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Dion (N10-008) > OSI Model > Flashcards

OSI Model Flashcards

1
Q

OSI Model/Stack (7 Layers)

A

1) Physical (Bits)
2) Data Link (Frames)
3) Network (Packets)
4) Transport (Segments)
5) Session (Data)
6) Presentation (Data)
7) Application (Data)

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2
Q

OSI Model Data Types

A

Bits (Physical)
Frames (Data Link)
Packets (Network)
Segments (Transport)
Data (Session, Presentation, Application)

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3
Q

Layer 1 (Physical): Functions

A

Transmission of bits across the network
How bits are represented
Physical Topology/Wiring Standards
Synchronizing bits
Bandwidth usage
Multiplexing strategy

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4
Q

Layer 1 (Physical): How Bits are Represented

A

Electric voltage (copper) or light (fiber)

Current State:
0 volts = 0
+/- 5 volts = 1

Transition Modulation: If it changed during the clock cycle, then a 1 is represented (otherwise 0)

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5
Q

Layer 1 (Physical): Cable Connections

A

Layer 1 devices view networks from a physical topology perspective

Bus, Ring, Star, Hub & Spoke, Full Mesh, Partial Mesh

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6
Q

Layer 1 (Physical): Communication Synchronization

A

Asynchronous: Uses start bits & stop bits to indicate when transmissions occur from sender to receiver.

Synchronous: Uses a reference clock to coordinate the transmissions by both sender & receiver

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7
Q

Layer 1 (Physical): Bandwidth Utilization
(B vs. B)

A

Broadband: Divides bandwidth into separate channels (Cable TV)

Baseband: Uses all available frequency on a medium (cable) to transmit data & uses a reference clock to coordinate the transmissions by sender & receiver

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8
Q

Layer 1 (Physical): TDM

A

Time-Division Multiplexing:
Each session takes turns, using time slots, to share the medium between all users

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9
Q

Layer 1 (Physical): StatTDM

A

Statistical Time-Division Multiplexing:
More efficient version of TDM, it dynamically allocates time slots on an as-needed basis instead of statically assigning

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10
Q

Layer 1 (Physical): FDM

A

Frequency-Division Multiplexing:
Medium is divided into various channels based on frequencies and each session is transmitted over a different channel (broadband)

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11
Q

Layer 1 (Physical): Examples

A

Cables (Ethernet, Fiber Optic)
Radio Frequencies (Wi-Fi, Bluetooth)
Infrastructure Devices (Hubs, WAPs, Media Converters)

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12
Q

Layer 2 (Data Link): Functions

A

Packages data into frames & transmitting those frames on the network, performing error detection/correction, and uniquely identifying network devices with a MAC address, and flow control.
(Physical addressing, logical topology, method of transmission)

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13
Q

Layer 2 (Data Link): LLC

A

Logical Link Control:
Provides connection services
Acknowledgement of receipt of a message

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 expected data frame wasn’t received or was corrupted by using a checksum

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14
Q

Layer 2 (Data Link): Communication Synchronization

A

Isochronous: Network devices use a common reference clock source & create times slots for transmission (less overhead than synchronous or asynchronous)

Synchronous: Network devices agree on clocking method to indicate beginning & end of frames (uses control characters or separate timing channel)

Asynchronous: Network devices reference their own internal clocks & use start/stop bits

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15
Q

Layer 2 (Data Link): Examples

A

NICs
Bridges
Switches

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16
Q

Layer 3 (Network): Functions

A

Forwards traffic (routing) with logical address (IPv4/IPv6)
Logical addressing
Switching
Route discovery & selection
Connection services
Bandwidth usage
Multiplexing strategy

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17
Q

Layer 3 (Network): Logical Address

A

Numerous routed protocols were used for logical addressing over the years:
AppleTalk, Internetwork Packet Exchange (IPX), Internet Protocol (IP)

Only IP remains dominant (IPv4, IPv6)

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18
Q

Layer 3 (Network): Data Routing/Forwarding
(3 Switching Types)

A

Packet Switching: Data is divided into packets & forwarded.
Looks for most efficient route available. Once data reaches destination, packets are reassembled.

Circuit Switching: Dedicated communication link is established between two devices (sender/receiver). (Not ideal for data, best for voice)
Line remains idle between transmission spurts, wasting bandwidth unless using voice.

Message Switching: Data is divided into messages, similar to packet switching, except these messages may be stored, then forwarded.

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19
Q

Layer 3 (Network): Connection Services

A

Flow Control: Prevents sender from sending data faster than receiver can get it.

Packet Reordering: Allows packets to be sent over multiple links & across multiple routes for faster service.

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20
Q

Layer 3 (Network): ICMP

A

Internet Control Message Protocol:
Used to send error messages & operational info about an IP destination.
Not regularly used by end-user apps
Used in troubleshooting (ping/traceroute)

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21
Q

Layer 3 (Network): Examples

A

Routers, multilayer switches, IPv4/IPv6, ICMP

22
Q

`Layer 4 (Transport): Functions

A

Dividing line between upper/lower layers of the OSI model
Data is sent as segments
TCP/UDP
Windowing
Buffering

23
Q

Layer 4 (Transport): TCP

A

Transmission Control Protocol:
Connection-oriented protocol
Reliable transport of segments (if dropped, it’s detected and will get resent)
Acknowledgements received for successful communications
Segment sequencing
Used for all network data that needs to be assured to get to its destination

24
Q

Layer 4 (Transport): UDP

A

User Datagram Protocol:
Connectionless protocol
Unreliable transport of segments (unaware of drops)
No retransmission, no segment sequencing
Good for audio/video streaming
Lower overhead for increased performance

25
Q

Layer 4 (Transport): Windowing

A

Allows clients to adjust the amount of data sent in each segment
Continually adjusts to send more/less data per segment transmitted

Adjusts lower as number of retransmissions occur
Adjusts upwards as retransmissions are eliminated

26
Q

Layer 4 (Transport): Buffering

A

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 buffer overflows, segments get dropped

27
Q

Layer 4 (Transport): Examples

A

TCP
UDP
WAN Accelerators
Load Balancers
Firewalls

28
Q

Layer 5 (Session): Functions

A

Think of a session as a conversation that must be kept separate from others to prevent intermingling of the data
Setting up, maintaining, and tearing down sessions

29
Q

Layer 5 (Session): Setting up a Session

A

Check user credentials
Assign numbers to session to identify them
Negotiate services needed for session
Negotiate who begins sending data

30
Q

Layer 5 (Session): Maintaining a Session

A

Transfer the data
Reestablish a disconnected session
Acknowledging receipt of data

31
Q

Layer 5 (Session): Tearing Down a Session

A

Due to mutual agreement (after transfer)
Due to other party disconnecting

32
Q

Layer 5 (Session): Examples

A

H.323 - Used to setup, maintain, & tear down a voice/video connection

NetBIOS - Used by computers to share files over a network

33
Q

Layer 6 (Presentation): Functions

A

Responsible for formatting the data exchanged & securing that data with proper encryption
Data formatting
Encryption

34
Q

Layer 6 (Presentation): Data Formatting

A

Formats data for proper compatibility between devices
(ASCII, GIF, JPG)
Ensures data is readable by receiving system
Provides proper data structures
Negotiates data transfer syntax for the Application layer

35
Q

Layer 6 (Presentation): Encryption

A

Used to scramble the data in transit to keep it secure from prying eyes
Provides confidentiality of data
Example: TLS to secure data between device/website

36
Q

Layer 6 (Presentation): Examples

A

HTML, XML, PHP, Javascript
ASCII, EBCDIC, UNICODE
GIF, JPG, TIF, SVG, PNG
MPG, MOV
TLS, SSL

37
Q

Layer 7 (Application): Functions

A

Provides application level services (not Word or Notepad)
Layer where the users communicate with the computer
Application services, Service advertisement

38
Q

Layer 7 (Application): Application Services

A

Application services unite communicating components from more than one network application.
(File transfers, email, remote access, network management activities, client/server processes)

39
Q

Layer 7 (Application): Service Advertisement

A

Some applications send out announcements
States the services they offer on the network
Some centrally register with the AD server instead
(Printers, file servers)

40
Q

Layer 7 (Application): Examples

A

Email (POP3, IMAP, SMTP)
Web Browsing (HTTP, HTTPS)
DNS
FTP/FTPS
TELNET/SSH
SNMP

41
Q

Encapsulation

A

The process of putting headers (and sometimes trailers) around some data.

Moving down the OSI layers from 7 to 1.

42
Q

Decapsulation

A

The action of removing the encapsulation that was applied.

Moving up the OSI layers from 1 to 7.

43
Q

PDU

A

Protocol Data Unit:
A single unit of info transmitted within a computer network.

Layer 1 = Bits
Layer 2 = Frames
Layer 3 = Packets
Layer 4 = Segments (TCP), or Datagrams (UDP)

44
Q

SYN Flag

A

Synchronization Flag:
Used to synchronize the connection during the three-way handshake.

45
Q

ACK Flag

A

Acknowledgement Flag:
Used during the three-way handshake, but is also used to acknowledge the receipt of packets.

46
Q

FIN Packet

A

Finished Packet:
Used to tear down the virtual connections created using the three-way handshake and the SYN flag.

Always appears when the last packets are exchanged between a client/server & host is ready to shutdown the connection.

47
Q

RST Flag

A

Reset Flag:
Used when a client or server receives a packet that it was not expecting during the current connection.

48
Q

PSH Flag

A

Push Flag:
Used to ensure that the data is given priority and is processed at the sending or receiving ends.

49
Q

URG Flag

A

Urgent Flag:
Like the Push flag, identifies incoming data as urgent.

PSH is used by sender to indicate data with a high priority.

URG is sent to tell the recipient to process immediately & ignore anything else in the queue.

50
Q

EtherType Field

A

Used to indicate which protocol is encapsulated in the payload of the frame.

Layer 4 = Source/destination ports
Layer 3 = Source/destination IPs
Layer 2 = Source/destination MACs

Dion (N10-008) (27 decks)

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