Chapter 4: Making Connections

This chapter discusses the different ways to connecting a computer to various peripherals.The connection between the PC and peripheral is the interface. The process of connecting a personal computer to these peripherals is called interfacing.

Characteristics of interface standards:

Before a company can develop a new product to interact with PCs and peripherals, the company is recommended to conform to the general standard interface protocols. The organizations that are involved in creating the interfacing standards are:

• International Telecommunication Union (ITU)
• Electronic Industries Association (EIA)
• Institute of Electrical and Electronics Engineers (IEEE)
• International Organization for Standardization (ISO)
• American National Standards Institute (ANSI)

Two basic characteristics of interface standards: 1) they have been created and approved by an acceptable standards-making organization; 2) they consist of one to four components which are the electrical component, mechanical component, functional component, and the procedural component.

Universal Serial Bus (USB):

Universal Serial Bus(USB): is a digital interface that uses a standardized connector for all serial and parallel type devices. The USB has a couple of advantages; avoids the introduction of noise, is considered to be "hot pluggable," which means that it can be simply plugged into a device and the device will recognize and establish the interface, provides the electrical power that is required to operate a peripheral, and daisy-changing is possible. The disadvantage of USBs is the slow speed of transferring data between devices.

There are four types of USB cables: type A, type B, mini, and micro USB cables. Type A and B both contain four pins, while the mini and micro contain five pins. The fifth pin is considered to be the "signal pin." There are two terms related to the four types of USB cables: bus and polling. Bus is a "high-speed connection to which multiple devices can attach." Polling is a "process in which a computer will ask a peripheral if it has any data to transmit to the computer." A USB can be a "polled bus," which will initiate all data transfers. There are four types of data transfers the USB can support; control transfers, bulk data transfers, interrupt data transfers, and isochronous data transfers.

Other interface standards:

There are other interface standards such as FireWire, Thunderbolt, Lighting, SCSI and iSCSI, InfiniBand and Fibre Channel. FireWire was introduced by Apple in the mid-1990s and was standardized by the IEEE. Just like the simple USB, FireWire avoids noise introduction when transferring data between devices. FireWire is also "hot pluggable" like the USB as well. Thunderbolt is another interface standard that was created by Apple. This interfacing connection provides 10-Gbps connection between peripheral devices. The connector uses and existing protocol called "PCI Express." The connection supports "daisy-chaining" and will soon support 100-Gbps data rates soon. Lightning is also another connector that was created by the Apple company. According to the book, even though the connector has its advantages, some question why Apple created the connector because it has a small amount of advantages over other USB connections. SCSI and iSCSI (Small Computer System Interface) is a "technique for interfacing a computer to high-speed devices such as hard disk drives, tape drives, CDs, and DVDs. The SCSI connection was designed to support devices of a more permanent nature. This connection is considered to be a "systems interface." To use this interfacing connection, the user needs to install an adapter onto his or her computer. A different variation of the SCSI connection is the iSCSI. This connection will interface a disk storage to a computer via internet. InfiniBand and Fibre Channel are both modern protocols uses to interface a computer to input/output devices over a high-speed connection. The InfiniBand is a serial connection or bus that can carry multiple channels of data at the same time. Fibre Channel is similar to the InfiniBand, but it can only support up to 126 devices.

Data Link Connections:

There are three different types of data link connection: asynchronous, synchronous, and the isochronous connections. Asynchronous connection has a single character, or byte of data, as the unit of transfer between the sender and the receiver. This connection consists of the start bit, stop bit, and the parity bit. The synchronous connection has a sequence of units of transfer between the sender and the receiver. This connection consists of the flag byte, control byte, address, checksum, and an end sequence flag. Isochronous connection is a special kind of data link. This link supports various types of real-time applications.

Chapter 3: Conducted and Wireless Media

Chapter three discusses mainly the two categories of communications media. The categories are physical or conducted media and radiated or wireless media. Later in the chapter, the section will explain the seven basic group of wireless media used for data transfer, which includes terrestrial microwave, satellite transmission, cell phone systems, broadband wireless distribution services, Bluetooth, wireless LAN, and various more.

Conducted Media:

There are three types of conducted media: twisted pair, coaxial cable, and fiber optic. Twisted pair "comes as two or more pairs of single-conductor copper wires that are twisted together." The twisting of the pairs of wires helps reduce the chances of crosstalk. Crosstalk is when a current or signal in one wire produces unwanted currents or signals in the second wire. This twisted pair comes in many different forms. To help categorize each form, the Category 1-7 (CAT 1-7) was created. Category 1 is used for standard telephone wires and has few to no twists. Category 2 twisted pairs are also used for telephone wires and some low-speed LANs. This category has some twist, which will help reduce noise. Category 3 pairs are designed to conduct 10Mbps of data over a LAN for distances up to 100 meters. A repeater can be used to extend this distance further than 100 meters. Category 4  was designed to transmit 20Mbps of data for the same distance as category 3.   Category 5 was designed to transmit 100 Mbps for 100 meters as well. Category 6 was created to support signals at 250 MHz for 100 meters. Category 7 supports data transmissions up to 600 MHz. The second type of cable is the coaxial cable. Coaxial cable is a single wire wrapped in a foam insulation, surrounded by a braided metal shield and then covered in a plastic jacket. This cable is excellent for carrying analog signals with a wide range of frequencies. Therefore, it is good for video channels and cable tv. There are two major coaxial cable technologies which are baseband coaxial and broadband coaxial. Baseband coaxial transmits data using digital signals. Broadband coaxial transmits data using analog signals. Fiber-optic cable helps avoid electromagnetic interference completely. Fiber-optic cable is in a thin glass cable, surrounded by a plastic coating. The downfall for fiber-optic cable is that it can only transmit light pulses one way. Therefore, if you want to transmit pulses two, you need to cables. Fiber-optic cables are also expensive, so if you need two cables to transmit data back and forth, expect high expenses.

Wireless Media:

There are several different types of wireless media. However, all types of wireless media transmit data using radio waves. The types of wireless media include terrestrial microwave, satellite transmission, cell phone systems, broadband wireless distribution services, Bluetooth, wireless LAN, and various more. Terrestrial microwave transmits focused beams of radio signals from one antenna to another. Satellite microwave transmits beams of radio signals from an antenna to a satellite and then back down to a ground station. Broadband wireless systems transmit voice, data, and video over high radio frequencies. Bluetooth uses low-power and short-range radio frequencies to communicate between two or more devices. Wireless local area networks (WIFI) transmits data in the 2.4 GHz frequency range.

Media Selection Criteria:

This next section discusses the different criteria anyone should follow to select the best type of media. The criteria that will be discussed are costs, speeds, expandability and distance, environment, and security.

Chapter 2: Fundamentals of Data and Signals

In chapter two, there are three main parts. The first part discusses what data and signals are, the second moves on to explain how data can be converted into signals, and finally the text continues to describe the different data codes that are used when transmitting data.

Introduction:

The text first explains the four different combinations of data and signals. 1)Analog data can be converted into analog signal. The most commons devices that perform this technique are radio tuners and TV tuners. 2) Digital data can be converted into digital signals. The most common devices that perform this kind of technique are digital encoders. Local area networks and telephone systems will use this kind of device. 3)Digital data can be converted into analog signals. Modems will perform this kind of conversion. Dial-up internet access, DSL, and cable modems all would use these conversion techniques. 4)Finally, Analog data can be converted into digital signals. A common device that uses this technique is a codec. Music systems will perform these kinds of conversions.

Data and Signals:

This section will explain the differences between digital data and signals from analog data and signals. Data are "entities that convey meaning within a computer or computer systems" (White, 29). Signals are "the electric or electromagnetic impulses used to encode and transmit data" (White, 30). Both data and signals can "exist in either analog or digital form." Analog data and analog signals are continuous wave forms that can contain an infinite number of points between some given minimum and maximum. The minimum and maximum values are represented as voltages. The text provides an example from the human voice. When individuals talk into a telephone, the receiver will convert the airwaves into analog data. The downfall of analog data and signals is "noise" interference. If someone were to speak into the telephone receiver, while someone else is talking right next the individual, the receiver has the possibility of picking up that extra set of airwaves which the receiver will convert into analog data. The telephone system will then send the analog data through transmission of analog signals, which will also contain the noise interference. When data is converted into analog form, it becomes very difficult to separate the noise from the original data. Digital data and signals have a different approach. Digital data and digital signals are created by sets of discrete or fixed numbers of value. Digital data takes on the form of binary 1s and 0s. Digital signals are different. Digital signals create two separate forms. The first form is called "square wave." These patterns contain simple high and low voltage values. The second form contains the combination of "modulate analog signals." In this kind of form, the "noise" that is introduced into the digital signal can be separated easily.

White moves on to explain the three basic components of analog and digital signals. These components are amplitude, frequency, and phase. Amplitude of a signal is "the height of the wave above or below a given reference point." Frequency is the number of times a signal will make a complete cycle within the time frame. Phase is the position of the waveform relative to a given moment of time. The text explains that signals have a tendency to lose power due to friction. This loss of power or signal strength is called attenuation. To measure the attenuation of a signal, we use decibels(dB).

Converting Data into Signals:

This section explains the conversion of data into signals and reminds the reader the four main combinations of data and signals which are: analog data transmitted using analog signals, digital data transmitted using square-wave digital signals, digital data transmitted using discrete analog signals, and analog data transmitted using digital signals.

To transmit analog data with analog signals, we use the process of modulation. Modulation is the process of sending data over a signal by varying its amplitude, frequency, or phase.

Transmitting digital data into square-wave digital signals, we would use the nonreturn to zero digital encoding schemes, manchester digital encoding schemes, bipolar-AMI encoding scheme, or the 4B/5B digital encoding scheme. There are two schemes for the nonreturn to zero digital encoding scheme. The first is the nonreturn to zero-level (NRZ-L), which transmits 1s as zero voltages and 0s as positive voltages. The second is the nonreturn to zero inverted (NRZI), which will transmit at the beginning of 1 as a voltage and will transmit a no voltage at the beginning of a 0. The problem with these two schemes is a synchronization problem. If there is a long sequence of 0s, it would be hard to read because the signal would never change. The Manchester scheme contains two different schemes: the manchester encoding scheme and the differential manchester encoding scheme. The manchester encoding scheme will transfer 1s from low to high voltages in the middle of an interval and will transmit 0s from high to low voltages in the middle of an interval. The differential manchester scheme is similar to the manchester scheme, but instead of changing voltages in the middle of an interval, the voltage will change from the beginning. The next scheme is the Bipolar-AMI encoding scheme. This scheme will transmit voltages on three levels. For 0s, there will be zero voltage and for 1s there can be positive voltages or negative voltages. If the 1 was transmitted as a positive, the next 1 will be transmitted as a negative. 4B/5B digital encoding scheme is the last scheme for transferring digital data with square-wave digital signals. This scheme takes 4bits of data and converts the data into a unique 5-bit sequence. The 5-bits sequence is then encoded using the NRZI scheme. This helps with the baud rate and provides efficiency. The only issue is the extra bit.

There are three ways to transmitting digital data with discrete analog signals. The first is amplitude shift keying. Low amplitudes can represent 1s and higher amplitudes could represent 0s. The problem with this technique is it can be susceptible to sudden noise. The next technique is the frequency shift keying. This approach will use two different frequency ranges to represent the 1s and 0s. Lower frequency signals can be 1s and higher frequency signals can 0s. The downfall for this approach is intermodulation distortion, which is when frequencies of two or more signals mix together and create new frequencies. The final approach is the phase shift keying. The changes in the phase of the waveforms can represent the 1s and 0s. If there was no phase change, that section could be a 0. If there was a phase change of 180 degrees, that section could be a 1.

To transmit analog data with digital signals we could use the pulse code modulation or the delta modulation. Pulse code modulation (PCM) will track the analog wave form and take snapshots of the analog data at fixed intervals. While taking the snapshot, the height or voltage will be calculated for the waveform. This calculation will be converted into a binary value. Delta modulation will track the analog data by assessing the waveforms in up or down steps. For each time period, the codec will decide whether the waveform has risen or fallen. If the waveform drops, it will be represented by a 0. If the waveform rises, it will represent a 1.

Data Codes:

The text explains that there are three important data codes. Those data codes are EBCDIC, ASCII, and Unicode. Extended binary coded decimal interchange code (EBCDIC) is an 8-bit code that will allow 256 combinations of textual symbols. The American standard code for information interchange (ASCII) is a 7-bit version that will allow 128 possible combinations of textual symbols. This data code is governed by the United States and is actually the most widely used data code in the world. Unicode can provide unique coding values for every character in any language.

Chapter 1: Introduction to Computer Networks and Data Communications

Chapter one is literally an introduction to computer networks and data communications. Curt M. White, author of the text, introduces the readers to various concepts of networks and data communications. These concepts include: the language of computer networks, the big picture of networks, common examples of communications networks, convergence, and network architectures. White starts with the language of computer networks to help the reader gain a better understanding and to help with the emphasis of the textbook.

Language of Computer Networks:

The first concept White discusses is the language of computer networks. According to the author, computer networks is "an interconnected group of computers and computing equipment using either wires or radio waves that can share data and computing resources" (White, 3). Within this group of interconnected computers and computing equipment, there are various different types of networks. These networks include: personal area networks (PANs), local area networks (LANs), campus area networks (CANs), metropolitan area networks (MANs), and wide area networks (WANs). Another network that has become popular today is the cloud based network. Cloud based networking is only the storage of data or information on the internet in a remote location rather than storing the information or data on a local drive. An example of this is Google's Google Drive application. Google Drive lets the user store a certain amount of data or information on the internet, which they secure of course. This will give the user the ability to use any device and download the user's files onto that device as long as they enter the correct credentials for the account. The text explains that there are two important building blocks to understanding computer networks. The two important concepts are data and signals. Data is "information that has been translated into a form more conducive to storage, transmission, and calculation" (White, 4). This just means that the data is converted in a way to make it more acceptable to store, transmit, and calculate. Signals are used to transmit the data or information. This is normally described as data communications, "the transfer of digital or analog data using digital or analog signals" (White, 4). The author then explains what we must do in order for users to connect any device to a computer network. White only gives the reader a brief explanation what the term is to connect a device to a computer network which is, interfacing. The section moves onto two ways of transmitting signals efficiently. These two ways consist of multiplexing, which is the "transmission of multiple signals on one medium," and compression, which "squeez[es] the data into a smaller package... reducing the amount of time needed to transmit the data" (White, 4). The section then ends with a discussion on the term convergence. Convergence is the merging of data network and voice network. Voice network transmitted telephone signals, while data network transmitted computer data. What convergence means is that voice network is now transmitting telephone data rather than telephone signals. The next concept that is considered is the big picture of networks. 

The Big Picture of Networks:

The author gives the reader an overview of what an actual set of networks would look like. White combines both the WAN and LAN together to give us a better idea of how everything works together. According to White, LANs require hardware such as workstations, servers, switches, and routers. WANs consist of nodes, high-speed transmission line, and subnetworks. In order for any user to request any kind of information from web servers, the individual must have both the "necessary hardware and software" to communicate with WANs. The user also needs a modem to connect to the web page as well. Another requirement is software to enable a computer to "speak" the language of the internet which is TCP/IP. TCP/IP or also known as Transmission Control Protocol/Internet Protocol, is a process of sending and receiving data packets through various steps. 

Common Examples of Communications Networks:

This section explains various ways users connect to networks on a day-to-day basis. These examples include desktop computers connecting to the internet, laptop computers connecting to wireless connections, cell phone systems, and various other means of common networks. There are also sensor networks, satellite and microwave networks as well. 

Convergence:

The convergence concept was explained earlier in the text. This concept is the combination of voice networks and computer networks. White discusses the three different types of convergence, which are the technological convergence, protocol convergence, and the industrial convergence. An example of the technological convergence is the transmission of voice networks through data transmission. Instead of sending voice signals, we now transmit voice through data packets. This is called Voice over Internet Protocol (VoIP). Other examples can be photos that are sent over the internet like SnapChat. 

Network Architectures:

This section explains the two most common network architectures, or also considered as communications models. The two most common of these models are the TCP/IP protocol suite and the Open Systems Interconnection (OSI) model. The TCP/IP protocol suite was created by a group of scientists to support a new kind of network which was called the ARPANET. This network was being installed across the US through the 1960s and the 1970s. The protocol has designed and based on a number of layers. This protocol consists of five layers for the user to connect to; the application layer, transport layer, network layer, network access layer, and the physical layer. When all layers are operating correctly, their jobs are to send data over a network of computers and to ensure the quickest route possible through the network of computers. The first layer is the application layer. There are various applications that are used which are hypertext transfer protocol (HTTP), simple mail transfer protocol (SMTP), file transfer protocol (FTP), telnet, and simple network management protocol (SNMP). The text explains that a common example of an application would be an e-mail. E-mails send and receive messages throughout the day. The application layer will ask the user to enter the message he or she would like to send to another user over the network. The application layer would then create a data packet that consists of the message and the address of the intended receiver. Once this job is completed, the application layer will send the contents to the transport layer. The transport layer's responsibility is to ensure transport integrity. This layer is supposed to establish a connection, monitor flow between sender and receiver, and retrieve any lost data that went missing during transportation. The next layer is the network. This layer would take the packet and add routing information so the information will find its way through the network. After the network layer, the network access layer would insert error-checking information and prepare the package for transmission. The final layer is the physical layer, which this layer's job is to actually transmit the data packet over wire transmission or wireless transmission. 

The second common network architecture is the OSI Model. The OSI model consists of seven layers. There is the application layer, presentation, session, transport, network, data link, and the physical layer. The presentation layer will perform various functions that will sometimes be needed when presenting the data package to the receiver. These functions include character conversions, encryption and decryption of documents, and compression of data. The session layer is responsible for establishing sessions between various users. The session layer can consist of a token management software or will establish synchronization points. Another layer the TCP/IP protocol does not have is the data link layer. The data link layer is similar to the transport layer of the TCP/IP protocol. This layer will take the data from the network layer and transform it into a "frame." All other layers within the ISO model are similar to the TCP/IP protocol suite. Two other terms are discussed which are the logical connections and the physical connections. Logical connections are nonphysical connections between sender and receiver that allows an exchange of commands and responses. For example, application layer will have a logical connection with the receiver’s application layer. Physical connections are direct connections between the sender and the receiver. This is the connection where the 1s and 0s are actually transmitted over wires or airwaves. This will only happen with the physical layer.