Lecture#10 Quality of service The Bonch-Bruevich Saint-Petersburg State University of Telecommunications Series of lectures “Telecommunication networks”

Lecture#10

Quality of service

The Bonch-Bruevich Saint-Petersburg State University of Telecommunications

Series of lectures “Telecommunication networks”

Instructor: Prof. Nikolay Sokolov, e-mail: [email protected]

Definitions

In the Recommendation E.800 and in a number of other ITU-T documents several similar definitions of the term "Quality of service" are formulated: 1. Totality of characteristics of a telecommunications service that bear on its ability to satisfy stated and implied of the user of the service (E.800).2. The collective effect of service performance which determine the degree of satisfaction of a user of a service. It is characterised by the combined aspects of performance factors applicable to all services, such as; - Service operability performance; - Service accessibility performance; - Service retain ability performance; - Service integrity performance; and - Other factors specific to each service (Q.1741).3. The collective effect of service performances which determine the degree of satisfaction of a user of the service (Y.101).4. The collective effect of service performance which determine the degree of satisfaction of a user of a service. It is characterized by the combined aspects of performance factors applicable to all services, such as bandwidth, latency, jitter, traffic loss, etc (Q.1703).

Dynamics of speech quality The "Quality of service" paradigm is constantly changing. New quality of service indices appear. Subscribers’ requirements change. Data related to the speech quality rating is shown in the table. Quality acceptable for subscribers is compared to the talk of two persons positioned on a certain distance from each other.

Equivalent distance during normal talk, m Type of connection in PSTN 1923 1933 1950 1985 Optimal

Local 14 8.3 3.5 2.0 Long-distance 25 11.7 5.0 2.0

Comfort distance

Estimates for the latter decades are absent, but general tendency is obvious. By implication it is confirmed by at least two factors. Firstly, many communications Administrations, basing only on results of research, reduce the value of admissible attenuation of speech path between telephone terminals. Secondly, some subscribers began to use telephone communications service in the 7 kHz band. Signal coding in this band is carried at the 64 kbit/s speed.

Recommendation ITU-T E.800 (1)

Recommendation ITU-T E.800 (2)

Recommendation ITU-T E.800 (3)

Recommendation ITU-T E.800 (4)

Recommendation ITU-T E.800 (5)

Recommendation ITU-T E.800 (6)

Main terms (1)

1. Quality. The totality of characteristics of an entity that bear on its ability to satisfy stated and implied needs. Note – The characteristics should be observable an/or measurable. When the characteristics are defined, they become parameters and are expressed by metrics.

2. Service. A set of functions offered to a user by an organization constitutes a service.

3. Item (entity; element). Any part, device, subsystem, functional unit, equipment or system that can be individually considered.

4. User. A person or entity external to the network, which utilizes connections through the network for communication.

5. Customer. A user who is responsible for payment for the service.

Main terms (2)

6. Service accessibility performance. The ability of a service to be obtained, within specified tolerances and other given conditions, when requested by the user.7. Service integrity performance. The degree to which a service is provided without excessive impairments, once obtained.8. Network performance. The ability of a network or network portion to provide the functions related to communications between users.9. Trafficability performance. The ability of an item to meet a traffic demand of a given size and other characteristics, under given internal conditions.10. Dependability. Performance criterion that describes the degree of certainty (or surety) with which the functions is performed regardless of speed or accuracy, but within a given observation interval.

Main terms (3)

11. Service integrity performance. The degree to which a service is provided without excessive impairments, once obtained.12. Network performance. The ability of a network or network portion to provide the functions related to communications between users.13. Trafficability performance. The ability of an item to meet a traffic demand of a given size and other characteristics, under given internal conditions.14. Availability. The ability of an item to be in a state to perform a required function at a given instant of time or at any instant of time within a given time interval, assuming that the external resources, if required, are provided.15. Reliability performance. The ability of an item to perform a required function under given conditions for a given time interval.

Main terms (4)16. Transmission performance. An indication of a communication signal at the egress of network compared to its performance at the ingress to the network. The indication of performance is expressed by a choice of pertinent parameters for the application or service in question.17. Propagation performance. The ability of a propagation medium, in which a wave propagates without artificial guide, to transmit a signal within the given tolerances.18. End-to-end quality. Quality related to the performance of a communication system, including all terminal equipment.19. End-to-end IP network. The set of exchange link and network section that provide the transport of IP packets transmitted from source host to destination host.20. End-to-end IP network performance. Measurable relative to any given unidirectional end-to-end IP service.

Service Level Agreement (SLA)

For some subscribers, the quality of service determines business processes to a great extent. According to USA financial institutes’ data, the losses due to inaccessibility of the telecommunication services during one hour (downtime cost) of 25% of American companies do not exceed 50 thousand dollars, of another 25% — 100 thousand dollars, and of the rest half of the companies — more than 100 thousand dollars. For the American brokerage firms, the value of that index is assessed at 6 million dollars.

SLA is considered as a part of a service contract where some indices have been defined. SLA is an individual negotiation between two parties: ROA and customer. It records the common understanding about services, priorities, responsibilities, guarantee, etc. with the main purpose to agree on the level of service. For example, it may specify the levels of availability, serviceability, performance, operation or other attributes of the service like billing and even penalties in the case of violation of the SLA.

QoS and NGN (1)

CO1 TE1 TE2 CO21TS TS

ACO ATLАSL АSLATE ATE ACOATL ATL

R1PC PC

T1 PCNPAN PANT2 T3 T4PCN PCN

R2 R3 R4

a) Information transmission for technology “channels switching”

b) Information transmission for technology “packets switching”

QoS and NGN (2)

1,0

0

F(t) – distribution function of the IP packets delay

Time

ΔF(t)=0,001

TMIN TMAX

QoS and NGN (3)

Talker

G.711 Coder

RTP (X mc payload size)

UDP

IP

Lower layers Lower layers

Listener

G.711 Decoder (Packet Loss Concealment)

Jitter Buffer (delay Y mc)

UDP

IP

Lower layers

Transfer of IP packets

QoS and NGN (4)

Density of distribution function of the IP packets delay

Time

S1(1) S2

(1)

f1(t) f2(t)

IPTD

Problem of the transition to NGN

PSTN Operators should find viable strategy of the transition to NGN, which provides protection of investments in circuit-switched technology.

Source: B. Jacobs. Economics of NGN deployment scenarios: discussions of migration strategies for voice carriers. – www.ieee.org.

It is necessary to combine PSTN’s quality of service and IP technologies’ economic efficiency!

QoS aspect: time irreversibility

Speech quality impairment compensation in networks with circuit switching:

Elaboration of the new speech signal processing algorithms;

Signal amplification (when necessary).

Speech quality impairment compensation in IP networks under condition of the excessive packet transfer delay:

Impossible in principle!!!

QoS supportNetwork planning

Traffic controlTraffic measurement

Ideal network Working network

Malfunctioning network

Recommendation ITU-T G.107 (1)

Recommendation ITU-T G.107 (2)

send loudness rating (SLR)receive loudness rating (RLR)overall loudness rating (OLR)weighted listener echo path loss (WEPL)sidetone masking rating (STMR)listener sidetone rating (LSTR)talker echo loudness rating (TELR)D-Value of telephone, receive side (Dr)D-Value of telephone, send side (Ds)

Recommendation ITU-T G.107 (3)

Recommendation ITU-T G.107 (4)

Recommendation ITU-T G.107 (5)

Instructor: Prof. Nikolay Sokolov, e-mail: [email protected]: Prof. Nikolay Sokolov, e-mail: [email protected]

Questions?

Quality of service