56k modem advantages and disadvantages

Introduction

Analog to digital and digital to analog conversions are processes that are transparent to the naked eyed but is complex in nature and require careful conversions. There are distinct advantages to both and their uses depend on the task at hand. Both are still in use today with digital being more prevalent because of large amounts of data that it can easily transmit over great distances. Both of these two communication mediums are not going away anytime soon and each has a place in today’s networking community.

Analog-to-digital and digital-to-analog conversions in telecommunications

Analog signal is one that increases or decreases in nature due to the fluctuations of the item being transmitted. This can be compared to the highs and lows of a radio signal in which the analog signal will rise and drop based on the radio signal being transmitted. Analog to digital conversion happens all of the time in telecommunications. For example an analog phone call made from home is converted to a digital signal at the main office switch. This conversion happens again when you scan a photo with a scanner by converting the image into digital information.

Digital to analog conversion occurs when a Digital to Analog Converter known as a (DAC) converts digital data into an analog signal (Goleniewski, 2007). This is heard when listening to a CD; the digital data on the CD is converted in to analog signal thus producing the music. Digital to analog conversion does occur but the use of digital signal far exceeds the use of analog for multiple reasons. Digital is preferred over analog because it uses less power, use of encryption can, discrete signal, and high bandwidth capabilities just to name a few.

Advantages and disadvantages of amplitude modulation, frequency modulation, phase modulation, and Quadrature Amplitude Modulation (QAM)

Amplitude and frequency modulation both use electromagnetic waves to transmit information. Amplitude modulation (AM) varies the amplitude wave based on the data being sent with frequency remaining unchanged. Frequency modulation (FM) happens by encoding sound by varying frequency of wave with amplitude remaining the same. Its advantages are it is resistant to noise, resilient to fluctuations in signal strength, and does not need a linear amplifier.

Phase modulation happens when a carrier signal is varied to match the phase of modulated signal keeping the frequency unchanged. The phase shift will depend on amplitude or modulation of the signal used. It advantage is there is less static interference than in frequency modulation. Its disadvantages are there is data loss, high degree of phase ambiguity, and specialized equipment needed.

Quadrature Amplitude Modulation (QAM) is both analog and digital in nature. Two analog and digital signals are modulated out of phase by 90 degrees using amplitude shift-keying modulation. Advantages of QAM are it allows for multiple signals to be sent over the same channel simultaneously and it can be used with analog and digital formats. Its disadvantages are that it has distortion, attenuation, channel interference.

Applications of Modern Modulation Techniques

With advancement in technology, modulation techniques continue to gain popularity while at the same time improving through optimization. Though we can trace several years back when we talk about the use of current networking technologies, each year has never failed to realize a new advancement. Each year has been marked by an improved modulation technique. Below, we are going to shift our focus on significant advancements in modulation.

V.90 (56K modem)

Dial-up connections have been one of the major milestones as far as information technology is concerned today. The creation of 56K or V.90 modem marked the peak of information technology. Even a decade down the line, 56K modem has not lost its popularity and is still being used today. 56K modem uses simple PAM with 8000 symbols per second with each symbol being coded from seven bits of each eight bit PCM word (Gao, 1998). The resultant signal is of amplitude 128. Upstream 56K modems are usually limited to earlier V.34 modulation version and can only manage 33.8 Kbps.

ADSL

Asymmetric Digital Subscriber Lines, abbreviated as ADSL, marked a mega forward step in internet user connectivity (Alturayef, 2007). The best thing about ADSL is that it made use of the already in use twisted pair telephone lines, whereby at the time a greater percentage of American homes were using it (Alturayef, 2007). Dial-up to DSL advancement was made possible through the combination of several modulation techniques. A form of QAM (Quadrature Amplitude Modulation) that was developed by AT&T, Carrierless Amplitude Phase (CAP), was used utilized during early ADSL implementations. However, due to advancements in technology, it has been replaced by DMT or Discrete Multi-tone Modulation. Currently, DMT is the universally standardized and most prevalent ADSL method.

DMT splits the available bandwidth into several sub-channels. Each single sub-channel uses QAM modulation on a separate carrier in order to maximize throughput. In ADSL, DMT divides the downstream bandwidth into 4.3125 kHz wide channels while the upstream channels re divided into 32 4.3125 kHz channels (Alturayef & Rodriguez, 2007). This results in 8.1 Mbps downstream and a 1.5 Mbps upstream throughput. In order for them to coexist with POTS, reservation of the first six channels is made specifically for voice so that ADSL and POTS can function simultaneously.

Wi-Fi (802.11[x])

Wi-Fi has been a revelation in modern connectivity and many people are still working hard to build upon. Modulation has played a vital role in Wi-Fi development from its initial throughput of 1-2 Mbps to the current 504 Mbps. The first Wi-Fi standard that was widely adopted was 802.11b operating in 2.4GHz-spectrum. In order to reach its maximum speed of 11Mbs, 802.11b made use of Direct Spread Spectrum Sequencing (DSSS) (Bhatia, 2007).

802.11a introduced a new modulation technique, the Orthogonal Frequency Division Multiplexing (OFDM). 802.11g made use of OFDM, bringing it to the 2.4 GHz spectrum with backward compatibility offered with 802.11b. 802.11g is similar to 802.11a in that it transmits a four microsecond symbol an 800 nanosecond interval (Cisco, 2011).

As mentioned earlier, OFDM carries into the latest 802.11 standard 802.11n, and it is still being pushed to greater limits. With a 5/6 rate encoder and multiple carriers per channel, 802.11n raised the data rate to 65Mbps over a single transmission. 802.11n manages to do this with the use of the same 20MHz wide channels similar to 802.11a and 802.11g. Since it is in a position to transmit up to four channels, the maximum throughput it can achieve with the same 20MHz channels is 260MHz. Furthermore, 802.11n standard also introduced 40MHz channels with up to 108 subcarriers. This brings the maximum data rate of all the four available channels to an incredible 540Mbps.

Hierarchy of T(X) and SONET

SONET (Synchronous Optical Networking) is a standardized multiplexing protocol used in the transfer of multiple digital bit streams over coherent light from light-emitting diodes or optical fiber lasers (Pal, 2013). Less transmission rates are required in this mode of transmission. SONET equipment is usually under the management of TL1 protocol, which is a telecom language specifically used for managing as well as reconfiguring any SONET network element. SONET has quite a number of advantages, and they include:

· Provision of high-capacity fiber optic transport

· Defining a system of synchronous signal level

· It supports automatic switching for protection

· It offers reliability and fault tolerance

· Lower network costs

Among the disadvantages of SONET are:

· It is not suitable for everyday network at home

· It requires use of strict schemes during synchronization

· Its costly and complex equipment makes SONET financially demanding

T(X) is another name for T-1 or T-3 data lines and so on. These lines make use of digital transmission in order to transfer digital data from point to point or even point to multipoint communication channel. These lines can use optical fiber, copper wire or wireless to facilitate communication. In order for transmission to be achieved, data information forms such as voice; image or text is converted into binary code, characterized by a combination of zeros and ones. Upon reaching the receiver end, the code is changed again into its original format. For instance University of Phoenix spelled in binary code would look like the following:

· 010101010110111001101001011101100110010101110010011100110110100101110100011110010010000001101111011001100010000001010000011010000110111101100101011011100110100101111000

There are quite a number of advantages of using these lines:

· The T-3 has the ability to transport a large amount of data

· According to Theodorou (2008), the T3 internet line has up to 672 separate channels that allows up to 672 people to browse the net at the same time without compromising on speed

· T-3 can provide high connection speeds rising as high as 44.6 mbps

However, there are a few disadvantages associated with them:

· T3 bandwidth is very expensive and can cost up to $15,000/month (Johnson, 2011)

· T1 line can cost as much as $1,000/month hence not suitable for home network

· In order to add either a T1 or T3 line to your home or business, physical installation of the line will have to be done

The fact about these types of data communication lines is that they are not suitable for home network. Installation cost can surge beyond ones financial ability and only large companies are in a very good position of financing them.

References

Alturayef, M., Rodriguez, D.(2007).ADSL Technology, Retrieved January 13, 2012 from http://ecee.colorado.edu/~ecen4242/adsl/adsltechnology.htm

Bhatia, A (2007) 802.11 Retrieved January 13th, from http://it.toolbox.com/wiki/index.php/802.11

Gao, F (1998) An Introduction to the V.90 (56K) Modem . January 13, 2012 from http://www.eetimes.com/design/communications-design/4018048/An-Introduction-to-the-V-90-56K-Modem

Goleniewski, L. (2007). Telecommunications Essentials: The Complete Global Source, Second Edition. Upper Saddle River, NJ: Pearson Education, Inc.

Johnson, J. (2011, July 11). What is t3 bandwidth?Retrieved January 13, 2012 from

http://www.ehow.com/info_8720239_t3-bandwidth.html

Theodorou, V. (2008, April 30). T3 internet. Retrieved January 13, 2012 from

http://www.squidoo.com/t3-internet