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Transcript of OSI Model
Conceptual Model of a communications system
Breaks network up into 7 layers:
Application (layer 7)
Presentation (layer 6)
Session (layer 5)
Transport (layer 4)
Network (layer 3)
Data Link (layer 2)
Physical (layer 1)
What is the OSI Model?
The hardware of the network
Transmits bits (on / off electrical signals)
Transmits via physical connections between nodes
Everything physical about the network is defined here
Transmits from the Data Link layer into signals understandable by the hardware
Is also in control of radio and wireless interfaces
Layer 1: Physical
Session: Deals with requests and responses between applications
Layer 5 opens, closes, and manages communication sessions, and does session recovery (in case of lost connection). So if a connection drops, the session will attempt to reconnect.
Manages multiple incoming session streams (called "Flow Control")
Synching audio + video while streaming
Multiple AV sessions in web conferencing (Person A's voice matches up with Person A talking)
Layer 5: Session Layer
Layer 2: Data Link
By: Alex McMorine, Zohaib Qureshi, Dorian Wang, Nathnael Tobias
- Deals with the functional and procedural means of moving information between nodes in one network.
Layer 3: Network Layer
Layer 4: Transport Layer
-Allows end-to-end communication, routing data through other nodes.
This layer takes data, and converts it into a more usable form. For example, turning 0110100001101001 to "hi"
Layer 6: Presentation Layer
The OSI Model
Provides protocols for transferring data between nodes
Can have error-correction functionality to patch up physical errors
Not for inter-network travel or global (internet) travel
Only concerned with node-to-node transport, not final destination
Deals with collision errors when two chunks of data try to access a node at the same time
Layer 7: Application Layer
-This supports application and end user process.
-Identification, Quality, and Authentication services are run on layer 7.
-It provides application services for file transfers, e-mail, remote login, and other network software services.
-it also contains Telnet and FTP applications.
- Moves information in packets.
- Can be related to the IP portion of the TCP/IP protocol, which is a subset of the functionality of this layer, and foundational in its functioning.
- takes part in the disassembly and reassembly of packets as they move between nodes.
- Routes and delivers datagrams, but is not always reliable in its delivery of the datagrams.
-Connection oriented communications
-Allows for synchronous data flow, and flow control (ensures that the speed at which the sender sends .
-TCP resides mostly on this layer. TCP "guarantees" any precision wanted.
-UDP is another protocol, with less functionality than TCP. It simply sends, and then looks for confirmation.
This layer may use different protocols, but it is the application that sets the protocol. Encryption is typically done on this level (It is possible to do it on many of the other ones though).
The presentation layer is usually built into programs, and splits data into variables, pixels, etc. This is also where the data is "given" to the correct program.
datagram - transfer unit for packet switched networks. Arrival time, arrival order, and delivery are NOT guaranteed by network.
-addressing (assigns address)
-routing (picks best route)
-encapsulation (translations allow data to change protocols, allowing it to travel through a network)
-fragmentation and re-assembly (self explanatory)
-error handling (ICMP, simply sends error reports, gives feedback)