ADSL Modulation Scheme Attributes

I could not find any reliable comprehensive source and don't want to read all the specs.... Therefore I compiled a short summary of commonly used DSL modulation schemes and their key attributes.

Different max. speed is given on different sources. I will complete this table step by step as I find reliable figures.

Specification Spectrum Remark Up Dn Line Length
ITU G.922.1 Annex A (G.dmt) 25-138/138-1100 over-POTS 640kb 6Mb  
ITU G.922.1 Annex B (G.dmt) 138-276/276-1100 over-ISDN      
ITU G.992.3 (ADSL2)Annex A   over-POTS      
ITU G.992.3 (ADSL2)Annex B   over-ISDN      
ITU G.992.3 (ADSL2)Annex L ("reach extended")   over-POTS 1Mb 12Mb  
ITU G.992.3 (ADSL2) Annex M   over-POTS 3.5Mb    
ITU G.992.3 (ADSL2) Annex J ?-276/276-? NO POTS 3.5Mb 12Mb  
ITU G.992.5 (ADSL2+) Annex A 25-138/138-2200 over-POTS      
ITU G.992.5 (ADSL2+) Annex B 138-276/276-2200 over-ISDN      
ITU G.992.5 (ADSL2+) Annex L   over-POTS 1Mb 24MB  
ITU G.992.5 (ADSL2+) Annex M 25-276/276-3300 over-POTS 3.5Mb 24Mb  
ITU G.992.5 (ADSL2+) Annex J
  NO POTS 3.5Mb    

Annex A: ADSL-over-POTS
Annex B: ADSL-over-ISDN 138-276 kHz up / 275-1104 dn
Annex M: More BW for uplink, over POTS, 3.5 MB up
Annex L: extended reach, over-POTS
Annex J: NO POTS (but ISDN???), 3.5Mb up

Example: ADSL line in Bangkok, ISP Telephone Organisation of Thailand (TOT)

Subscribed package: "Best Fit", 8Mbps dn / 1Mbps up

Selected mode remark dn att dn SNR dn speed up att up SNR up speed
G.dmt Annex A   28.5 13.5 8064 15.0 12.0 800
G.dmt Annex M invalid ->2+            
ADSL2 Annex A   24.0 12.0 9151 14.7 16.5 737
ADSL2 Annex M   25.0 12.0 8045 13.5 18.8 1278
ADSL2+ Ann. A   28.0 23.3 10240 14.7 13.0 729
ADSL2+ Ann. I no sync.            
ADSL2+ Ann. A/L =A            
ADSL2+ Ann. M   30.0 22.7


19.7 13.5 1278
ADSL2+ Ann. A/I/J/L/M =M            

Modem default was A/L, which led to "A". In this mode the possible uplink speed could not be fully utilized. Annex M assigns more spectrum to the uplink, almost doubling the speed. There is still enough BW for the uplink to allow the maximum uplink speed of 10Mbps.

This ADSL line connect earlier with 8192 / 1023 kbps (Annex M mode). Recently the downlink limit seems to be lifted up to 10 Mbps, while the uplink might be unlimited (?) and only the line quality is the limit.

Annex J could improve the uplink even more, but is not specifically selectable. Also the phone line would be unusable for POTS.


0 #1 Nino 2013-02-05 13:57
Check out
You will see that there's no such thing as ADSL2+ annex L (yet). Maybe you want to add annex I. And why not stick to alphabetical order? :-)
Annex J is often marketed as ISDN-like because an annex J line often comes with 2 voice "channels" and 3 or more telephone numbers included, at least with Deutsch Telekom. Technically everything runs over IP.

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