Analog and Digital Comparison
Learning Team D:
Juan C. Godinez, Luke Wade,
Jonathan Selinksi
NCT/362
March 16th, 2015
Richard Bohn

Analog and Digital Comparison
Data, media, networking and transfer technology has evolved immensely throughout the years. When it comes to transmissions, two prerequisites must be satisfied to have successful communication. The first prerequisite is understandability. The transmitter and receiver must speak the same language. The second prerequisite is the capability to detect errors as they occur and to have some procedure for resolving those errors. (Goleniewski, L., 2007). Picture this similar to the different languages people can speak all over the world. Without proper translation and understanding, the conversation is pointless; this analogy is similar for analog and digital transmissions.
Beginning with an analog signal, which is a continuous variable along amplitude and frequency. Analog circuits need to have a defined frequency band in which it operates. Different modulation schemes can vary the speed in which they operate, the quality of wire they require, the immunity to noise, and their overall complexity. The variety of modulation schemes in existence can be a disadvantage as this means many incompatibilities can exist within a single application. Such modulations include: * Amplitude modulation (AM) - modem relies on amplitude and associates high amplitude/zeros with low amplitude. Amplitude modulation can be demodulated using a circuit consisting of very few components but lacks a bit of quality, much like with AM radio frequencies. * Frequency modulation (FM) - modem altars the frequency value and decodes original bit patterns based on the frequency of the received signal. Frequency modulation has the advantage that, as amplitude variations do not carry any information on the signal, it can be limited within the receiver to remove signal strength variations and noise. This is the reason that FM radio sounds so much better than AM. * Quadrature Amplitude Modulation (QAM) - modulates both the amplitude and phase such as in over-the-air transmissions (such as TV). * Phase modulation (PM) - positioning of the waveform at a particular instant in time. Modems use the phases to differentiate between ones and zeros. Phase modulation is the basis for many forms of digital modulation based around phase shift keying (PSK), which is a form of phase modulation. Very good for constantly shifting frequencies or whatever the situation may call for.
Digital transmissions can be a bit simpler in operation. Instead of a continuously variable waveform, digital transmission is a series of discrete pulses representing one bits (1) and zero bits (0). An obvious advantage of digital signals is that of the higher bandwidth. Analog supports a low 4KHz bandwidth, which translates to low data transmissions because of the channel. Whereas the transmission rates of digital signals can be significantly higher, dependent of the medium in which is carrying the signal. (Goleniewski, L., 2007).
Using that same logic, the same applies to network capacity. Analog signals can only support one conversation per telephone where as digital allows for multiplexing that allows multiple conversations on a single channel. Multiplexing is essentially a digital traffic controller. This is a multiple input, single output switch. Several signals may share a single device or transition conductor (such as fiber optic cable), and the MUX separates the signals carried and outputs them to their one desired use.
Digital signals can also be encrypted whereas that can be rather difficult to do with an analog signal without disturbing the original content and making it unrecognizable. (Goleniewski, L., 2007).
SONET (Synchronous Optical Network) is a standardized protocol that transfers multiple digital bit streams synchronously over optical fiber (or LED's). This standard applies to networks worldwide as opposed to PDH (Plesiochronous digital hierarchy). SONET is the American National Standards Institute (ANSI) standard, which is part of SDH (synchronous digital hierarchy), and it is used in North America. The European Telecommunication Standards Institute for Europe originally defined SDH, and it is now one of the most common forms used in most countries. SONET and SDH use different schemes for determining the rate of sending their packets over fiber optic cable, but end up with the same line rate. Within the digital transmission hierarchy, all facility types are usually referred to as "T x", where "x" is the Digital Signal level within the hierarchy (e.g. T1 refers to the DS1 rate of 1.544 MBPS).
The Sonet/SDH hierarchy of protocols consists of:

Goleniewski, L. (2007). Telecommunications Essentials (2nd ed.). Boston, MA: Addison-Wesley.
When it comes to converting information from one to the other, a codec (coder-decoder) converts analog signals into digital signals. A modem (modulate and demodulate) is used to infuse digital data onto transmission facilities and vice versa. Codecs can minimize the number of bits per second required to carry voice digitally through the PSTN. The book specifically states that a conversion is a point at which network troubles can occur, an opportunity for errors and distortions to be introduced. On a traditional analog line bands are limited and are susceptible to large amounts of noise that can interfere with the signal.
U-Law is the standard codec algorithm for PCM (pulse code modulation). The u-law came from the CCIT (Consultative Committee for International Telephone and Telegraph). U-Law makes it possible to improve the signal-to-noise ratio without requiring the addition of more data. Typically 12..14 bit samples (linear scale) sampled at 8 kHz sample are compounded to 8 bit (logarithmic scale) for transmission over 64 kbit/s data channel. In the receiving end the data is then converter back to linear scale (12..14 bit) and played back.
A perfect example to digitizing analog signals would be DSL modems. DSL modems converts data from a piece of terminal equipment into electronic signals in the 200 Hz to 3.4 kHz frequency band and vice versa. This allows the existing public network to transmit electronic data in the same way it traditionally would a human voice.
It is very easy to get overwhelmed with the amount of information coming in in regards to analog and digital signals. The technologies are continuously changing and will continuously advance and so will the forms of hardware we use to translate those signals. With that being said, it is important to understand how conversions between analog and digital occur. Without a good understanding, it becomes increasingly difficult to design a cohesive network design, let alone support one.

Reference
Benedetto, S. & Biglieri, E. (1999). Principles of digital transmission with wireless applications. New York: Kluwer Academic/Plenum Press.
Goleniewski, L. (2007). Telecommunications Essentials (2nd ed.). Boston, MA: Addison-Wesley.
Waveform Coding Techniques. (2006). Retrieved March 17, 2015, Retrieved from, http://www.cisco.com/c/en/us/support/docs/voice/h323/8123-waveform-coding.html