Chapter 2 Flashcards
Name the 7 OSI layers
Application (7), Presentation (6), Session (5), Transport (4), Network (3), Data Link (2), Physical (1)
What is the purpose of the application layer?
The purpose of the application layer is to provide a user interface and facilitate communication between applications and the underlying network. It is responsible for locating network resources broadcast by a server and can incorporate flow control and error control mechanisms, depending on the choices made by the application developer.
What is the purpose of the presentation layer?
presents data to the Application layer and is responsible for data translation and code formatting, like ASCII to non-ASCII conversions
What is the purpose of the session layer?
sets up, maintains, and terminates sessions between applications.
What is the purpose of the transport layer?
uses virtual circuits to create a reliable connection between two hosts
What is the purpose of the network layer?
The network layer is responsible for logical addressing and routing, ensuring data packets are correctly forwarded across an internetwork—a network of interconnected networks that enables communication between different devices, organizations, or geographic locations.
What is the purpose of the data link layer?
provides framing and placing of data on the network medium
What is the purpose of the physical layer?
responsible for taking 1s and 0s and encoding them into a digital signal
for transmission on the network segment
What are the two sub-layers of the data link layer?
LLC (Logical Link Control) & MAC (Media Address Control)
What is the purpose of the LLC sub-layer of the data link layer?
An LLC header tells the Data Link layer what to do with a packet once
a frame is received. Identifies network layer protocols and then encapsulates them. The LLC sublayer is responsible primarily for the multiplexing of Network layer protocols
What is the purpose of the MAC sub-layer of the data link layer?
It controls how devices on a network can access the shared transmission medium, deciding when a device can send data without collisions.
What layer do hubs operate on?
Layer 1
What layer do repeaters operate on?
Layer 1
We generally consider that a device operates at the ____ layer it supports
Highest
What layer do switches operate on?
Layer 2 - because they understand and make decisions based on Layer 2 addresses (Data link layer)
What layer do bridges operate on?
Bridges operate at Layer 2 (Data Link Layer) of the OSI model. They use MAC addresses to filter and forward traffic between network segments, helping to reduce collisions and improve efficiency.
What layer do routers operate on?
Layer 3- because they route based on network addresses
What layer(s) do workstations operate on?
Application layer, or “all layers”
Which layer is responsible for converting frames from the Data Link layer into electrical signals?
Physical Layer
Which layer chooses and determines the availability of communicating partners along with the resources necessary to make the connection, coordinates partnering applications, and forms a consensus on procedures for controlling data integrity and error recovery?
The Application Layer, being the topmost layer in the OSI model, directly interacts with user applications and is responsible for identifying potential communication partners, checking their availability, and establishing the necessary resources for a connection.
At which layer is routing implemented, enabling connections and path selection between two end systems?
Routing is implemented at Layer 3 (Network Layer) of the OSI model. This layer enables connections and path selection between two end systems by using IP addresses to determine the best route for data transmission across networks.
Which layer defines how data is formatted, presented, encoded, and converted?
Presentation Layer
Which layer is responsible for creating, managing, and terminating sessions between applications?
Session Layer
Which layer manages the transmission of data across a physical link and is primarily concerned with physical addressing and the ordered delivery of frames?
The layer that manages data transmission across a physical link and focuses on physical addressing and ordered delivery of frames is the Data Link Layer.
Which layer is used for reliable communication between end nodes over the network and provides mechanisms for establishing, maintaining, and terminating virtual circuits as well as controlling the flow of information?
Transport Layer
Which layer provides logical addressing that routers use for path determination?
Network Layer
Which layer specifies voltage, wire speed, and connector pin-outs and moves bits between devices?
Physical Layer
Which layer combines bits into bytes and bytes into frames and uses MAC addressing?
Data Link Layer
How do session and transport layers differ in the kind of connection they describe?
Key Differences
Functionality:
The transport layer is primarily concerned with the reliable transmission of data across the network, while the session layer focuses on managing sessions between applications.
Connection Type:
The transport layer can establish connection-oriented or connectionless communication, while the session layer deals specifically with maintaining a continuous connection for application sessions.
Scope of Operation:
The transport layer operates at a lower level, dealing directly with data packets, whereas the session layer operates at a higher level, managing application-specific communication.
Difference between LLC (Logical Link Control) & MAC (Media Address Control)
LLC dictates the logic of communication between devices, while MAC manages the physical access to the network medium.
LLC:
Provides an interface to the Network Layer (Layer 3). It presents a consistent interface to the network layer protocols, regardless of the underlying MAC protocol.
Error control: LLC can provide error detection and correction, although it’s not universally implemented.
Flow control: Similar to error control, LLC can manage the rate of data transmission to prevent overwhelming the receiver.
Addressing: LLC header information often includes fields for multiplexing different network layer protocols over a single data link.
Encapsulation: Adds the LLC header and trailer around the data (payload) received from the network layer.
MAC:
Media Access Control: This is the core function. MAC governs how devices share the physical transmission medium (e.g., Ethernet cable, Wi-Fi radio waves) to avoid collisions and ensure orderly communication. This is the “traffic cop” of the network.
Physical Addressing (MAC Addresses): Each network interface card (NIC) has a unique hardware address, the MAC address. MAC addresses are used to identify individual devices on a local network.
Framing: MAC is responsible for creating data frames, encapsulating data received from the LLC sublayer, and adding headers and trailers containing information like source and destination MAC addresses, and sometimes error detection codes (e.g., CRC).
Media Access Methods: MAC protocols implement access methods that determine how devices get access to the shared medium (e.g., Carrier Sense Multiple Access with Collision Detection (CSMA/CD) for Ethernet, or CSMA/CA for Wi-Fi).
Addressing:
LLC: Logical protocol identifiers.
MAC: Physical MAC addresses (hardware).
Standards:
LLC: IEEE 802.2
MAC: IEEE 802.3 (Ethernet), 802.11 (Wi-Fi), etc.
Analogy: LLC is “what” data, MAC is “how” data is sent over the physical network. LLC above MAC.
What is multiplexing?
The individual network signals are input into a multiplexer (mux) that combines them into a composite signal, which is then transmitted through a shared medium. When the composite signal reaches its destination, a demultiplexer (demux) splits the signal back into the original component signals and outputs them into separate lines for use by other operations.
