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The quality of service for POTS lines is changing with the lnternet!

Millions of analogue telephone lines are installed around the world and work reliable for their dedicatedservice: voice transmission.

The reason why the majority of private Internet users are using analogue lines is the availability and the

price. Though most of the already installed lines work sufficiently for voice, problems may come up withexpected 56kbit/s transmission speed. Since V.90 is defined as the actual Internet modem standard, 56k(max. payload speed: 53k) transmission speed is expected.Phase and amplitude modulation are specially affected by phase hits and impulsive noise. These twotransmission problems do not influence voice transmission unless they are enormous.But complaints and the request for quality of service start after the first contact with the Internet.

Reasons for a slow transmission speed over analogue V.90 connections and the wayto find the problem.

1.Bottlenecks at the Internet providers access point.- Typically the transmission speed decreases during busy hours. This can be proved easily bycomparing thetransmission speed during different times or weekdays.

2. The local access copper line causes the problem. The reason can be one or several of the followingpoints.a) Corrosion and aged connectors, means a higher attenuation and therefore a lower signal level.b) Nearby disturbance sources like railways, power lines, elevators, traffic produce white band and impulsivenoise to the access line.c) Signals on cables in the same cable bundle can impact the signal seriously. Additional damaged insulationor split pairs may reduce the line quality.d) Defect telephones connected in parallel to the modem at the customers side will cause wrong lineimpedance, additional noise and as a result a reduced signal level.

3. Defect line cards are often the reason for impulsive noise and phase hits. These two problems may not benoticed as long as the telephone line is used for voice telephony only. The reduced transmission speed of a

56k modem will prove the opposite.A defect line card can cause several other l ines faults.

4. The network itself, especially if packet switched networks are used for Internet telephony, can produceserious impacts to the voice quality. To detect unacceptable variations of the signal delay, a round trip delaymeasurement is the only way to check the quality of service for Internet telephony. Additionally the alreadymentioned phase hits and impulsive noise can be produced by network elements connected to the digital sideof the line card.

Requirements for a quality of service tester:

- Complete test of all critical parameters combined with a minimum of test time.- Automatic end to end test.

-Pass/Fail comparison against limits

- Detailed result analysis- Easy to use- Field proved- Battery powered- The name must be ASA-200

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Trouble shooting at analogue telephone lines

A. The lnternet user has a speed problem

Questions to the complaining V.90 Internet user:1. Is the transmission speed decreased during dedicated busy hours only and do you get more than

50kbit/s during other times or weekdays?YES Ask your lnternet provider for improvement and enjoy your 56k connectionNO Go to questions 2 and 3 first

2. Ask your lnternet provider if they are offering a 56k connection to you? Or are they using slowermodems only?

3. Have you checked your modem for correct settings?YES Check your own house installation with questions 4 and 5

4. Do you have more than one wall socket for one telephone line?YES Unplug all connected equipment except the modem

5. Do you get a faster transmission speed?YES Check the unplugged equipmentNO Ask an electrician to disconnect the telephone wire at the first wall socket of other

Installations, then plug the modem to the first wall socket.

6. Do you get a faster transmission speed?YES Check and repair youre in house installationNO Ask your telephone company to check the line

B. The Telco technician gets a call out to the customer

What does he need to identify the problem?1. One ASA-200 connected as an exchange unit to a known, good analogue telephone line.

2. One ASA-200 in his tool kit to perform all necessary line tests.

3. Experience to bring the test results and the problem togetherOr

4. The follow the questionnaire as attached in a tabular form

5. 10 ~ 30 minutes

Explanation:Line cards of different vendors or national differences may show different typical values for the single tests.

It will help to identify problems of the line or network if the typical values of known good lines* have beenmeasured before. This may also influence the limits for pass/fail results.

Please type these typical values in the field "typical values of a known good line" on the following table.

After (or during) the automatic measurement with the ASA-200 answer the questions in the table with YES orNO. Only one answer is possible per line. "YES, means no fault."NO" in the white fields of a row indicates a high probability of a problem of the appropriate networkelements (cabling, line card, switch, etc).Grey fields indicate a low probability and black fields are not relevant for the appropriate test.

The results of the "NO" fields will indicate the most likely faulty network element.

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Questions to the telecom service technician working with WWG ASA-200

Typical measurements affecting mainlymodem transmission

Typicalvalues ofknowngood

lines*

Cabling Linecard

Switch,Mux,

Network

Is the DC voltage between 15 and 70V DC?

Do you get phase hits of more than 2o?Is impulsive noise present on the line?

Typical measurements affecting mainly voicequality but can affect also modemtransmission

Typicalvalues ofknowngoodlines*

Cabling Linecard

Switch,Mux,

Network

Is the balance about earth better than 35dB?Is the wide band noise lower than 40dbm?

Is the attenuation referred to 1kHz lower than e.g.4dB or e.g. according to ITU-T M. 1040?

Is the impedance between 400 and 1400K?Is the return loss at 1kHz less than 14dB?

Is the round trip delay less than 25msec?

Additional measurements in case ofsignalling or connection problems

Typicalvalues ofknowngoodlines*

Cabling Linecard

Switch,Mux,

Network

Is the line seizing current correct? (e.g. 3 25mA)Is the line release current correct? (e.g. 1 25mA)Is the ringing voltage between 30 and 75 Vrms?

Is the dial tone present and >25dBm?Is the DTMF dialling OK?

Is the loop disconnecting dialling OK?

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