Home networking explained, Part 1: Here’s the URL for youApr 22, 2014
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A typical wireless router with LAN ports for Ethernet-ready devices and antennas for Wi-Fi clients. Dong Ngo/CNET
Editors’ note: This post is part of an ongoing series and is updated add more information as home networking evolves. For the other parts in the series, check out the related-stories section below. As the guy who reviews networking products, I generally receive a couple of emails from readers a day, and most of them, in one way or another, are asking about the basics of networking (as in computer-to-computer, I am not talking about social media here.) While I appreciate emails because, at the very least, it gives me the impression that there are real people out there amid the sea of spam, I’d rather not keep repeating myself. So instead of saying the same thing over and over again in individual messages, I’ll talk all about home-networking basics, in layman’s terms, in this series. Advanced and experienced users won’t need this, but for the rest, I’d recommend reading the whole thing. 1. Wired networkingA wired local network is basically a group of devices connected to one another using network cables, more often than not with the help of a router, which brings us to the very first networking term. Router: This is the central device of a home network that you can plug one end of a network cable into. The other end of the cable goes into a networking device that has a network port. If you want to add more network devices to a router, you’ll need more cables and more ports on the router. These ports, both on the router and on the end devices, are called Local Area Network (LAN) ports. They are also known as RJ45 ports. The moment you plug a device into a router, you have yourself a wired network. Networking devices that come with an RJ45 network port are calledEthernet-ready devices. More on this below. Note: Technically, you can skip a router and connect two computers together using one network cable to form a network of two. However, this requires manually configuring the IP addresses, or using a special crossover cable, for the connection to work. You don’t really want to do that.
LAN ports: A home router usually has four LAN ports, meaning that out of the box it can host a network of up to four wired networking devices. If you want to have a larger network, you will need to resort to aswitch (or a hub), which adds more LAN ports to the router. Generally a home router can handle up to about 250 networking devices, and the majority of homes and even small businesses don’t need more than that. There are currently two main speed standards for LAN ports: Ethernet, which caps at 100Mbps (or about 13MBps), and Gigabit Ethernet, which caps at 1Gbps (or about 125MBps). In other words, it takes about a minute to transfer a CD’s worth of data (around 700MB or about 250 digital songs) over an Ethernet connection. With Gigabit Ethernet, the same job takes just about 5 seconds. In real life, the average speed of an Ethernet connection is about 8MBps, and of a Gigabit Ethernet connection is somewhere between 45 and 80MBps. The actual speed of a network connection depends on many factors, such as the end devices being used, the quality of the cable, and the amount of traffic. Rule of thumb: The speed of a single network connection is determined by the slowest speed of any party involved. For example, in order to have a wired Gigabit Ethernet connection between two computers, both computers, the router they are connected to, and the cables used to link them together all need to support Gigabit Ethernet. If you plug a Gigabit Ethernet device and an regular Ethernet device into a router, the connection between the two will be capped at the speed of Ethernet, which is 100Mbps. In short, LAN ports on a router allow Ethernet-ready devices to connect to one another and share data. In order for them to also access the Internet, the router needs to also have a Wide Area Network (WAN) port. On many routers, this port may also be labeled the Internet port.
A typical CAT5e network cable.Dong Ngo/CNET Switch vs. hub: A hub and a switch both add more LAN ports to an existing network. They help increase the number of Ethernet-ready clients that a network can host. The main difference between hubs and switches is a hub uses one shared channel for all of its ports, while a switch has a dedicated channel for each of its ports. This means the more clients you connect to a hub, the slower the data rate gets, whereas with a switch the speed doesn’t change according to the number of connected clients. For this reason, hubs are much cheaper than switches with the same number of ports. However, hubs are largely obsolete now since the cost of switches has come down significantly. The price of a switch generally varies based on its standard (regular Ethernet or Gigabit Ethernet, with the latter being more expensive), and the number of ports (the more ports, the higher the price). You can find a switch with just 4 or up to 24 ports (or even more). Note that the total of extra wired clients you can add to a network is equal to the switch’s total number of ports minus one. For example, a four-port switch will add another three clients to the network. This is because you need to use one of the ports to connect the switch itself to the network, which, by the way, also uses another port of the existing network. With this in mind, make sure you buy a switch with significantly more ports than the number of clients you intend to add to the network. Wide-area network (WAN) port: Also known as the Internet port. Generally, a router has just one WAN port. (Some business routers come with dual WAN ports, so one can use two separate Internet services at a time.) On any router, the WAN port will be separated from the LAN ports, and is often distinguished by being a different color. A WAN port is used to connect to an Internet source, such as a broadband modem. The WAN allows the router to connect to the Internet and share that connection with all the Ethernet-ready devices connected to it.
Note: Since most Internet connections are slower than 100Mbps (a fast cable connection, for example, is about 50Mbps down and about 6Mbps up), an Ethernet-rated WAN port is sufficient in most cases. However, Gigabit Ethernet routers tend to also come with a Gigabit WAN port. That said, switching from an Ethernet router to a Gigabit Ethernet router generally doesn’t translate into faster Internet speeds; it usually just helps devices within your local network (LAN) to connect to one another faster.
Broadband modem: Often called a DSL modem or cable modem, a broadband modem is a device that bridges the Internet connection from a service provider to a computer or to a router, making the Internet available to consumers. Generally, a modem has one LAN port (to connect to a router’s WAN port, or to an Ethernet-ready device) and one service-related port, such as a telephone port (DSL modems) or a coaxial port (cable modems), that connects to the service line. If you have just a modem, you’ll be able to connect just one Ethernet-ready device, such as a computer, to the Internet. To hook up more than one device to the Internet, you will need a router. Some providers offer a combo device that’s a combination of a modem and a router or wireless router, all in one. Network cables: These are the cables used to connect network devices to a router or a switch. They are also known as Category 5 cables, or CAT5 cables. Currently, most, if not all, CAT5 cables on the market are actually CAT5e, which is capable of delivering Gigabit Ethernet data speeds. The latest network cabling standard currently in use is CAT6, which is designed to be faster and more reliable than CAT5e. The difference between the two is the wiring inside the cable and at both ends of it. CAT5e and CAT6 cables can be used interchangeably and in my personal experience perform basically the same, except CAT6 is more expensive. For most home usage, what CAT5e has to offer is more than enough. In fact, you probably won’t notice any difference if you switch to CAT6, but it doesn’t hurt to use CAT6 if you can afford it. Now that we’re clear on wired networks, let’s move on to a wireless network. 2. Wireless networking: Standards and devicesA wireless network is very similar to a wired network with one big difference: devices don’t use cables to connect to the router and one another. Instead, they use wireless connections called Wi-Fi (Wireless Fidelity), which is a friendly name for the 802.11 networking standards supported by the Institute of Electrical and Electronics Engineers (IEEE). Wireless networking devices don’t need to have ports, just antennas, which sometimes are hidden inside the device itself. In a typical home network, there are generally both wired and wireless devices, and they can all talk to one another. In order to have a Wi-Fi connection, there needs to be an access point and a Wi-Fi client.
Access point: An access point (AP) is a central device that broadcasts a Wi-Fi signal for Wi-Fi clients to connect to. Generally, each wireless network, like those you see popping up on your smartphone’s screen as you walk around a big city, belongs to one access point. You can buy an AP separately and connect it to a router or a switch to add Wi-Fi support to a wired network, but generally, you want to buy a wireless router, which is a regular router (one WAN port, four LAN ports, and so on) with a built-in access point. Some routers even come with more than one access point (see discussion of dual-band routers below). Wi-Fi client: A Wi-Fi client or WLAN client is a device that can detect the signal broadcast by an access point, connect to it, and maintain the connection. (This type of Wi-Fi connection is established in the Infrastructure mode, but you don’t have to remember this.) Most, if not all, laptops, smartphones, and tablets on the market come with built-in Wi-Fi capability. Those that don’t can be upgraded to that via a USB or PCIe Wi-Fi adapter. Think of a Wi-Fi client as a device that has an invisible network port and an invisible network cable. This metaphorical cable is as long as therange of a Wi-Fi signal broadcast by an access point. Note: Technically, you can skip an access point and make two Wi-Fi clients connect directly to each other, in the Ad hoc mode. However, as with using a crossover network cable, this is rather complicated and inefficient, and is far less common than using the Infrastructure mode. Wi-Fi range: This is the radius an access point’s Wi-Fi signal can reach. Typically, a Wi-Fi network is most viable within about 150 feet from the access point. This distance, however, changes based on the power of the devices involved, the environment, and, most importantly, the Wi-Fi standard. A good Wireless-N access point can offer a range of up to 300 feet or even farther. The Wi-Fi standard also determines how fast a wireless connection can be and is the reason Wi-Fi gets complicated and confusing, especially when the Wi-Fi frequency bands are mentioned, which I just did. Frequency bands: These bands are the radio frequencies used by the Wi-Fi standards: 2.4GHz, 5GHz,and 60GHz. The 2.4GHz band is currently the most popular, meaning, it’s used by most existing network devices. That plus the fact that home appliances, such as cordless phones, also use this band, makes its signal quality generally worse than that of the 5GHz band due to oversaturation and interference. The 60GHz band is used only by the 802.11ad standard (more below).
 Depending on the standard, some Wi-Fi devices use either the 2.4GHz or the 5GHz band, while others use both of these and are called dual-band devices. A few tri-band devices also support the 60GHz band. Following are the existing Wi-Fi standards, starting with the oldest: 802.11b: This was the first commercialized wireless standard. It offers a top speed of 11Mbps and operates only on the 2.4GHz frequency band. The standard was first available in 1999 and is now totally obsolete; 802.11b clients, however, are still supported by access points of later Wi-Fi standards. 802.11a: Similar to 802.11b in terms of age, 802.11a offers a speed cap of 54Mbps at the expense of much shorter range, and uses the 5GHz band. It’s also now obsolete, though it’s still supported by new access points for backward compatibility. 802.11g: Introduced in 2003, the 802.11g standard marked the first time wireless networking was called Wi-Fi. The standard offers the top speed of 54Mbps but operates on the 2.4GHz band, hence offering better range than the 802.11a standard. It’s used by many older mobile devices, such as the iPhone 3G and the iPhone 3Gs. This standard is supported by access points of later standards. 802.11n or Wireless-N: Available since 2009, 802.11n has been the most popular Wi-Fi standard, with lots of improvements over the previous ones, such as making the range of the 5GHz band more comparable to that of the 2.4GHz band. The standard operates on both 2.4GHz and 5GHz bands and started a new era of dual-band routers, which with two access points, one for each band. There are two types of dual-band routers: selectable dual-band routers that can operate in one band at a time, andtrue dual-band routers that simultaneously offer Wi-Fi signals on both bands. On each band, the Wireless-N standard is available in three setups, depending on the number of spatial streams being used: single-stream, dual-stream, and three-stream, offering cap speeds of 150Mbps, 300Mbps, and 450Mbps, respectively. This in turns creates three types of true dual-band routers: N600(each of the two bands offers a 300Mbps speed cap), N750 (one band has a 300Mbps speed cap while the other caps at 450Mbps), and N900 (each of the two bands offers up to 450Mbps cap speed).
Note: In order to create a Wi-Fi connection, both the access point (router) and the client need to operate on the same band, either 2.4GHz or 5GHz. For example, a 2.4GHz client, such as an iPhone 4, won’t be able to connect to a 5GHz access point. If a client supports both bands, it will use only one of the bands to connect to an access point at a time, and when applicable it tends to “prefer” the 5GHz band to the 2.4GHz band, for better performance. 802.11ac: Sometimes refered to as 5G Wi-Fi, this latest Wi-Fi standard operates only on the 5GHz frequency band and currently offers Wi-Fi speeds of up to 1.3Gbps (or 1,300Mbps) when used in the three-stream setup. The standard also comes with dual-stream and single-stream setups that cap at 900Mbps and 450Mbps, respectively. (Note that the single-stream setup of 802.11ac is as fast as the top three-stream setup of 802.11n.) Currently, 802.11ac is the first Wi-Fi standard that can realistically operate with more than three spatial streams to offer even faster Wi-Fi speeds. In May 2013, Quantenna announced the first quad-stream 802.11ac chipset, called QSR1000, with a ceiling speed of 1.7Gbps. Devices supporting this new standard are not yet available on the market, however. For now the fastest 802.11ac routers on the market still have a Wi-Fi cap of 1.3Gbps. Technically, the 802.11ac standard is about three times faster than the 802.11n (or Wireless-N) standard, and therefore is much better for battery life (since it has to work less to deliver the same amount of data). In real-world testing so far, I’ve found that 802.11ac is about twice the speed of Wireless-N, which is still very good. (Note that the real-world sustained speeds of wireless standards are always much lower than the theoretical speed cap. This is partly because the cap speed is determined in controlled, interference-free environments.) The fastest real-world speed of an 802.11ac connection I’ve seen so far is around 65MBps (or 520Mbps), which is close to that of a Gigabit Ethernet wired connection. On the same 5GHz band, 802.11ac devices are backward-compatible with Wireless-N and 802.11a devices. While 802.11ac is not available on the 2.4GHz band, for compatibility purposes, an 802.11ac router will also come with a Wireless-N access point. That said, all 802.11ac chips on the market support both 802.11ac and 802.11n Wi-Fi standards. 600Mbps 802.11n: As mentioned above, the top commercial speed of 802.11n is 450Mbps. However, in June 2013, Broadcom introduced a new 802.11ac chipset with TurboQAM technology that raises the speed of 802.11n to 600Mbps. And also for this reason, 802.11ac routers now are generally marketed asAC1900, AC1750, or AC1200. This designation basically means it’s an AC-enabled router that offers a combined wireless speed on both bands equal to the number. For example, an AC1900 router is capable of providing up to 1,300Mbps on the 5GHz band and up to 600Mbps on the 24GHz band. That said, let me state the rule of thumb one more time: The speed of a single network connection is determined by the slowest speed of any of the parties involved. That means if you use an 802.11ac router with an 802.11a client, the connection will cap at 54Mbps. In order to get the top 802.11ac speed, you will need to use a device that’s also 802.11ac-capable. 802.11ad or WiGig: The 802.11ad wireless networking standard just became part of the Wi-Fi ecosystem during CES 2013. Prior to that, it was considered a different type of wireless networking. 802.11ad uses the 60GHz frequency band to offer a data rate of up to 7Gbps (about seven times the speed of wired Gigabit Ethernet), but has much shorter range (about 30 feet) than other Wi-Fi standards. On top of that it generally requires a clear line of sight, meaning no obstacles between devices, to work well. 802.11ad, by itself, is not backward-compatible with any existing Wi-Fi standards and is designed not to replace but to coexist with them.
A wireless router and USB client, both with their Wi-Fi Protected Setup (WPS) button.Dong Ngo/CNET 3. More on wireless networkingIn wired networking, a connection is established the moment you plug the ends of a network cable into the two respective devices. In wireless networking, it’s more complicated than that. Since the Wi-Fi signal broadcast by the access point is literally in the air, anybody with a Wi-Fi client can connect to it, and that might pose a serious security risk. To make it so that only approved clients can connect, the Wi-Fi network needs to be password-protected (or in more serious terms: encrypted). Currently, there are a few methods used to protect a Wi-Fi network, called “authentication methods”: WEP, WPA, and WPA2, with WPA2 being the most secure, while WEP is becoming obsolete. WPA2 (as well as WPA) offers two ways to encrypt the signal, which are Temporal Key Integrity Protocol (TKIP) and Advanced Encryption Standard (AES). The former is for compatibility, allowing legacy clients to connect; the latter allows for faster connection speeds and is more secure but only works with newer clients. From the side of the access point or router, the owner can set the password (or encryption key) that clients can use to connect to the Wi-Fi network. If the above paragraph seems complicated, that’s because Wi-Fi encryption is very complicated. To help make life easier, the Wi-Fi Alliance offers an easier method called Wi-Fi Protected Setup. 
Wi-Fi Protected Setup or WPS: Introduced in 2007, Wi-Fi Protected Setup is a standard that makes it easy to establish a secure Wi-Fi network. The most popular implementation of WPS is the push-button. Here’s how it works: On the router (access point) side, you press the WPS button. Now, within 2 minutes, you press the WPS button on the Wi-Fi clients, and that’s all you need to do to make them connect to the access point. This way you don’t have to remember the password (encryption key) or type it in. Note that this method only works with devices that support WPS. Most networking devices released in the last few years do, however. Wi-Fi Direct: This is a standard that enables Wi-Fi clients to connect to one another without a physical access point. Basically, this allows one Wi-Fi client, such as a smartphone, to turn itself into a “soft” access point and broadcast Wi-Fi signals that other Wi-Fi clients can connect to. This standard is very useful when you want to share an Internet connection. For example, you can connect your laptop’s LAN port to an Internet source, such as in a hotel, and turn its Wi-Fi client into a soft AP. Now other Wi-Fi clients can also access that Internet connection. Wi-Fi Direct is actually most popularly used in smartphones and tablets, where the mobile device shares its cellular Internet connection with other Wi-Fi devices, in a feature called personal hotspot. 4. Power line networkingWhen it comes to networking, you probably don’t want to run network cables all over the place, making Wi-Fi a great alternative. Unfortunately, in some places, such as that corner in the basement, a Wi-Fi signal can’t reach, either because it’s too far away or because there are thick concrete walls in between. In this case, the best solution is a pair of power line adapters. Power line adapters basically turn the electrical wiring of a home into network cables for a computer network. You need at least two power line adapters to form the first power line connection. The first adapter is connected to the router and the second to the Ethernet-ready device at the far end. There are some routers on the market, such as the D-Link DHP-1320, that have built-in support for power line connections, meaning you can skip the first adapter. More on power line devices can be found here. Currently there are two main standards for power line networking, HomePlug AV and Home Plug AV2. They offer speed caps of 200Mbps and 500Mbps, respectively. That’s it. Now if you haven’t found your questions answered, send them to me via facebook, Twitter, or just post them in the comments section below. Want to learn more about how to best optimize your Wi-Fi network? Check out Part 2 of this series.
Via the original article here – bookmark for reference later. Walbrandt Technologies can help you with planning, installation and support of any size or type of network you might have. Call or email us today if you need any help getting your technology running properly.
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来自： astrotycoon > 《网络》
