1. Network Models Flashcards
OSI Layer 7
Application
User-facing software that is being used to engage with a network. Could be anything from LAN file sharing to a browser. APIs provide service to the programs that the users see.
PDU: data
OSI Layer 6
Presentation
Translates data from the lower layers into formats usable by applications, and vice versa. This is where encryption happens.
PDU: data
OSI Layer 5
Session
Handles the process of differentiating between various types of connections on a PC. This layer initiates sessions, accepts incoming sessions, and opens and closes existing sessions.
PDU: data
OSI Layer 4
Transportation
This is where data is ‘packetized’ into sections that can be passed individually through a network. Data is broken up and sequence numbers for TCP segments are added so the receiving computer can assemble correctly.
PDU: segment
OSI Layer 3
Network
Creates and addresses packets. The IP addressing enables routers to make sure the packets get to the correct system without worrying about the type of hardware used for transmission.
Device: Router
PDU: packet
OSI Layer 2
Data Link
The only layer with sublayers. Home of the NIC. Puts the final frame on the data before getting passed through the network.
Device: Switch
PDU: frame
OSI Layer 1
Physical
Any medium on which data travels, even radio waves.
Devices: cables, hubs
PDU: bit
LLC
Logical Link Control
Sublayer of the Data Link Layer 2. Handles multiple network protocols and provides flow control.
MAC
Media Access Control
Sublayer of Data Link Layer 2. It adds the NIC’s own MAC address and attaches MAX addresses to the frames and adds or checks the FCS.
The number is represented in hexadecimal and it split into 2 parts. The first being the Organizationally Unique Identifier (OUI) and the second being the device ID.
FCS
Frame Check Sequence
The resulting remainder of a division problem applied to a frame’s data. Allows the receiving computer to verify all the data was received.
NIC
Network Interface Card
Houses the LLC and the MAC
TCP/IP Layer 1
Link Layer / Network Interface Layer
Covers the first two layers of the OSI model (switches, frames).
TCP/IP Layer 2
Internet Layer
Same as the OSI’s Network Layer. Covers anything involved with IP, including packets, addressing, and routing.
TCP/IP Layer 3
Transport Layer
Similar to the OSI Transport layer except that the PDU is either a TCP segment or a UDP datagram, depending on the protocol used. Also, port numbers are added, and in the case of TCP, sequence numbers.
TCP/IP Layer 4
Combines the top three OSI layers. The session component works similarly, the presentation doesn’t exist, and connection to an application is implied.
API
Application Programming Interface
Provide a standard way for programmers to enhance or extend an applications capabilities.
EUI-48
The IEEE’s official term for a MAC address
CRC
Cyclic Redundancy Check
aka FCS
datagram
The PDU of the UDP (the TCP version would a segment).
physical address
Synonymous with the MAC address
device ID
The second half of a MAC address.
EUI-48
The IEEE’s official term for a MAC address / physical address.
frame
The structure in which data gets passed around a network. Contains a header, payload, and trailer.
header
First section of a frame, contains the MAC address and data type
TCP/IP model
Transmission Control Protocol / Internet Protocol
..
IP address
A unique numeric identifier.
aka logical address
logical address
aka IP address
logical addressing
Refers to digital addressing which can be configured.
MAC-48
Synonymous with EUI-48, MAC address, and physical address
network protocol
How computers handle addressing large networks
payload
The actual data in a frame, excluding the header and any other metadata.
packet
The PDU of the Network layer. The packet is inside the frame containing the payload and a separate header. The header contains source address, destination address, protocol, and sequence number.
protocol
An agreement between devices defining how they will exchange data.
reassembly
The reverse of segmentation. TCP segments are put back together in the proper order.
router
A device that routes data to the next point in the network without needing to know its final destination.
segment
The PDU of the TCP
segmentation
The process of the local computer “packetizing” it’s data into sections that can be passed individually through the network.
session software
Connects applications to other applications and ensures that they are compatible.
subnet
Technically a division of a network by range of IP address. Represents a subnet of hosts which can be reached over a network interface.
TCP segment
TCP accepts a data stream, divides it into sections and adds a TCP header. Thus, a TCP segment is born.
trailer
Metadata attached to the end of a
