1. What is the difference between the bit rate
and the baud rate?
Answer - Each
line change transmits two bits. So if the baud rate is 1,000
baud in other words, if
the line state changes 1,000 times per second then the
bit rate will be 2,000 bps.
So in this the bit rate will be twice the baud rate.
Although the bit rate is
faster than the baud rate in this case, it is slower under
certain conditions.
2. Define digital transmission. Define analog
transmission. What is the
difference between digital and binary?
Answer - Digital
transmission : time is devided into periods of fixed length; the
line iskept in one of only
a few possible states (condition) during each time
period; at the end of each
time period; it may change abruptly to another of
these states.
- Analog transmission : the state of line can vary continuously and smoothly
among an infinite number
of state.
- Binary transmission is a special case of digital transmission. Binary
transmission is allways
digital, but not all digital transmission is binary.
3. Explain the main propagation effects.
Answer - Propagation
effects can make it difficult or impossible for receiver to
identify the line state
represented by the disturbance. All propagation effects
have the same impact. They
make the received singnal (disturbance) different
form the transmitted singnal.
4. What are the three main wire transmission media?
Which is used most
frequently to the desktop? Why? Which is used
most frequently over longer
distances? Why?
Answer - Wire
transmission media มี 3 ชนิด คือ
1.Unshielded Twisted Pair
(UTP)
2.Optical Fiber
3.Coaxial Cable
- UTP is normally used for the final run to the desktop. Because desktop
runs
offten have to line on the
floor, optical fiber links would break constantly.
- Optical Fiber is over a long enough disstance, different rays will travel
different disstances . Because
they will be internal reflected a different number
of times.
5. As bandwidth increases in a channel, how does
maximum transmission
speed though that channel change? What does broadband
mean literally? How
is the term broadband commonly used?
Answer - The second
factor limiting the maximum transmission speed is the
bandwidth. The more bandwidth
the channel has, the faster you can send information.
- Broadband is synonymous with high speeds.
- There is a growing tendency to refer to all high- speed system as "
broadband" singnals.
6. In PC serial ports, how many pins are used
for data transmission? In
general, what are other pins for?
Answer - many
PC serial plugs have 9 pins, aithough they standard calls for 25 pins.
- Pin 5 is an electrical ground, providing the second pin for DTE-to-DCE-
transmission.โดยที่ DTE
is the data terminal equipment (the PC's serial port)
DCE is the data circuit
terminating equipment (the modem)
7. Define modulation. Define demodulation. Do
not just say translation
between digital and analog or analog and digital.
For both modulation and
demodulation, characterize whether the transmission
line is analog or digital
and whether the device attached to the transmission
line is analog or digital.
Answer - Modulation
คือ การแปลงสัญญานจาก digital(ความถี่) ให้เป็น analog(คลื่น)
- Demodulation คือ การแปลงสัญญานจาก analog(คลื่น) ให้เป็น digital(ความถี่)
8. Which modem form is easier to install-internal
or external? What is the
advantage of internal modems over external modems?
What is the most
expensive modem form?
Answer - External
modems are easy to install.
- ข้อดีของ internal modems ที่ดีกว่าของ external modems คือ
สะดวกไม่ต้องมาเชื่อมต่อสายอะไรอีก
และราคาถูกกว่า
- External modems is the most expensive.
9.What is the speed of a V. 34 modem? What are
the speeds of a V. 90
modem? Be specific.
Answer - V. 34
modem มีความเร็ว 33.6 kbps
- V. 90 modem มีความเร็ว 56 kbps receiving และ 33.6 kbps sending
10. What is "training" in initial modem communication
If a V. 34 modem tries to
communicate with a 14.4 kbps V. 32 bis modem,
what will happen?
Answer - โมเด็มที่ใช้ในการติดต่อในช่วงแรก
คือ V. 34 modem และ V. 32 bis modem
- your modem will compress the data down to 14.4 kbps for transmission
over
the telephone network
11. What is the maximum reception speed for V.90
modems? What is the
maximum transmission speed? To use a V. 90 modem,
can you use your
ordinary home telephone line, or do you need
an additional line?
Answer - ความเร็วสูงสุดของ
V.90 เท่ากับ 56 Kbps
- Maximum transmision speed คือ ความเร็วสูงสุดในการส่งข้อมูล
12. Distinguish between full-duplex and half-duplex
transmission in terms of
who can communicate simultaneously. What is flow
control, and why does
full-duplex transmission allow it? What is error
correction, and why does
full-duplex transmission allow it?
Answer - ข้อแตกต่างระหว่าง
full-duplex และ half-duplex คือ full-duplex สามารถส่งข้อมูลกลับได้ทันที่
( สามารถสวนทางกันได้ ) ส่วน
half-duplex จะสามารถส่งข้อมูลกลับได้เมื่อผู้ส่งมาส่งเสร็จก่อน
- flow control that is asking the other side to slow down or pause because
it is
sending too quickly for
the receiver to process the information
- error correction in which the receiver asks the sender to retransmit
incorrect information
13. Daistinguish between serial and parallel transmission
in terms of bit rate
for a given clock cycle (and baud rate).
Answer - Parallel
transmission uses several wires to Send information in one direction.
If there are eight wires,
a parallel system can send eight bits perclock cycle.
This obviously moves information
faster than one bit per clockcycle - eight time faster.
Parallel transmission is
always faster than serial transmission , given comparable clock cycles.
14. In ISDN, what is 2B+D? What is the maximum
reception speed for ISDN?
What is the maximum transmission speed? To use
ISDN, can you use your
ordinary home telephone line, or do you need
an additional line?
Answer - ใน ISDN
, 2B+D คือ The ISDN line coming Into your home multiplexes ( mixes)
three
Distinct data channels onto
the single pair of UTP wire running from your home to the
First switching office .
Two of these are 64 Kbps "B" channels , and one is a 16 Kbps
"D" channel. For this reason,
the service that ISDN brings to the desktop is called 2B + D
- ISDN modems allow you to transmit and Recive data at 128 Kbps without
a
telephone connection.
- This allow you to talk on the telephone while simultaneously transmittingand
receiving computer data
at 64 Kbps.
- เมื่อใช้ ISDN จะต้องใช้ ISDN Modem เท่านั้นด้วย จะใช้ Modem ทั่วไปไม่ได้
15. What is multiplexing? How does it apply to
ISDN?
Answer - Multiplexing
คือ การส่งข้อมูลผ่าน 3 Multiplexed channels on One Pair or Telephone wires
( 2B +D)
และเป็น ALL-digital Service.
- In addition, as in the case of 56 Kbps V.90 medem.ISPs usually charge
more
if you use ISDN connection,
because you place a heavier load on their router
and transmission link to
the internets.
16. What type of organization offers cable modems?
What type of organization
of fer digital subscriber lines (DSLs)? How do
cable modems and DSLs
compare to 56 kbps V. 90 modems in terms of speed
and cost?
Answer - Cable
modems offer speeds of up to 10 Mbps.
- DSLs offer transmission speeds of 384 Kbps to several megabit per second.
- DSLs เร็วกว่า Cable modem และ Cable modem แพงกว่า DSLs
17. When you use an alternative to ordinary modem
transmission, what four
daaitional costs do you incur?
Answer - For this
reason, some home users of the Internet are turning to higher-speed connection
devices.
- ทำให้เกิดค่าใช้จ่ายมีดังนี้
1. the devices are more
expensive than modem.
2. the telephone company
will change more for monthly transmission service to
connect
you to the ISP.
3. Internet service provider
will change more because you are placing a heavier load on the ISP's
network.
18. If you have a digital device communicating
over an analog transmission
line, what type of translation device do you
need, if any? If you have an analog
device communicating over a digital transmission
line, what type of translation
device do you need, if any? If you have a digital
device communicating over a
digital transmission line, what type of translation
device do you need, if any?
Answer - digital
device communicating over an analog transmission line need a translation
device called a
modem.
- analog device communicating over a digital transmission line need a translation
device called a
codec.
- digital device communicating over a digital transmission line need a
translation device called a
data service unit (DSU).
