1A Comparing OSI Model Network Functions Flashcards
Acronym Used to remember OSI model from bottom up
Please Do Not Throw Sausage Pizza Away
Acronym Used to remember OSI model from top to bottom
All People Seem To Need Data Processing
OSI Model Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Network Protocol 2 principal functions
Addressing & Encapsulation
Addressing
Describing where data messages should go.
Encapsulation
Describing how data messages should be packaged for transmission. Similar to an envelope for a letter with the distinction that each layer requires its own envelope.
OSI reference model
Open Systems Interconnection - promotes understanding of how components in a network system work.
Same layer interaction
protocol running at each layer communicates with its equivalent (or peer) layer on the other node.
Adjacent Layer Interaction
Transmit or receive a communication on each node, each layer provides services for the layer above and uses the services of the layer below.
Layer 1
(Physical Layer) responsible for transmission and receipt of the signals that represent bits of data from one node to another.
Devices that operate at the Physical Layer include
Transceiver, Repeater, Hub, Media converter, Modem
Transceiver
The part of the network interface that sends and receives signals over network media
Repeater
A device that amplifies an electronic signal to extend the maximum allowable distance for a media type
Hub
A multiport repeater, deployed as the central point of connection for nodes
Media converter
a device that converts one media signaling type to another (ex: copper wire to fiber optic)
Modem
A device that performs some type of signal modulation and demodulation, such as sending digital data over an analog line. Creates a physical connection to another network.)
Layer 2
(Data Link Layer) Responsible for transferring data between nodes on the same logic segment. Organizes the stream of bits arriving from the physical layer into structured units called frames. Frames contain a network layer packet as its payload. Layer 2 adds control info to payload in form of header fields. Fields include source & destination hardware addresses + basic error check making sure received frame is intact.
Layer 2 devices
NIC, Bridge, Switch, Wireless Access Point (AP)
Logical Topology
At the Data Link Layer (L2) segment is one where all nodes can send tragic to one another using hardware addresses, regardless of whether they share access to the same media. A Layer 2 segment might include multiple physical segments.
Layer 3
(Network Layer) - responsible for moving data around a network of networks, known as an internetwork or the internet. Moves info around by using logical network and host IDs.
Layer 3 devices
Router, basic firewall (packet filtering firewall)
Layer 4
Transport Layer - AKA the end-to-end or host-to-host layer. can understand payload/data itself. identifies each type of network app by assigning it a port number. Ex: data from HTTP web app is identified as port 80. Tags segments with application port numbers and passes it on to the network layer for delivery.
Layer 4 PDUs
Segments
PDU (network not hardware)
Protocol Data Unit - A unit of information transmitted between entities on a computer network.
First 3 Layers of OSI Models are primarily concerned with…
moving frames and datagrams between nodes and networks. only read the header of the data packet.
Layer 4 Devices
Load Balancer, Advanced Firewall, Intrusion Detection System (IDS)
Layer 5
Session Layer - most app protocols require exchange of messages b/w client and serer - this exchange is called a session or dialog. Session layer represents functions that administer process of establishing a dialog, managing data transfer and ending the session.
Layer 6
Presentation Layer - Supports data compression and encryption. transforms data between the format required for the network ad the format required for the app.
Layer 7
Application Layer - doesn’t encapsulate or provide services to any protocol. Provides an interface for software programs on network hosts.
Upper Layer Protocols provide…
most of the services that make a network useful rather than just functional, including web browsing, email and communications, directory lookup, remote printing and database services.
PDUs at each layer
Layer 4 - Segment
Layer 3 - Datagram
Layer 2 - Frame
Layer 1 - Transceiver
Devices used at each layer
Layer 3 - basic firewall, router
Layer 2 - Bridge, Switch, Access point?
Layer 1 - Cable, Media Converter, Hub, Access point?
What Layer are IP addresses introduced?
Layer 3 - Network
What layer are MAC addresses/EUIs introduced?
Layer 2 - data link
At which OSI layer is the concept of a port number introduced?
Transport
At which Layer of the OSI model is no header encapsulation applied?
Physical
What component performs signal amplification to extend the maximum allowable distance for a media type?
A repeater
Which OSI layer packages bits of data from the physical layer into frames?
Data Link
True or False? The session layer is responsible for passing data to the network layer at the lower bound and the presentation layer at the upper bound.
False, the session layer is between the transport and presentation layer
