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International Regulatory BodiesITU-T

Is to fulfil the purposes of the Union relating to telecommunication standardization by studying

technical, operating and tariff questions and adopting Recommendations on them with a view to

standardizing telecommunications on a world-wide basis.

Performance Objectives and availability objectivesDimensioning of network connection is based on the required availability objective

and performance

Dimension a network must meet the standard requirements recommendations by ITU

The performance objectives are separated from availability objectives

Factors to be considered

radio wave propagation

hardware failure

Resetting time after repair

Frequency dependant interference problems

ITU-T Recs for Transmission in GSM Net

All BTS, BSC and MSC connections in GSM network are defined as multiples of the

primary rate if 2 Mbps,

ITU-T Rec G.821 applies as the overall standard for GSM network.

ITU-T Rec G.826 applies for SDH.

The ITU-T Recommendations (Standards)

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The ITU-T target standard are based on two

recommendations:

ITU-T Recommendation G.821,intended for digital connection with

a bit rate of 64 kBit/s. Even used for digital connection with bit rates

higher than 64kBit/s. G.821 will successively be replaced by G.826.

ITU- T Recommendation G.826, used for digital connection with bit

rates of or higher than 2,048 kBit/s (European standard) or 1,544

kBit/s (USA standard).

The main difference between G.826 and G.821 is that

G.826 uses Blocks instead of bits in G.821

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ITU-T G.821 some definitions

HRX : hypothetical Reference Connection

This a model for long international connection, 27,500 km

Includes transmission systems, multiplexing equipment and switching

HRDP: Hypothetical Reference Digital Path

The HRDP for high grade digital relay systems is 2500 km

Doesnt include switching

HRDS: Hypothetical Reference Digital Section

It represents section lengths likely to be encountered in real networks

Doesn't include digital equipments, such as multiplexers/demultiplexers.

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ITU-T G.821 some definitions (course contents)

SES : Severely Errored Seconds

A bit error rate (BER) of 10-3 is measured with an integration time of 1 second.

DM : Degraded Minutes

A bit error rate (BER) of 10-6 is measured with an integration time of 1 minute.

ES : Errored Seconds

Is the second that contains at least one error

RBER: Residual Bit Error Rate

The RBER on a system is found by taking BER measurements for one month

using a 15 min integration time, discarding the 50 % of 15 min intervals whichcontain the worst BER measurements, and taking the worst of the remaining

measurements

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Digital Systems and BER

Performance of digital transmission system can be

evaluated by BER, Bit Error Rate

Telephony BER degradation versus audible degradation:

10-6: Noise not audible

10-5: Barely audible

10-4: audible, understandable

10-3: disturbing

More than 10-3: sync loss, link loss

Data and in particular multimedia media application

require a very low BER

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ITU-T G.821 some definitions

The system is considered unavailable when one or both of the

following conditions occur for more than 10 consecutive seconds

The digital signal is interrupted

The BER in each second is worse than 103

Unavailable Time (UAT)

Begins when one or both of the above mentioned conditions occur for 10

consecutive seconds

Available Time (AT)

A period of available time begins with the first second of a period of 10

consecutive seconds of which each second has a bit error ratio (BER) better than

10-3

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ITU-T G.821 Availability

Route availability equals the sum of single link

availabilities forming the route.

Unavailability might be due to

Propagation effect

Equipment effect

Note: Commonly used division is to allocate 2/3 of the allowed total

unavailability to equipment failure and 1/3 to propagation related

unavailability

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ITU-T G.821 Performance Objectives

SES : Severely Errored Seconds

BER should not exceed 103 for more than 0.2% of one second intervals in any

month

The total allocation of 0.2% is divided as: 0.1% for the three classifications

The remaining 0.1% is a block allowance to the high grade and the medium grade

portions

DM : Degraded Minutes

BER should not exceed 106 for more than 10% of one minute intervals in any

month

The allocations of the 10% to the three classes

ES : Errored Seconds

Less than 8% of one second intervals should have errors

The allocations of the 8% to the three classes