Otherwise, bandwidth-based CAC does not operate properly. Load-based CAC incorporates a measurement scheme that takes into account the bandwidth consumed by all traffic types including that from clients , co-channel access point loads, and collocated channel interference, for voice applications.
In load-based CAC, the access point continuously measures and updates the utilization of the RF channel that is, the percentage of bandwidth that has been exhausted , channel interference, and the additional calls that the access point can admit.
The access point admits a new call only if the channel has enough unused bandwidth to support that call. Load-based CAC is supported only on lightweight access points. When the controller receives this request, it attempts to facilitate the urgency of the call in any way possible without potentially altering the quality of other TSPEC calls that are in progress.
You can apply expedited bandwidth requests to both bandwidth-based and load-based CAC. Expedited bandwidth requests are disabled by default. In addition to extending battery life, this feature reduces the latency of traffic flow delivered over the wireless media.
Because U-APSD does not require the client to poll each individual packet buffered at the access point, it allows delivery of multiple downlink packets by sending a single uplink trigger packet.
It reports both packet latency and packet loss. You can isolate poor voice quality issues by studying these reports. The metrics consist of a collection of uplink client side and downlink access point side statistics between an access point and a client device that supports CCX v4 or later releases.
The client and access point measure these metrics. The access point also collects the measurements every 5 seconds, prepares second reports, and then sends the reports to the controller. To store this data, the controller requires 32 MB of additional memory for uplink metrics and 4.
The controller saves the configuration in flash memory so that it persists across reboots. After an access point receives the configuration from the controller, it enables TSM on the specified radio band. This table shows the upper limit for TSM entries in different controller series. This leads to partial output. TSM cleanup occurs every one hour.
Entries are removed only for those APs and clients that are not in the system. If you choose the SIP codec as G. The default value is 0, which indicates that there is no check for maximum call limit. Once the client reaches the value specified, the access point rejects new calls on this network.
The controller reserves this much bandwidth from the maximum allocated bandwidth for roaming voice clients. If this parameter is set to zero 0 , the controller assumes that you do not want to do any bandwidth allocation and, therefore, allows all bandwidth requests. This page shows the TSM statistics for this client and the access point to which it is associated.
The statistics are shown in second intervals. The timestamp text box shows the specific interval when the statistics were collected. This page shows the TSM statistics for this access point and a client associated to it.
Suppose an AP has to be rebooted when a voice client associated with the AP is on an active call. After the AP is rebooted, the client continues to maintain the call, and during the time the AP is down, the database is not refreshed by the controller. Therefore, we recommend that all active calls are ended before the AP is taken down. The optional all command shows all access points to which this client has associated. Information similar to the following appears:.
The optional all command shows all clients associated to this access point. The verbose mode is an optional argument. When the verbose option is used, all debug messages are displayed in the console. You can use this command to monitor a maximum of two If one of the clients is a non-WiFi client, only the It is implicitly assumed that the clients being monitored are on call.
This feature is known as voice prioritization. These calls are given priority over other clients utilizing the voice pool. If the bandwidth is available, it takes the normal flow and allocates the bandwidth to those calls. You can configure up to six preferred call numbers. When a call comes to one of the configured preferred numbers, the controller does not check on the maximum call limit.
It invokes the CAC to allocate bandwidth for the preferred call. The bandwidth allocation is 85 percent of the entire bandwidth pool, not just from the maximum configured voice pool.
The bandwidth allocation is the same even for roaming calls. You must configure the following before configuring voice prioritization:. To remove a preferred call, hover your cursor over the blue drop-down arrow and choose Remove. Enhanced distributed channel access EDCA parameters are designed to provide preferential wireless channel access for voice, video, and other quality-of-service QoS traffic.
If you deploy video services, admission control ACM must be disabled. We do not recommend you to enable low latency MAC. This feature enhances voice performance by controlling packet retransmits and appropriately aging out voice packets on lightweight access points, which improves the number of voice calls serviced per access point. The default value is disabled. Download this chapter.
Bandwidth-Based CAC Bandwidth-based, or static, CAC enables the client to specify how much bandwidth or shared medium time is required to accept a new call and in turn enables the access point to determine whether it is capable of accommodating this particular call. Load-Based CAC Load-based CAC incorporates a measurement scheme that takes into account the bandwidth consumed by all traffic types including that from clients , co-channel access point loads, and collocated channel interference, for voice applications.
Note Load-based CAC is supported only on lightweight access points. Airtime, as described earlier in this article, is the amount of time it takes for a device to send a payload of data.
The access point can constrain the airtime for any data frame it sends to or receives from a client through the configuration of transmission opportunity TXOP. However, the access point can only measure airtime for data frames that it "hears" from each client, as it cannot strictly limit the number of data frames any individual client sends.
Note that only airtime in the downlink direction access point to client can be controlled accurately by the access point. Although airtime in the uplink direction client to access point can be measured, it cannot be strictly controlled on a cumulative basis. It is important to note that if a client exceeds the airtime limit, packets will be delayed. However, only packets in the downlink direction are delayed.
This is because delaying downlink packets access point to client frees up airtime. Dropping or delaying uplink packets client to access point does not do anything to free up airtime since the packet has already been transmitted over the air by the client. Once the packet has been on the air, that airtime cannot be reclaimed. This can mean that a client that is transmitting a lot of uplink traffic can exhaust airtime. This is essentially a denial-of-service attack that is outside the scope of what Cisco Airtime Fairness addresses.
More information on this type of attack can be found in our Air Marshal documentation. Meraki's firmware includes airtime fairness enabled by default on all Meraki Access points. In the downlink direction, the queues that feed the EDCA output buffers are serviced in such a way as to permit airtime to be distributed or allocated differently per client. All rights reserved. All trademarks, logos, and copyrights are property of their respective owners.
Stations that support Although bandwidth is not guaranteed there are four Access Classes AC defined as outlined in the table below:. A mechanism called Controlled Contention Mechanism provides a way for stations to obtain a Transmit Opportunity TXOP which is used to provide varying levels of priority.
0コメント