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300-365 · Question #53

A corporation has a Cisco Unified Wireless Network that has been deployed for voice coverage. The wireless data rates have been tuned to mandatory rates of 18 Mbps and 36 Mbps. Some wireless clients…

The correct answer is A. Clients are roaming at lower data rates and are not maintaining 36Mbps connectivity. Multicast video is transmitted at the lowest mandatory data rate, so clients that fall below that rate during roaming miss the multicast frames and experience video drops.

Wireless Troubleshooting and Optimization

Question

A corporation has a Cisco Unified Wireless Network that has been deployed for voice coverage. The wireless data rates have been tuned to mandatory rates of 18 Mbps and 36 Mbps. Some wireless clients have been experiencing drops streaming multicast video while moving throughout the building. What is the cause of the drop in video?

Options

  • AClients are roaming at lower data rates and are not maintaining 36Mbps connectivity.
  • BClients are not roaming due to coverage. This is causing the multicast data to drop due to the
  • CClients are connected at 18Mbps; however, other clients are connecting at 12Mbps and are
  • DClients are maintaining a 12Mbps rate and cannot receive the stream at 18Mbps.

How the community answered

(25 responses)
  • A
    52% (13)
  • B
    8% (2)
  • C
    28% (7)
  • D
    12% (3)

Why each option

Multicast video is transmitted at the lowest mandatory data rate, so clients that fall below that rate during roaming miss the multicast frames and experience video drops.

AClients are roaming at lower data rates and are not maintaining 36Mbps connectivity.Correct

In 802.11, multicast and broadcast frames are always transmitted at the lowest mandatory (basic) data rate - in this case 18 Mbps. When clients roam between APs and temporarily associate or negotiate at rates below 18 Mbps, they cannot decode the multicast frames, causing video stream drops. The two-rate mandatory set of 18 and 36 Mbps means any link degradation below 18 Mbps during roaming directly interrupts multicast reception.

BClients are not roaming due to coverage. This is causing the multicast data to drop due to the

A true coverage gap would cause complete disconnection and packet loss for all traffic, not specifically multicast video drops during roaming transitions.

CClients are connected at 18Mbps; however, other clients are connecting at 12Mbps and are

Clients cannot associate at 12 Mbps when 18 Mbps is configured as a mandatory rate, because all clients must support every mandatory rate to join the BSS.

DClients are maintaining a 12Mbps rate and cannot receive the stream at 18Mbps.

A client operating at 12 Mbps would be unable to associate with the WLAN at all given that 18 Mbps is the lowest mandatory rate, making this scenario technically impossible in this configuration.

Concept tested: Multicast transmission at lowest mandatory data rate

Source: https://www.cisco.com/c/en/us/support/docs/wireless/aironet-1200-series/70502-multicast-wlan.html

Topics

#multicast video#data rates#roaming#mandatory rates

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