Specifications

Installation and Operation Manual Chapter 1 Introduction
ASMi-54C LRS-102 Ver. 2.0 Functional Description 1-9
In general, the line rate is determined by the number of payload timeslots
that need to be transmitted over the line served by the corresponding
modem, which is user-selectable from a minimum of 3 timeslots to a
maximum of 89 timeslots.
If the number of timeslots routed to the corresponding port is lower than the
maximum rate, any unused timeslots in the SHDSL signal frame is filled with the
idle timeslot code.
Because of the modulation method used by SHDSL modems, a lower rate
reduces the bandwidth needed on the external SHDSL line, and thus enables
operation over longer ranges (it also reduces the power consumption of the
ASMi-54C module).
Another way to increase range is to use multiple-pair bonding (M-pair mode
defined in ITU-T Rec. G.991.2), which distributes the available traffic over two or
four twisted pairs.
The minimum payload data rate supported by an SHDSL signal, however, is
192 kbps (corresponding to three timeslots on the SHDSL line), which results,
together with the SHDSL overhead (8 kbps) in a minimum line rate of
200 kbps. Therefore, you cannot select data rates lower than 192 kbps.
However, for packet applications (that is, when only Ethernet traffic is
transmitted over the line), it is possible to allow the modem configured as
STU-C to automatically select the highest possible line rate, by performing a
special handshaking process in cooperation with the STU-R modem (line
probing in accordance with ITU-T Rec. G.991.2). This process can also be used
to renegotiate the line rate when the performance is degraded by noise, and
thus it also enables adapting to varying operating conditions. Line probing
can be used only when using the 64/65-octet TC layer.
• The receive path of the SHDSL modem line interface section regenerates the
line signal and recovers the data stream transmitted by the STU-R. The
recovered SHDSL data stream is then processed by the receive path of the
digital processor, which decodes and demultiplexes the data stream to
retrieve the various types of data sent by the STU-R. The payload is sent to
the payload multiplexer, and the overhead data is used internally.
The receive path of the SHDSL modem can provide performance statistics for
evaluating SHDSL line transmission quality.
Payload Multiplexer
The payload multiplexer participates in the bonding of several SHDSL lines (two or
four lines) to operate as a single logical link (4-wires and 8-wires mode,
respectively), a capability referred to as the M-pair mode per ITU-T Rec. G.991.2.
For this mode, which is available when using the HDLC TC (Transmission
Convergence) layer (see the
Ethernet Service section on page 1-3 ), the payload
multiplexer distributes the payload among the bonded SHDSL lines. All the lines
must use identical SHDSL parameters, and therefore, when lines are bonded, one
of the lines (the line with the lowest port index in the group) is automatically
selected as the master line, from which all the other lines copy their parameters.
Note
Note