4-qos in telecommunications
TRANSCRIPT
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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
EE5302 Network Design and Management 4Dr. W Yao, Brunel University
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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EE5302 Network Design and Management 5Dr. W Yao, Brunel University
Principal performance parameters
EE5302 Network Design and Management 6Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 7Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 8Dr. W Yao, Brunel University
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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EE5302 Network Design and Management 9Dr. W Yao, Brunel University
Derivation of overall reference equivalent
EE5302 Network Design and Management 10Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 11Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 12Dr. W Yao, Brunel University
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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EE5302 Network Design and Management 17Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 18Dr. W Yao, Brunel University
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)
EE5302 Network Design and Management 19Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 20Dr. W Yao, Brunel University
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
delay variance is unspecified
loss ratio is less than 10-3
application example including signaling
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EE5302 Network Design and Management 21Dr. W Yao, Brunel University
Class 4: Low loss only application
mean delay upper bound is 1 s
delay variance is unspecified
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
EE5302 Network Design and Management 22Dr. W Yao, Brunel University
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
EE5302 Network Design and Management 23Dr. W Yao, Brunel University
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