ATL Telecom AM2048 - Manual (Page 27)

ATL TELECOM USER GUIDE
AM2048A
51
clock skew is a problem.
For G.703:
1
Check that the G.703 port configuration matches that of the connected equipment.
2 Check the “Performance>User Port” screen
a) If Bipolar violations are occurring there could be problems with the receive data path,
i.e. the link is too long or there is interference in the cable.
b) If clock slips are occurring the timing mode may not be set correctly. The likely cause is
that in the “Configuration>User Port” screen the timing is set to ‘internal’ whereas the
timing should be set to ‘transparent’ to lock to the incoming clock.
3 If CRCs are enabled and only one copper pair is being used for transmission, ensure that
the idle pattern is set correctly in the “Configuration>User Port” Screen.
The front panel loops appear not to work
With the management terminal connected at the ELU, go to the “Test > User Port” screen if
using version 4 software (go to “Configuration > Front panel” for version 5)
See that the Front Panel Enable is checked.
Use F8 to view the NTU configuration, again, see that the Front Panel Enable is checked.
Check that no conflicting tests are already activated.
What does the ‘Quality Factor’ mean in the Performance > Transmission Line Screen?
The quality factor is a rough measure of the signal to noise ratio of the received signal.
Apply the following formula:
Received S/N (dB) = 58.4 – 10log10 (QF)
Different types of noise will have different QF levels that give a 1xE-7 BER. For some types of
coloured noise the SQ will be lower. For non-linear distortion and impulse noise, the QF will be
higher. Because of its qualitative nature it is best used as an indicator of long term variations.
For example, introduction of additional interferers into a cable, flooded cable ducting, etc.
The quality factor may be different between the ELU and the NTU because:
a
Different tolerances between components.
b Different noise sources at either end.
For a two pair link, one would expect the quality factor at each end to be similar for each line.
Results in the lab show the ELU to have a higher QF than the NTU. Also, the QF may vary from
one line synchronisation to the next.
9
50 ATL TELECOM USER GUIDE
AM2048A
Using the F8 function key check to see if the performance statistics are roughly the same for
each line and for each end (ELU and NTU) of the line.
If there is a difference it could be that one end of the link is near a source of interference,
either in the cable bundle or externally, such as a source of RF power.
Check the line connections to see if they are all OK.
If the equipment is connected to a very long line near to the limit of operation, it is possible
that one or more of the circuit ends can work error free whereas another end might have a
high bit error rate.
There are no alarms but data transfer is not happening
For all interface types
1
Check that no test loops are active. (The front panel TEST LED should be off on all units).
2 Go to the “Configuration>Timeslot Map” screen. Check to see that the Network
Timeslots (nTS) and the Customer Timeslots (cTS) are suitable for your application.
Pressing F5 will restore the timeslot map to its default setting.
For X.21/V.35
1 Check that the interface is in the correct mode, i.e. DTE or DCE. The user interface
module has hardware links that may be used to change the setting. The factory default
setting is DCE. When connecting the AM2048 to terminal equipment, either the AM2048
must be set to be a DCE and the terminal equipment to a DTE or vice versa. The setting of
the links may be checked without opening the box by going to the “Information>System”
screen.
2 Does the connected V.35 DTE implement RTS? If not, go to the “Configuration>User
Port” screen and use the circuit clamps to ensure that the AM2048 will accept data.
Note: For V.35
Circuit 105 = RTS Request to send.
Circuit 106 = CTS Clear to send.
Circuit 107 = DTR Data terminal ready.
Circuit 109 = CD Carrier detected.
3 Check that the interface has been set to the correct speed. Go to the
“Configuration>User Port” screen and check the value of N (x64) and the given data rate,
matches the rate expected by the connected data terminal. If there is a doubt, go to the
Configuration> User Port Screen and press ‘Enter’.
4 When the AM2048 is configured as a DCE and if the connected DTE provides a TX clock,
go to the “Configuration>User Port” screen and select the “DTE clock enable” option.
For data terminals that do not provide a clock, try using the “Invert Receive Clock’.
This will change the position at which the receive data is sampled and may help if cable