Quiz 1 - OSI Layer, Cabling, & Topology (Ch. 1-3)

Question 1

What is the best mnemonic for remembering the layers of the OSI model?

Answer 1

• *A**
• *P**ussy
• *S**o
• *T**ight
• *N**o
• *D**ick
• *P**enetrates

Question 2

OSI Model layers and functions

Answer 2

• Application (7) – APIs: Tools / APIs to access network
• Presentation (6) – data conversion: Presents understandable data
• Session (5) – tracking/naming: Manages comms between systems
• Transport (4) – assembly/disassembly: Data transfer to upper layers
• Network (3) – router: Host to host transfer on different networks
• Data Link (2) – NIC: Defines rules for accessing/using media
• Physical (1) – cabling/hubs: Method of moving data

Question 3

Functions of the Network Interface Card

Answer 3

• Serves as an interface between the PC and the network
• Functions span both MAC & LLC sublayers
  
  • On one end frames move into and out of the NIC’s network cable connection
  • On the other end, data moves back and forth between the NIC and the network operating system software

Question 4

Format and function of MAC addresses

Answer 4

• A unique identifier burned into a ROM chip on the NIC by the manufacturer
• Also called Physical address
• No two MAC addresses are ever the same o 48 bits in length
• Represented using 12 hexadecimal characters
  
  • First six digits identifies the manufacturer of the NIC
  • Last six digits are the manufacturer’s unique serial number for that NIC
• Example: 00-40-05-60-7D-49

Question 5

Key characteristics of each network topology

Answer 5

• Bus
  
  • A bus is a single electrical cable
  • Termination required at ends to prevent data reflection
• Ring
  
  • Unidirectional—messages travel around the ring in only one direction
• Star
  
  • central signal-distributing device
• Mesh
  
  • Many links directly connect two nodes
  • Links may be shared by many nodes
• Hierarchical (Tree)
  
  • Each node is connected only to its immediate neighbor
  • Nodes at the top rank higher in order than those at the bottom
• Hybrid
  
  • Different topologies combined

Question 6

How can the same physical topology be logically different?

Answer 6

• A physical star can be a logical bus using a hub
• A physical star can be a logical mesh (full) using a switch

Question 7

UTP—Unshielded Twisted Pair

Answer 7

• By far the most common type of network cabling
• Widely used for telephone connections and Ethernet LANs

Question 8

STP—Shielded Twisted Pair

Answer 8

• Pretty rare
• Wire mesh or foil wrapped around twisted pair
• Added conductive shielding reduces EMI
• Used in locations with excessive electronic noise
• More expensive than UTP

Question 9

Coaxial

Answer 9

• central conductor wire surrounded by an insulating material, which is surrounded by a braided metal shield
• center wire and the braided metal shield share a common axis
• outer mesh layer shields the center wire from EMI
• Primarily used for connecting cable modems to ISP

Question 10

Coaxial vs Twisted pair cables

Answer 10

• Advantages of coaxial over twisted pair
  
  • Much greater capacity
  • Relatively immune from external interference
• Disadvantages of coaxial over twisted pair
  
  • More expensive
  • Bulkier
  • Difficulty to modify
  • Difficult to install around sharp bends

Question 11

Fiber-optic

Answer 11

• Good for high-EMI areas—not affected by EMI
• Good for long distance transmissions—very low attenuation
• Light emitting diodes (LEDs)
  
  • Used by most network technologies
  • Usually 850 nm wavelength
  • Referred to as multi-mode fiber
  • Uses thick core
  • Distance is limited by modal distortion
• Lasers
  
  • Usually 1310 or 1550 nm wavelength
  • Referred to as single-mode fiber
  • Uses very thin core
  • Prevents modal distortion
  • Enables phenomenally high transfer rates over incredibly long distances