Networking.docx

Multipurpose Cables and Connectors Some of the cables we’ve discussed so far can serve multiple purposes. For example, HDMI can transmit audio as well as video, and SCSI supports more than just hard drives. For the most part, though, we associate HDMI with video and SCSI with storage devices. Unlike...

Multipurpose Cables and Connectors Some of the cables we’ve discussed so far can serve multiple purposes. For example, HDMI can transmit audio as well as video, and SCSI supports more than just hard drives. For the most part, though, we associate HDMI with video and SCSI with storage devices. Unlike HDMI and SCSI, the cables and connectors in this section are specifically designed to connect a variety of devices. For example, someone may have a USB hub with a wireless mouse, network card, Lightning cable (to charge an iPhone), and flash drive all attached at the same time. Those four devices serve very different purposes, but they all share the USB connection in common. We’ll start with the highly popular USB and then discuss Lightning and Thunderbolt connectors. Universal Serial Bus Universal Serial Bus (USB) cables are used to connect a wide variety of peripherals to computers, including keyboards, mice, digital cameras, printers, scanners, hard drives, and network cards. USB was designed by several companies, including Intel, Microsoft, and IBM, and is currently maintained by the USB Implementers Forum. USB technology is fairly straightforward. Essentially, it is designed to be Plug and Play—just plug in the peripheral and it should work, provided that the software is installed to support it. Many standard devices have drivers that are built into the common operating systems or automatically downloaded during installation. More complex devices come with drivers to be installed before the component is connected. USB host controllers can support up to 127 devices, which is accomplished through the use of a 7-bit identifier. The 128th identifier, the highest address, is used for broadcasting to all endpoints. Realistically speaking, you’ll probably never get close to this maximum. Even if you wanted to try, you won’t find any computers with 127 ports. Instead, you would plug in a device known as a USB hub (shown in Figure 3.17) into one of your computer’s USB ports, which will give you several more USB ports from one original port. Understand that a hub counts as a device for addressing purposes. Hubs can be connected to each other, but interconnection of host controllers is not allowed; each one and its connected devices are isolated from other host controllers and their devices. As a result, USB ports are not considered networkable ports. Consult your system’s documentation to find out if your USB ports operate on the same host controller. Figure 3.17 A 4-port USB hub 149 Another nice feature of USB is that devices can draw their power from the USB cable, so you may not need to plug in a separate power cord. This isn’t universally true, though, as some peripherals still require external power. USB Standards Even though USB was released in 1996, the first widely used standard was USB 1.1, which was released in 1998. It was pretty slow—only 12 Mbps at full speed and 1.5 Mbps at low speed—so it was really only used for keyboards, mice, and printers. When USB 2.0 came out in 2000 with a faster transfer rate of 480 Mbps (called Hi-Speed), video devices were possible. The newer USB 3.0, 3.1, and 3.2 standards have increased throughput even further. Table 3.3 lays out the specifications and speeds for you. Table 3.3 USB specifications Specification Release Year Maximum Speed Trade Name Color USB 1.1 1998 12 Mbps Full-Speed White USB 2.0 2000 480 Mbps Hi-Speed Black USB 3.0 2008 5 Gbps SuperSpeed Blue USB 3.1 2013 10 Gbps SuperSpeed+ Teal USB 3.2 2017 20 Gbps SuperSpeed+ n/a 150 The USB 1.x and 2.x specifications didn’t recommend a specific color for the ports, but when USB 3.0 was released, the USB Implementers Forum suggested that the ports and cable connectors be colored blue, to signify that they were capable of handling higher speeds. Device manufacturers are not required to follow the color-coding scheme, so you may see some inconsistency. A red or yellow USB port means it’s capable of charging a connected device, even if the PC is sleeping or shut down. As of the time of this writing, there was no color specified for USB 3.2. Most USB 3.2 devices are expected to use a USB Type-C connector anyway. USB Cables and Connectors In order to achieve the full speed of the specification that a device supports, the USB cable needs to meet that specification as well. In other words, USB 1.x cables cannot provide USB 2.0 and 3.x performance, and USB 2.0 cables cannot provide USB 3.x performance. Otherwise, the connected device will have to fall back to the maximum version supported by the cable. This is usually not an issue, except for the lost performance, but some high-performance devices will refuse to operate at reduced levels. Note that all specifications are capable of Low Speed, which is a 1.5 Mbps performance standard that has existed since the beginning of USB time. Throughout most of its history, USB has relied upon a small suite of standard connectors. The two broad classifications of connectors are designated Type-A and Type-B connectors, and there are micro and mini versions of each. A standard USB cable has some form of Type-A connector on the end that plugs into the computer or hub, and some form of Type-B or proprietary connector on the device end. Figure 3.18 shows five USB 1.x/2.0 cable connectors. From left to right, they are as follows: Micro-USB Mini-USB Type-B Type-A female Type-A male Figure 3.18 Standard USB connectors  By Techtonic (edited fromUSB types.jpg) [Public domain], via Wikimedia Commons 151 Small form factor devices, including many smartphones and smaller digital cameras, use a micro-USB or mini-USB connector, unless the manufacturer has developed its own proprietary connector. Micro-USB connectors (and modified ones) are popular with many Android phone manufacturers. In 2014, a new connector named USB Type-C (or simply USB-C) was developed. USB-C is designed to replace Type-A and Type-B, and, unlike its predecessors, it’s reversible. That means no more flipping the connector over several times to figure out which way it connects. Type-C cables will also be able to provide more power to devices than classic cables were. Figure 3.19 shows a Type-C connector and a Type-A connector. Figure 3.19 USB Type-C (top) and Type-A (bottom)  One point of confusion for many is dissociating the connector type from the standard. Because USB 3.1 and USB-C were both released around the same time, people often think that they are one in the same—but they’re not. USB 3.1 can be implemented using classic A and B connectors, and USB 2.0 can work over a Type-C connector. USB was designed to be a short-distance technology. As such, USB cables are limited in length. USB 1.x and 2.0 can use cables up to 5 meters long, whereas USB 3.x can use cables up to 3 meters long. In addition, if you use hubs, you should never use more than five hubs between the system and any component. Despite the seemingly locked-up logic of USB connectivity, it is occasionally necessary to alter the interface type at one end of a USB cable. For that reason, there are a variety of simple, passive converters on the market with a USB interface on one side and a USB or different interface on the other. Along with adapters that convert USB Type-A to USB Type-B, there are adapters that will convert a male connector to a female one. In addition, you can152convert USB to a lot of other connector types, such as USB to Ethernet (shown in Figure 3.20), USB to SATA, USB to eSATA, USB to PS2, USB to serial, and a variety of others. Figure 3.20 Kensington USB to Ethernet adapter USB Power As mentioned previously, USB ports provide power to devices plugged into them. Typical power for attached USB devices is 5V. The maximum current (amps) and wattage will depend on the connected device and USB standard being used. All USB ports are also capable of functioning as charging ports for devices such as tablets, smartphones, and smart watches. The charging standard, called USB Battery Charging, was released in 2007. USB Power Delivery (PD) was developed in 2012. Technically, they are different standards, but in practice, USB ports are capable of supporting both standards at the same time. Table 3.4 outlines some of the versions and the maximum power that they provide. Table 3.4 USB power standards Standard Year Maximum Power USB Battery Charging 1.0 2007 5V, 1.5A (7.5W) USB Battery Charging 1.2 2010 5V, 5A (20W) USB Power Delivery 1.0 2012 20V, 5A (100W) USB Power Delivery 2.0 (specified use of Type-C connectors but only up to 15W) 2014 5V, 3A (15W) USB Power Delivery 3.0 2015 20V, 5A (100W) A smartphone or tablet typically needs a minimum of about 7.5 watts to charge properly. The Battery Charging 1.0 standard was good enough, but not for larger devices.153For example, about 20 watts is required to power a small laptop computer, and standard 15-inch laptops can require 60 watts or more. With USB PD, one USB port can now provide enough power for a laptop as well as a small printer. Because of the capabilities of USB PD, it’s possible that in the next few years you will see devices up to laptop size lose their standard AC power ports and adapters—they may just have a USB-C port instead. To get the full capabilities of USB PD, you need to use a USB-C port and cable.  For more information on USB, check out www.usb.org. Lightning Introduced in 2012 with the iPhone 5, the Lightning connector is Apple’s proprietary connector for iPhones and iPads. It’s an 8-pin connector that replaced Apple’s previous 30-pin dock connector. A standard Lightning cable has a USB Type-A connector on one end and the Lightning connector on the other, as shown in Figure 3.21. It’s not keyed, meaning that you can put it in with either edge up. Figure 3.21 Lightning cable Lightning cables support USB 2.0. You will find cables that are USB-C to Lightning, as well as various Lightning adapters, such as those to HDMI, DisplayPort, audio, and Lightning to female USB Type-A (so you can plug a USB device into an iPad or iPhone). There are rumors that Apple may do away with the Lightning connector in its 2019 iPhone release and instead use USB-C. The same rumors have persisted since the iPhone 8 was released in 2017, and it seems that Apple has little reason to move away from its proprietary connector. 154 Thunderbolt Where there’s lightning, there’s thunder, right? Bad joke attempts aside, in computer circles Lightning connectors don’t have much to do with Thunder(bolt). Thunderbolt, created in collaboration between Intel and Apple and released in 2011, combines PCI Express 2.0 x4 with the DisplayPort 1.x technology. While it’s primarily used for video (to replace DisplayPort), the connection itself can support multiple types of peripherals, much like USB does. Thunderbolt Standards Because Thunderbolt includes a separate I/O function from the DP video technology, it is rated for power and transfer rates in the same way as technologies such as USB and eSATA. Both of the initial versions of Thunderbolt, v1 and v2, operate at 20 Gbps of aggregate bandwidth. The v2 offering does so with more flexibility by combining the two 10 Gbps channels instead of allowing each one to perform as either only transmit or only receive. Each Thunderbolt port provides a total of 18V and 9.9W of power to the one or more attached peripherals. Thunderbolt 3 was released in 2015 and doubles the bandwidth to 40 Gbps. It supports PCIe 3.0 and DisplayPort 1.2, meaning that it can support dual 4K displays at 60 Hz or a single 4K display at 120 Hz. Thunderbolt Cables and Connectors The most common Thunderbolt cable is a copper, powered active cable extending as far as 3 meters, which was designed to be less expensive than an active version of a DisplayPort cable of the same length. There are also optical cables in the specification that can reach as far as 60 meters. Copper cables can provide power to attached devices, but optical cables can’t. Additionally, and as is the case with USB, Thunderbolt devices can be daisy-chained and connected via hubs. Daisy chains can extend six levels deep for each controller interface, and each interface can optionally drive a separate monitor, which should be placed alone on the controller’s interface or at the end of a chain of components attached to the interface. Figure 3.22 shows two Thunderbolt 2 interfaces next to a USB port on an Apple MacBook Pro. Note the standard lightning-bolt insignia by the port. Despite its diminutive size, the Thunderbolt port has 20 pins around its connector bar, like its larger DisplayPort cousin. Of course, the functions of all the pins do not directly correspond between the two interface types, because Thunderbolt adds PCIe functionality. Figure 3.22 Two Thunderbolt 2 interfaces 155 Thunderbolt 3 uses standard USB-C connectors, as shown in Figure 3.23. Figure 3.23 Two Thunderbolt 3 interfaces  By Amin - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=67330543 Converters are available that connect Thunderbolt connectors to VGA, HDMI, and DVI monitors. Active converters that contain chips to perform the conversion are necessary in situations such as when the technology is not directly pin-compatible with Thunderbolt—as with VGA and DVI-A analog monitor inputs, for example. Active converters are only slightly more expensive than their passive counterparts but still only a fraction of the cost of Thunderbolt hubs. One other advantage of active connectors is that they can support resolutions of 4K (3840 × 2160) and higher. Other Peripheral Cables and Connectors The vast majority of peripherals that you will encounter use one of the connector types we’ve already discussed in this chapter. However, there’s the off chance that you will run into some others, and that’s what this section is for. Think of this as the random grab bag of things you might see. If nothing else, it’s knowledge that you can impress your friends and family with at your next social event. Serial Ports Of all the connectors and cable types in this section, this is the one that’s a CompTIA A+ exam objective. We’ve talked a bit about serial ports and serial transmissions already, but here we’ll look at ports and connectors. Remember that before USB came along around 20 years ago, serial ports were considered slow and inferior to parallel ports. Still, serial enjoyed use among peripherals that didn’t need to transfer information at high speeds, such as mice, modems, network management devices, and even printers. Figure 3.24 shows a 9-pin serial port. It’s the one marked “Serial,” and it’s also the only male connector on the back of the PC. Figure 3.24 Several peripheral ports 157 As you might expect, a serial cable attaches to the serial port. Figure 3.25 shows a female DB-9 serial connector. To make things more confusing, sometimes you will hear people refer to the image in Figure 3.25 as an RS-232 cable or connector. Even though the terms are often used interchangeably, there is a technical difference. Figure 3.25 DB-9 serial connector If you’ll recall from earlier in the chapter, DB-9 refers to a specific type of D-sub connector that has 9 pins. RS-232, on the other hand, is a communications standard for serial transmission. In other words, systems may communicate with each other using RS-232 over a DB-9 connection. But RS-232 can also be used on other types of serial cables as well, such as DB-15 or DB-25. Generally speaking, if someone asks for an RS-232 serial cable, they mean a DB-9 cable with female connectors. But it’s always best to confirm. RS-232 did have a few advantages over USB—namely, longer cable length (15 meters vs. 3–5 meters) and a better resistance to electromagnetic interference (EMI). Still, USB has made old-school serial ports nearly obsolete. About the only time they are used today is for management devices that connect to servers or network routers with no keyboard and monitor installed. FireWire When FireWire (IEEE 1394) was standardized in 1995, it was going to be “the next big thing” in computing. It was very fast for the time (400 Mbps) and easy to use. Like USB, FireWire could provide power to attached devices. Up to 63 FireWire devices could be managed by one controller. Before its demise, FireWire supported speeds of 3.2 Gbps and was used for video as well as high-speed connections to external hard drives. Ultimately, though, it lost out to USB and video standards such as DVI and has basically been obsolete since around 2007. In Figure 3.24, the FireWire port is above two USB ports and is marked 1394. Audio/Video Ports Audio ports are pretty standard on PCs and laptops, and they haven’t changed much in a few decades. There are also several video connectors around that pre-date the ones currently in use today such as DVI and HDMI. Analog Sound Small, 1/8″ (3.5 mm) analog sound jacks have been around for a few decades, and they still look and work the same today as they did back then. The plugs provide left- and158right-channel stereo audio by making contact with their tip, rings (if they have any), and sleeve. While an older system might have had only one jack, newer PCs and sound cards may have a six-jack setup capable of 8-channel audio, also known as 7.1 surround sound. Figure 3.26 shows an example of a six-jack connector. Other soundcards may have three connectors: a green one for stereo audio output, a blue one for line-in (used for cheaper musical devices), and a pink one for a microphone. Most laptops and smaller devices will just have a single jack, which allows for the connection of a pair of speakers or headphones. Figure 3.26 Sound card jacks RCA The RCA jack (shown in Figure 3.27) was developed by the RCA Victor Company in the late 1940s for use with its phonographs—the original record players. Today, you may use RCA jacks and connectors to transmit both audio and video information, although this technology has been supplanted by HDMI. 159 Figure 3.27 An RCA jack (female) and RCA plug (male) RCA jacks are considered coaxial because the outer circular conductor and the center pin that collectively make up the unbalanced single transmit/receive pair have the same axis of rotation—that is, co-axial. An RCA jack and cable carry either audio or video, not both simultaneously. Therefore, you usually see them implemented in sets of threes: left audio (white), right audio (red), and video (yellow). Component Video When analog technologies outside the VGA realm are used for broadcast video, you are generally able to get better-quality video by splitting the red, green, and blue components in the signal into different streams right at the source. The technology, known as component video, performs a signal-splitting function similar to RGB separation. However, unlike RGB separation, which requires full-bandwidth red, green, and blue signals as well as a fourth pathway for synchronization, the most popular implementation of component video uses one uncompressed signal and two compressed signals, reducing the overall bandwidth needed. These signals are delivered over coax, either as red, green, and blue color-coded RCA plugs or similarly coded BNC connectors, the latter being seen mostly in broadcast-quality applications. The uncompressed signal is called luma (Y), which is essentially the colorless version of the original signal that represents the “brightness” of the source feed as a grayscale image. The component-video source also creates two compressed color-difference signals, known as Pb and Pr. These two chrominance (chroma, for short) signals are also known as B – Y and R – Y, respectively, because they are created by subtracting out the luma from the blue and red source signals. It might make sense, then, that the analog technology presented here is most often referred to and labeled as YPbPr. A digital version of this technology,160usually found on high-end devices, replaces analog’s Pb and Pr with Cb and Cr, respectively, and is most often labeled YCbCr. Figure 3.28 shows the three RCA connectors of a component-video cable. Figure 3.28 A component-video cable  By Evan-Amos - Own work, public domain, https://commons.wikimedia.org/w/index.php?curid=11339108  As a slightly technical aside, luma is a gamma-correcting, nonlinear display concept related to but not equivalent to luminance, which is a linear, non-gamma-corrected measure of light intensity. Display devices perform nonlinear gamma decompression, which means a complementary nonlinear gamma compression (correction) must have been performed by the transmitter for the resulting image to be displayed properly. Thus luma, not luminance, is the appropriate term when discussing component video. Furthermore, although Y is commonly used to represent luma, it actually stands for luminance. As a result, if you ever see a reference to Y’PbPr or Y’CbCr, the Y-prime refers correctly to luma. The more common, yet less correct, Y is used here to refer to luma. Note that the foregoing discussion did not mention a green component-video signal. In fact, the often green-colored lead in the component-video cable carries the luma. There is no need for a separate green color-difference signal. Essentially, the luma signal is used as a colorless map for the detail of the image. The receiving display device adds the luma signal from the Y lead back to the blue and red color-difference signals that were received on the Pb and Pr leads, re-creating compressed versions of the full blue and red source signals.161Whatever details in the luma version of the image have weak representation in the blue and red versions of the image are inferred to be green. Therefore, you can conclude that by providing one full signal (Y) and two compressed signals (Pb and Pr) that are related to the full signal (Pb = B – Y and Pr = R – Y), you can transmit roughly the same information as three full signals (R, G, and B) but with less bandwidth. Incidentally, component video is capable of transmitting HD video at full 1080p (1920 × 1080, progressive-scan) resolution. However, the output device is at the mercy of the video source, which often is not manufactured to push 1080p over component outputs. Composite Video When the preceding component-video technologies are not feasible, the last related standard, composite video, combines all luma and chroma leads into one. Composite video is truly the bottom of the analog-video barrel. However, the National Television System Committee (NTSC) signal received by over-the-air antennas or by cable-TV feeds is composite video, making it a very common video signal. Unfortunately, once the four signals are combined into one, the display equipment has no way of faithfully splitting them back out, leading to less than optimal quality but great cost efficiency. Composite video is implemented as a single yellow RCA jack, which is the one shown in Figure 3.27. While still fairly decent in video quality, composite video is more susceptible to undesirable video phenomena and artifacts, such as aliasing, cross coloration, and dot crawl. PS/2 (Keyboard and Mouse) At one time, the most popular connectors for keyboards and mice were round connectors called Personal System/2 (PS/2) connectors. The PS/2 connector (there are two on the left in Figure 3.24) is a smaller 6-pin mini-DIN connector. Many PCs included a PS/2 keyboard connector as well as a PS/2 mouse connector right above it on the motherboard. The keyboard connector was colored purple, and the mouse one green. The ends of the keyboard and mouse cables would be purple and green as well. Today, the PS/2-style connector has been replaced by the USB port.