White Paper

The maximum number of simultaneous telephone calls an AP can support is determined by dividing the total available bandwidth by the percentage of bandwidth used for each individual call. Approximately 20- 40% of the AP bandwidth is reserved for channel negotiation and association algorithms, so 60-80% of the total available bandwidth should be used for calculating the maximum call capacity per AP. Lower overall bandwidth is available when there are a greater number of devices associated with an AP. For example if all calls on an AP are using a theoretical 4.5% of the bandwidth at 11 Mb/s, the actual number of calls expected at that rate would be about 13 (60% of bandwidth available / 4.5% theoretical bandwidth utilized per call). The actual number of calls expected at 2 Mb/s using the NetLink Telephony Gateway and a 20 ms sample rate is about 7 (70% of bandwidth available / 10% theoretical bandwidth utilized per call).

Even with all of the known variables, there are many other vendor- specific characteristics associated with individual access points that make it difficult to quantify the concurrent calls per AP without thoroughly testing specific configurations. As a general rule based on lab tests and experience, wireless LAN designs for NetLink Wireless Telephones should consider no more than 12 simultaneous calls at 11 Mb/s or no more than 7 calls at 2 Mb/s using either G.711 or NetLink Telephony Gateways. Using the G.729 codec will yield roughly 50% more calls at these mentioned data rates, but the general performance of NetLink Wireless Telephones using this codec on various APs has not been well tested.

To allow for bandwidth to be available for data traffic, SpectraLink provides the ability to limit the number of calls per access point within the NetLink Telephony Gateway and SVP Server. The “Calls per Access Point” setting will limit the number of active NetLink Wireless Telephone calls on each access point. Wireless Telephones are free to associate with other APs within range that have not reached the set maximum number of calls. SpectraLink recommends this setting be equal to or below the maximum number of calls discussed in the previous paragraph.

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