Interband Roaming; Multicast - Cisco 7925G Deployment Manual

Interband Roaming

Some deployments may use one frequency band for indoor (e.g. 5 GHz) and the other for outdoor coverage (e.g. 2.4 GHz). In
this case, set the phone to either Auto-a or Auto-b/g mode, depending on the preferred frequency band.
For Auto-a and Auto-b/g modes, this is giving preference to one frequency band over another. At power on, the Cisco Unified
Wireless IP Phone 7925G, 7925G-EX, and 7926G will scan all 2.4 GHz and 5 GHz channels then attempt to associate to an
access point for the configured network using the preferred frequency band if available. If the preferred frequency band is not
available, then the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will try to use the less preferred frequency
band if available. If the phone roams out of coverage of the preferred frequency band, where less preferred frequency band
signal is available, then the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will attempt to associate to that
less preferred frequency band.
As of the 1.3(4) release, seamless interband roaming between 5 GHz and 2.4 GHz bands is supported as both frequency bands
are now scanned simultaneously when on call or in idle if Continuous scan mode is enabled.
In order for the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G to roam from the preferred frequency band to
the less preferred frequency band (e.g. roam to 2.4 GHz when configured for Auto-a mode), all access points in the preferred
frequency band must have a signal lower than the preferred frequency band signal threshold as well as one access point in the
less preferred frequency band meeting the RSSI differential threshold for roaming must be met. In order to roam back to the
preferred frequency band, there must be at least one access point with sufficient signal matching the preferred frequency band
signal threshold.
Prior to the 1.3(4) release, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G would have to roam out of
range of the current band before it would attempt to roam to an access point on the other frequency band when configured for an
Auto 802.11 mode (e.g. Auto-a, Auto-b/g, Auto-RSSI), where the user may experience choppy audio with the weak signal
connection, followed up with a small second audio gap before associating to the new frequency band. Once the Cisco Unified
Wireless IP Phone 7925G failed over to a less preferred frequency band (e.g. associated to 802.11b/g when the phone is
configured for Auto-a), there was no mechanism to guarantee the Cisco Unified Wireless IP Phone 7925G would roam back to
the preferred frequency band when available again or not as only the connected frequency band would be scanned.
It is recommended to perform a spectrum analysis to ensure that the desired frequency ranges can be enabled in order to
perform seamless interband roaming.

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, 7925G-EX, and 7926G use the DTIM period to receive the queued broadcast and
multicast packets.
If proxy ARP from CCX is enabled and the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G are not
participating in a multicast session currently, then the access point is responsible to answer any ARP requests on behalf of the
client and the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G can remain in sleep mode longer thus optimizing
battery life.
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 guarantee that the packet will be received the by the client.
The multicast traffic will be sent at the highest mandatory / basic data rate enabled on the access point, so will want to ensure
that only the lowest enabled rate is configured as the only mandatory / 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, 7925G-EX, and 7926G support 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.
It is recommended to enable Multicast Direct in the Cisco Unified Wireless LAN Controller.
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Deployment Guide
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