Qos Measurements in Celullar Networks

8/3/2019 Qos Measurements in Celullar Networks

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DATA AND VOICE

QoS

MEASUREMENTSIN CELULLAR

NETWORKS



INTRODUCTION

} Modern networks support traffic beyond the traditional data types,

such as email, file sharing, or web traffic. Increasingly, data networks

share a common medium with more sensitive forms of traffic, like

voice and video..

} As much higher data rates are being required and many more

communication technologies become integrated, these sensitive

traffic types often require guaranteed or regulated service.

} Good reliability and availability of the services must be maintained.



INTRODUCTION

} This paper looks at the metrics for measuring quality of service,

} Bottlenecks in the networks,

} Implementation of QoS.

} In Packet-Switched networks,

} And in Digital Television networks.



PACKET-SWITCHED NETWORKS

} VoIP

} VoIP (Voice-over-IP) refers to the transmission of voice using IPtechnologies over packet switched networks.

} VoIP transports voice packets as ordinary data, thus allowing the

use of well-known supported techniques to control their flows in

data networks.} Voice requires low jitter, low delay and low loss.

} To withstand such needs, a certain level of QoS mechanism isneeded.



DEGRADATION FACTORS

} Degradation factors comprise all influences in a network that

negatively affect the quality of service.

} Various factors have been identified in data networks and are the

additional and application-specific sources of degradation.



DEGRADATION FACTORS

} Delay ± Latency that occurs when traffic is sent end-end on a

network.

} Jitter ± Fragmentation that occurs when data arrives at irregular

times and in the wrong order. It is therefore a measure of delay

variance.

} Packet loss ± Packet losses occur due to congestion in traffic,

bandwidth limiting and datagram collisions among other factors.



ACCEPTED METRICS TO MEASURE

QOSFOR NETWORK BASED SERVICES

} Thr oughput ± the rate at which packets travel through the network.

Maximum rate is always preferred. (maximize)

} Delay ± the time taken for a packet to travel from one end to the

other in a network. This has to be as low as possible. (minimize )

} Packet loss rate ± the rate at which packets are dropped, lost or get

corrupted while going through the network. (M inimize ).

} Delay jitter ± the variation in delay encountered by similar packets

following the same route in a network. (M inimize)



QoS METHODOLOGIES

} Integrated services(IntServ):

} Based on resource reservation protocol(RSVP).

} Establishes QoS by providing end-end QoS guarantees by establishing a

suitable path for every flow in the network.

} Has four components: RSVP, Admission control , classifier and packet

scheduler.

} RSVP is a signaling protocol that signals for the network to reserve

resources before transmission.

} Admission control decides whether a request for resources can be

granted.(high or low priority)

} Classifier will identify then organize and put a packet in a queue according

to service requirements.

} Packet scheduler schedules packets so that they meet QoS requirements.



QoS METHODOLOGIES

} Differentiated services:

} Diffserv splits the whole network into domains

} DS domain is a continuous set of nodes that support commonresource policies and well defined boundaries.

} Packets are classified and conditioned at entry to the network and

assigned different DiffServ code points (DS bits).

} Packets are conditioned by metering, marking, shaping and

dropping.



DiffServ Packet Classification and Marking

} Classification

} Behavioral aggregate classification ±selects packets based on

their DS code points.

} Multi-Field classifiers- selects packets based on values of multiple

header fields.

} Conditioning

} Traffic is classified to determine the class it belongs to.

} Packets are measured against the appropriate traffic profile from the

TCA.

} Packets are marked by setting the DS value to a correct codepoint(6bits).

} Traffic is shaped by increasing the delay time and buffers the stream

to make it compliant with the traffic profile. Packets may be dropped if

the buffer limit is reached.



QoS MEASUREMENT ARCHITECTURE

} Round trip (RT) performance ± this includes RT jitter, RT delay, RT

packet loss«

} Service response time

} Single point traffic statistics

Measurement tool

Round trip performance

terminal network server

logical application connection

A. Single-point measurements




Measurement tool Measurement tool

Common time reference

(optional)

End-to-end performance

Uplink (UL

) performance

Downlink (DL) performance

Terminal networkserver

Logical application connection

Logical measurement tool connection

B. Two ± point measurements




C. Multipoint measurements

} Traffic is captured from various measurement points (MP) in the

network

} Network performance is divided into performances of network

segments



QoS MEASUREMENT TOOLS

} QoSMeT (VTT) is a passive tool for measuring one-way end-to-end

network QoS from the application¶s point of view



QoS MEASUREMENT TOOLS

} Real-time measurements & accurate per packet statistics

} Is able to measure QoS of real-time applications (e.g., VoIP, video

conferencing), but other networking applications can be measured as

well.

} The tool works practically over any kind of network as long as IP is

supported

} QoSMeT can be run in the same device with the measured

application or within the network path at desired points

} Measures e.g.: Delay, Jitter, Packet loss, Connection break duration

(e.g., during a handover), Throughput and Offered load, and the

volume of data sent/received

} GPS is used for clock synchronization



DIGITAL TELEVISION NETWORKS(DVB ²T/H)

} ITU-T Recommendation E.800 defines QoS as ³The collective effect of

service performance, w hic h determines t he degree of satisfaction of a

user of t he service´ .

} Therefore, the quality of the service being offered will depend on the

perception of each user of that service.

} A set of parameters and their values have to be defined against which the

performance of the service can be evaluated.

} These values have to be met to ensure a proper function of the system

and a good quality of service for the end-user, i.e. the values should

always remain above the threshold value by a certain margin.



DVB-T/H RELATED QoS REQIUREMENTS

Video/audio coders

and multiplexerModulator Demodulator

MPEG-Decoder

MFER FER

Input

program

IP1

TS1 RF1 TS2 IP2

DVB-T/H Chain



QoS REQUIREMENTS AT IP1 AND IP2

} Service bit rate

} This is measured at IP1 and IP2, this measurement evaluates the

bit rate of the service (e.g. video, Audio) including the UDP, IP and

TP header.

} For QoS to be achieved, the service bit rate should remain within

a pre-defined band around a pre-defined nominal value, e.g.

256kbps +/- 4% or 4.0 Mbps +/- 100kbps.

Video/audio coders

and multiplexerInput

program

IP1

MPEG-Decoder

MFER FER

IP2




} IP packet error rate

} Measured at IP1 and IP2, this parameter shows the number of

corrupted IP packets vs. the number of all IP packets. To ensure

QoS, the IP packet error rate at IP1 should be very low and at IP2

certain degradation factors have to be taken into account.

} The threshold at both points is determined by the service bit rate

and the acceptable probability of visual distortions. E.g. 10-6

(for 4Mbps this translates to roughly 1 visible artifact per hour)

} At IP2: 3*10-5 (at the end-user terminal, higher IP packet error

rates are acceptable, e.g. 1 visible artifact every 2 minutes)




} IP packet jitter

} IP packet jitter is the variation in delay of the arrival of the IP

packet.

} At IP1 i.e. the input of the encoder jitter is not normally very

critical because of the buffering process in the encoder.

} At IP2, the jitter should be very minimal as it can cause problems

in the receiver buffer management, for example a peak-to ±peak

value of less than 120ms at IP1 and less than 40ms at IP2.

Video/audio coders

and multiplexerInput

program

IP1

MPEG-Decoder

MFER FER

IP2



QoS REQUIREMENTS AT TS1 AND TS2

} TS synchronization loss} TS_sync_loss is the loss of the MPEG-2 transport stream.

} the input to the modulator at TS1 should be long term stable

} any loss in synchronization is a severe problem and should be

attended to promptly

} At TS2 loss of synchronization is indicative of lack of coverage for

the receiver in a mobile environment*.

} At TS1 the loss of synchronization of once per month is

acceptable, while at TS2 no loss of synchronization should be

experienced as long as the receiver is within the nominal

coverage area.MPEG-Decoder

MFER FER

TS2ModulatorTS1




} Sync bite error

} Sync_bite_error is measured at TS1 and TS2,

} Sync_ byte _error occurs when content of sync byte in TS header is

not equal to 0x47.

} The correct spacing between sync bites should be checked at TS1 to

avoid synchronization problems in the receiver.

MPEG-Decoder

MFER FER

TS2ModulatorTS1




} BER

} Bit error rate is measured at TS2.

} BER before RS (Reed-Solomon) or LDPC (Low density parity

check) in DVB-T2 can be measured quickly and gives a good

overview of BER after RS or LPDC coding in a receiver.

} A BER of around 10-4 before Reed-Solomon is usually assumed

to give "Quasi-Error-Free" (QEF) performance after Reed

Solomon.

} To maintain QoS, a low BER of the order of 10-4 before coding

must be used to obtain an acceptable level of visible distortion.

MPEG-Decoder

MFER FER

TS2



QoS REQUIREMENTS FOR RF1 AND RF2

} RF Level} Points RF1 and RF2 are measurement points for the RF/IF signal

power.

} The RF power level is measured as the power of DVB-T/H signal

within the nominal channel bandwidth. At RF1, the RF level must

be within a narrow tolerance of the specified transmitter output

level.

} At RF2, the RF level should be above the minimum input level of

the receiver frontend by a certain margin; the minimum input level

required by the receiver to produce a data stream with a BER

below a pre-defined threshold, depends on the selected

transmission mode and the channel conditions including the

speed with which the receiver is moved.



QoS REQUIREMENTS FOR RF1 AND RF2

}MER

} Modulation Error ratio (MER) provides a single "figure of merit"

analysis of the modulated signal.

} It includes various signal degradations such as noise, amplitude

imbalance, quadrature error and residual errors.

} MER determines how much margin the system has before failure.

} At RF1, MER gives a good overview of the quality of thetransmitter output signal; RF2, the MER measurement can help

identifying potential problems in the receiver. As a rule of thumb,

an MER value of 32dB should be used for 256 QAM.



End of slide

Cedric Nshimba

Qos Measurements in Celullar Networks

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