ZyXEL Communications IES-1248-51A, User Manual

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Chapter 16 xDSL Port Setup
IES-1248-51V User’s Guide
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to configure ADSL ports efficiently. You can configure all of the ADSL ports with
the same profile, thus removing the need to configure the ADSL ports one-by-one.
You can also change an individual ADSL port by assigning it a different profile.
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.
16.4 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.
16.4.1 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.
16.5 Configured Versus Actual Rate
You configure the maximum rate of an individual ADSL port by modifying its
profile (see
Chapter 17 on page 139 ) or assigning the port to a different profile
(see Section 16.7.1 on page 124 ). 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 using the Edit Profile screen, 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.