OSI Model Layers: Physical to Application Protocols and Communication Methods

(Layer 1)

Physical (Bits)

Physical Layer(Bits)

Contains all the physical and electrical elements of OSI, like cords and cables.

Broadband (Layer 1)

Divides bandwidth between separate channels.

Baseband (Layer 1)

Uses all the bandwidth at the same time.

Multiplexing (Layer 1)

Enables simultaneous usage of baseband.

Time-Division Multiplexing (TDM)

Allows different sessions to be allocated during a time slot.

Statistical Time-Division Multiplexing (StatTDM)

Refers to TDM but on an as-needed basis.

Frequency Time-Division Multiplexing (FTDM)

Divides the medium into separate sessions.

Layer 2

Data Link (Frames)

Data Link Layer Layer 2

Packages data into frames and transmits them to the network.

MAC

Layer 2: Media Access Control, the numerical identifiable address of a device to the network.

Logical Link Control

Layer 2: Allows the recipient to verify that your message got to its intended destination.

Isochronous Mode

Layer 2: Uses a time clock to create slots for transmission.

Synchronous Mode

Layer 2: A clocking method that tells when communication can begin and end.

Asynchronous Mode

Layer 2:All network devices operate on their own communication timing.

Layer 3

Network (Packets)

Packet Switching

Layer 3: being divided into packets and forwarded.

Circuit Switching

Layer 3: A dedicated communication link between two devices.

Message Switching

Layer 3: Stored and forwarded; packet switching does not store.

Flow Control

Layer 3: Allows the device to determine if there is too much data being sent or not enough.

Packet Re-ordering

Layer 3: Reassembles packets that don't usually send in order.

ICMP

Layer 3: Internet Control Message Protocol, sends error messages and information to a certain IP address.

Layer 4

Transport (Segments)

TCP

Layer 4:Transmission Control Protocol that transports segments of data across a network.

UDP

Layer 4: User Datagram Protocol that transports segments across a network, very unreliable.

Windowing

Layer 4: Allows the client to adjust the amount of data that goes through or comes through.

Buffering

Layer 4: Stuffs segments that aren't ready to be used yet in an allocated space.

Layer 5

Session (Data)

Setup Session

Layer 5: Sets up user credentials to help the system identify them.

Maintain Session

Layer 5: Involves transferring data, reestablishing connections, and acknowledgment receipt.

Tearing Down Session

Layer 5: Ends the connection mutually or when the task is complete.

Layer 6

Presentation (Data)

Formatting Data

Layer 6: Ensures that all computers and devices can understand the data.

Encryption

Layer 6: Secures the data in transit.

Layer 7

Application (Data)

Application Services

Layer 7: Unites communicating components for more than one network application.

Encapsulation

Layer 7-1 :The process of putting all the layers into an 'envelope' and sending it.

Decapsulation

Layer 1-7: The process of taking apart the 'envelope' to process the layers.

PDU

Layer 7: Protocol Data Unit, a single unit of information transmitted in a computer network.

SYN

Layer 4: Used to sync connection during TCP 3-way handshake.

ACK

Layer 4: Used during 3-way handshake to acknowledge the successful connection.

FIN

Layer 4:Used to tear down or end the connection of the 3-way handshake.

RST

Layer 4: Used when an unexpected package is received.

PSH

Layer 4:Indicates the priority of data by the sender.

URG

Identifies urgent data and tells the recipient to process immediately.

EtherType

Layer 2:Used to indicate which type of protocol is in the frame.