802.11e defines a wireless LAN service quality (quality-of-service, QOS), such as voice-IP (voice-over IP) support. 802.11e standard defines the Hybrid Coordination Function (HCF). HCF access method to the new place of DCF and PCF, in order to provide improved access to bandwidth and reduce latency of high priority communications. This is called
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Mechanism Looking access parameters specified four EDCA access parameters access type, each type corresponds to a class of data. Configured for each access category four parameters: CWmin - the minimum contention window; CWmax - maximum contention window; TXOP - Send opportunities were limited; AIFS - Arbitration Interframe interval. Data set for each type of these parameters allows the network administrator depending on the application mix and traffic shaping network. In the DCF application, a site that has data to be transmitted when idle to wait until the media can be sent. However, the use of 802.11e standard, the site waiting for the extra time period. The length of extra time to send the data according to type. Access to this data set AIFS value of the defined class of extra waiting time. The data access classes for voice,
paul smith wallet, AIFS value should be set smaller; classes for e-mail and FTP data, AIFS value should be set larger. Voice requires a short delay time. Small AIFS value means less sensitive voice and data communication can be faster than to start the next phase of network competition. After a period of time after the AIFS, CWmin this site generates a random number between and CWmax. Access to high-priority class should be set low CWmin and low CWmax. AIFS, CWmin and CWmax should be set together. Thus, high-priority data in most cases can get permission to access the network. For the high-priority data set AIFS value and CWmax value and should be greater than the sum of the low priority data for the set AIFS value and the sum of CWmin value, so that low-priority data will not be completely blocked. TXOP for a visit to the definition of the class to send the maximum length of time. If you are sending data too large to be sent within the TXOP limit, the site put the data in multiple transmission. TXOP limit for the voice data is small, because the voice packets is very short. For FTP, email and network data, it should set a larger TXOP limit, so that when sending data to the data points do not need to repeatedly sent. Access point operating mechanism can be transmitted through the use of standardized (TSPECs) control network workload. An access point to require that each site visit for each class to send a transmission specification request. The request will specify the site for each data access class of applications and can withstand long delay. If you calculate an access point requests received from various sites over the network capacity, it will reject the request. If an application was refused, requesting that the site no longer sends the data access class, and must be combined with this data access class to low priority data. As with the PCF, HCCA is a polling protocol. When used, it will always be able to gain access to the media rights, as it waits longer than the shortest of any EDCA users even shorter AIFS time. HCCA can be configured individually for each application quality of service settings. Mixed in the access point coordinator (HC) turns a single site query, and has been configured according to the specific approval of the quality of service to set the permissions to access the media. There is no competition, therefore, the delay of high priority data traffic will increase as the network was lost. Prospect of the current IEEE 802.11e standard provides voice and multimedia applications require quality of service and enhanced network performance. With the development of new applications using the IEEE 802.11e standard and gained experience, no doubt will require further study and expansion of the agreement. More Atlas Atlas entry Open Category: LAN
Hybrid Mode
