A measure of parameters that affect the level of performance a network offers a specific type of traffic. QoS parameters include access priority, bandwidth availability, latency, jitter, and packet loss. Toll quality, real-time compressed and uncompressed voice and video require fairly immediate network access, guaranteed availability of bandwidth throughout the call, low latency, zero jitter, and zero loss. E-mail is at the opposite end of the QoS spectrum, as it is highly tolerant of a low level of priority; high levels of latency, jitter, and loss; and does not require any bandwidth availability guarantees during the course of a mail transfer. QoS also must ensure that granting a QoS level to one traffic type or call does not violate the data flow requirements of another traffic type or call.The circuit-switched public switched telephone network (PSTN) offers all applications the highest level of QoS. Asynchronous transfer mode (ATM) offers multiple QoS levels appropriate for different traffic types. Frame relay, Internet Protocol (IP), and Ethernet networks can employ various priority mechanisms to offer differential grade of service (GoS) levels, but cannot guarantee QoS. See also ATM, compression, Ethernet, frame relay, GoS, IP, jitter, latency, loss, and PSTN.
(1) (Quality Of Service) A defined measure of performance in a system. For example, the maximum response time to complete a transaction must be no longer than 10 seconds.
(2) (Quality Of Service) In general, to be able to prioritize one type of transmission over another in a communications network.
(3) (Quality Of Service) A defined measure of performance in a communications network. For example, to ensure that real-time voice and video are delivered without annoying blips, a traffic contract is negotiated between the customer and network provider that guarantees a minimum bandwidth along with the maximum delay in milliseconds that can be tolerated. Because dedicated channels are set up between parties, the plain old telephone system (POTS) delivered the highest QoS for years. However, when data are broken into packets that travel through routers in a LAN or WAN, QoS mechanisms are used to give higher priority to real-time data, such as voice over IP (VoIP), than to non-real-time data, such as file downloads. Another option in packet switching is to overbuild the network, ensuring that it will accommodate all traffic fed to it. See packet switching. ATM was one of the first packet technologies to build in modes of service. Today, almost everything is built around IP, and there are a variety of methods that provide QoS in IP networks (see 802.11e, TOS, RSVP, Diffserv and MPLS).