Tspec Call Admission Control; Wmm™ Power Save; Cisco Compatible Extensions (Ccx); 802.11H - ASCOM VoWiFi System System Description

System Description
Ascom VoWiFi System
2.4.3

TSPEC Call Admission Control

This feature supports an optional element of WMM. The TSPEC feature helps ensure
predictable voice quality and encourages roaming by managing the total voice load on the
AP. Call Admission Control (CAC) keeps the number of active voice calls from exceeding the
configured limits of an AP. With this feature, phones are always connected to an AP but not
necessarily on an active call. This helps ensure that the voice quality of existing calls is
maintained.
TSPEC describes characteristics of traffic streams, such as data rate, packet size, delay, and
service interval and provides the mechanism for controlling admission, establishment,
adjustment and removal of traffic streams.
If data traffic is overloading a link in the network it can be delayed or even dropped and re-
sent. Voice traffic cannot be handled the same way since real-time traffic such as voice, is
sensitive to both latency and packet loss and it would jeopardize the QoS expected by the
users. CAC determines whether the required network resources are available to provide
suitable QoS for a new call, before the new call is placed.
2.4.4 WMM™ Power Save
WMM Power Save is a set of features for WiFi networks that increase the efficiency and
flexibility of data transmission in order to conserve power. WMM Power Save has been
optimized for mobile devices running latency-sensitive applications such as voice, audio, or
video, but can benefit any WiFi device. WMM Power Save uses mechanisms included in the
IEEE 802.11e standard and is an enhancement of IEEE 802.11 legacy power save. With
WMM Power Save, the same amount of data can be transmitted in a shorter time while
allowing the WiFi device to remain longer in a low-power state.
Note: The battery life time and the speech time are highly dependant on which power save
mode that is used. We recommend that U-APSD is used to achieve optimal battery lifetime.
Other parameters that can affect the power consumption are Beacon period and DTIM.
Location in the system will also affect the speech time. For more details, see the document
System Planning, Ascom VoWiFi System, TD 92408EN.
2.5

Cisco Compatible Extensions (CCX)

CCX is a Cisco proprietary collection of functions and requirements. Some requirements are
just to ensure compatibility with Cisco infrastructure, while other features are developed to
improve the behaviour of WLAN communication. Security and roaming enhancements are
worth mentioning as vital parts of CCX.
2.6

802.11h

IEEE 802.11h amendment was originally developed to extend WLAN operation in Europe to
the 5 GHz band, where WLAN devices need Dynamic Frequency Selection (DFS) and
Transmit Power Control (TPC) to coexist with the band's primary users, that is radar and
satellite systems. 802.11h defines mechanisms that can reduce both interference and
power consumption.
DFS detects the presence of other devices on a channel and automatically switches the
network to another channel if and when such signals are detected.
TPC reduces the radio-frequency (RF) output power of each network transmitter to a level
that minimizes the risk of interference to and from other systems, while still allowing
satisfactory network performance.
7 September 2011 / Ver. G
TD 92313EN
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