

Transport Layer

Answer 16

Layer 4 of the OSI model, which acts as a dividing line between the upper layers and the lower layers. Specifically, messages are taken from the upper layers (Layers 5–7) and encapsulated into segments for transmission to the lower layers (Layers 1–3). Similarly, data streams coming from lower layers are decapsulated and sent to Layer 5 (the session layer) or some other upper layer, depending on the protocol.

Question 17

Session Layer

Answer 17

Layer 5 of the OSI model, which is responsible for setting up, maintaining, and tearing down sessions.

Question 18

Presentation Layer

Answer 18

Layer 6 of the OSI model, which is responsible for the formatting of data being exchanged and securing the data with encryption.

Question 19

Application Layer

Answer 19

Layer 7 of the OSI model, which provides applications access to network services

Question 20

Network interface layer

Answer 20

The layer of the TCP/IP stack (also known as the network access layer) that encompasses the technologies addressed by Layers 1 and 2 (that is, the physical and data link layers) of the OSI model.

Question 21

Internet layer

Answer 21

The layer of the TCP/IP stack that maps to Layer 3 (the network layer) of the OSI model. Although multiple routed protocols (for example, IPv4 and IPv6) may reside at the OSI model’s network layer, the Internet layer of the TCP/IP stack focuses on IP as the protocol to be routed through a network.

Question 22

transport layer (TCP/IP stack)

Answer 22

Layer 3 of the TCP/IP stack that maps to Layer 4 (the transport layer) of the OSI model. The two primary protocols found at the TCP/IP stack’s transport layer are TCP and UDP.

Question 23

application layer (TCP/IP stack)

Answer 23

In software-defined networking, the logical layer that presents the applications to the network manager. These applications allow simple control over the environment, permitting the engineer to configure and monitor the network as needed.

Question 24

time-division multiplexing (TDM)

Answer 24

A method of transmitting different communication sessions (for example, different telephone conversations in a telephony network) on the same physical medium by allowing sessions to take turns. For a brief period of time, defined as a time slot, data from the first session is sent, followed by data from the second session. This continues until every session has had a turn, and the process repeats.

Question 25

Transmission Control Protocol (TCP)

Answer 25

A connection-oriented transport protocol that provides reliable transport, in that if a segment is dropped, the sender can detect that drop and retransmit that dropped segment. Specifically, a receiver acknowledges segments that it receives. Based on those acknowledgments, a sender can determine which segments were successfully received.

Question 26

User Datagram Protocol (UDP)

Answer 26

A connectionless transport protocol that provides unreliable transport, in that if a segment is dropped, the sender is unaware of the drop, and no retransmission occurs.