Lecture 6

Question 1

What is Deadlock

Answer 1

• 2 processes each waiting for the other to release a resource being held so processes can advance.
• Stuck in a circular wait

Question 2

What is starvation

Answer 2

-Starvation occurs when a process waits for

a resource indefinitely.

Question 3

Deadlock vs Starvation

Answer 3

Deadlock implies starvation, but starvation does not imply deadlock

Question 4

Deadlock can occour on what level

Answer 4

Hardware (like for memory) or software, for sending messages

Question 5

What are the conidtions for deadlock

Answer 5

1. Mutual exclusion
   only one process may use resource at a time
2. Hold and wait
   a process may hold allocated resources while waiting to receive others requested
3. No pre-emption
   no resource may be forcibly taken from a process holding it

Question 6

What is circular wait

Answer 6

a closed chain of processes such that each holds ≥ 1 needed by next process in
chain

Question 7

What can we do to prevent deadlock

Answer 7

1. prevention
2. detection
3. avoidance

Question 8

How can we prevent deadlock?

Answer 8

-Disallow mutual exclusion: so must be one at a time
(but not really feasible)
-Hold and Wait: require a process to request all of its resources before it begins running (effective, but wasteful)
-Pre-emptiom (allow pre-emption): a process requesting resources may be denied and have resources taken away
from it
-OR-
a process already holding resources is denied further requests because another
process is already waiting for [other] resources
(this works, but not really useful for many resources)
-Circular Wait: Assign an ordering to resource types, so requests must be in order
(works, but wasteful)
-Ostrich: Stick you head in the sand and hope for the best (most OSs already do this)

Question 9

OSI Layer 1 needs _____ transfer to occur for the movement of the data.

Answer 9

energy

Question 10

Wire is susceptible to

Answer 10

Noise and degradation

Question 11

What is wire noise?

Answer 11

Since wire is a conductor, any electromagnetic field that moves past it can induce electricity, in the wire. Rise in tempature can indicate this.

Question 12

Two types of signals for transmitting data can be:

Answer 12

analog (continuous valued) or digital

Question 13

Copper wire benifit?

Answer 13

Short distances, inexpensive, but always has thermal noise

Question 14

Any signal on wire is subject to:

Answer 14

Attenuation with distance and noise

Question 15

What do signal amplifers do?

Answer 15

Take a weakened signal and repeat to increase distance, both analog and digital

Question 16

The problem of moving data in the real world gets works as you look at the slopes of data transmission and you end up with significant signal _______

Answer 16

degradation

Question 17

Data on a channel can be shared by multiple data streams though ______

Answer 17

multiplexing

Question 18

What are the 5 ways that we can multiplex:

Answer 18

• Frequency Division (FDM) - like radio spectrum within a cable; not good environment for data due to noise from “baseband loading”
• Time Division (TDM) - interleaves bits from slower data streams onto a single, faster data stream
• Statistical (STDM) - takes advantage of idle time on links to get more streams into TDM- not good for data because there may not be any idle time
• Time Division Multiple Access (TDMA) - used with radio and satellite; transmitters take turns sending in closely spaced slots- generally wasteful of spectrum
• Wavelength Division (WDM) - sends multiple wavelengths of light through the same fiber (over 100 wavelengths currently)

Question 19

What are the different types of copper wires avaiable for data transmission

Answer 19

• Network cable (twisted pair is most common)
• Coax
• power (noisy)

Question 20

What are the differences between lower wave-lengths and higher wave-lengths

Answer 20

Lower (higher frequency): bounce off the atmosphere

Higher (lower frequency): go straight, like microwave, and some repeaters like satallites