tu n'as toujours pas integré que Free 'fait avec' ce que le parc de modems Adsl v1 est capable de négocier ! selon , pour rappel, la procédure "standard" de base ci-dessous
quels sont tous ces modems Adsl V1 capables de négocier plus de 800kbits ; cite les alors...
pour le reste, je laisse "le menteur" 
te répondre
la négo 'standard' Adsl v1 , tel que tout modem , jeune ou vieux, peut la conduire ....jusqu'à 800k probablement entre le modem DSLAM Free et un modem Machepro 
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(en italique un pavé sur les modalités de renégo; un peu indigeste; peut etre 'sauté' !)
The first ADSL modem TRX1 is the so called central office modem whilst the second ADSL modem TRX2 is the remote terminal modem.
The two modems TRX1 and TRX2 operate in accordance with the specifications of the ANSI Standard on ADSL to transmit data empacked in discrete multi tone (DMT) symbols
These DMT symbols are carried by a set of 256 equidistant carriers. The bits constituting the DMT symbols are thereto spread over the different carriers
In the initialisation procedure, the two ADSL modems, TRX1 and TRX2, negotiate a downstream bit rate and an upstream bit rate, and decide, based on signal-noise-ratio measurements for each carrier, how much bits will be modulated on each particular carrier and at which power level each particular carrier will be transmitted. This is done in what is usually called the bit allocation procedure
At the end of this procedure, both ADSL modems, TRX1 and TRX2, know for instance that carrier 1 carries 2 bits, modulated thereon via 4 QAM modulation, and is transmitted with a 0,9 dB gain, carrier 2 carries 5 bits, modulated thereon via 32 QAM modulation, and is transmitted with a 1.2 dB gain, carrier 3 carries 4 bits, modulated thereon via 16 QAM modulation, and is transmitted with a 1.3 dB gain, and so on........
Obviously, the downstream and upstream data rates are determined when the bit constellation is given
To negotiate the upstream and downstream data rates, and to obtain the bit constellation, the modems TRX1 and TRX2 produce and respond to a specific set of precisely time initialisation signals
The "Channel Analysis" procedure of the ADSL Standard contains the first phase, PROPOSAL, and second phase, CHANNEL ANALYSIS,
In the first phase, PROPOSAL, the central office modem TRX1 downstream transmits a message PROPOSE_12 which contains four optional data rate values for the downstream and upstream direction
the first message PROPOSE_12 is called the C-RATES1
Upon the propose-12 message, the remote terminal modem TRX2 replies with a PROPOSE_21 message wherein four optional upstream data rate values are proposed to the central office modem TRX1
It is noticed that the message PROPOSE_21 is called the R-RATES1 message in this paragraph
the second phase, CHANNEL ANALYSIS, the central office modem TRX1 transmits a wideband pseudo-random signal allowing the remote terminal modem TRX2 to estimate the signal-noise-ratio, to determine therefrom the maximum bit allocation for downstream carriers , the maximum downstream data rate and which one of the four optional downstream data rate values proposed by TRX1 in PROPOSE_12 is likely to be used.
The wideband pseudo-random signal is called C-MEDLEY in the draft ADSL Standard
In the opposite direction, the remote terminal modem TRX2 transmits also a wideband pseudo-random signal, called R-MEDLEY in the referenced ADSL Standard, which allows the central office modem TRX1 to estimate the signal-noise-ratio for upstream carriers, to determine therefrom the maximum bit allocation for the upstream carriers, the maximum upstream data rate and which one of the four optional upstream data rate values proposed by TRX2 in PROPOSE_21 is likely to be used
The "Exchange" procedure of the ADSL Standard contains the third phase, SELECTION, and fourth phase, CONFIRMATION
In the third phase, SELECTION, the remote terminal modem TRX2 replies to the PROPOSE_12 message of TRX1 by transmitting to the central office modem TRX1 a message SELECTION_21 containing the selected optional data rate for downstream transmission and the highest data rate that can be supported for downstream transmission based on the signal-noise-ratio measurements for the downstream carriers in the CHANNEL ANALYSIS phase.
this SELECTION_21 message is called the R-RATES2 message in the ADSL Standard
Table 41 on page 103 of this draft Standard lists the predetermined reserved bit patterns which have to be used by the remote terminal modem TRX2 to indicate in R-RATES2 which one of the four optional downstream data rates is selected. In the opposite direction, i.e. the downstream direction, the central office modem TRX1 replies to the PROPOSE_21 and SELECTION_21 messages by transmitting to the remote terminal TRX2 a message SELECTION_12 containing the selected optional data rates for downstream and upstream transmission.
For upstream transmission, the selected optional data rate value is determined based on the signal-noise-ratio measurements for the upstream carriers in the CHANNEL ANALYSIS phase
For downstream transmission, a copy is made of the information in the SELECTION_21 message produced and transmitted by the remote terminal modem TRX2.
It is noticed that the SELECTION_21 message is called the C-RATES2 message in the draft ADSL Standard
Table 39 on page 100 of this draft Standard lists the predetermined reserved bit patterns which have to be used by the central office modem TRX1 to indicate in C-RATES2 which one of the four optional downstream and four optional upstream data rate values is selected.
The C-RATES2 message is accompanied by a so called C-B&G message
This C-B&G message contains bits and gains information for the upstream carriers : for each upstream carrier, the C-B&G message indicates the number of bits to be modulated thereon by the remote terminal modem TRX2, and the gain or power level that should be used to transmit this carrier.
When the C-RATES2 message contains the bit pattern which indicates that a new data rate proposal will be produced, the C-B&G message obviously contains superfluous information which is needlessly transported. The next step to be executed then is the first phase, PROPOSAL, wherein the central office modem TRX1 proposes new upstream and downstream data rate values to the remote terminal modem TRX2. Since the central office modem TRX1 has determined the highest data rate that can be supported for upstream transmission during the CHANNEL ANALYSIS phase and since the central office modem TRX1 is told the highest data rate that can be supported for downstream transmission by the remote terminal modem TRX2 in the SELECTION_21 message, the newly proposed optional upstream and downstream data rate values can be chosen very efficiently.It may thus be expected that the second execution of the PROPOSAL, CHANNEL ANALYSIS and SELECTION phase already results in a selected upstream and downstream data rate value which are well-adapted to the highest upstream and downstream data rates that can be supported on the telephone line TL. If however, the second selection of upstream and downstream data rate values does not yet satisfy the central office modem TRX1 at the time the SELECTION_12 message has to be sent, the central office modem TRX1 may again transmit the predetermined reserved bit pattern which indicates that a new proposal of upstream- and downstream data rates will be produced.The phases PROPOSAL, CHANNEL ANALYSIS and SELECTION are thus repetitively executed until a satisfactoring adapted upstream and downstream data rate value are found and communicated to the remote terminal modem TRX2 via the SELECTION_12 message
In the fourth phase, CONFIRMATION, the remote terminal modem TRX2 transmits the bits and gains information with respect to the downstream channel to the central office modem TRX1: in the so called R-B&G message , the remote terminal indeed indicates for each downstream carrier the number of bits to be modulated thereon and the gain or power level to be applied when transmitting this downstream carrier.
The initialisation protocol is terminated herewith.
Message édité par kobaia le 23-08-2005 à 11:03:51
