WiFi 及WLAN基础知识(专 业英语)

WiFi 及WLAN基础知识(专 业英语) What is WLAN ? The term wireless means any technology which is used without any hard wired connection, such as Bluetooth, GSM/GPRS, and 3G. Among all, the wireless technology broadly refers to the WLAN, as is “Wireless Local Area Network”, which links more than two devices without entangling wires. The wireless network enables you to surf the internet anywhere in the house. You can save both the cost of extra Ethernet cables and times to set up the network. All you need to do is install the adapter and upgrade your PC into the wireless network; you can then enjoy the benefit of it. What is Wi-Fi ? The Term “Wi-Fi”, as short for ”Wireless Fidelity”, is invented by the Wi-Fi Alliance, which is intended to improve the interoperability of wireless local area network products. “Wi-Fi” was originally referring to the Wi-Fi Alliance and the Wi-Fi Certification applicable only to 802.11b standard. Today it is broadly referring to any of the IEEE 802.11 WLAN Standards, including 802.11b, 802.11a, 802.11g, and the latest 802.11n standards. (See What are WLAN standards?) Wi-Fi Alliance and Wi-Fi Certified The Wi-Fi Alliance is a nonprofit international association to certify a set of interoperable WLAN products based on the IEEE802.11 standards. Manufacturers that are members of Wi-Fi Alliance and whose products pass the interoperability tests hold by the Wi-Fi Alliance will be approved as “Wi-Fi Certified” and can mark their products with the Wi-Fi logo. Meanwhile a user who carries a "Wi-Fi Certified" product can use any brand of access point with any other brand of client hardware that also is certified. What are WLAN standards ? WLAN Standards is also known as the IEEE802.11 technologies developed by the IEEE (Institute of Electrical and Electronics Engineers, Inc), which specifies an over-the-air interface between the client and base station or two wireless clients. According to different encryption and data rate, IEEE802.11 technologies mainly consist of 802.11b, 802.11a, 802.11g, and 802.11n. 802.11b The 802.11b specification was the first widely accepted wireless networking standard. It operates in the 2.4 GHz ISM band, and has a maximum speed of 11Mbps within the range up to 50 meters. Since 802.11b operates at the frequency of 2.4GHz as the common channel frequency, it can be interfered with obstacles like microwave or cordless phones. 802.11a Compared with 802.11b, the 802.11a specification operates at the frequency of 5 GHz, which can be less affective by other devices in the crowded 2.4GHz range. It speeds up to 54Mbps better than the 11Mbps as 802.11b, but performs within the range only up to 30 meters. 802.11a is incompatible with both 802.11b/g as they operate on separate bands; except if using devices that provide dual band functionality. 802.11g The 802.11g specification operates at the frequency of 2.4GHz, the same as 802.11b. But compared with 11Mbps for 802.11b, 802.11g offers transmission up to 54Mbp like 802.11a does. Since the 802.11b and 802.11g works at the same frequency, the equipment with both specifications is interoperable. The 802.11g is backward compatible with 802.11b so that devices with 802.11g specification also work with 802.11b. However, 802.11g and 802.11b both suffer from the same interference of crowded 2.4 GHz band. The performance might be affective by other devices like microwave, Bluetooth devices, and cordless phones. 802.11n (draft 2.0) 802.11n specification is the next generation of 802.11 Wi-Fi technologies. It is estimated to deliver at the maximum speed of 600Mbps, within range of 100 meters. 802.11n is backward compatible with 802.11b/g standards as well as supports high-data rate transmission applications like HD video or audio streaming, gaming and more. Comparison for 802.11a/b/g/n WLAN Standard Chart Standard bandwidth Range Frequency Remark Fast data rate transmission Suffers less from signal 802.11a 54Mbps 30 meters 5GHz interference with other devices. Suits for homes and offices that need to transfer within a short distance。 Long-range transmission; 802.11b 11Mbps 50 meters 2.4GHz Most acceptable ; lowest price Fast data rate transmission; Long-range transmission; 802.11g 54Mbps 30 meters 2.4GHz Compatible with 802.11b equipment Compatible with 802.11b/g; Up to 5 times faster than 802.11n 150~600Mbps 100 meters 2.4GHz/5GHz 802.11g; Up to 2 times farther than 802.11g , 802.11g operates compatibly with 802.11b, which are more acceptable than 802.11a. , 802.11a suffers less from signal integrity and supports 54Mbps over a relatively short distance. , 802.11n performs up to 5 times faster and 2 times farther than 802.11g. How does 802.11n work ? (About the MIMO Technology) Building on previous 802.11 standards, 802.11n adds the MIMO technology. MIMO stands for “Multi-Input Multi-Output” and uses multiple transmitter and receiver antennas to improve the performance of radio communication systems. In MIMO there can be a separate RF chain for each antenna allowing multiple chains to coexist, so the MIMO system can process more signals and accommodate more data as multiple radio signal are carried on the same frequency simultaneously. These allow the wireless network to improve the speed and throughput as well as reduce the dead spots without additional bandwidth or transmit power. Is wireless network secure? One consideration of the wireless network is security. Some of the main technologies to prevent attackers from home network are as following: 1. WEP WEP is short for the Wired Equivalent Privacy and refers to a security protocol for WLAN defined in the 802.11b standards. It is designed to provide the same level of security similar to that provided by the physical security inherent in a wired LAN. WEP aims to provide security by encrypting data over radio waves so that it is protected as it is transmitted from one end point to another. Since WEP was an early encryption technique to secure Wireless connection, some of its weakness has been identified. It was then superseded by Wi-Fi Protected Access (WPA) and 802.11i (also know as WPA2) for better security. In spite of its weakness, WEP is capable of a level of security to prevent casual snooping. WEP is usually presented as the first security choice in most installation instructions. 2. WPA WPA (Wi-Fi Protected Access), based on the IEEE802.11i draft 3, is wireless security greater protection than WEP. WPA serves as an intermediate solution between WEP and 802.11i networks, and has backward compatible WEP supports for older devices. WPA adds authentication to WEP’s basic encryption. It operates in either WPA-PSK mode (aka Personal mode) or WPA-802.1x mode (aka Enterprise mode). The Personal mode uses a pre-shared key (PSK) for authentication with less security since every user is given the same passphrase, while the Enterprise mode uses an IEEE802.11x authentication server for better security. WPA uses Temporal Key Integrity Protocol (TKIP) mechanism. TKIP dynamically changes keys as the system is used. This is difficult for hackers to read messages so as to improve the security in the WPA over WEP. 3. WPA2 WPA2 is the following security protocol to WPA and backward interoperable with WPA. WPA2 operates based on the full IEEE802.11i specification. WPA2 provides support for all of the mechanisms available in WPA. Both offer a high level of assurance for end-users and network administrators that their data will remain private and access to their network restricted to authorized users. Both have the Personal and Enterprise mode of operation for the authentication. Compared with WPA, the enhanced WPA2 uses Advanced Encryption Standard (AES) in addition to TKIP. This provides a stronger encryption mechanism. FAQ AW-GA200 Common Problem Q: There is a message that says this device has been owned by “xxxx” and I cannot connect to it. A: On the advanced setting page of wireless audio utility, current user can lock the utility and reject the other users connecting to this device. Hence, you cannot connect to AW-GA200. Q: What is my device’s default IP Address? A: The device’s default IP address is 192.168.0.10. Q: What should I do if I forget all the default settings? A: You may reset to the default settings of AW-GA200 by pressing and holding the reset button on the rear panel for 10 seconds then go to Setup Wizard to configure again. Q: My Device has a wired connection to my network. Why can’t I see the Device on my Device Utility? A: Restart the PC and try again. Check all the cable connections and power. Q: My device is wirelessly connected to my network, why can’t I see the Device on my Device Utility? A: Restart the PC and try again. If it happens again, please return to the Setup Wizard again and make sure you configure the Device properly or move your Device closer to your wireless access point and try again. Music Adapter Q: What kind of music format I can play with AW-GA200? A: You can use anything that plays on your PC. Q: I cannot hear the music A: Please check Audio LED(Blue), make sure the blue LED is turned on and flashing. If blue LED is turned off, please check your wireless connection, and open the AzureWave Wireless Audio Utility to connect to the AW-GA200. Please check your wireless audio utility, it will display device status, make sure you are the person connect to the device. If blue LED is turn on but not flashing, it means wireless audio connection is successful but NO audio stream is running. Please restart your PC audio player and play the audio. Q: Can I listen to music from more than one AW-GA200 at the same time? A: Yes, you can stream PC audio to multiple AW-GA200 devices. Warning: This feature only support AW-GA200 is working under “Client” mode. Due to AW-GA200 hardware limitation, when AW-GA200 work as Access Point and support this feature, it could be cause the sound break occasionally. Q: I hear some sound breaks occasionally, what can I do? A: This should not happen in normal cases, but could happen due to some wireless RF interference, especially if there are many wireless devices nearby, such as access points or routers, a microwave oven, Bluetooth device, cordless phone, etc. Keep your AW-GA200 away from these devices. If you are using an Intel Centrino based laptop or some old WLAN card/dongle, it may have a short period of suspending time for background scanning around every minute. It may also cause sound streaming break. Please contact your wireless adapter factory to download the latest driver of your WLAN card. This problem only exists on Intel old driver version. You can also change the power management setting of your wireless adapter from Max power saving to Max performance Q: The music is coming from PC’s speaker and not the speaker that connects to the AW-GA200. A: Please open the AzureWave Wireless Audio Utility to connect to the AW-GA200, and restart your PC audio player. Q: My Wireless Device has been detected and connected to the utility, but there is no music coming from the speaker. A: Check LED on front panel, make sure the wireless audio LED (blue one) is lighting up and flashing. If yes, please check following item. 1.Check your audio cable connection. 2.If cable connection is correct, please close, then re open the audio player 3.Reboot the PC and try again. If wireless audio LED (blue one) is turn-off, please check your wireless network, make sure your PC is connecting to AW-GA200. If wireless audio LED (blue one) is lighting up but not flashing, please check your wireless audio utility, make sure you already connect to AW-GA200. Basic AP Functions Q: My device does not turn on. No LED’s light up. A: Connect the power adapter to your AP and plug it into the power outlet. Note: Only use the power adapter provided with your AP. Using any other adapter may damage your AP. Q: LAN Connection Problems - I can’t access my AP. A: Make sure your AP is powered on. Make sure that your computer has a compatible IP Address. Be sure that the IP Address used on your computer is set to the same subnet as the AP. For example, if the AP is set to 192.168.0.10, change the IP address of your computer to 192.168.0.15 or another unique IP Address that corresponds to the 192.168.0.X subnet. Use the Reset button located on the rear of the AP to revert to the default settings. Q: I can’t connect to other computers on my LAN. A: Make sure that each computer has a unique IP Address. And the IP must be in the same subnet as the AP. Make sure that the Link LED is on. If it is not, try a different network cable. Check each computer for correct network settings. Wireless Troubleshooting Q: I can’t access the Wireless AP from a wireless network card A: Make sure that the Mode, SSID, Channel and Encryption settings are set the same on each wireless adapter. Make sure that your computer is within range and free from any strong electrical devices that may cause interference. Check your IP Address to make sure that it is compatible with the Wireless AP. Q: I can’t establish connection with Wireless AP with WPA2 encryption by using Windows Zero Configuration A: Update Windows XP with latest Wi-Fi Protect Access 2 (WPA2) through windows update, or alternatively search Microsoft’s support site for latest copy of service pack or patch for WPA2. 单词 throughput n.生产量, 生产能力, 吞吐量\ supersede [ 7sju:pE5si:d ] vt.代替, 取代, 接替, 紧接着...而到来, [律]延期 vi.推迟行动