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Understanding Call Admission Control

Call admission control (CAC) regulates the addition of new voice over IP (VoIP) sessions on access point radios, guaranteeing a higher quality of service to a fixed number of voice clients by limiting the number of calls. Call admission control is configured in the WLAN Service profile using either Wi-Fi Multimedia (WMM) or, for older equipment, the legacy SpectraLink Voice Priority (SVP). CAC is used in the call setup step and applies only to real-time media traffic as opposed to data traffic.

Note: SVP is a legacy technology—Spectralink's new phones use WMM.

You can turn off call admission control (set it to none), or you can enable either session-based admission control or VoIP-based admission control:

  • None (default)
  • Session-based: Session-based call admission control limits the number of sessions (14 by default) on one WLAN Service profile. When used in conjunction with QoS, a small number of clients (0 through 100) are given priority access, while clients on other WLAN Service profiles are forced to use best effort. Configure session-based call admission control when an SSID will handle both data and voice.
  • Voip-call: Call admission control limits only the number of voice sessions on one WLAN Service profile. VoIP-call is designed to be used with a voice-only Radio profile and SSID.

    Note: We recommend creating voice-only SSIDs, either WMM VoIP-call or SVP VoIP call, for best performance.

This topic describes:

What Radios Does Call Admission Control Affect?

Call admission control is enabled in a WLAN Service profile and affects radios using the Radio profile associated with the WLAN Service profile (SSID).

Note: To ensure voice quality, do not map other WLAN Service profiles to a Radio profile you plan to use for dedicated voice traffic or use QoS to force all packets on other WLAN Service profiles to use best-effort priority.

How Do I Configure Call Admission Control?

Call admission control is enabled in a WLAN Service profile (SSID) and configured in the associated Radio profile.

For information about enabling call admission control, see Creating and Managing a WLAN Service Profile. For information about configuring call admission control, see Creating and Managing a Radio Profile.

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