SpectraLink NetLink Wireless Telephones Best Practices White Paper Wireless Telephone - Manual (Page 12)

White Paper
Page 11
4.0 Quality of Service
4.1 SpectraLink
Voice Priority
(SVP)
Quality of Service (QoS) is a means of guaranteeing a level of service
that will result in a network connection of adequate quality. Typically this
results in providing different levels of service for different applications,
depending on their requirements. When data and voice are competing
for bandwidth it is necessary to have a prioritization method that provides
a controlled preference to voice packets. The initial 802.11 standards
did not provide a practical QoS mechanism, so SpectraLink developed
SpectraLink Voice Priority to allow real-time voice applications to coexist
with data applications on a Wi-Fi network without compromising voice
quality.
Voice quality is ensured on a shared network with SVP, a QoS
mechanism for quality of service that is fully compatible with Wi-Fi
networks. Adopted by the leading wireless LAN vendors, SVP
guarantees audio quality in a shared voice and data network. Access
points generally use random backoff intervals and require all types of
traffic to contend for bandwidth with equal rights. Treating all traffic
equally can cause significant delays to voice traffic. Modifying the AP
behavior to recognize and prioritize voice packets increases the
probability of better performance while continuing to treat asynchronous
data packets normally. The two operations that comprise SVP in the
AP, minimizing random backoff and priority queuing, require a packet
filtering mechanism. Packet filtering requires recognizing the packet’s
protocol identifier, which for SpectraLink packets is registered protocol ID
119 for the SpectraLink Radio Protocol (SRP). The NetLink SVP Server
also performs packet delivery timing in the link to the Wireless
Telephones that is critical for ensuring seamless handoffs among APs
and for enhanced battery management processes.
4.1.1 SVP-enabled
Access Points
SVP-enabled APs are required for all NetLink Wireless Telephone
installations, even if the wireless LAN is being used only for voice. SVP
is required to ensure the timing and delivery of SpectraLink voice
packets. Without a method of prioritization for voice packets, the lack of
a controlled delivery method will result in poor audio quality, even with
only voice devices on the network.
Information regarding APs that are compliant with SVP, or otherwise
support a compatible voice QoS mechanism, can be found on
SpectraLink’s website in the NetLink product section at
http://www.spectralink.com/products/svp.html. Configuration notes for
specific AP models are also available on the website are should be
closely followed to ensure the proper implementation of SVP.
4.1.2 SVP
Infrastructure
To trigger SVP in the APs from the wired side of the network, a NetLink
Telephony Gateway and/or NetLink SVP Server is required. NetLink
Telephony Gateways can provide SVP support for small installations
with four or fewer Gateways. If NetLink Telephony Gateways are used
for SVP, the NetLink Wireless Telephones are limited to a maximum