Quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

(QoS) mechanism controls the performance, reliability and usability of a telecommunications service. Mobile cellular service providers may offer mobile QoS to customers just as the fixed line

PSTN The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

services providers and

Internet service providers An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise privatel ...

may offer QoS. QoS mechanisms are always provided for

circuit switched Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full b ...

services, and are essential for non-elastic services, for example

streaming multimedia Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content it ...

. It is also essential in networks dominated by such services, which is the case in today's mobile communication networks. Mobility adds complication to the QoS mechanisms, for several reasons: * A phone call or other session may be interrupted after a

handover In cellular telecommunications, handover, or handoff, is the process of transferring an ongoing call or data session from one channel connected to the core network to another channel. In satellite communications it is the process of transfe ...

, if the new

base station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile telephony, wireless com ...

is overloaded. Unpredictable handovers make it impossible to give an absolute QoS guarantee during a session initiation phase. * The pricing structure is often based on per-minute or per-megabyte fee rather than

flat rate A flat fee, also referred to as a flat rate or a linear rate refers to a pricing structure that charges a single fixed fee for a service, regardless of usage. Less commonly, the term may refer to a rate that does not vary with usage or time of us ...

, and may be different for different content services. * A crucial part of QoS in mobile communications is

grade of service In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service (GoS) and the quality of service (QoS). Grade of service is the probability of a call in a ...

, involving outage probability (the probability that the mobile station is outside the service coverage area, or affected by co-channel interference, i.e. crosstalk)

blocking probability The erlang (symbol E) is a dimensionless unit that is used in telephony as a measure of offered load or carried load on service-providing elements such as telephone circuits or telephone switching equipment. A single cord circuit has the capac ...

(the probability that the required level of QoS can not be offered) and

scheduling starvation A schedule or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such things are i ...

. These performance measures are affected by mechanisms such as

mobility management Mobility management is one of the major functions of a GSM or a UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be deli ...

radio resource management Radio resource management (RRM) is the system level management of co-channel interference, radio resources, and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless local area networks, ...

admission control Admission control is a validation process in communication systems where a check is performed before a connection is established to see if current resources are sufficient for the proposed connection. Applications For some applications, dedicated ...

, fair scheduling, channel-dependent scheduling etc.

Factors affecting QoS

Many factors affect the quality of service of a mobile network. It is correct to look at QoS mainly from the customer's point of view, that is, QoS as judged by the user. There are standard metrics of QoS to the user that can be measured to rate the QoS. These metrics are: the coverage, accessibility (includes GoS), and the audio quality. In coverage the strength of the signal is measured using test equipment and this can be used to estimate the size of the cell. Accessibility is about determining the ability of the network to handle successful calls from mobile-to-fixed networks and from mobile-to-mobile networks. The audio quality considers monitoring a successful call for a period of time for the clarity of the communication channel. All these indicators are used by the telecommunications industry to rate the quality of service of a network.

Measurement of QoS

The QoS in industry is also measured from the perspective of an expert (e.g. teletraffic engineer). This involves assessing the network to see if it delivers the quality that the network planner has been required to target. Certain tools and methods (protocol analysers, drive tests and Operation and Maintenance measurements), are used for this QoS measurement: *Protocol analysers are connected to BTSs, BSCs, and MSCs for a period of time to check for problems in the cellular network. When a problem is discovered the staff can record it and it can be analysed. *Drive tests allow the mobile network to be tested through the use of a team of people who take the role of users and take the QoS measures discussed above to rate the QoS of the network. This test does not apply to the entire network, so it is always a statistical sample. *In the Operation and Maintenance Centres (OMCs), counters are used in the system for various events which provide the network operator with information on the state and quality of the network. *Finally, customer complaints are a vital source of feedback on the QoS, and must not be ignored.

Cellular GoS

In general,

(GoS) is measured by looking at traffic carried, traffic offered and calculating the traffic blocked and lost. The proportion of lost calls is the measure of GoS. For cellular circuit groups an acceptable GoS is 0.02. This means that two users of the circuit group out of a hundred will encounter a call refusal during the busy hour at the end of the planning period. The grade of service standard is thus the acceptable level of traffic that the network can lose. GoS is calculated from the Erlang-B formula, as a function of the number of channels required for the offered traffic intensity.

Cellular audio quality

The audio quality of a cellular network depends on, among other factors, the modulation scheme (e.g.,

FSK FSK may refer to: * FSK (band), a German band * Federal Counterintelligence Service, (Russian ') of Russia * Fiskerton railway station, in England * Forskolin, a diterpene * Forsvarets Spesialkommando, a Norwegian special forces unit * Fort Scott M ...

QPSK Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a ...

) in use, matching to the channel characteristics and the processing of the received signal at the receiver using

DSP DSP may refer to: Computing * Digital signal processing, the mathematical manipulation of an information signal * Digital signal processor, a microprocessor designed for digital signal processing * Yamaha DSP-1, a proprietary digital signal ...

s.Chitamu. P.J., Telecommunications Access Networks. University of the Witwatersrand, Johannesburg, 2005.

References

{{DEFAULTSORT:Mobile Qos Teletraffic Wireless networking