Assignment 2 Solution

1. How much disk space is taken by a minute-long uncompressed digital stereo audio file sampled at 11 KHz, 16 bits per sample? [2] 
   • 60 seconds x 11,000 samples/second x 2 bytes/sample x 2 stereo channels = 2.64 megabytes
2. What do Manchester and Differential Manchester encoding have in common? Why do they not just use a high voltage for 1 and a low voltage for 0? [2]
   • They both combine the clock signal with the data signal before sending.
   • It would be difficult to determine the boundaries between bits, especially for a long string of 1s or 0s. 
3. What are both 4 bit/5 bit and 5 bit/6 bit encoding designed to prevent? [1] 
   • a long string of 1s or 0s transmitted within the data portion (which could be confused with the start or end of the message)
4. Give three differences between baseband and broadband communication. [3]
   1. Baseband uses the entire communication channel for one signal.
      • Baseband transmits faster than broadband.
      • Broadband divides the channel into bands for sending multiple signals at a time.
      • Broadband wastes some of the bandwidth on separating the bands.
   2. Baseband is usually bi-directional; broadband is usually uni-directional.
   3. Baseband is digital; broadband is analog. 
5. Give two advantages of conducted media and two advantages of radiated media. [4]
   1. Conducted media is more secure, radiated media can be received by anyone with a receiver.
   2. Conducted media generally provides higher speed.
   3. Radiated media does not require a physical connection and is better for long distances and mobile transmission.
   4. Radiated media can be broadcast to a virtually unlimited number of recipients.
6. What is the physical difference among the different types of radiated signals? Which types of radiation tend to have the highest transmission speeds? [2]
   • Radiated signals are all forms of electromagnetic radiation. They differ in their frequencies (and energies).
   • The higher the frequency, the higher the transmission speeds.
7. What is a hot swappable component? What types of server components are most likely to be hot swappable? [3]
   • A hot swappable component can be removed while the computer is running.
   • Disks and power supplies are often hot swappable.
8. What are three specific features you should look for when buying a network card? [3]
   1. speed (e.g. 10 or 100 Mbps)
   2. connectors (RJ-45, BNC, etc.)
   3. bus (PCI or ISA)
9. List three components or devices that are particularly important to the reliability of a server and therefore the network. [3]
   1. power supplies and protection, including surge protector and UPS (uninterruptible power supply)
   2. disks
   3. backup devices and systems
10. What are the meanings of the three parts of the names of popular LAN standards such as 10baseT and 1000baseSX? [3]
    1. The first number is the speed of the standard in Mbits per second.
    2. The middle word is the type of transmission, e.g. baseband or broadband.
    3. The last letters are the media type, e.g. twisted pair or fibre optic cable.
11. If NICs using p-persistent CSMA may transmit every 20 microseconds with probability 0.2, what is the average wait before transmitting? [1]
    • average delay = (1-p)/p slot times = (1 - 0.2)/0.2 * 20 microseconds = 80 microseconds
12. In CSMA/CD binary exponential backoff,
    If a collision is detected, the NIC will wait 0 to 1 slot times before transmitting.
    If another collision occurs, the NIC will wait 0 to 3 slot times.
    If a third collision occurs, how long will the NIC wait? [1]
    • wait time = 0 to 2ⁿ-1 slot times = 0 to 2³-1 slot times = 0 to 7 slot times
13. If collision detection requires listening and re-transmission, why is it used more often than collision avoidance? [2]
    • Collision avoidance does not perform as well because it requires a delay before sending.
    • If the system is not heavily loaded, collision detection will not incur any delay most of the time.
14. What type of media access should be used for a small network with low performance requirements? [1]
    • Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
15. Why does a token bus have more complex token-passing algorithms than a token ring? [1]
    • Stations must be sequenced by their addresses and know the address of the previous and next machine.
16. What is the purpose of a MAC address? [1]
    • A MAC address uniquely identifies a network card on a network.
17. Why must IEEE 803.2 frames be at least 64 bytes? [1]
    • If the frame is too small, it might be received before a collision could be detected.
18. What part of the network software allows you to read or write to a file on the network as if it were on the local PC? [1]
    • redirector (Microsoft) or network shell
19. Give an advantage of disk mirroring over RAID and two advantages of RAID over mirroring. [3]
    1. Disk mirroring is more reliable because it is a complete copy of the disk.
    2. RAID is less expensive because only one disk is needed to back up several disks.
    3. RAID performs better because only parity information must be stored.
20. A system has full backups every week at the end of the day on Sunday.
    At the end of each of the remaining six days, the system has a differential or incremental backup.
    If a user discovers her file missing on Friday, at most how many backups would need to be consulted to find the file
    1. if differential backups were used?
    2. if incremental backups were used? [2]
       1. For differential backups you would need only two backups: Sunday's and Thursday's.
       2. For incremental backups you would need five: Sunday's through Thursday's.
21. What type of software licence would be best to buy for
    1. an infrequently used software package to be installed on 100 computers?
    2. a heavily used software package in a large building with a variable number of computers? [2]
       1. restricted number of concurrent users
       2. unlimited use at one site
22. Name the database of network objects used in
    1. Novell NetWare 3.x
    2. Novell NetWare 4.x
    3. Windows 2000 [3]
       1. Bindery
       2. Novell Directory Services
       3. Active Directory
23. Which networking protocol is built in and used by default in
    1. Novell NetWare?
    2. Windows 9x/NT?
    3. UNIX? [3]
       1. SPX/IPX
       2. NetBEUI
       3. TCP/IP
24. List two ways that users and computers are grouped in Windows. [2]
    1. workgroups
    2. domains