3 - OSI + TCP/IP Model

Question 1

OSI Model

Answer 1

• 7 layers
• Each layer servers the layer above
• When a packet is sent, it starts at layer 7 and works it’s way down

Question 2

OSI Layers

Answer 2

7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Data Link
1 - Physical

Question 3

OSI v TCP/IP

Answer 3

Application —
Presentation —> Application
Session —

Transport —> Transport

Network —> Internet

Data Link —> Network Access
Physical —>

Question 4

PDU

Answer 4

Protocol Data Unit

• A PDU is the entire communication from layer 7 to layer 1
• They are what’s exchanged in transfer
• PDU is correct terminology but everyday slang is packet

Question 5

TCP/IP Terminology

Answer 5

• Application layer = Data
• Transport layer = Segment
• Internet = Packet
• Network Access = Frame

Question 6

OSI Layers

Answer 6

7 to 5 don’t overly concern network engineers

Question 7

OSI Layer 7

Answer 7

Application

- Provides network services to the applications of the user

Question 8

OSI Layer 6

Answer 8

Presentation

• Ensures the data sent by the application layer is readable by the application layer of another host
• It can translate between multiple formats using a common format

Question 9

OSI Layer 5

Answer 9

Session

• Establishes, maintains and terminates sessions between 2 hosts
• Manages data exchange between presentation layers

Question 10

OSI Layer 4

Answer 10

Transport

• Main characteristics are whether TCP or UDP is used and port numbers
• Provides segmentation services which breaks down large amounts of data into smaller, more manageable sized segments
• Smaller segments means they are less likely to incur transmission errors

Question 11

OSI Layer 3

Answer 11

Network

• Manages the connectivity of hosts by providing logical addressing
• Logical Addresses = IP Addresses
• Provides path selection between hosts too
• Routers operate on layer 3

Question 12

OSI Layer 2

Answer 12

Data Link

• Provides physical addressing = MAC Addresses
• Defines how the data is formatted for transmission and how access to physcial media is controlled
• Typically includes error detection + correction

Question 13

OSI Layer 1

Answer 13

Physical

• Concerns the physical components of the network ie cables
• Defines specifications needed for activating, maintaing and deactivating physical links
• E.g. voltage levels, max transmission distances, physical connectors