Avaya Communication Server 1000 Installation And Commissioning Manual page 71

Number of WLAN
IP Telephony
Manager 2245
units
2
3
4
For example, if there are two subnets for handsets in a campus and some handsets are
directed to one subnet and some to the other, there are two Call Admission Control domains
operating independently. Specifically, if both specified a limit of seven calls for each AP, it is
possible to have seven calls admitted by each WLAN IP Telephony Manager 2245 on the same
AP—therefore, the AP is oversubscribed by 2:1.
If multiple subnets are required, the best way to support them is to leverage the Layer 3 WLAN
IP Telephony Manager 2245 design. With this design, the WLAN IP Telephony Manager 2245
units are clustered in one subnet and the traffic from the handset is routed from the appropriate
WLAN IP Telephony Manager 2245 unit in the cluster. Although this is a supported
configuration, all the engineering guidelines for latency, jitter, and packet loss must still be
maintained. The Layer 3 design guidelines for having clients and WLAN IP Telephony Manager
2245 in different subnets does not mean that the WLAN IP Telephony Manager 2245
clustermaster and slavescan also be separated by routers. All the WLAN IP Telephony
Manager 2245 units in the cluster must still be collocated in the same subnet.
WLAN handsets
The WLAN Handsets 2210/2211/2212 and Avaya 6120/6140 WLAN Handsets support both
G.711 and G.729 codecs, but only using a 30 ms packetization rate.
The WLAN IP Telephony Manager 2245 translates between packetization rates, meaning that
from the WLAN IP Telephony Manager 2245 to the handset, the call uses the packetization
rate specified by the Communication Server 1000 (for example, 20 ms). Avaya recommends
that the Communication Server1000 paketization rate match the 2245 at 30ms. For Avaya
BCM, the packetization rate must be 30ms.
The handsets encapsulate their voice payloads in SVP for QoS. The handsets further
synchronize communications, so that the handsets are able to avoid collisions with each other
more effectively than the usual 802.11 collision avoidance mechanisms. Each handset
maintains a list of up to four APs as potential candidates for roaming. The handsets are
aggressive in roaming to other APs, which tends to prevent them from using a suboptimal data
rate when another AP can provide better service. The handsets also communicate with the
WLAN IP Telephony Manager 2245 and discover which APs are at full call capacity, so that
the handsets can direct their calls through an AP that has call capacity available.
Under optimal conditions, meaning no interference and all devices in proximity of the AP, up
to 10 voice calls from a handset are supported on a single AP 2330. When configuring the
maximum call parameter of a WLAN IP Telephony Manager 2245, never configure it above
10. A more realistic rule of thumb that allows for devices to move about and rate scale
accordingly is anywhere from six to eight calls per AP. A noisy RF environment can impact the
numbers further.
Avaya WLAN IP Telephony Installation and Commissioning
Number of handsets WLAN IP
Telephony Manager 2245-10
20
30
40
WLAN IP Telephony Manager 2245 planning
Number of handsets WLAN IP
Telephony Manager 2245-20
40
not applicable
not applicable
November 2010 71