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Functional Description 700-701-100-02
14 August 9, 2002 UTU-701 and ETU-751 List 1
RATE SELECTABLE APPLICATION MODES AND OPTIONS
Applications for single-pair rate-selectable HDSL are those that require transport of voice and data at various rates
over various distances on a single pair of wires. Depending on line noise and the HDSL rate selected, spans of up
to 7.1 km
(4.4 miles) can be deployed without the use of doublers. The HDSL line rate depends on the number of
time slots selected. The UTU-701C and ETU-751C each have 32 time slots with a bandwidth of from 256 kbps
to 2048 kbps (1 to 32 time slots selected). Each time slot represents a 64 kbps increment of the available
bandwidth.
The available rate selectable application modes and options are:
• single
• structured
• unstructured
• CRC-4
Single Mode
Single is the only application mode displayed in the Config System Settings menu. It means the system uses a
single pair of twisted copper wires to transport data.
Structured Mode
When less than 32 time slots are selected, the line and desktop units automatically operate in the structured
mode (see “G.704 Framing and Rate Selectable HDSL” on page 17). There is no structured mode menu selection.
In structured mode, data at the G.703 interface is framed according to G.704. This permits fractional allocation of
the total 2048 kbps bandwidth to and from the G.703 interface, insertion of idle code into unused time slots at the
G.703 output, and monitoring of the G.703 input for CRC-4 multiframe errors.
A typical structured mode application is illustrated in Figure 6. The settings for this application are listed in
Table 7. Time slots 1-15 and 17-25 are transported as telephony voice channels between the G.703 ports of the
two units. Time slots 26-31 are unused and are set to idle code FF. In structured mode, time slot 1 is the beginning
time slot; time slot 0 is regenerated at the G.703 output. With the CRC-4 mode enabled, the input G.703 signal is
monitored for CRC-4 multiframe errors and at the G.703 output, a new CRC-4 code is generated. Time slot 16 is
transported transparently between G.703 ports and may be used for telephony signaling.
Figure 6. Typical Structured Mode Application