OSI Flashcards
OSI model or reference model
Reference Model is used to categorize the functions of a network in the OSI Model during troubleshooting efforts.
Seven layers of the OSI model
- Physical
- Data Link
- Network
- Transport
- Session
- Presentation
- Application
Data form wen passing through OSI model
At layer 1, 2, and 3, it’s called data.
At layer 4 it becomes segments.
At layer 5, it becomes packets.
At layer 6, it becomes frames.
At layer 7, it becomes bits.
Two main ways of terminating RJ45
TIA/EIA-568A and 568B
Broadband
Divides bandwidth into separate channels
Baseband
Uses all available frequencies on a medium like cable to transmit data.
Multiplexing
A technique used in communication systems to send multiple signals over a single channel.
Data Link Layer
Packages data into frames and transmits those frames on the network.
Logical Link Control(LLC)
Allows recipients to acknowledge the receive of messages and provides basic error control functions such as if data frames are not received or they are corrupted.
Isochronous
Data is sent at regular, predictable time intervals.
Synchronous
Data is sent in a continuous stream, synchronized by a clock signal.
Asynchronous
Data is sent without a shared clock, using start and stop bits to indicate when a transmission begins and ends.
Three main ways to route data across network:
- Packet switching
- Circuit Switching
- Message Switching
Packet Switching
Data is divided into packets and then forwarded based on the IP address.
Circuit Switching
Constant and dedicated communication path is maintained for an amount of time.
Message Switching
Data is divided into message which may be stored and then forwarded.
Route Discovery and Selection
Manually configured as a static route or dynamically through a routing protocol like RIP, OSPF, EIGRP.
Layer 1 (PHY) devices
- Transceiver: the part of a network interface that sends and receives signals over the 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.
Layer 2 Devices
- Network adaptor or NIC — Joins an end system to network media (cable or wireless) and enables it to communicate over the network by assembling and disassembling frames.
- Bridge — A type of intermediate system that joins physical network segments while minimizing the performance reduction of having more nodes on the same network. A bridge has multiple ports and each function as a network interface.
- Switch — Switches are advanced types of bridge and they have more ports which can create links between a large number of ports.
- Wireless access point (AP) — An AP allows nodes with wireless network cards to communicate and creates a bridge between wireless networks and wired ones.
Layer 3 Devices (network)
Routers, multi-layer switches, IPv6, IPv4, ICMP.
Windowing
Allows the clients to adjust the amount of data in each segment.
Buffering
Buffering is the temporary storage of data in a memory space (buffer) before processing or forwarding.
Layer 4 devices and protocols
TCP/UDP, WAN accelerators, Load balancers, multi-layer switches, and other security appliances like IDS, IPS, and firewalls.
Three parts of the Session layer
- Set Up Session: checking of user credentials and assigning numbers to sessions to help identify them. We assign a number to a session to help identify it after a user authentication.
- Maintain session: where data transfers back and forth across the network. It has three parts:
- Transfer data
- Reestablish connection
- Acknowledge receipt
- Tear Down Session: ending of a session after the transfer is done or when the other party disconnects. Tearing down a session can be done mutually or after the communication has finished.
Data formatting
means data is formatted by the computer to have compatibility between different devices.
Encryption
Used to scramble the data in transit to keep it secure from prying eyes and provide data confidentiality.
Layer 6 things
Scripting languages, Standard text, Pictures, movie files, encryption algorithm
Application Services
Unites communicating components from more than one network application.
Service Advertisement
Sending out of announcements to other devices on the network to state the services they offer like a printer that is managed by AD, can do the advertisement.
Layer 7 things
- Email applications such as POP3, IMAP, SMTP
- web browsing application like HTTP, HTTPS
- DNS
- FTP like FTPS, or SFTP
- Remote access like Telnet or SSH
Encapsulation
The process of putting headers (and trailers) around some data like when you write a letter for someone and put it in an envelope. You encapsulate the letter.
