osi model Flashcards
what layer do frames get fragmented
layer 3 network layer
what does layer 3 work with
ip address, routers, packets
What is OSI Model short for?
Open Systems Interconnect Model
What are the 7 OSI model layers?
Application
Presentation
Session
Transport
Network
Data Link
Physical
What are the upper layers?
Application
Presentation
Session
What are the lower layers?
Transport
Network
Data Link
Physical
What does the OSI Application layer do?
Provides network services to the end host’s applications
makers sure applications can communicate with other applications on different networks
eg - Email, FTP, Telnet
What does the OSI Presentation layer do?
Ensures that data can be understood between two end hosts
reformatting, compressing, encrypting
eg - ASCII character encoding
What does the OSI Session layer do?
Manages sessions between end hosts
control and tunneling protocols happen here
eg - Web server tracking its open connects to web browser clients
What does the OSI Transport layer do?
1) Breaks up data between sender and receiver into smaller parts
2) Establishes end to end connectivity
3) Can ensure reliable delivery (ie - error detection and retransmission)
What is segmentation?
The process used by Layer 4 (Transport layer) to break data between sender and receiver into smaller parts
Name two layer 4 protocols
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol)
What OSI layer do TCP and UDP work at?
Layer 4 (Transport)
What does the OSI Network layer do?
- Provides connectivity and path selection (eg - routing)
- Defines logical addressing (eg - IPv4 and IPv6 addresses)
What layer do IPv4 and IPv6 work at?
Layer 3 - Network layer
What does the OSI Data Link layer do
Defines data format for transmission (eg - Ethernet, Frame Relay, PPP)
- Controls access to physical media (eg - Ethernet CSMA/CD)
- Defines physical addressing (eg - ethernet MAC address)
- Typically has error detection (eg - Cyclical Redundancy Check (CRC))
What are Data Link layer protocols
Ethernet
PPP(Point-to-Point Protocol)
What does the OSI Physical layer do?
sends bits over a wired or wireless connection
- Defines physical media properties
* Electrical Functions
* Physical data rates
* Physical connectors
* Cable distances
* Optical wavelengths
* Wireless frequencies
What layer do Repeaters and Hubs work at?
Layer 1 - Physical
Why use layers?
- Devices need to be aware only of their own layer
- Allows interoperability between devices and vendors
What is encapsulation
adding a header to the data from the layer above
Name the process where data is removed when adjacent layers talk
Decapsulation
What is a PDU?
A Protocol Data Unit - it is the resulting data that a layer creates
What happens during decapsulation?
The process removes data formatting on the receiving host to expose a PDU
What is a PDU at the Transport layer called?
A Segment for tcp and a datagram for udp
What is a packet?
A PDU at layer 3 (Network layer)
What is a frame?
A PDU at layer 2 (Data Link layer)
What is a PDU at layer 1 called?
A Bit
What direction does encapsulation occur?
From layer 7 to layer 1
What is an encapsulation header?
New data added to the front by a layer during encapsulation
What is an encapsulation trailer?
New data added to the end by a layer during encapsulation
Describe the decapsulation process
Data moves up the stack (layer 1 -> 7)
- Each layer removes its own header/trailer
- Data is passed to the layer above
- Process repeats until data reaches the application layer
