Chapter 2: Concepts Flashcards
Generally describe OSI Reference Model
The bottom layers perform physical functions. The middle layers coordinate network communications between nodes. The top layers perform work that directly affects software applications and data presentation.
What are the seven layers of the OSI Reference Model?
Physical Layer (Layer 1), Data Link layer (Layer 2), Network Layer (Layer 3), Transport layer (Layer 4), Session layer (Layer 5), Presentation layer (Layer 6), Application layer (Layer 7)
What are the Physical Layer functions?
- Provides transfer medium (eg, cable)
- Translates data into a transmission signal
- Sends signal along the transfer medium
- Includes physical layout of network
- Monitors for transmission errors
- Determines voltage levels for data signal transmissions and to synchronize transmissions
- Determines signal type (eg, digital or analog)
What are the Data Link layer functions?
- Constructs data frames
- Creates CRC information; checks for errors
- Retransmits data if there is an error
- Initiates communications link; makes sure it is not interrupted (ensures node-to-node physical reliability)
- Examines device addresses
- Acknowledges receipt of a frame
- Data link frame contains fields consisting of address and control information
- Two important sublayers
- Logical link control (LLC)
- Media access control (MAC)
- Connectionless service versus connection-oriented service
What are the Network layer functions?
- Determines network path for routing packets
- Helps reduce network congestion
- Establishes virtual circuits
- Routes packets to other networks, resequencing packet transmissions when needed
- Translates between protocols
What are the Transport layer functions?
- Ensures reliability of packet transmissions
- Ensures data is sent and received in the same order
- Sends acknowledgement when packet is received
- Monitors for packet transmission errors and resends bad packets
- Breaks large data units into smaller ones and reconstructs them at the receiving end for networks using different protocols
What are the Session layer functions?
- Establishes and maintains communications link
- Determines which node transmits at any point in time
- Disconnects when communication session is over
- Translates node addresses
What are the Presentation layer functions?
- Translates data to a format the receiving node understands (eg, from EBCDIC to ASCII)
- Performs data encryption
- Performs data compression
What are the Application layer functions?
- Enables sharing remote drivers and printers
- Handles e-mail messages
- Provides file transfer services
- Provides file management services
- Provides terminal emulation services
What are the advantages of bus topology?
- Works well for small networks
- Relatively inexpensive to implement
- Easy to add to it
What are the disadvantages of bus topology?
- Management costs can be high
- Potential for congestion with network traffic
What are the advantages of ring topology?
- Easier to manage; easier to locate a defective node or cable problem
- Well-suited for transmitting signals over long distances on a LAN
- Handles high-volume network traffic
- Enables reliable communication
What are the disadvantages of ring topology?
- Expensive
- Requires more cable and network equipment at the start
- Not used as widely as bus topology
- Fewer equipment options
- Fewer options for expansion to high-speed communication
What are the advantages of star topology?
- Good option for modern networks
- Low startup costs
- Easy to manage
- Offers opportunities for expansion
- Most popular topology in use; wide variety of equipment available
What are the disadvantages of star topology?
- Hub is a single point of failure
- Requires more cable than the bus
