4-qos in telecommunications

7/31/2019 4-QoS in Telecommunications

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EE5302 Network Design and Management 1EE5302 Network Design and Management 2Dr. W Yao, Brunel University

Introduction

What is Quality:

Current definition for quality by the International StandardsOrganization :

Degree to which a set of inherent characteristics fulf ils requirement

Quality of service management is an essential function inthe provision and maintenance of a telecommunicationservice

Features of QoS in telecommunication Measured and expressed on an end-to-end basis

Service specific

Different priority for different user sectors

Level of performance may be different among users within the same usersectors

Quality requirements are dynamic

EE5302 Network Design and Management 3Dr. W Yao, Brunel University

Quality/network performance relationship


QoS criteria in telecommunication

billing errors

waiting lists for provision of service

wrong number

time to repair

poor transmission

fault incidence

failure of call completion

dial tone/post-dialing delay


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Principal performance parameters


Performance impairments

Transmission performance

the ability to transport information between source and destinationwithout distortion or under loss and is mainly influenced by theperformance of transmission systems

Call processing performance

this relates to the ability of a network to accept and interpret routinginformation from the customer and establish a connection to the

required destination within prescribed response time

Availability performance

the proportion of time for which satisfactory service is given


Transmission Plan

a set of network design guidelines recommended by ITU-T toensure that end-to-end transmission is stable and acceptable tousers

including

overall signal strength at various point in the connections

control of signal loss and electrical stability of the connection limits on acceptable signal propagation time

limit on acceptable noise disturbance

control of sidetone and echo

limits on acceptable signal distortion, crosstalk and interference


Transmission Loss

is the ratio of the input power to output power expressed in dB

it comprises of

the loss in translating sound into electrical input -- the Send LoudnessRating (SLR)

the loss across the network

the loss incurred at receiver -- the Receive Loudness Rating (RLR)

The overall loss between the customers -- Overall Loudness Rating(OLR)

OLR=SLR+Network Loss+RLR


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Derivation of overall reference equivalent


Stability

Why there is Stability loss

insufficient loss around the 4-wire loop could result in positive feedbackand the circuit oscillating in an uncontrolled manner

if the balance of the hybrid transformer that converts the 2-wire to 4-wire is distributed, it will cause a low loss between the 4-wireconnections

Definition of Stability Loss

the lowest loss between equi-relative points at a 4-wire interface, fromthe receive to send port, measured at any single frequency in the band

0-4000Hz


Echo

echoes are caused by reflection of the speakers voice back fromthe distance receiving end due to an imperfect line balance at thehybrid that causes part of the signal energy transmitted in onedirection to return in the other

echo loss: the loss between equi-relative level points at a 4 wire

interface, from the receive to send ports measured as a weightedquantity in frequency band 300-3400Hz

the mean value of echo loss presented by national network is notless than (15+n), where n is the number of circuits in the nationalchain

echo control devices should be incorporated for the one-way delayof echo path exceeds 25ms


Delay

Propagation defined as the time taken by a signal applied at theinput of an equipment to reach the output of that equipment

Excessive delay not only incurs the risk of echo but also impairscommunication

ITU-T recommends that, maximum one-way delay should not

exceed 400ms for an international connection The one-way delay for connections originating and terminating in

the UK is 23 ms

Connections that are routed within the UK network to, or from, an

international gateway should not exceed a one-way delay of 12 ms


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Call Processing Performance

Those affecting the call processing phase are

delay to dial tone

removal of dial tone

connection establishment delay

connection establishment failure due to network congestion

connection establishment failure due to no tone

misrouting of calls

incorrect network tones or announcement

premature release of established connection

delay to connection release

connection release failure


Network Congestion

a network is of dimension to meet the peak demand, with a smallproportion of calls rejected due to insufficient equipment. Thiscongestion is represented by Grade of Service ()

= traffic lost/traffic offered= probability of congestion

Availability

describe how much of the time a system or network will be availableand operating, measured as the ratio of uptime to total time, aspercentage

the overall unavailability is influenced by the reliability of equipment,which is measured by Mean Time Between Failure (MTBF), MeanTime to Repair/Replace/Restore (MTTR), Mean Time to Failure(MTTF), and Mean Down Time (MDT)


ITU-T proposes grouping IP telecommunicationstransactions into 6 unique classes defined according to thedesired performance QoS objective

Class 0: Real time, highly interactive applications, sensitive to jitter.

mean delay upper bound is 100ms

delay variance is less than 50 ms

packet loss is less than 10-3

application example: Voice, Video Teleconference

Class 1: Real time, interactive applications, sensitive to jitter.

mean delay upper bound is 400 ms

delay variance is less than 50 ms

loss ratio is less than 10 -3

application: VoIP, Video Teleconference


Class 2: Highly interactive transaction data

mean delay upper bound is 100ms

delay variance is unspecified

packet loss ration is less than 10-3

application example including signaling

Class 3: Interactive transaction data mean delay upper bound is 400ms


loss ratio is less than 10-3

application example including signaling


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Class 4: Low loss only application

mean delay upper bound is 1 s


loss ratio is less than 10-3

application example including short transactions, bulk data, videostreaming

Class 5: Unspecified application with unspecified meandelay, delay variance and loss ratio

application example including traditional applications of default IP

network


Task1: Specify the Service for which QoS needs to bemeasured

the real-time services as voice and video

the non-real-time as email, web browsing, streaming

Task2: Define end users transaction

measure the QoS parameters

Task3: Define QoS parameters

define the accessibility, continuity and fulfillment parametersimpacting the quality of the specified transaction

Task4: Decide on measurement approach

active measurement

passive measurement


Task5: Sampling plan and data collection

involves many activities including the desired confidence level andaccuracy and validity of the collected data

Task6: Trend analysis

Task7: Set thresholds

set the threshold against which the QoS parameters need to becontrolled

Task8: Detect, diagnose and resolve

4-qos in telecommunications

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