OSI Model Flashcards
How is data referred to at each layer?
mnemonic device: Don’t Some People Forget Birthdays
Layer 1 Physical -Bits
Layer 2 Data Link- Frames
Layer 3 Network- packets
Layer 4 Transport- Segments
layer 5,6,7 Session, Presentation, Application- Data
What is Layer one of OSI model? What are some examples of layer one devices?
Physical Layer:
Ethernet, Fiber Cables,
Radio frequencies such as WiFi or bluetooth
Also: Hubs, Wireless access points, media converters
What is multiplexing and what does it do?
- Multiplexing is taking a limited amount of resource and using it more efficiently
- Multiplexing allows multiple people to use a baseband connection at the same time
What are the two types of bandwidth? How are they different?
Bandwidth-2 Types : Broadband and Baseband
Broadband divides into separate channels
Baseband uses all frequencies of cable all the time
What is Layer 2 of OSI model? What are some examples of layer 2 devices?
Data Link Layer
Examples of layer 2 devices: NIC, Bridges, Switches, MAC Addresses
What are the 3 types of ways that communication is synchronized
- Isochronous mode
- Synchronous mode
- Asynchronous mode
Describe Isochronous mode of communication synchronization.
Isochronous mode-network devices use a common reference clock source and create time slots for transmission with less overhead than synchronous or asynchronous methods
Describe Synchronous mode of communication synchronization.
Synchronous mode- network devices are on clocking method to indicate beginning and end of frames and can use control characters or separate timing channels.
takes up a lot of networking bandwidth
Describe Asynchronous mode of communication synchronization.
Asynchronous mode- network devices reference their own internal clocks and use start/stop bits. No real control over how devices communicate
What does Logical Link Control (LLC) do?
Logical link Control (LLC)-Provides connection services and allows acknowledgement or receipt of messages. It is also the most basic form of flow control. uses checksum to verify data is not corrupted or missing data
What form are MAC addresses written in?
What do the first 6 letters in a MAC address represent?
What do the last 6 letters represent?
MAC addresses are written hexadecimally where each number or letter = 4 bits
The first 24 bits or 6 letters are the VENDOR code
the last 24 bits or 6 letters is for exact machine
What does the Data Link layer do?
packages data into frames on the network, performing error detection/correction, uniquely identifying network devices with an address (MAC) and providing flow control
What is layer 3 of the OSI model? What are some examples of Layer 3?
Network Layer:
Routers, multilayer switches, IPv4 and IPv6 Protocol, ICMP
What is ICMP and what is it’s function?
Internet Control Message Protocol (ICMP)- Used to send error messages and operational information about an IP destination
What are some examples of routing protocols?
RIP, OSPF, EIGRP,etc..
What are the 2 types of route discovery and selection?
Manually configured as a static route
or
Dynamically through a routing protocol
What is Message Switching?
data is divided into messages similar to packet switching, except these messages may be stored then forwarded
messages are stored and forwarded similar to email
What is Circuit Switching?
Circuit switching is dedicated communication link is established between two devices, uses same path each time
example would be phone call where all data back and forth is traveling through the same path
What is Packet Switching?
packet switching =routing, this is normal how we use internet and is referenced to the mailbox and letters method of delivery
What are the three ways that data can be forwarded or routed?
Packet switching(most commonly used), Circuit switching or Message switching
How many bits in one Byte?
How many Bytes in an IP address?
8 Bits in a Byte
4 Bytes in an IP address
What is layer 3 switching referred to as? What does this get confused with?
Layer 3 switching is ROUTING
Gets confused with physical switches that operate at layer 2
What is Layer 3 on OSI model? What does it do?
Layer 3 Network - Forwards traffic (routing) with logical address (IPv4 or IPv6)
What is Layer 4 of OSI model? What are some examples of layer 4 devices/functions?
Transport Layer
TCP, UDP, WAN accelerators, Load balancers, Firewalls
What is buffering?
Buffering- occurs when devices, such as routers, allocate memory to store segments if bandwidth isnt readily available
What is windowing?
Windowing-allows the clients to adjust the amount of data sent in each segments and continually adjusts to send more or less data per segment transmitted
What is TCP?
Transmission Control Protocol (TCP) Connection-oriented protocol that is a reliable way to transport segments across the network
reliability features like windowing and buffering
What is UDP?
User Datagram Protocol (UDP)- Connectionless protocol that is an unreliable way to transport segments across the network
used for video streaming and audio streaming
Which is a more reliable transport protocol, TCP or UDP?
TCP
What transport protocol is faster, TCP or UDP?
UDP
Differences between TCP and UDP
TCP- Reliable, connection-oriented, segment retransmission and flow control through windowing, segment sequencing, acknowledges segments
UDP- Unreliable, Connectionless, no windowing or retransmission, no sequencing, no acknowledgement
What is Layer 5 of OSI model? What protocols are examples of layer 5?
Session Layer
Examples:
RTP, NetBIOS, and H.323
What is NetBIOSs function?
used by computers to share files over a network.
What is H.323
H.323 is used to set up, maintain, and teardown voice and video connections(STREAMING facetime/skype)-Operates on Real-Time Protocol (RTP)
What does RTP stand for?
Real-Time Transport Protocol
used for streaming audio or video calls (ex:facetime)
What are the 3 parts of the Session layer?
Setting up a session
Maintaining a session
Tearing down a session
Best way to describe how layer 5 works.
Best thought of a conversation that has to be kept separate from all the others to prevent the intermingling of data
What is Layer 6? What are some examples of Layer 6 for text, pictures, videos, and encryption?
Examples at Layer 6:
HTML, XML, PHP, JavaScript- all tell text based ASCII how to display on screen
ASCII, EBCDIC, UNICODE-Different ways to display texts from ones and zeroes
GIF, JPG, TIF, SVG, PNG- all different ways of displaying ones and zeroes as different graphical format
MP4, MPG, MOV-Video files
TLS and SSL-Encryption
What is TLS? What layer does it operate on?
Type of encryption: Transport Layer Security (TLS)-encrypted tunnel between server and client
-Updated more secure version of SSL
Layer 6
What is data formatting?
Data formatting - data is formatted by the computer to have compatibility between different devices Examples: ASCII (American Standard Code for Information Interchange) is basically text.
GIF, JPEG, PNG JPG- all types of formatting
What is ASCII?
ASCII (American Standard Code for Information Interchange)
-text based language -ensure data is readable by receiving system (Making sure that we’re all speaking the same language)
- Provides proper data structure
- Negotiates data transfer syntax for the application layer (Layer 7)
What layer of the OSI model does data formatting and encryption occur at?
layer 6 Presentation Layer
What is Layer 7 of the OSI model? What are some examples?
Application Layer
- Email (POP3, IMAP, SMTP)
- Web browsing (HTTP, HTTPS)
- Domain Name Service (DNS)
- File Transfer Protocol (FTP, FTPS,SFTP)
- Remote Access (TELNET, SSH)
- Network Management Protocol (SNMP)
What is a service advertisement?
This is where applications send out announcements to other devices on the network to state the services they offer
(example: new printer on a network advertising itself saying “HI im a printer! Use me too print things!”
