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Chapter 6: Configuring DSL Parameters April 14, 2006
6-4 MM70xG2-UM-03
2
(cont.)
• Startup Margin
The target signal-to-noise margin, in decibels, that the modem must achieve with a BER of 10
-7
or
better to successfully complete synchronization. The default margin value is -10 dB. A lower margin
may result in a higher data rate, but it can increase noise on the line. Possible values are -10 dB
through 10 dB, or to completely Disable the margin. The default value is -10 dB.
• Data Rate (kbps)
Data rate determines the maximum transmission rate, in kilobits per second, up to which the modem
can negotiate and synchronize with another device (modem or a DSLAM) to which it is attached.
When the Bit Rate Mode (see “Bit Rate Mode” below) is set to Fixed, the range of values are (ADC
modems comply with the standard G.shdsl data rate range):
– for the MM702G2 modem, 384 kbps to 4608 kbps, in 128 kbps increments
– for the MM701G2 modem, 192 kbps to 2304 kbps, in 64 kbps increments
Rates down to 64 kbps are supported only when operating in single-pair, point-to-point mode with
another ADC modem. (see Chapter 7: Implementing a Point-To-Point LAN Extension).
When the Bit Rate Mode (see “Bit Rate Mode” below) is set to Adaptive for an MM701G2 (Adaptive is
default value) or for an MM702G2 set to Single Wire Pair Mode only (see “Bit Rate Mode” below),
this field is automatically set to Adaptive. The default value is Adaptive.
• Wire Pair Mode
Indicates whether the G.shdsl modem is operating in a two-wire mode (Single), a four-wire mode
(Dual), or a Dual Enhanced mode. For the MM701G2 modem, Single mode is the only setting
available. For the MM702G2 modem, you can select Single, Dual mode, or Dual Enhanced mode.
The default value is Single.
• Power Spectrum Distribution
The Power Spectral Density (PSD) plots the variations of signal power with signal frequency for the
G.shdsl transmission between the modem and the DSLAM or the modem and another modem.
Symmetric PSD indicates that the PSD mask for both sides of the transmission (the CO- and remote-
side) are the same (symmetric).
Asymmetric PSD indicates that the PSD mask for both sides of the transmission (the CO- and
remote-side) are not the same (asymmetric). There are two unique numeric values
(AsymmetricRate1 and AsymmetricRate2) used to determine the asymmetric PSD mask based on
the Annex A or Annex B standard that you selected (see page 6-3). AsymmetricRate1 is 784 kbps for
Annex A and 2312 kbps for Annex B. AsymmetricRate2 is 1552 kbps for Annex A and 2056 kbps for
Annex B.
Both ends of the connection must be set for the same Symmetric or Asymmetric PSD. The default is
Symmetric.
• Bit Rate Mode
Bit rate mode indicates how the modem synchronizes with the device to which it is attached in either
a Fixed or Adaptive mode. The default for the modem is Adaptive mode.
– Fixed mode indicates that the modem will synchronize with the other end (a DSLAM or another
modem) at a fixed bit rate through negotiation. The modem will synchronize at the best rate, up to
the data rate specified (see “Data Rate (kbps)” above), that can be achieved by both ends.
– Adaptive mode indicates that prior to modem negotiating a rate, the modem performs an
adaptation phase to determine a best possible rate based on conditions of the line. After adaptive
mode, the modem negotiates the best rate that can be achieved with the other end, based on the
adaptation results.
Step Action