新的无线局域网标准

　　计算机专业英语词汇指与计算机硬件、软件、网络等多方面有关的英语词汇，主要包括硬件基础、计算机系统维护、计算机网络基础、软件、程序设计语言、计算机网络技术、IT职场英语等词汇。下面是小编为您收集整理的新的无线局域网标准，供大家参考!

　　新的无线局域网标准

　　With portable computers and wireless LANs, users can enjoy greater productivity while away from their desks, whether they are in conference rooms, public areas or remote offices.

　　Until recently, however, wireless LANs were too slow for most enterprise applications.based on the IEEE 802.11 standdrd, they ran at 1M to 2M bit/sec.

　　Now a new high-rate extension to the standard, 802.11b, lets wireless networks support data rates to 11M bit/sec.

　　Ratified in 1997, the original 802.11 standardunited the wireless industury by defining a low-level protocol architecture that worked with conventional upper-layer enterprise protocol stacks. Also, 802.11 maintained compatibility with the three most popular radio transmission types: direct sequence spread spectrum, frequency-hopping spread spectrum, and infrared.

　　Essentially, this new architecture added intelligence at the medium access control(MAC)layer 2 and at the physical(PHY)layer 1, fosteing cooperation between the two layers in performing the critical tasks involved with initiating and maintaining wireless communi-cations.

　　For instance, to ensure reliability of the wireless link, MAC and PHY work together to determine if a clear path exists before they start a transmission.

　　During transmission, they employ special collision-avoidance and arrival-acknowledgment techniques that are not required in wired ethernet LANs.

　　In september 1999, the IEEE approved a new designation, known as 802.11.intended to retain the error-correction，security, powermanagement and other advantages of the original, a key ingredient-a thchnique for increasing bandwidth to 11M bit/sec.

　　Called complementary code keying(CCK)the technique works only in conjunction with the DSSS technology sprcified in the original standard . it does net work with frequency-hopping or infrared transmissions.

　　What CCK does is apply sophisticated mathematical formulas to the DSSS codes, a permitting the code to represent a greater volume of informitter is now able to send multiple bits of information with each DSSS code, enough to make possible the 11M bit /sec in the original standard .

　　The 802.11b standard benefits users by delivering wireless ethernet speeds of 11M bit/sec that can reliably support everyday business applications, e-mail, internet and server network access.

　　With support from the new wireless ethernet from the new wireless ethernet compatibility alliance, founded by 3com, lucent, nokia and several other companies in the wireless LAN business, the new standard will also promise certified interoperability across multivendor platforms.

　　Finally, the 802.11b standard serves as a clamoring for a simplified wireless LAN landscpape.

　　Vendors can now focus on a single, high-speed standard, and users can cut through the clutter of wireless options by fovusing on a standard that delivers multibvendor interoperability and the performance to meet their application needs.

　　有了便携式和无线局域网，用户在离开其办公桌的时候，不管是在会议室、公共区域还是在远处办公室，都能享有更高的生产效率。

　　然而，时至今日，无线局域网对多数企业应用来说还是太慢。依据IEEE802.11标准，他们运行速度为1兆至2兆位/秒。

　　现在对此标准的一个新的更高速扩展，能让无线网支持高达11兆位/秒的数据速率。

　　最初的802.11标准是在1997年提出的，通过定义能与常规的上层企业协议组一起工作的低级协议体系结构，把无线行业团结起来了。802.11也保持了与三种最流行的无线电传输方式(直接顺序扩频、跳频扩频和红外线)的兼容性。

　　本质上，这种新的体系结构在介质接入控制(MAC)层(第二层)和物理层(第一层)增加了智能，建立这两层之间在执行及开始和保持无线通讯的关键任务时的协作关系。

　　例如：为确保无线连接的可靠性，MAC层和物理层一起工作，以确定在他们开始传输之前是否有一条清晰的路径。

　　在传输过程中，他们采用有线以太网不需要的、特殊的避免碰撞和到达应答技术。

　　1999年9月，IEEE批准了称作802.11B的新名称，作为802.11的高速扩展。此新的802.11B标准在保留原标准的纠错、安全、电源管理和其他优点的情况下，增加了一项关键内容，即把带宽增加到11兆位/秒的技术。

　　此项技术叫做互补码键控(CCK)，他只与原标准中规定的直接顺序扩频(DSSS)技术一起工作，不能用跳频或红外线传输方式工作。

　　CCK所做的工作是把复杂的数学公式应用于DSSS代码，以允许该代码在每个时钟周期表示更多的信息。现在发射机能在每个DSSS代码中发送多个信息位，足以实现每秒11兆位/秒的数据传输率，而不是原标准的2兆位/秒。

　　802.11B 标准给出11兆位/秒的无线以太网速度，给用户带来好处，速度能可靠地支持日常的业务应用、电子邮件、因特网和服务器网络的接入。

　　由3COM、LUCENT、NOKIA和其他几家有无线局域网业务的公司组成的“无线以太网兼容性联盟”支持新的标准，此标准也有望实现跨多厂商与用户团结起来的作用。

　　现在，厂商能专注在单一的高速标准上，用户也能以通过关注给出厂商互用性和性能。以满足他们应用要求的标准上，解决了从一大堆无线网中作选择的难题。

　　目录允许网络

　　Almost three years ago, cisco and microsoft annouced the directory enabled network(DEN)initiative, which sought to develop a standard for storing information about network devices, applications and users in a single directory.

　　This directory would bind a user's name and network resource access profile to policies for granting or restricting that access, and delegating bandwidth priorities and privileges.work on standardizing specifications for the directory were handed off to the distributed manage-ment task force (DMTF).

　　In march, the DMTF announced it had completed work on a new version of the common infor-mation model that facilitates the mapping of the CIM schema into a lightweight directory access protocol(LDAP)-compliant directory. CIM defines how to represent network device, system and application data in a directory so it can be easily shared for DEN and enter-prise management purposes.

　　By mapping the CIM schema into an LDAP directory, users will be able to further integrate directory information into an overall enterprise management system, the DMTF says.

　　Customers will make DEN-compliant products a priority once the DMTF makes a little more progress on DEN specifications-such as defining a pollicy schema that would specify data structures for binding directory profiles to network security and quality-of-service (QOS)policies and products soon follow.

　　Perhaps, vendors still have to determine how to use directories to prompt network and applications to configure themselves based on business policies. For example, when a user logs on to a network, the directroy would recognize the user's name, department, location and rank within the company, and bind this information with the user's network access or restriction policies. then the IT infrastructure would configure itself accordingly to enable or disable that a access.

　　One of the killer applications for DEN when it was announced was the ability to link QoS policies to users via dircetories. But bandwidth has become cheaper and more plentiful in the LAN over the past two years, and that's made QOS much less of an issue.

　　Instead of prioritizing bandwidth allocation, users can inexpensively overprovision band-width when they need to support delay-sensitive traffic such as voice and video. Also, simple mechanisms such as setting 802.1p bits on ethernet frame or type-of -service bits in IP headers are enough for LAN QOS.

　　Nonetheless, there 's still a huge demand among enterprise users for directories to enable self-configuring networks based on business policy.

　　DEN for QOS may still apply for WAN applications, edholm says. Indeed cisco has made more strides with DEN in the service provider market than in the enterprise arena.

　　Service providers are looking to DEN to integrate multivendor products into an interoperable operational support system.

　　So despite the silnece, progress on DEN is being the silnece, progress on DEN is being made and activty is expected to pick up once standards become a little more solidiffed.

　　差不多三年前，思科公司和微软公司宣布了目录允许网络(DEN)倡议，该公司要求开发一个在单一目录中存储有关网络设备、应用程序和用户等信息的标准。

　　此目录把用户的名字和网络资源访问简表与允许或限制访问的政策和安排带宽优先级别及特权挂起钩来。此目标标准规范的研究工作交给了分布管理任务组(DMTF)。

　　今年三月，DETF 宣布完成了新版公共信息模型(CIM)的研究工作，此模型实现了CIM模式映射到简便目录访问协议(LDAP)的相应目录中，CIM 定义如何在目录中表示网络设备，系统和应用数据，因而它很容易为DEN 和企业管理目的而被共享。

　　DMTF 称， 通过把CIM 模式映射到LDAP 目录，用户就能进一步把目录信息与整个企业管理系统结合起来。

　　一旦DMTF在DEN 规范上取得更多一些进展，如定义一个为把目录简表与网络安全和服务质量(QOS)政策捆绑在一起而规定数据结构的政策模式，以及随之而来的产品，客户将优先使用符合DEN的产品。

　　厂商们也许还不得不确定怎样利用目录来提示网络和应用程序以便依据商业政策来配置他们自己。例如：当一用户登录上网时，目录将会识别出用户的名字、所在的部门、地点及在公司中的级别，把这些信息与用户的网络访问或限制政策捆绑在一起。然后，IT 基础设施就能相应地配置自己，以便实现或不让实现访问。

　　当年宣布DEN 的最具冲击力的应用之一是通过目录把QOS 政策与用户联系起来的能力，但在过去两年局域网中带宽变的更为便宜和充足，是QOS不再是个问题。

　　当用户需要支持对延迟敏感的流量，如声音和视频图象时，他们可以廉价地获得很大的带宽，而不用对带宽进行优先等级分配。同时，在以太网桢上设置802.1P 位或者在IP 报头中设服务类型位等简单机制对局域网的QOS 来说已经足够了。

　　然而，在企业用户中对目录还存在着巨大需求，以便能够依据商业政策自行配置网络。

　　EDHOLM说：“实现QOS 的DEN 还可以应用于广域网上的应用程序。实际上。思科公司利用DEN 在服务供应商市场上取得了比企业市场更大的进步。服务供应商正期待着把DEN 做进更多厂商产品中去，成为一个可互用的运行支持系统。

　　尽管(DEN)比较沉默，但DEN 正在取得进步，一旦此标准变的更为稳定，DEN 可望会有所作为。