Slow Upload Speeds
One of my students asked me what could cause customers to have problems with ADSL upload speed while their download speeds seemed to be fine. If you are showing slow upload speeds, it is not the infrastructure. It is more likely that it is a compatibility issue between the DSLAM and the modem or a configuration issue. It is not a problem in the outside plant or inside station wire.
While the typical response to this type of complaint is “when in doubt, dispatch out,” it’s an expensive and often unnecessary response. You can not only troubleshoot this effectively without a truck roll, while you are there you can do some proactive maintenance to quality circuits for both POTS and bandwidth.
Here are some ideas that might save a truck roll.
The Cable Pair
The cable pair must be free of any DC type fault, such as a shorted or grounded cable pair, crossed battery, or split cable pair. Begin by removing the battery from the cable pair and testing for any voltage tip or ring to ground. Any identified voltage >-3VDC should be located and the root cause repaired. If no voltage is present, test for a shorted or grounded cable pair. Any short or ground more solid than 10 Megohms should be located and fixed.
When the pair tests clean and a split pair is suspected, apply identification tone to the pair at the cross-connect box, remote, or central office. Other pairs will have less tone, and the pair that is split with your pair will show the same amount of tone. Use a TDR in the crosstalk feature to locate the splice where the split occurred.
Test the pair for capacitive and resistive balance. Capacitive balance should show greater than 98%, and the resistive balance should be within 5 ohms tip and ring to ground.
That being said, if the above parameters are met, the cable pair will show a longitudinal balance greater than 60dB. I prefer a longitudinal balance greater than 70dB for ADSL and FTTN IPTV.
The Network Interface and Inside Station Wire
Visually inspect the network interface ground to see that it is tied to the power ground electrode. It should test from 0 to 25 ohms. A difference of potential between the telephone network interface ground and the power ground electrode creates a myriad of problems for ADSL and IPTV.
Test the inside station wire (IW) for any DC type faults and series resistance. Replace any defective station wire with at least CAT5 type wire. With all customer equipment removed, the wire should test clean greater than 10 Megohms tip to ring and tip and ring to ground.
If the original install included filters, remove them and place a POTS splitter at the network interface. In many instances not all jacks are filtered, especially those that do not have phones plugged in. They cause reflected energy to corrupt the data and slow both upstream and downstream data.
Quality Circuit Testing
When pair tests are completed on the cable pair and inside station wire, a transmission test will qualify the POTS portion of the service and indicate reach problems and AC interference problems.
Loop current should test greater than 23 milliamps. This measurement is done directly to dial tone. Next, dial the milliwatt tone generator and measure circuit loss. If circuit loss is greater than -8dBm, the reach for ADSL has been exceeded. Excessive loss will also indicate bridged tap and too much 26 gauge wire in the circuit and this could explain slow upstream rates.
Dial the quiet line termination and measure power influence (PI), and circuit noise. PI should measure less than 80dBrnC and circuit noise should measure less than 20dBrnC.
When PI exceeds 80dBrnC, the root causes are bonding and grounding issues or power distribution issues, or a combination of both. Continuous bonding is most important, because it mitigates all frequencies above 1 kHz. This reduces the effect of AM and Ham radio.
One must keep in mind that in aerial cable the strand carries a great deal of current flow. Just because PI is less than 80dBrnC it does not mean that the sheath is continuously bonded. Most good DSL test sets have a voice band spectrum analyzer and a wide band spectrum analyzer. If the wide band spectrum analyzed indicates AM or Ham radio interference bonding is in order.
A trained field technician using a quality multifunctional test set should be able to cut down on truck rolls by conducting the above tests. In many cases, DSL problems are not outside plant problems.
I hope to see many of you at OSP EXPO 2009 in Minneapolis, my old stomping grounds. There are many excellent sessions and demos to attend, as well as my “Ask the OSP Expert” seminar on Thursday. For more information, go to www.ospmag.com/expo. For questions on problems you are having, tips for others, or comments on my columns, contact me at firstname.lastname@example.org.
What is your experience with this? Tell your fellow readers now!