Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
31
When channel parking is active, the Cisco Unified Wireless IP Phone 7925G Series will discontinue the scanning of the 5 GHz
band and potentially roam to a 2.4 GHz neighbor, but also may stay on the currently connected 5 GHz AP if that is the strongest
signal received.
Channel parking will occur when the phone is in idle mode and there are at least four 2.4 GHz access points available where at
least one of those four access points has met the RSSI threshold to enable channel parking.
If configured for Auto-a and continuous scanning is enabled, the phone can potentially roam to 2.4 GHz when in idle even when
the phone is in good 5 GHz coverage as the Auto-RSSI logic is used when in idle, regardless of whether 5 GHz channels are
parked or not. When on call the local configured mode will be used (i.e. Auto-a), so it will attempt to associate to the preferred
band if available.
Channel parking will become inactive either when there are less than four 2.4 GHz access points, the RSSI for all 2.4 GHz
access points is low enough to meet the RSSI threshold to disable channel parking or there is a current inbound or outbound
call. When channel parking becomes inactive, the phone will rapidly scan the 5 GHz band, where it can potentially roam back
to 5 GHz if configured for Auto-a, as roaming is based on band preference and then RSSI when on call.
When the call is terminated, channel parking may become active again.
Multicast
When enabling multicast in the wireless LAN, impacts on battery life, performance, and capacity must be considered.
The Cisco Unified Wireless IP Phone 7925G Series uses the DTIM period to receive the queued broadcast and multicast
packets.
If there are many packets queued up, then they client may have to stay awake longer thus potentially reducing battery life.
With multicast, there is no reliability that the packet will be received the by the client.
The multicast traffic will be sent at the highest basic data rate enabled on the access point, so will want to ensure that only the
lowest enabled rate is configured as the only basic rate.
The client will send the IGMP join request to receive that multicast stream. The client will send the IGMP leave when the
session is to be ended.
The Cisco Unified Wireless IP Phone 7925G Series supports the IGMP query feature, which can be used to reduce the amount
of multicast traffic on the wireless LAN when not necessary.
Ensure that IGMP snooping is also enabled on all switches.
Note:
If using Coexistence where 802.11b/g and Bluetooth are being used simultaneously, then multicast voice is not
supported.
Designing the Wireless LAN for Voice
The following network design guidelines must be followed in order to accommodate for adequate coverage, call capacity and
seamless roaming for the Cisco Unified Wireless IP Phone 7925G Series.
For more information about these topics, refer to the “VoWLAN Design Recommendations” chapter in the
Enterprise Mobility
Design Guide
at this URL:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/eMob4.1.pdf
Planning Channel Usage
Use the following guidelines to plan channel usage for these wireless environments.
