homework

นส. สุภาวดี ปัทมาวิไล 400323
นส. ศิริวรรณ ระย้าทอง 400483

1. What is the difference between the bit rate and the baud rate?

Bit rate measures the rate at which we send actual information whicyh usually is encoded as ones or zeroes.

Baud rate is the number of times per second the state of the transmission line changes.

2. Define digital transmission. Define analog transmission. What is the difference between digital and binary?

Digital transmission time is devided into periods of fixed length; the line is kept in one of only a few possible states (conditions) during each time period; at the end of each time period, it may change abrubtly to another of these states.

Analog transmission the state of line can vary continuously and smoothly among an infinite number of states.

The differrent between Digital and Binary transmission is that binary transmission is always digital, but not all digital transmission is binary, because each bit period can be only a zero or a one for binary transmission but 10 state from 0 through 9 was the original meaning of the term digital.

3. Explain the main propagation effects.

Propagation Effect that change the signal as it travels down the medium. Propagation effects can make it difficult or impossible for the receiver to identify the line state represented by the disturbance. All propagation efffects make the received signal different from the transmitted signal.

4. What are the three main wire transmission media? Which is the used most frequently to the desktop? Why? Which is used most frequently over longer distances? Why?

1. Unshielded Twisted Pair (UTP) this one is used most frequently to the desktop. Because it is less expensive than optical fiber and easier to connect. UTP is more durable.

2. Optical Fiber

3. Coaxial Cable

5. As bandwidth increases in a channel, how does maximum transmission speed through that channel change? What does broadband mean literally? How is the term broadband commonly used?

The bandwidth masimum transmission speed through the channel is about 35 kHz.

Broadband is with UTP and optical fiber, we inject the signal directly into the medium. In effect, this means that we have a single channel. When channels are used, this is called broadband transmission.

In commonly use, broadband is synonymous with high speeds. Although it is not correct technically, there is a growing tendency to refer to all high-speed systems as broadband signals, even when baseband transmission is being used.

6. In PC serial ports, how many pins are used for data transmission? In general, what are other pins for?

There are 9 pins and 25 pins. 2 pins are using to send data and another pins are using for signals.

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.

Modulation - converting a digital source signal into an analog transmitted signal.

Demodulation - converting the transmitted signal back to a digital source signal

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?

External Modem is easier to install. But Internal Modem is less expensive. And the most expensive modem form is PC card modem.

9. What is the speed of a V.34 modem? What are the speeds of a V.90 modem? Be specific.

The specific speed of V.34 modem is allowed at a 33.6 kbps. And the speed of V.90 modem is 35 kbps.

10. What is "training" in initial modem communication? If a V.42 modem tries to communicate with a 14.4 kbps V.32 bis modem, what will happen?

Training is which the two modem exchange messages to learn what the other modem can do. If modem V.42 and V.34 try to communicate it will be a problem during the training period. The modem that can do compression automatically agrees not to compress its data before transmission.

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?

V.90 modem can receive data at the highest speed of 56 kbps. And we can use the ordinary telephone line to use V.90 modem. No need to add anything.

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?

Half-duplex, both sides share a single channel. Only one side can transmit at a time.

Full-duplex, transmission requires two channels, one in each direction. But doesn't mean that both sides always are transmitting at the same time, only that they can transmitat the same time. Only Full-duplex can communicate simultaneously.

Flow control is to asking the other side to slow down or pause because it is sending too quickly for the receiver to process the information. It also allows error correction, in which the receiver asks the sender to retransmit incorrect information.

13. Distinguish between serial and parallel transmission in terms of bit rate for a given clock cycle (and baud rate).

Serial transmission sends information in each direction one bit at a time, along a single wire. n each clock cycle, one bit is sent along the wire in each direction.

Parallel transmission uses several wireds to send information in one direction. If there are eight wires, a parallel system can send eight bits per clock cycle.

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?

2B means that the modem has 2 "B" channel that can connect to other 2 machines. And a "D" is for a signal controller. The highest transmit speed of ISDN modem is at a 64 kbps, and the highest reception speed is at 128 kbps. But we can't use the ordinary home telephone line with ISDN modem. We have to add something more.

15. What is multiplexing? How does it apply to ISDN?

16. What type of organization offers cable modems? What type of organization offers digital subscriber lines (DSLs)? How do cable modems and DSLs compare to 56 kbps V.90 modems in terms of speed and cost?

The cable television companies are beginning to offer data transmission services at DSL speeds but you need a cable modem.

The telephone companies are beginning to offer an even faster serveice, the Digital Subscriber Line(DSL). Compare to the 56 kbps V.90 modem, cable modem and DSL give a higher speed but higher cost also.

17. When you use and alternative to ordinary modem transmission, what four additional costs do you incur?

1. You must have a translation device between your PC (and possibly your telephone line) and the transmission line.

2. You must pay the carrier for the transmission line. You cannot use your ordinary telephone line, so this is an incremental cost.

3. Your ISP probably will charge you more because your higher download speeds (and perhaps upload speed) will require more ISP resources.

4. YOu will need a port faster than a serial port.

18. If you have a digital device communication over an analog transmission line, what type of translation device do you need, if any? If you have and 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?