OSI Model Flashcards
Used to
- categorize functions of the network into particular layers
- compare technologies across different manufacturers
> by understanding its functions, you can understand how best to
communicate with that device
- Useful in troubleshooting networks
- Serves as a reference model in networks
OSI Model
Name the layers of OSI Model
Layer 1 - Physical Layer 2 - Data Link Layer 3 - Network Layer 4 - Transport Layer 5 - Session Layer 6 - Presentation Layer 7 - Application
Please Do Not Teach Students Pointless Acronyms
Match different data types to the layers of the OSI Model
Layer 7, 6, 5 - Application, Presentation Session --> Data Layer 4 - Transport --> Segments Layer 3 - Network --> Packets Layer 2 - Data Link --> Frames Layer 1 - Physical --> Bits
Don’t Some People Fear Birthdays?
- Transmission of bits across the network
- Physical and electrical characteristics
> how bits are represented on the medium
> wiring standards for connectors and jacks
> physical topology
> synchronizing bits
> bandwidth usage
> multiplexing strategy - Devices in this layer view networks from a topological perspective such as: bus, ring, star, hub-and-spoke, full mesh, partial mesh
Layer 1 - Physical
How are bits represented on the medium?
Electrical voltage (copper wiring) or light (Fibre optics) represent 1’s and 0’s
If it changed during the clock cycle, then a 1 is represented, otherwise a 0
Transition modulation
- Standard wiring for RJ-45 cables and ports
TIA/EIA-568-B
TIA/EIA-568-B is standard wiring for ______ cables and ports
RJ-45
Crossover cables use ________
T-568A and T-568B
T-568A and T-568B are used in what type of cables?
Crossover cables
Re: Layer 1 communication synchronization
- Uses start bits and stop bits to indicate when transmissions occur from sender to receiver
- Think of voicemail
Asynchronous communication
Re: Layer 1 communication synchronization
- Uses a reference clock to coordinate the transmission by both sender and receiver
- Think of a real time phone conversation
Synchronous communication
- Divides bandwidth into separate channels
- Uses Frequency-Division Multiplexing (FDM)
- Example: cable TV
Broadband bandwidth
- Uses all available frequency on a medium (cable) to transmit data and uses a reference clock to coordinate transmissions by both sender and receiver
- Example: Ethernet, telephone
Baseband bandwidth
Name an example of broadband bandwidth utilization
Cable TV
Name an example of baseband bandwidth utilization
Ethernet
- Each session takes turns, using time slots, to share medium between all users
Time-Division Multiplexing (TDM)
- More efficient version of TDM
- Dynamically allocates time slots on an as-needed basis instead of statically assigning
Statistical Time-Division Multiplexing (StatTDM)
- Medium is divided into various channels based on frequencies and each session is transmitted over a different channel
- Example: broadband
Frequency-Division Multiplexing (FDM)
What layer of the OSI Model are the following cables?
- Ethernet
- Fibre optic
Layer 1
What layer of the OSI Model are the following radio frequencies?
- WiFi
- Bluetooth
Layer 1
What layer of the OSI Model are the following infrastructure devices?
- Hubs
- Wireless Access Points
- Media converters
Layer 1
Straight-thru cables use ________
Typically T-568B on both ends, but could also use T-568A
- Taking some limited amount of resource and using it more efficiently
- Allows multiple people to use a baseband connection at the same time
Multiplexing
- OSI Layer that packages data into frames and transmits those frames on the network, performing error detection/correction, and uniquely identifying network devices with an address (MAC), and flow control
> MAC
> Physical addressing
> Logical topology
> Method of transmissionLayer 2 - Data Link
Which layer of the OSI Model uses MAC addresses?
Layer 2 - Data Link
- Physical addressing
> uses 48-bit address assigned to a network interface card (NIC) by
manufacturer
> first 24-bits is the vendor code
> second 24-bits is a unique value - Written hexademically e.g. D2:51:F1:3A:34:65
MAC address (Media Access Control)
- Provides connection services
- Acknowledgement of receipt of a message
- The most basic form of flow control
> limits amount of data sender can send at one time to keep receiver from
becoming overwhelmed - Error control
> allows receiver to let sender know when an unexpected data frame wasn’t
received or was corrupted by using a checksum
Logical Link Control (LLC)
Re: Layer 2 communication synchronization
- Network devices use a common reference clock source and create time slots for transmission
- Less overhead
Isochronous
Re: Layer 2 communication synchronization
- Network devices agree on clocking method to indicate beginning and end of frames
- Uses control characters or separate timing channel
Synchronous
Re: Layer 2 communication synchronization
- Network devices reference their own internal clocks and use start/stop bits
Asynchronous
The following are examples from which layer of the OSI Model?
- Network Interface Cards (NICs)
- Bridges
- Switches
- MAC Addresses
Layer 2 - Data Link
- OSI Layer that forwards traffic (routing) with logical address (e.g. IPv4 or IPv6)
> Logical addressing
> Switching (Layer 3 switching) aka routing
> Route discovery and selection
> Connection services
> Bandwidth usage
> Multiplexing strategy
Layer 3 - Network
Numerous routed protocols were used for ______ addressing over the years, but only Internet Protocol (IP) remains dominant e.g. IPv4 and IPv6
Logical (addressing)
Internet Protocol (IP) is an example of what type of addressing?
Logical addressing
What are the three main ways to forward or route data?
Packet switching, circuit switching, message switching
Known as “routing”, where data is divided into packets and forwarded
> like mailing a letter
Packet switching
Packet switching is also known as ______, where data is divided into packets and forwarded
Routing
Dedicated communication link is established between two devices
> like picking up a phone and making a phone call; for the entire call, the communication is using the same path
Circuit switching
Data is divided into messages, similar to packet switching, except these messages may be stored then forwarded
Message switching
- Routers maintain a routing table to understand how to forward a packet based on destination IP address
- Manually configured as a static route or dynamically through a routing protocol
> RIP
> OSPF
> EIGRP
Route discovery and selection
- Layer 3 augments Layer 2 to improve reliability
- Flow control
> Prevents sender from sending data faster than receiver can get it - Packet reordering
> Allows packets to be sent over multiple links and across multiple routes for faster service
Connection Services
Prevents sender from sending data faster than receiver can get it
Flow control
Allows packets to be sent over multiple links and across multiple routes for faster service
Packet reordering
- Used to send error messages and operational information about an IP destination
- Not regularly used by end-user applications
- Used in troubleshooting (ping and traceroute)
Internet Control Message Protocol (ICMP)
The following are examples from which layer of the OSI Model?
- Routers
- Multilayer switches
- IPv4
- IPv6
- Internet Control Message Protocol (ICMP)
Layer 3 - Network
- Dividing line between upper and lower layers of the OSI Model
- Data is sent as segments
- TCP/UDP
- Windowing
- Buffering
Layer 4 - Transport
- Connection-oriented protocol
- Reliable transport of segments
> If segment is dropped, protocol detects it and resents segment - Flow control through windowing
- Segment sequencing
- Acknowledgments received for successful communication
- Used for all network data that needs to be assured to get to its destination
Transmission Control Protocol (TCP)
- Connectionless protocol
- Unreliable transport of segments
> If dropped, sender is unaware - No retransmission or windowing
- No sequencing
- No acknowledgment
- Good for audio/visual streaming
- Lower overhead for increased performance
User Datagram Protocol
- Allows the clients to adjust the amount of data sent in each segment
- Continually adjusts to send more or less data per segment transmitted
> Adjusts lower as number of retransmissions occur
> Adjusts upwards as retransmissions are eliminated - Layer 4 - Transport
Windowing
- Devices, such as routers, allocate memory to store segments if bandwidth isn’t readily available
- When available, it transmits the contents of the buffer
- If the bugger overflows, segments will be dropped
- Layer 4 - Transport
Buffering
The following are examples from which layer of the OSI Model?
- TCP
- UDP
- WAN Accelerators
- Load balancers
- Firewalls
Layer 4 - Transport
Which layer of the OSI Model?
- Setting up sessions
- Maintaining sessions
- Tearing down sessions
Layer 5 - Session
A conversation that must be kept separate from others to prevent intermingling of data
Session
The following are steps to do what?
- Check user credentials
- Assign numbers to session to identify them
- Negotiate services needed for session
- Negotiate who begins sending data
Setting up a session
The following are steps to do what?
- Check user credentials
- Assign numbers to session to identify them
- Negotiate services needed for session
- Negotiate who begins sending data
Setting up a session
The following are steps to do what?
- Transfer data
- Re-establish a disconnected session
- Acknowledging receipt of data
Maintaining a session
The following are steps to do what?
- Due to mutual agreement, after the transfer is done
- Due to other party disconnecting
Tearing down a session
The following are examples from which layer of the OSI Model?
- H.323, used to setup, maintain, and tear down a voice/video connection
- NetBIOS, used by computers to share files over a network
- RTP
Layer 5 - Session
What layer of the OSI Model is NetBIOS?
Layer 5 - Session
- Used by computers to share files over a network
- Layer 5 - Session
NetBIOS
What layer of the OSI Model is H.323?
Layer 5 - Session
- Used to setup, maintain, and tear down a voice/video connection
- Layer 5 - Session
H.323
RTP
Streaming audio, streaming video
Streaming audio, streaming video (what Layer 5 protocol?)
RTP
Which layer of the OSI Model?
- Responsible for formatting the data exchanged and securing that data with proper encryption
- Functions
- Data formatting
- Encryption
Layer 6 - Presentation
- Formats data for proper compatibility between devices
> ASCII
> GIF
> JPG - Ensures data is readable by receiving system
- Provides proper data strictures
- Negotiates data transfer syntax for the Application Layer (layer 7)
Data formatting
- Used to scramble the data in transit to keep it secure from prying eyes
- Provides confidentiality of data
- Example: TLS to secure data between your PC and website
Encryption
The following are example from which layer of the OSI Model?
- HTML, XML, PHP, JavaScript
- ASCII, EBCDIC, UNICODE
- GIF, JPG, TIF, SVG, PNG
- MPG, MOV
- TLS, SSL
Layer 6 - Presentation
Which layer of the OSI Model?
- Provides application level services
> Not Microsoft Word or Notepad
- Layer where the users communicate with the computer
- Functions:
> Application services
> Services advertisementLayer 7 - Application
- Unite communicating components from more than one network application
- Examples:
> File transfers and file sharing
> E-mail
> Remote access
> Network management activities
> Client/server processes
Application Services
- Some applications send out announcements
- States the services they offer on the network
- Some centrally register with the Active Directory server instead
- Examples:
> Printers
> File servers
Service Advertisement
The following are examples from which layer of the OSI model?
- Email (POP3, IMAP, SMTP)
- Web browsing (HTTP, HTTPS)
- Domain Namer Service (DNS)
- File Transfer Protocol (FTP, SFTP)
- Remote Access (TELNET, SSH)
- Simple Network Management Protocol (SNMP)
Layer 7 - Application
