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uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

DMT Carrier Frequency Allocation in ADSL



 
 
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  #1  
Old December 11th 06, 04:49 AM posted to comp.dcom.xdsl,uk.telecom.broadband,can.internet.highspeed,aus.comms
[email protected]
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Posts: 1
Default DMT Carrier Frequency Allocation in ADSL

Hi,


I'm quoting from Biju Sukumaran's DSL document:

"During the initialisation phase of the setting up of an ADSL
connection, the capacity of each carrier of the DMT is evaluated and
the maximum number of bits that can be stuffed into each carrier is
determined. The bits to be transmitted are then distributed across
these carriers, such that the carrier with the best performance gets
the most bits and the most noisy one gets the least, or no bits. This
means that the high performance carriers, which are usually the low
frequency ones, are very finely modulated to a maximum of 15 bits.
This is done in real time as well, so that the bit rate remains
unaffected by the time varying nature of the noise in the channel."

My question now is, does the bit allocation of each frequency is
determined only during initialization phase or does it change over
time? In other words, after I have made the initial ADSL connection,
does the bit allocations remain constant unless a resynchronization
between ADSL modem and DSLAM is made?

Thanks,
ennui

  #2  
Old December 11th 06, 10:04 AM posted to comp.dcom.xdsl,uk.telecom.broadband,can.internet.highspeed,aus.comms
Ian Stirling
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Posts: 807
Default DMT Carrier Frequency Allocation in ADSL

In uk.telecom.broadband wrote:
Hi,


I'm quoting from Biju Sukumaran's DSL document:

"During the initialisation phase of the setting up of an ADSL
connection, the capacity of each carrier of the DMT is evaluated and
the maximum number of bits that can be stuffed into each carrier is
determined. The bits to be transmitted are then distributed across
these carriers, such that the carrier with the best performance gets
the most bits and the most noisy one gets the least, or no bits. This
means that the high performance carriers, which are usually the low
frequency ones, are very finely modulated to a maximum of 15 bits.
This is done in real time as well, so that the bit rate remains
unaffected by the time varying nature of the noise in the channel."

My question now is, does the bit allocation of each frequency is
determined only during initialization phase or does it change over
time? In other words, after I have made the initial ADSL connection,
does the bit allocations remain constant unless a resynchronization
between ADSL modem and DSLAM is made?


"This is done in real time as well..." seems clearly to me to say the latter.
 




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