OSI Model Flashcards
1
Q
Explain the background of the OSI model.
A
- International Organization for Standardization (ISO)
- late 1970s
- Define and categorize interactions in computer network
2
Q
Why is the OSI model important?
A
- used independently of media, network architecture, computer platform
- provides manufacturing standards
- saves work: standards and layered protocols mean developers don’t need to figure out all those functions
- allows dissimilar networks to be interconnected
- used as a tool in troubleshooting
- allows uniform data transfer
3
Q
Layer 7: name, function, type of data
A
- Application layer
- communication, functions, standardized services between user-level software or nodes with their counterparts
- determines which data to transmit, format for data, how it’s identified
- protocol data unit (PDU)
4
Q
Layer 6: name, function, type of data
A
- Presentation layer
- controls formats of screens and files–how data is presented
- generalizes data from application so it’s transparent to the network
- protocol data unit (PDU)
5
Q
Layer 5: name, function, type of data
A
- Session layer
- communication between programs (manages, maintains, controls) > “dialogue manager” or stop light
- attempts to reconnect in case of failure
- protocol data unit (PDU)
6
Q
Layer 4: name, function, type of data
A
- Transport layer
- end-to-end connection (not route taken)
- first layer concerned with world beyond computer processor
- defines rules for information exchange
- flow control and error recovery
- segments
7
Q
Layer 3: name, function, type of data
A
- Network layer
- appends header with unique network address to send data through the network to correct destination
- corrects some errors
- routes packets (controls routing)
- translating logical names to physical addressing (msn.com > 193.160.32.1)
8
Q
Layer 2: name, function, type of data
A
- Data link layer
- groups bits from physical layer into frames
- attach header describing MAC address
- control flow between nodes (send when receiver can accept)
- checks for errors, does not fix
- defines begin & end of data fields
- frames
9
Q
Layer 1: name, function, type of data
A
- Physical layer
- outgoing data translated to signals for the network media
- incoming signals translated to bits to data link
- physical means of getting message from one node to the next
- bits
10
Q
What are the four upper layers? Summarize their collective functions.
A
- Software application and internetworking functions
- Application, Presentation, Session, Transport
- convert info to data and send to transport layer
- transport turns it into segments and adds headers
11
Q
What are the three lower layers? Summarize their collective functions.
A
- networking hardware functions
- Network, Data Link, Physical
- network layer converts to packets; adds logical headers
- data link converts to frames, adds headers (physical source/destination address)
- physical converts to bits to go on network media
12
Q
What is a header? Another term for it?
A
- AKA “overhead”
- bytes
- added at each layer; read at corresponding layer on another node
13
Q
What is a peer protocol?
A
Dialogue between same-level entities.
14
Q
Describe data flow.
A
- Data moves down (output from sender) and up (incoming to receiver) through layers
- Layers communicate with adjacent layers, but are shielded from others
- Headers added at each layer + trailer at Level 2; removed at corresponding layers on peer
- standards guarantee a level of service to adjacent layers
15
Q
What are the Data Link sublayers?
A
- Media Access Control (MAC): how devices will share media channel
- Logical Link Control (LLC): how communication between devices are established and maintained
