Chapter 1 - OSI Model Flashcards
The OSI Model
Seven layer model where each layer defines an important function in computer networking.
Layer 7- Application
Layer 6- Presentation
Layer 5- Session
Layer 4- Transport
Layer 3- Network
Layer 2- Data Link
Layer 1- Physical
Layer 7
Application Layer
Layer 6
Presentation Layer
Layer 5
Session Layer
Layer 4
Transport Layer
Layer 3
Network Layer
Layer 2
Data Link Layer
Layer 1
Physical Layer
Physical Layer
Layer 1
Defines the method of moving data between computers. Anything that moves data from one system to another- copper cabling, fiber optics, even radio waves
Data Link Layer
Layer 2
Focuses on physical addressing; adds in MAC address of the receiving endpoint
Checks received data to ensure it wasn’t corrupted in transit
NICs and Switches included here
Network Layer
Layer 3
Responsible for locating the destination of your request, uses logical addressing (IP addresses)
Transport Layer
Layer 4
Selects the protocol to send the data over (TCP or UDP) then divides it into segments or datagrams for transmission
Also does reassembly on the other end
Session Layer
Layer 5
Creates and maintains separate sessions between other computers
Presentation Layer
Layer 6
Translates the data into a standardized format, as well as handling any encryption, compression or other transformations to the data
Application Layer
Layer 7
Provides networking options to programs running on a computer
(APIs)
In the Transport Layer, encapsulated data is referred to as ____
Segments or Datagrams depending on whether TCP or UDP is being used
At the Network Layer, encapsulated data is referred to as ___
Packets
At the Data Link Layer, encapsulated data is referred to as ___
Frames
What Layer is the only one to add a trailer in addition to a header?
Data Link
NIC
Network Interface Card
Serves as the interface between the PC and the network. Each one has a unique MAC address for identification
MAC Address
Unique, 48-bit identifier. No two NICs ever share the same MAC address
Any company that makes NICs must contact IEEE and request a block of MAC addresses
MAC-48
Original name for the format assigned to MAC addresses by IEEE. Means the MAC address will be 48 bits, with the first 24 bits defining the OUI
OUI
Organizationally Unique Identifier; first 24 bits of MAC address and unique to each manufacturer
EUI-48
Current term for format IEEE uses for MAC Addresses.
Extended Unique Identifier
48 bits with first 24 bits being the OUI
Frame
Container for discrete chunks of data moving across a network
Operates at Layer 2 and uses MAC addresses
FCS
Frame Check Sequence
The trailer for a Frame; this is checked by the receiving NIC to validate that data arrived intact
The three sections of a frame
Header- MAC address and Type
Payload- Whatever is encapsulated in the frame
Trailer- FCS
Broadcast Address
Layer 2 MAC Address of FF-FF-FF-FF-FF-FF
Used to broadcast out to all NICs on a network to discover the MAC of a specific device
Any frame addressed specifically to another device’s MAC address is called a ___
Unicast Frame
Logical Link Control (LLC)
Sublayer of Layer 2
Aspect of the NIC that talks to the system’s OS (usually via device drivers). The LLC handles multiple network protocols and provides flow control
Media Access Control (MAC)
Sublayer of Layer 2
Creates and addresses the frame
Adds the NICs own MAC address and attaches MAC addresses to the frames
Adds or checks the FCS
NICs operate at which layer(s)?
Both Layer 2 and 1 as they handle MAC addressing AND putting the data on the network cable.
If forced to pick between one or the other, the most common answer is layer 2
Internet Protocol
Primary logical addressing protocol for TCP/IP
Makes sure that a piece of data gets to where it needs to go on the network by giving each device on the network an IP address
Router
Operates at layer 3, connects each subnet and forwards data using IP addresses
Encapsulation
The entire process of preparing data to go onto a network
Includes all steps from the application to the following layers where more info is added:
Application
Presentation
Session
Transport
Network
Data Link
De-Encapsulation
Reverse of encapsulation where the receiving computer strips away all extra header information
TCP
Transmission Control Protocol
Connection-oriented protocol, meaning a verification of a good connection is required, as well as confirmation of receipt
UDP
User Datagram Protocol
Connectionless protocol, “fire and forget”
TCP segment
Container with fields that ensure data gets to its destination.
Includes source and destination ports, sequence number, checksum, flags, acknowledgement, and the data itself
Port
Logical value assigned to specific applications or services
