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| reply to mrhuggles
Re: Here is a Qwest DOC explaining the interference problem ...
said by mrhuggles  :what exactly is IP-based dsl and why isnt it effected? My impression from reading that Doc is that that is what they are calling FTTN.
Remote Terminal (RT) deployment of Internet Protocol (IP) broadband or also referred to as Fiber-to-the-Node (FTTN) where the serving Central Office has ATM-based DSL are overlay areas and may cause interference or degradation of the ATM-based DSL service in some cases.
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knotpc
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|  The issue is POWER interference. All DSL circuits are meant to be spectrally compatible. For more information see the DSL Forum and ADSL specifications. These specifications all are based on the assumption that all the circuits start at the same place, which means they all would have the same power level.
As ADSL travels from the CO on an F1 (feeder pair) it eventually connects to an F2 (distribution pair). The connection is made using a copper pair jumper in a "Crossbox". The F2 is what eventually goes down your street and connects to a drop wire that connects to an SNI (station network interface) located on or in your home or business.
In the world of FTTN the IPDSLAM is placed beside the Crossbox. An ADSL2+ circuit is connected via jumpers directly to your F2, the pair that physically feeds your home. F2 feed cables can be quite large however, as they go through your neighborhood they begin to shrink, generally speaking the F2 going down your backyard or alley is likely to be 25 to 50 pairs, telephone plant is grouped into 25 pair complement. For FTTN to work and provide ROI to Qwest the IPDSLAM must be placed within ~2500 feet of your home. ADSL2+ achieves high download transfer rates on short loops after 2500 feet it begins to act like its elder sister ADSL.
Now back to the POWER interference issue. ADSL begins losing power as soon as it leaves the DSLAM in the CO on the F1 pair. By the time the ADSL circuit reaches the Crossbox and is connected to the F2 it might very well be on its last leg, having little power left to mitigate the effects of a nearby ADSL2+ circuits. The ADSL2+ circuit that is connected at the same Crossbox leaves at FULL power able to destroy its older sibling.
Qwest also mentions binder separation which is a technical joke. To have appropriate separation between TWO ADSL and ADSL2+ circuits with differing POWER LEVELS as described above, the F2 feeder cable would need to be at least 100 pairs (four 25 pair compliments). With the single ADSL circuit in the first 25 pair bundle and the ADSL2+ circuit located in either two of the last 25 pair bundles. The reason this is a joke is that telephone plant was designed to offer 1.5 copper pair lines to each home. A normal block has a single 25 pair to 50 pair feed, which provides no way to separate a single ADSL circuit from a single ADSL2+ circuit.
If you notice I keep referring to SINGLE ADSL and SINGLE ADSL2+ circuits. This is intentional as it is far more likely that the F2 going through your neighborhood carries more than ONE single ADSL or ADSL2+circuit. One ADSL2+ circuit installed on a F2 pair, as described, would cause POWER interference issues on ALL ADSL circuits located within 75 pairs of it. Again, the issue is POWER. The ADSL2+ circuit is simply overpowering the ADSL circuit.
To alleviate the issue Qwest could simply adjust the power output of the IPDSLAM. Which would make the FTTN project fail as the ADSL2+ circuits would not be able to deliver the desired download speeds with reduced power.
So this is not a marketing issue it is a POWER issue. If the CLECS want to survive they will need to fight for interconnect rights to the FTTN network, which in my opinion is a losing legal battle. |
