Voice over Wireless LAN Solution Guide v1.0 December 2005
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WTM 2245s Calls per
WTM 2245 Total
Calls Erlangs
#Handsets
10% use #Handsets
15% use #Handsets
20% use
1 80 80 65 500 433 325
2 64 128 111 1000 740 555
3 60 180 160 1500 1067 800
4 58 232 211 2000 1407 1055
5 57 285 262 2500 1747 1310
6 56 336 312 3000 2080 1560
7 56 392 367 3500 2447 1835
8 55 440 415 4000 2767 2075
9 55 495 469 4500 3127 2345
10 55 550 524 5000 3493 2620
11 55 605 578 5500 3853 2890
12 54 648 621 6000 4140 3105
13 54 702 674 6500 4493 3370
14 54 756 728 7000 4853 3640
15 54 810 782 7500 5213 3910
16 54 864 836 8000 5573 4180
Table 1: WTM 2245 Scaling
The number of handsets a WTM 2245 (or group of WTM 2245s) can support is similar to a voice
trunk engineering calculation and is beyond the scope of this document. As an example of how
WTM 2245 capacity calculations differ from a pure call capacity number, a single WTM 2245
could support an aggregate of 500 handsets if no more than 15 percent are making calls
simultaneously.
2.5 QoS This section addresses QoS from an end-to-end perspective. It is not enough to cover just the
QoS features of the WSS 2300, WTM 2245, and AP 2330 when there is other equipment
connecting those devices together.
2.5.1 WLAN Security Switch 2300 and WLAN AP 2330
The WSS 2300 and AP 2330 work together to solve some aspects of the over-the-air QoS
problem. These products support the SpectraLink Voice Priority (SVP) protocol by providing
prioritization of SVP packets. SVP has a number of QoS features in addition to the functionality
provided by the WLAN 2300 products. For non-SVP-based voice traffic (that is, MVC 2050, IP
Softphone 2050, and MCS Client), the WLAN 2300 series can still provide SVP-like prioritization
to the traffic through ACLs. In general, though, the WLAN 2300 series prioritization of SVP-based
voice will result in an overall higher quality voice experience than WLAN 2300 series prioritization
of non-SVP-based voice devices. This higher quality is due to the additional QoS features that
SVP offers between end devices, not because of any difference in the way the WLAN 2300 series
performs prioritization of the two types of calls.
The WSS 2300 and AP 2330 also support WMM for over-the-air QoS. One key advantage of
WMM over SVP is that WMM specifies four distinct classes of traffic instead of the binary
distinction offered by SVP, that is, SpectraLink voice and everything else. This capability is key to
supporting true multimedia over WLAN. SVP and WMM are not incompatible technologies with
respect to implementation on a WLAN; however, there are some limitations to support of WMM