计算机专业时文选读(981)
VoWLANVoWLAN(VoiceoverWLAN)isamethodofsendingvoiceinformationindigitalformoverawirelessbroadbandnetwork.Essentially,VoWLANisVoIPdeliveredthroughwirelesstechnology.Thetechnologyissometimescalled“VoWi-Fi”or“Wi-FiVoIP”becauseitusestheIEEE802.11setofspecificati
VoWLAN
VoWLAN (Voice over WLAN) is a method of sending voice information in digital form over a wireless broadband network. Essentially, VoWLAN is VoIP delivered through wireless technology. The technology is sometimes called“VoWi-Fi”or “Wi-Fi VoIP”because it uses the IEEE 802.11 set of specifications (informally known collectively as Wi-Fi) for transporting data over wireless local area networks and the Internet.
VoWLAN requires a voice-enabled wireless device, most commonly a PDA or a“Wi-Fi handset,”which looks and operates like a cell phone, but sends voice as discrete data packets rather than an analog voice stream. Callers can also use a software-based phone, known as a softphone, that resides on devices including laptop and desktop computers. The VoWLAN system routes calls from the phone to a WLAN access point and then to a VoIP gateway or IP PBX. The call is sent to its appropriate destination within the private network or out onto the Internet or PSTN.
The VoWLAN system allows all regular functions and messaging applications available on wired phones to be available on the VoWLAN devices. Like VoIP, VoWLAN also contributes to cost efficiency. Because calls can be routed over the data network internally or over the Internet externally, mobile telephony costs can be eliminated or decreased significantly.
Major barriers to VoWLAN include inconsistent voice performance and the need for quality of service (QoS); slow and unreliable encryption and authentication; and the proprietary nature of current products. The IEEE and the Wi-Fi Alliance have been developing standards improvements to mitigate VoWLAN limitations. The recent 802.11i standard implemented intelligent security to speed up authentication while Roaming. Other upcoming standards enhancements include:
● The 802.11e standard will define QoS measures that will prioritize voice traffic using two methods, Wireless MultiMedia (WMM) and WMM Scheduled Access
● 802.11r will specify a fast-roaming protocol to minimize packet loss when users move from one access point to another within a WLAN
● 802.11k will include the Radio Resource Management protocol to enable a handset to pre-discover the conditions of the WLAN network and choose the best available paths.
VoWLAN is most frequently found in the retail, manufacturing and health care industries, where WLAN was adopted early and use has progressed quickly. In the long term, VoWLAN deployment is a significant step toward interoperability and seamless mobile connectivity between private WLANs and public wireless and cellular networks.
VoWLAN
VoWLAN(无线局域网电话)是一种在无线宽带网络上以数字形式发送声音信息的方法。本质上，VoWLAN是通过无线技术提供的IP电话。有时，此项技术被称为VoWi-Fi或者Wi-Fi VoIP, 因为它采用一组IEEE 802.11规范(非正式地统称为Wi-Fi)在无线局域网和因特网上传送数据。
VoWLAN需要实现声音的无线设备，最常用的是PDA(个人数字助理)或Wi-Fi手持设备，它们看上去很像手机电话，但它们是以离散的数字包而不是模拟的声音流发送声音的。呼叫者也能使用基于软件的、留驻在便携式和台式计算机等设备中的电话，称之为软电话。VoWLAN系统将呼叫从电话机路由到无线局域网的接入点，然后路由到VoIP网关或IP电话小交换机。最终呼叫被送到专网中的目的地或者外送到因特网或传统电话网。
VoWLAN系统使得在有线电话上能实现的所有常规功能和传信应用在VoWLAN设备上也能实现。VoWLAN与VoIP一样，节约了成本。因为呼叫能在内部的数据网或者外部的因特网上路由，所以能消除或者大大减少移动电话的成本。
VoWLAN的主要障碍有声音性能的不一致和需要服务质量(QoS)保证，缓慢和不太可靠的加密和认证，以及目前产品的专有性。IEEE和Wi-Fi联盟一直在对标准进行改进，以减少VoWLAN的局限性。最新的802.11i标准实现了智能安全，提高了漫游时的认证速度。其他将要问世的标准改进还有：
● 802.11e标准定义利用了两种方法，即利用无线多媒体(WMM)和WMM预定访问使声音流量优先化的QoS措施。
● 802.11r将制订快速漫游协议，使用户在无线局域网中从一个接入点移到另一个接入点时包丢失减至最小。
● 802.11k将包括无线电资源管理协议，以便使手机预先发现无线局域网的状态和选择最好的可用方式。
VoWLAN在零售、制造和卫生行业最常见，这些行业较早采用无线局域网，发展很快。从长远看，部署VoWLAN是朝着专用无线局域网和公共的无线网络以及蜂窝网络之间互操作和无缝移动连接的关键一步。
