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MSAP2000 AAM User’s Guide
For example, you could set up different profiles for different kinds of accounts (for
example, economy, standard and premium). Assign the appropriate profile to an
ADSL port and it takes care of a large part of the port's configuration maximum
and minimum transfer rates. You still get to individually enable or disable each
port, as well as configure its channels and operational mode. See later in this
chapter for how to configure profiles.
7.4 Interleave Delay
Interleave delay is the wait (in milliseconds) that determines the size of a single
block of data to be interleaved (assembled) and then transmitted. Interleave delay
is used when transmission error correction (Reed- Solomon) is necessary due to a
less than ideal telephone line. The bigger the delay, the bigger the data block size,
allowing better error correction to be performed.
Reed-Solomon codes are block-based error correcting codes with a wide range of
applications. The Reed-Solomon encoder takes a block of digital data and adds
extra "redundant" bits. The Reed-Solomon decoder processes each block and
attempts to correct errors and recover the original data.
7.4.1 Fast Mode
Fast mode means no interleaving takes place and transmission is faster (a "fast
channel"). This would be suitable if you have a good line where little error
correction is necessary.
7.5 Configured Versus Actual Rate
You configure the maximum rate of an individual ADSL port by modifying its
profile or assigning a different profile to the port. However, due to noise and other
factors on the line, the actual rate may not reach the maximum that you specify.
Even though you can specify arbitrary numbers for a profile, the actual rate is
always a multiple of 32 Kbps. If you enter a rate that is not a multiple of 32 Kbps,
the actual rate will be the next lower multiple of 32Kbps. For instance, if you
specify 60 Kbps for a port, the actual rate for that port will not exceed 32 Kbps,
and if you specify 66 Kbps, the actual rate will not be over 64Kbps.
Regardless of a profile's configured upstream and downstream rates, the
MSAP2000 AAM automatically limits the actual rates for each individual port to
the maximum speeds supported by the port's ADSL operational mode. For
example, if you configure a profile with a maximum downstream rate of 25000
Kbps, and apply it to a port set to use G.dmt, the MSAP2000 AAM automatically
uses a maximum downstream rate of 8160 Kbps. This means that if you
configure a profile with very high rates, you can still use it with any port. See Table
14 on page 83 for a list of the maximum rates supported by the different ADSL
standards.