Quality Of Service - Alcatel-Lucent OmniPCX Enterprise R7.1 Manual

Voice over WLAN Mobile IP Touch Design Guide R2.0

2.2. Quality of Service

The QoS management responsibilities are shared between the SVP Server and the OmniAccess
infrastructure components. The first responsibility of the SVP Server is to control the number of
simultaneous voice calls permitted per Access Point. While the absolute maximum limit of simultaneous
voice conversations per Access Point is 14, assuming ideal conditions, the actual limits enforced per
Access Point must take competition (bandwidth and radio spectrum sharing with data clients) and signal
quality (distance from AP and radio obstacles/interference) into consideration.
The SVP Server is also tasked with the coordination and synchronization of MIPT traffic on each AP in
order to avoid the collision of MIPT voice flows with each other and other traffic forms. These
coordination and synchronizations activities are performed with a limited congestion avoidance but
without traffic shaping mechanisms. This makes SVP efforts towards QoS, in the R 2.0 offer, a partial
prioritization function.
(No current VoWLAN offer supports better QoS facilities than the SpectraLink solution employed by
Alcatel-Lucent. The SVP server becomes a "de facto" standard.)
Summary of SVP Server Functions
- CAC : Call Admission Control (Maximum quantity of Voice calls per AP).
- Flow prioritization at AP level for Downlink Voice flows (SRP protocol).
- Voice prioritization at radio level for uplink and downlink (MAC).
- Time Delivery reducing upstream messages collision.
- Battery saving (due to Time Delivery).
- Upstream and Downstream Voice packets re-synchronization.
Infrastructure components, such as the OmniAccess Wireless Switch and/or OmniAccess Wireless
Appliance possess the ability to assure certain levels of prioritization of voice traffic over data traffic.
This can only be performed in a single direction (using Weighted Fair Queuing), from the infrastructure
towards the MIPT handset. No infrastructure facility (such as IEEE 802.11e) is presently included in
Alcatel-Lucent's MIPT VoWLAN R2.0 solution to provide for QoS from the MIPT handset towards the wired
LAN. For prioritization from the MIPT handset in the wireless environment towards the wired LAN, only
proprietary methods and adaptations of the IEEE 802.11 PIFS (PCF Interframe Spacing) option are
currently offered (Further information on these proprietary methods can be found in the SpectraLink SVP
Whitepaper).
Figure 7: QOS on WLAN solution
As with all other forms of Voice over IP, strict prioritization on the wired LAN is essential in order to
eliminate the effects of traffic competition on quality. For this reason, VLAN prioritization using IEEE
802.1q (VLAN priority option) and traffic prioritization using 802.1p by the data network elements are
considered mandatory for connections between infrastructure components and the OmniPCX Enterprise.
This is especially important for connects to devices like the SVP Server, which can not current stamp
packet priority labels on traffic.
ESD/ Central Pre Sales / DF/ PH 19/45 January 2007 – Ed 01