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