Audio and video programs can move through the network at the same time as email, web surfing, and instant messages.
For detailed information about setting up and using a home entertainment network, see Chapter Video Cameras and Home Security Devices A stand-alone video camera often with a built-in microphone connected to your home network can have several uses. You can place a camera at the front door to identify visitors, or use one in a nursery or playroom to keep an eye on your children from computers in other parts of the house. Other devices can use special sensors to detect smoke and fires, unlocked or open doors and windows, broken glass, or flooding and other problems and send alerts to the homeowner on a local computer or to a home protection service through the Internet.
Chapter 15 explains how to connect and use cameras and other security devices to your network. Chapter 15 provides basic information about home automation systems and devices and explains how to connect them to a computer network. Without these rules, the people using the network cannot be sure that their computers will communicate successfully. For example, the plugs at the ends of data cables must match the sockets on each computer and other network hardware. The same thing applies to the electrical voltages, timing, error checking, and other issues.
There are many different kinds of networks, each with its own rules. You can treat individual network components as a series of black boxes, but you still have to know which black boxes to use. As you probably know, computers reduce all information to only two information states: Either a signal is present, or there is no signal. These two conditions are usually described as 1 and 0, or on and off, or mark and space. The form that each 1 or 0 takes is different in different types of communication channels. It could be a light, sound, or electrical charge that is either on or off; a series of long and short sounds or light flashes; or two different audio tones, electrical voltages, or radio frequencies.
A byte is the basic building block of computer communication. Figure shows a typical sequence of two bytes. ASCII is fine for text, but a computer can also convert many other forms of information to digital data. For example, it can divide every second of sound from a microphone or an analog recording into thousands of very short segments and use 16 or 24 bits to specify the content of each segment, or divide a picture into millions of individual points called pixels, short for picture elements and use a series of bits to specify the color of each bit.
A wire or other data link can carry only one bit at a time. Obviously, a parallel connection can be eight times faster than sending one bit at a time through a single wire, but those eight wires cost eight times as much as a single wire. The alternative is to send your message to a switching center that will hold it until a link to the destination becomes available. This is known as a store and forward system. If the network has been properly designed for the type of data and the amount of traffic in the system, the waiting time will be insignificant.
If the communications network covers a lot of territory, you can forward the message to one or more intermediate switching centers before it reaches the ultimate destination. To make the network even more efficient, you can divide messages that are longer than some arbitrary limit into separate pieces, called packets or frames.
Packets from more than one message can alternate with packets containing other messages as they travel between switching centers, and reassemble themselves into the original messages at the destination. The great advantage of this approach is that many messages can share the same circuits on an as-available basis. The packets from a single message might alternate with packets from one or more other messages as they move through parts of the network. For example, if you send a message to a recipient in another city, the packets usually move through an inter-city channel along with many other messages.
Some of this information provides additional error checking and instructs the switching centers T yp es of N etw ork C on ne ct ion s 11 where to forward each packet, while other information tells the destination device how to reassemble the data in the packet back into the original message. Between the origin and the destination, network routing equipment sometimes adds more headers or trailers that contain routing instructions and other administrative information.
Figure shows how a network adds and removes headers and trailers at different stages of a communication session. That same pattern repeats every time you add another layer of activity to a communications system. Each layer may attach additional information to the original message and strip off that information after it has done whatever the added information instructed it to do.
By the time a message travels from a laptop computer on a wireless network through an office network and a gateway to the Internet, and onward to a distant computer connected to another local network, a dozen or more information attachments might be added and removed before the recipient reads the original text. A package of data that includes address and control information ahead of the bits that 12 C ha pt er 2 contain the content of the message, followed by an error-checking sequence, is called a frame. Both wired and wireless networks divide the data stream into frames that contain various forms of handshaking information along with the original data.
NOTE The network deals with packets and frames at different places during the process of transmitting data. Error Checking In a perfect transmission channel, the signal that goes in at one end would be absolutely identical to the one that comes out at the other end. Noise is defined as anything that interrupts or is added to the original signal; it could be caused by a lightning strike, interference from another communications channel, devices not working correctly, or dirt on an electrical contact someplace in the circuit or in the case of carrier pigeons, an attack by a marauding hawk.
Whatever the source, noise in the channel can interrupt the flow of data. In a modern communications system, those bits are pouring through the circuit extremely quickly—millions of them every second—so a noise hit for even a fraction of a second can obliterate enough bits to turn your data into digital gibberish. Therefore, your data stream must include a process called error checking.
Error checking is accomplished by adding some kind of standard information to each byte. In a simple computer data network, the handshaking information is called the parity bit, which tells the device receiving each byte whether the sum of the ones and zeroes inside the byte is odd or even. This value is called a checksum. If the receiving device discovers that the parity bit is not correct, it instructs the transmitter to send the same byte again. More complex networks, including wireless systems, include additional error-checking handshaking data with each string of data.
First it has to warn the device at the other end that it is ready to send and make sure the intended recipient is ready to accept data. I have some data for you. Did you get it? In a complex network such as a wireless data channel, as much as 40 percent or more of the transmitted data is handshaking and other overhead. Ethernet Ethernet was introduced in the s as a method for connecting multiple computers and related equipment in the same building.
It has become an industry standard supported by dozens of manufacturers, so you can use different brands of equipment in the same network. Today, more than 85 percent of all local area networks LANs , including just about every modern home and office network, use some form of Ethernet to provide the physical connection between computers through twisted-pair cables, coaxial cables, or fiber optic cables.
Every time a network node is ready to transmit a frame, it checks if another frame is already using the network; if the network is clear, the node sends the frame. But if the node detects that another frame is using the network a condition called a collision , it waits a random period of time before it tries again. There are many Ethernet specifications that cover different data transfer speeds and different kinds of cables and connectors.
A 10Base-T device can work on a Base-T network, but it will force the whole network to drop down to 10 Mbps. It might be appropriate for a business that moves very high volumes of data through its LAN. As the cost of Gigabit Ethernet drops, it will become the preferred choice for home and small business networks. You might also see the word Ethernet used to identify the connector on a computer, printer, or other network device that mates with an Ethernet cable to connect the device to a network.
The instruction manual or the label on every piece of Ethernet-compatible equipment should tell you which type of connection it uses.
Twisted-pair cables are bundles of wires in which each pair of wires is twisted together, as shown in Figure Because data normally moves in only one direction through each pair of wires, a 10Base-T or Base-T network connection uses two pairs—one for each direction. The most common Ethernet cables include a total of eight wires in four color-coded wire pairs, so you can use the remaining wires as spares.
Figure A typical Ethernet cable contains four twisted pairs of color-coded wires. Most of the remaining chapters of this book are dedicated to features and functions of Ethernet networks. If you have inherited a working network, the best thing you can do is to leave it alone. Wi-Fi Wi-Fi short for wireless fidelity is a category of networks that use radio signals instead of wires to connect computers and other devices.
Another name for Wi-Fi is wireless Ethernet, because Wi-Fi uses many of the same data-handling rules and specifications as a wired Ethernet network. However, every Wi-Fi packet must include additional handshaking data, so the overall data transfer speed is often slower than a conventional Ethernet link. Rather than string cables through walls and provide a network outlet at every desk, you can distribute access to the network through antennas in between each computer and a base station an access point in a central location. When you travel with a laptop computer, a handheld PDA personal digital assistant , or a mobile Internet device, such as a BlackBerry or an iPhone, you can often connect it to the Internet via Wi-Fi by simply turning it on.
Many home and small business networks use a combination of Ethernet and Wi-Fi; the Wi-Fi base station doubles as a connection point for Ethernet cables, so the same LAN includes both wired and wireless nodes. Chapter 8 contains information about installing and using Wi-Fi network links. Each computer connects through a parallel port, a USB port, or an Ethernet port to a data adapter that plugs directly into an AC wall outlet.
The same power transformer that feeds your house wiring also isolates your data network from your neighbors. The greatest advantage of HomePlug and other powerline networks is that the wires are already in place. Every AC wall socket in the house can double as a network connection point. Wi-Fi signals are often blocked by thick walls and other obstacles that make no difference to a powerline system. NOTE You must plug all your powerline adapters directly into wall outlets.
All equipment that follows the HomePlug specifications should work together in the same network. Figure The HomePlug certification mark indicates that a powerline networking product has been approved by the HomePlug Powerline Alliance. If installing Ethernet wiring is not practical in your building, a HomePlug network might be your best choice. When it works, which it does in most houses, it provides an easy, reliable network. These systems use the internal telephone wiring that connects extension telephones in several rooms or the coaxial cable coax that provides cable TV signals.
However, if the phone boxes or cable outlets are already in convenient locations, it might be practical to consider HomePNA or MoCA as an alternative to Wi-Fi or separate Ethernet wiring. Data can move through a wire in only one direction. Therefore, a network device uses separate inputs and outputs on the same multipin connector. The specific pin assignment is different in different connection types, but the inputs and outputs are always different pins or sockets. The problem arises because every output must connect to an input.
Therefore, when you connect two pieces of equipment, the outputs at each end must go to inputs at the other end. If Pin 2 on one device is an output, Pin 2 on the other device must be an input. Most standard data cables connect each connector pin to the same numbered pin at the other end, so connecting two devices through a cable is exactly the same as plugging one device directly into another.
Data terminal equipment includes remote terminals, computers, some printers, and other network endpoints. Data communications equipment includes modems, hubs, 18 C ha pt er 2 switches, and other control devices. When you connect a terminal to a control device, the output pins on the DTE device connect to the input pins on the DCE device. The problem arises when you want to connect two computers without a control device in between. When you connect two DTE devices with serial data ports, you connect the output on one computer to the output on the other computer, and the input to the input, so neither computer will actually receive any data.
Therefore, you must flip the connections, so each output connects to an input. A cable or adapter that connects output pins to input pins is called a null modem. Figure shows a typical null modem adapter. Figure A null modem adapter or cable connects inputs directly to outputs.
Point-to-Point Networks Most of the time, we think of a computer network as a structure that can link one computer to any other computer connected to the same network.
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But sometimes all you need is a direct connection between two computers. This kind of connection is called a point-to-point network. Figure shows both network types. A point-to-point connection is handy when you want to transfer data from one computer to another when one or both of them are not already connected to a network. Point-to-point networks can use wires, radio signals, or infrared light to exchange data between the two endpoints.
For a pointto-point Wi-Fi link, you must configure it as an ad hoc connection. Most of the wireless remote control units that you use with your television, DVD player, and home stereo system also use infrared light signals. Many laptop computers have built-in IrDA ports, usually in an inconspicuous location along the edge of the case. The IrDA port is usually an infrared lens under a transparent plastic cover, like the one shown in Figure When two computers with active IrDA ports are in the same room, they will usually detect each other automatically.
NOTE The infrared port on a laptop computer can detect an IrDA signal from another computer in the same room and automatically set up a network link between the two devices. To disable or enable infrared communications in Windows, open the Device Manager Control Panel System Hardware Device Manager , expand the list of infrared devices, right-click the name of the infrared port, and choose Disable or Enable from the pop-up menu.
IEEE is used most often for high-speed data transfer from audio and video equipment to computers, but it can also exchange data between two computers through a special cable. A network connection through a telephone line uses a modem to convert digital computer data to sounds that can pass through the PTSN. A second modem at the other end converts those sounds back to digital data.
The communications programs in Windows and other operating systems send control codes that instruct the modem to transmit telephone numbers and adjust the data transfer speed and other configuration settings. Most new laptops have built-in PTSN modems. Separate modems for desktop computers are available as internal expansion cards or external devices that connect to the computer through a serial data port or a USB cable.
Figure shows the dial-up modem control panel used in Windows XP to connect a computer to a distant network or an Internet service provider ISP. Figure shows the setup screen for the HyperTerminal program. Other programs have different layouts, but they all do essentially the same thing: They dial a telephone number and log in to the computer that answers the call. Advanced properties specify the type of network connection, the data speed, and other configuration settings. Figure The Connect To dialog in HyperTerminal includes space for an area code and telephone number.
Figure The Connect dialog in Windows specifies the telephone number that a modem will call and the login and password that the computer will send after the connection goes through. You can connect to another computer as a remote terminal through a LAN, through a dial-up telephone line, or through the Internet. For example, Figure shows the login sequence from a remote terminal program connected to The Well, a text-based online community that runs on a Unix host computer in Sacramento, California.
You might see similar text-based host computer displays from library catalogs or mainframe computers. Figure A remote terminal allows a user to operate a remote computer through a network. You can connect to a computer as a remote terminal through the Internet, using a category of programs called telnet that form the core of most terminal emulators, or you can connect directly to the host computer through a modem and a conventional dial-out telephone line.
Clients and Servers As your network grows, you might choose to add some computers and other devices such as printers to the network. In a network, a client is a computer or program that uses resources supplied by another device; a server is the device that provides those resources. Organizing a network into clients and servers is one way to make that network much more flexible and powerful than the individual computers connected to it.
As you plan a new network or expand the one you already have, you should think about each network activity as either a client program that runs on local computers or a server that supplies the program from a central source. The software that sends instructions to a server and receives data or other services is a client program. Each server communicates with a client program that sends it the correct set of requests and receives information in a particular format.
A network can take advantage of many kinds of clients and servers. Here are just a few: Mail server A computer that handles inbound and outbound mail for all network users File server A computer that stores data files and makes them available through any computer connected to the network Music server A specialized file server that stores music files and makes them available to computers and home entertainment systems Firewall server A computer that acts as a security firewall between the other computers on the network and the rest of the world Game server A computer that acts as host for a multiplayer game A server can be a separate computer that runs only specialized server software, a general-purpose computer that runs server programs along with other programs, or an even more specialized device that contains a specialpurpose internal computer processor.
For example, as Figure shows, a printer server could be a computer with a printer attached to it, or a printer with an internal or external network adapter connected directly to the network. When others in the house want to print something, they instruct their own computer to send it to the printer through the network to the computer in the kitchen.
Clients and servers are important because they are essential network building blocks. For more details about adding and using servers, see Chapter 9. Large networks can have very complicated structures with many branches and extensions, but the core of every network can be reduced to just a few patterns.
The simplified layout of a network is known as its topology. Figure shows simplified diagrams of each network topology. In the much more common hub system, each data packet travels to a central location, where a control device reads the address and sends it back out to the right destination. Ethernet networks, which include most small LANs, are hub systems.
Mesh topology is not common in small home or office networks, but the wide area networks that connect your small network to the Internet often use mesh designs. This chapter describes the equipment at the center of a star network that connects the computers and other nodes to one another, and the related devices that provide connections between networks.
Hubs and Switches Both hubs and switches are exchange points at the logical center of an Ethernet network, as shown in Figure Each computer or other network node connects to a hub or switch through a cable plugged into a socket called a port. In a small network, a hub or switch is almost always a tabletop 28 C ha pt er 3 box with indicator lights on the front and Ethernet ports on the back. In a larger network, the hub or switch might be a panel that mounts in an equipment rack. Ethernet hub Figure A hub or switch is the central connection point in an Ethernet network.
The maximum data transfer speed of a network is the data-handling speed of the hub or switch. Today, the most common hubs and switches are designed for both 10 Mbps and Mbps operation. The latest generation of switches and hubs supports even faster Gigabit Ethernet Mbps switches, often at prices only slightly higher than those of older Mbps versions.
Each node compares the address on the packet with its own address and either accepts it if the address is the same or ignores it if the packet is addressed to some other node. In order to prevent collisions, each node must examine the network to be certain that no other node is already using the hub before it transmits a packet. If all the computers in your network use Mbps network adapters but the printer connects through a 10 Mbps port, the whole network will run at only 10 Mbps or less.
Hub s , Sw it ch es , an d R ou te rs 29 As more nodes try to use a hub at the same time, the data transfer speed through the entire network drops. This could have a significant effect on a busy network that uses a hub: The actual data transfer could be only a fraction of the nominal 10 Mbps or Mbps. In general, hubs are slow, simple, and cheap. But the difference in cost between a hub and a switch is often insignificant, so a switch is almost always the better choice.
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Switches A data switch performs the same function as a hub—it connects the nodes of a network to one another—but it does the job quite differently. Rather than sending every packet to every port, a switch reads the address section of each incoming packet and sets up a direct connection from the source of each packet to its destination. In the meantime, if some other node tries to send a data packet to another unused port, the switch can set up the link without breaking the other connection. As Figure shows, a switch can handle more than one connection at the same time.
Both of these features—multiple segments and full duplex operation—mean that data can move through a switch more quickly than through a hub. Data switches and hubs come in several sizes and shapes. The smallest switches often have four, five, or eight ports, inside a box that can sit on a table or shelf, like the one shown in Figure When your network expands 30 C ha pt er 3 to need more ports than your original switch can provide, you can connect one or more additional switches to one of the ports on the original unit.
Photo courtesy of Linksys, a division of Cisco Systems, Inc. Figure This switch connects five network nodes. Networks in larger business offices usually run cables from each computer back to a central space where all the switching equipment is mounted on a wall plate or an equipment rack. This space is often called a wiring closet. All of the computers connected to a LAN can share peripheral devices such as a printer or a scanner , they can run programs and read data from other computers on the same LAN, and they all share a common connection to the Internet.
In a home network, the LAN might also include home entertainment systems and game controllers. A LAN also uses the same set of rules and settings to control communication among all the networked computers. These include the name of the network itself and names or address numbers, or both for each computer, and sometimes firewalls that protect the privacy of the people using the LAN. The Internet itself is a set of connection points that link a lot of WANs. Bridges and Routers Any time you connect two networks, you must use a tool that translates the address and control data used by each network into values that the other network can understand.
NOTE Bridges and routers operate between two different networks. However, many routers combine functions with a switch in a single device. This kind of router is sometimes called a gateway router because packets from your LAN must pass through it on their way to the Internet and, of course, packets from the Internet also pass through the router on their way to your LAN. The most common gateway routers are specifically designed to supply the right kind of signaling and address conversion required by DSL or cable TV connections. For example, a router that connects the network to the Internet could also include a built-in switch that connects several nodes, or a DSL modem might be matched with a gateway router.
Many other combinations are also widely available. Figure The cables connected to your network controls can often form a confusing mess. The most important are TCP transmission control protocol , which controls the way commands, messages, and files are broken into packets and reassembled at the other end, and IP Internet protocol , which provides the rules that guide each data packet through different kinds of networks to the correct destination. The information in Chapter 2 of this book provides as much detail as most users ever need.
But the Internet protocol is another matter; you should understand how your network and just about every other network connected to the Internet uses names and addresses for individual computers and other network nodes and how to use some of the standard software tools that are included in every network computer. Fortunately, internal routing through the Internet is automatic; if you enter a valid address in your web browser, email client, or other program, the Internet will almost always find a path to the computer with that address.
The formal sessions are often boring, but the after-hours parties are great. In networks, addressing conventions are actually the rules that everybody uses to identify the computers and other devices connected to a network and the people who use them. Every computer connected to a network has a unique name and address within that network, and every network connected to the Internet has its own unique numeric Internet address known as an IP address.
Numeric Addresses The technical committees, international standards organizations, and government agencies that manage the Internet have all agreed on a bit numeric address format shown as four numbers between 0 and , separated by periods, like this: Every computer connected to your LAN and every device or network connected to the Internet has a different address.
Some formal contracts with the US government are involved, but the real reason IANA can provide this service to the worldwide Internet community is that everybody agrees to respect their assignments. Your Internet service provider controls a block of numeric addresses, and it will assign you one address or more when you set up your new connections.
As far as the networks connected to that router are concerned, the router is just one more network connection with an IP address. The router presents a single address to the Internet that represents all the computers and other devices on your LAN; it performs a function called network address translation NAT that converts your public address to the addresses of individual network devices. In order to make this system work properly, IANA has reserved several blocks of IP address numbers for LANs; when a router receives a packet with an address in one of these ranges, it does not relay the packet to the Internet.
The reserved IP addresses are: A permanent assignment is called a fixed or static IP address; an automatic assignment is a dynamic address. Both fixed and dynamic IP address assignments can work equally well, but all the devices on the network must use the same system; otherwise, more than one device might use the same number at the same time. NOTE If your LAN includes laptops and other portables that connect and disconnect from the network, DHCP is the better choice because it allows the network to assign an address automatically when a user connects and to re-use the same address after the first user has disconnected.
Some Internet service providers and corporate network managers assign static IP addresses to each user, whereas others use DHCP to generate addresses. Chapters 10 and 11 explain how to set up your own computer and LAN to use either method. The Domain Name System Computers have no trouble handling long strings of numbers, but people often do. Addresses in the form of words rather than numbers are generally easier to remember and use.
In a LAN, each 38 C ha pt er 4 computer reads the name of every other device on the same network automatically; on the Internet, a computer called a Domain Name System server DNS server converts names to numeric addresses; when you type the name of a website into a browser, a DNS server finds the number that corresponds to that name and returns it to your browser, which connects to that numeric address. You or your network manager will assign a name to each computer when you set up your network; your Internet service provider should set up a domain name for your connection to the Internet.
In the Domain Name System, every name starts with a top-level domain name at the extreme right that can be either a generic description such as com, net, or edu or a twoletter country code such as uk for the United Kingdom or ca for Canada. As you move to the left, the next word or group of letters and numbers is a name called a subdomain that has been reserved by a specific owner—an individual, a business, a government agency, or some other formal or informal organization. Large organizations might have one or more additional subdomain names to the left of the first one.
Each part of the name is divided from the next one by a period read as dot. And within that department, the addresses of the research group studying evolutionary genetics is evolution. At the extreme left of a domain name, you will sometimes see a subdomain that identifies the type of server. This address might be the familiar www or some other Internet service such as ftp file transfer protocol. The http part stands for HyperText Transfer Protocol—the protocol that defines most websites.
Some top-level domains that use country codes have other structures that differ from one country to another. Domain names that have a us for United States top-level domain sometimes use subdomains also called secondlevel domains that identify the state and city where the owner is located, such as example. How C om put er N et work s Ar e O rg a ni zed 39 NOTE Just because a domain name address has a country code, the owner of that address is not necessarily located in that country.
For example, many American FM radio stations have obtained addresses in the. Table lists the most common generic top-level domains. Still others, such as. DNS servers perform what seems like a simple task, but this task is more complicated than it first appears because millions of domain names are out there, and new ones are added all the time.
Every DNS server in the world has to keep up with all the adds, moves, changes, and deletions.
It accomplishes this through a system of root servers that are continuously 40 C ha pt er 4 updated. When you set up your computer for access to the Internet, you must specify the DNS servers that the computer will use to convert domain names to numeric IP addresses. In most cases, your Internet service provider or network manager will give you the numeric address of one or more nearby DNS servers. If your primary DNS server is not accessible, your computer will look for an alternate server if you have provided an alternate address.
It will also allow you to set up two threeletter shortcuts to frequently used addresses and will automatically correct common keystroke errors such as typing example. All of these tools are simple text commands that you can use with just about any operating system. When you type a command, the system will display the results in the same window or screen. Subnet Mask. Default Gateway. Connection: DNS Suffix. The Subnet Mask tells the network which parts of the numeric address identify individual computers, and the Default Gateway is the numeric address within the LAN of the gateway router that connects your LAN to the Internet.
Primary Dns Suffix.
Node Type. IP Routing Enabled. Connection Physical Address. Dhcp Enabled. Autoconfiguration Enabled. IP Address. DHCP Server. DNS Servers. The Description identifies the type of network interface adapter that connects this computer to the network.
The format of the information display, however, varies in different operating systems. Therefore, the best place to find a detailed explanation of the ifconfig display produced by your own system is the man page for the ifconfig command. The key to successful network troubleshooting is to follow a logical problem-solving process, according to John Ross, the author of Network Know-How, a textbook from No Starch Press.
Network administrators need to understand the basics of designing and mapping a network in order to identify and solve common network problems. Ross suggests that network administrators look for easy solutions before they start a complex hardware or software diagnostic routine. Many of these suggestions are common sense but they're often overlooked. The chapter excerpt starts by introducing general troubleshooting techniques, followed by information on how to fix common networking issues.
In the book, Ross takes readers through the nuts and bolts of networks, explaining how to run cables, set up Wi-Fi access points, configure file sharing and printing and implement basic security measures. Copyright , No Starch Press. All rights reserved. Learn more about how to troubleshoot wireless networks and Ethernet networks in your environment.
Examining a bottom-up approach to network troubleshooting. An introduction to network troubleshooting and diagnostics. Ten network troubleshooting truths. Please check the box if you want to proceed. Video meetings are increasingly important as the workforce grows more distributed and joins meetings from personal devices, The vendor has also brought Webex Calling to its The vendor also released in beta software Apple's new line of iPhones made headlines for better battery life and cameras, but it's the improved security features that will Views Total views.
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