OSI model Flashcards
What are nodes?
Devices which communicate on a network
What must a node do to communicate?
Cycle through a series of seven tasks (OSI model)
Why is OSI normally drawn in a stack?
Because each task depends on the one that comes before them
What does OSI stand for?
Open Systems Interconnection model
What does each layer do?
Serves the connection and communication needs between the layer above and below it
What is layer one?
The Physical layer
What is defined in the physical layer?
How the connection is made
What does the physical layer control?
The way raw bit streamed data is sent and received over a physical medium
What are some examples of things that are defined in the physical layer?
- Type, quality and length of cable (copper or optic)
- Type of connector (RJ45)
- Pin configurations in connection
- Radio freq (wireless connections)
What is the physical layers main concern?
With transmission and reception of raw bit streamed data over the physical medium
What are some examples of physical layer?
Cables, hubs, connectors
What is layer two?
The Data link layer
What is the job of the data link layer?
Sending and interpreting data signals on the physical connection
What does addressing do?
Ensures that every computer on a network is identified.
What is an example of a data link protocol?
Ethernet
What does Ethernet do?
A protocol which allows more than two nodes to be connected on the same network
What is a MAC address and how many bytes are they?
Stands for Media access control and is an address unique to each computer on a shared network. They are 6 bytes
What does a hub do?
It transmit data to all computers on a network
What does a switch do?
It learns which computer it connected to which port and only forwards traffic to the relevant port rather than all ports
What is the data link layer concerned with?
Providing error free transfer of data frames between nodes over the physical layer
What are some examples of data link layer?
Switches, NIC card
What is the 3rd layer on the OSI?
The Network layer
What does the network layer do?
Allows us to leave our network and communicate with another network somewhere else
What is routing?
Routing is finding the best possible path between two networks
What is the most common network layer protocol?
IP (internet protocol)
What two issues do we need to deal with when it comes to sending information to another computer on in the world?
Addressing and routing
What does the subnet mask do?
It tells us if an IP address belongs to the local network or another physical network to determine if data is sent on network or to default gateway for routing.
What is the IP address 127.0.0.1?
IP address my first network interface
What does the network layer give us the ability to do?
Transfer data between two interconnected computer anywhere in the work
What are some examples of network layer?
Router, IP, address mapping
What does the network layer control?
Operations of the subnet deciding which physical path the data takes
What is the job of the transport layer
Is to allow reliable communication between nodes. This is performed by TCP
What is the best way to check for transmission errors?
Using checksums
What happens in the transport layer so the recipient knows that the message has been received?
An acknowledge is sent back
In the transport layer, what is used to ensure the packets are reassembled in the correct order?
Sequence numbers
What are examples of protocols operating on the transport layer?
TCP, UDP (message management)
What does the transport layer ensure?
That data is delivered error free, in sequence with no loss or duplication.
What is layer number 5 in the OSI model?
The Session layer
What does the session layer enable?
Multiple communication sessions with the same person at the same time
What does a session layer enable a computer to do?
Distinguish between different types of connections such as emails and web
How does a session layer enable different types of communication at the same time?
The use of concept of ports which is performed by TCP
What is a session?
A specific conversation between two network nodes
What four items do we need to properly distinguish a communication?
- Source IP address
- Source port
- Destination IP address
- Destination port
What do you need to establish a connection to a remote network?
- IP address
- Which port to connect to
What the first 1024 ports reserved for?
For servers to listen on so they are not available as source ports
What ports are allocated for:
- HTTP (Web)
- SMTP (Sending email)
- POP3 (Checking email)
- telnet (Remote computer)
- FTP (Upload/download files)
- 80
- 25
- 110
- 23
- 20 & 21
What is the session layer responsible for?
Starting, maintaining and terminating communication sessions and managing logical ports
What is the job of the presentation layer?
Making sure when data is delivered it will be understood by receiving computer
How must computers on a network send bytes so they are understood by a receiving computer?
Using the byte network order
What is the 7th layer on the OSI model?
The Application layer
What is the job of the application layer?
To format the data correctly for transmission and to interpret it when its received by the destination machine
What is a protocol on the application layer?
HTTP
What does the application layer serve as?
As a window for users and application processes to access network services
Which layer of the OSI model describes techniques for making sure that data is transmitted in a common format so that computers can understand each other?
Presentation
Which layer of the OSI model describes protocols that are used by clients and servers to display data to the user in a human-recognizable format?
Application
Which layer of the OSI model describes how to deliver traffic to any other computer on the Internet?
Network
What are the two layers of the OSI model in which TCP is used?
Session and transport
What is the main purpose of the OSI model?
To describe the functionality of networks
