OSI Model Layers

OSI Layers

Application Presentation Session Transport Network Data Link Physical

Session Layer assigns

Assignment of the session ID number to each session to keep data streams separate

Transport Layer provides connection services

Connection services, either reliable (connection-oriented) or unreliable (connectionless) deliver of data

Data Link Layer data

Data at this layer is referred to as a frame

Physical Layer data

Data at this level is referred to as bits

Network Layer data

Data on this layer is referred to as a packet

Transport Layer data

Data on this layer is referred to as a segment

Data Link Layer defines

Defines how hosts on the network are identified (Physical or MAC address) - device identification

Data Link Layer determines

Determines how and when devices can transmit on the network medium (MAC or logical topology) - how messages travel through the network

Network Layer determines

Determines the next network point to which data should be sent. (Routers use routing protocol to take into account various factors such as the number of hops in the path, link speed, and link reliability to select the optimal path for data)

Session Layer manages multiple sessions

Each client connection is called a session and a server can concurrently maintain thousands of sessions

Application Layer enables services

Enables Network Services

Presentation Layer encapsulates

Encapsulation of data into message envelopes by encryption and compression

Presentation Layer ensures

Ensures formatting and translation of data between systems

Presentation Layer primary function

Formats or "presents" data into a compatible form for the Application Layer or destination system

Application Layer Protocols

HTTP, Telnet, FTP, TFTP, SNMP

Data Link Layer defines rules

How devices control the rate of data transmissions between hosts (flow control)

Physical Layer sets standards

How digital data (bits are converted to electrical pulses, radio waves, or pulses of lights

Data Link Layer verifies

How to verify that the data received from the Physical Layer is error free (parity and CRC)

Network Layer Identifies

Identifies hosts and networks using logical addresses

Application Layer primary function

Integrates Network Functionality into the host operating system and enable Network Services

Physical Layer

Layer 1

Data Link Layer

Layer 2

Network Layer

Layer 3

Transport Layer

Layer 4

Session Layer

Layer 5

Presentation Layer

Layer 6

Application Layer

Layer 7

Network Layer maintains

Maintains a list of known networks and neighboring routers

Presentation Layer negotiates data transfer

Negotiation of data transfer syntax between systems by converting character sets to correct format

Transport Layer provides

Port and socket numbers

Session Layer primary function

Primary function is managing the sessions in which data is transferred

Network Layer primary function

Primary function is to describe how data is routed across networks and on to the destination

Transport Layer primary function

Primary function is to provide a transition between the upper and lower layers of the OSI model, making layers transparent from each other.

Application Layer provides capability

Provides capability for services to operate on the network (does not include specific applications that provide services)

Physical Layer standards

Provides specifications for cables and connectors

Presentation Layer restores

Restoration of data by decryption and decompression

Transport Layer segments

Segmentation, sequencing, and combination

Session Layer is the connection establishment

Set up, maintain, and tear down communication sessions

Physical Layer protocols identify

The physical topology - how to transmit data adn how to connect network hosts

Physical Layer primary function

The primary function of this layer of the OSI model sets standards for sending and receiving electrical signals between devices (Protocols)

Data Link Layer primary function

This Layer defines the rules and procedures for hosts as they access the Physical Layer with Logical Link Control (LLC) and Media Access Control (MAC)

Transport Layer controls

provides end-to-end flow control