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IEEE802.11e無線聯(lián)網(wǎng)標(biāo)準(zhǔn)

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在CFP中改進(jìn)的信道訪問和維持輪詢向后兼容性的能力，帶來了更高效率的輪詢 。另外還包括了傳輸調(diào)度和單一命令中鏈接輪詢序列的能力 。
這些機(jī)制提供了最大效率的高帶寬數(shù)據(jù)流、電力治理友善實(shí)現(xiàn)以及對(duì)可變位速率和脈沖式數(shù)據(jù)流的輪詢式訪問 。
QoS基線中采用的集中式調(diào)度器保證了避免沖突，因此，改進(jìn)了傳送時(shí)間要害的負(fù)荷的能力 。承諾重要的QoS合約（如延遲、抖動(dòng)和帶寬）的能力也大為改進(jìn) 。信道訪問與由子網(wǎng)帶寬治理器（類似于更高層的協(xié)議和機(jī)制）完成的分配聯(lián)系在一起，因此獲得了更高的系統(tǒng)可靠性 。
無線系統(tǒng)中信道的健壯性是一個(gè)重要的考慮因素，因?yàn)樵肼暋⒏蓴_和多路徑效應(yīng)在2.4GHz和5.xGHz頻段上導(dǎo)致信道吞吐量的變壞，負(fù)面地影響了對(duì)滯后敏感的和高帶寬的流量（如語音和視頻）的可靠傳輸?shù)哪芰?。
人們對(duì)改進(jìn)信道的健壯性非凡關(guān)注 。提議的方案包括FEC（正向糾錯(cuò)）和選擇性重發(fā) 。這些機(jī)制包含了在每個(gè)數(shù)據(jù)流的基礎(chǔ)上制定糾錯(cuò)、確認(rèn)和重發(fā)政策的能力，從而通過針對(duì)每種類型數(shù)據(jù)流專門制定政策的方式，適應(yīng)了多種不同的數(shù)據(jù)流類型 。
通過FEC、有選擇重發(fā)的滯后確認(rèn)和動(dòng)態(tài)信道變化，信道的吞吐量得到大大改進(jìn) 。甚至在企業(yè)環(huán)境中部署了大量的無線子網(wǎng)時(shí)，基線的那些必進(jìn)仍能支持QoS 。在這樣的環(huán)境中，多個(gè)IEEE802.11e子網(wǎng)可能共存于各個(gè)無線電覆蓋的范圍內(nèi)，在不同子網(wǎng)中的設(shè)備進(jìn)行通信時(shí)，會(huì)引起干擾和（或）沖突 。
QoS基線尚未獲得批準(zhǔn) 。在這一過程中，下一步是批準(zhǔn)規(guī)范草案，然后是批準(zhǔn)最終的規(guī)范 。
Improved channel Access during CFP, and the ability to retain polling for backward compatibility, result in more efficient polling. The ability to schedule transmissions and chain a sequence of polls in a single command is included.
These mechanisms provide for maximum efficiency for high-bandwidth streams, power-management friendly implementations, and poled-style access for variable bit rate and bursty streams.
The centralized scheduler used in the QoS Baseline guarantees collision avoidance and, therefore, improved ability to deliver time-critical payloads. The ability to honor critical QoS contracts sUCh as latency, jitter and bandwidth is much improved. Channel access is tied to the allocations made by subnet bandwidth manager –like higher layer protocols and mechanisms so system reliability is achieved.
Channel robustness in wireless systems is an important consideration because noise, interference and multipath effects lead to degraded channel throughput in the 2.4GHz and 5.xGHz bands, adversely affecting the ability to reliably transmit latency-sensitive or high-bandwidth traffic such as voice and video.
Special attention was paid to improving channel robustness. The proposed schemes include FEC and selective retransmission. These mechanisms include the ability to specify the correction, the ability to specify the correction, acknowledgement and retransmission policy on per-stream basis, thereby accommodating a range of traffic types with policies designed specifically for each.
Channel throughput is improved through FEC, delayed acknowledgements with selective retransmissions and dynamic channel change.
The Baseline enhancements support QoS even when wireless subnets are deployed densely, as in enterprise environments. In such environments, multiple IEEE802.11e subnets could be located within radio range of each other, which would cause interference and/or collisions during the communications by devices in different subnets.
The QoS Baseline has not been approved yet. The next steps in the process are the approval of a draft specification, followed by the approval of the final specification.

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