新的无线局域网标准

1、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 r

2、emote 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 o

3、riginal 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, freque

4、ncy-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 com

5、muni-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 ethe

6、rnet LANs.In september 1999, the IEEE approved a new designation, known ended 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 tec

7、hnique 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 inform

8、itter 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, i

9、nternet 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 multivend

10、or 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 pe

11、rformance 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

12、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1

13、1 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

14、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,

15、 applications and users in a single directory.This directory would bind a users 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 t

16、he 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 networ

17、k 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.Cust

18、omers 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.Per

19、haps, 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 users name, department, location and rank within the company, and bind

20、this information with the users 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 ban

21、dwidth has become cheaper and more plentiful in the LAN over the past two years, and thats 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, si

22、mple 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

23、 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

24、 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 (CI