OSI Model Flashcards
Explain the background of the OSI model.
- International Organization for Standardization (ISO)
- late 1970s
- Define and categorize interactions in computer network
Why is the OSI model important?
- 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
Layer 7: name, function, type of data
- 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)
Layer 6: name, function, type of data
- 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)
Layer 5: name, function, type of data
- Session layer
- communication between programs (manages, maintains, controls) > “dialogue manager” or stop light
- attempts to reconnect in case of failure
- protocol data unit (PDU)
Layer 4: name, function, type of data
- 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
Layer 3: name, function, type of data
- 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)
Layer 2: name, function, type of data
- 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
Layer 1: name, function, type of data
- 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
What are the four upper layers? Summarize their collective functions.
- 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
What are the three lower layers? Summarize their collective functions.
- 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
What is a header? Another term for it?
- AKA “overhead”
- bytes
- added at each layer; read at corresponding layer on another node
What is a peer protocol?
Dialogue between same-level entities.
Describe data flow.
- 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
What are the Data Link sublayers?
- Media Access Control (MAC): how devices will share media channel
- Logical Link Control (LLC): how communication between devices are established and maintained
What is the OSI model?
- stacks of layers with protocols and operational functions, repeated on each node
- groups similar functions to self-contained layers that act as interfaces to adjacent layers
- nodes demultiplex messages by passing bits through the layers
Layer 7 examples and protocol examples?
- file transfer, email, printing, application services
- FTP, HTTP, IMAP4, POP3, SMTP, SNMP
Layer 6 examples and protocol examples?
- data de/encryption, compression, translating
- ASCII, JPEG, GIF, MPEG, QuickTime
Layer 5 protocol example?
SIP
Layer 4 protocol examples?
Mobile IP, TCP, UDP
Layer 3 example protocols?
IGRP, IP, IPv6, IPSec, OSPF, RIP, RSVP
What does MAC mean? How is it determined?
- Media Access Control
- determined by Network Interface Card; hardwired by NIC manufacturer
Layer 2 example protocols?
ATM, Ethernet, IEEE 802.2, 802.3, Frame Relay, Token Ring
What structures, specifications, signaling types does Layer 1 include?
- structures: cables, transceivers, connectors, hubs
- electrical, optical, mechanical specifications
- signaling types: broadband, baseband
- also synchronization rules!
What is broadband vs baseband?
- broadband allows multiple simultaneous transmission of indiscrete channels, such as cable television
- baseband is one stream of data through media (such as LAN), and is prevalent in many networks
Which layer sends PDUs?
- Protocol Data Units
- Application (7), Presentation (6), Session (5)
Which layers sends segments?
- Transport (4)
Which layer sends packets?
- Network (3)
Which layer sends frames?
- Data link (2)
Which layer sends bits?
- Physical (1)
What protocols translate between Physical and Data Link layers? (In general)
Ethernet, Token Ring
Layer 1 example protocols?
IEEE 802, SONET
