White Paper Quality of Service | SpectraLink specification

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4.0 Quality of Service

4.1SpectraLink Voice Priority (SVP)

4.1.1SVP-enabled Access Points

4.1.2SVP Infrastructure

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.

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.

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

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