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Overview 700-701-100-02
2 August 9, 2002 UTU-701 and ETU-751 List 1
EMU FIRMWARE COMPATIBILITY
The EMU-830 Management Unit firmware must be Version 3.22.08 or later to support rate selectable HDSL units.
APPLICATION INTERFACE
The UTU-701C and ETU-751C provide G.703 interface ports with a rate selectable HDSL payload. The only
application mode is Single, indicating single pair.
The G.703 E1 application interface conforms with the ITU-T G.703 physical specification and can be configured
for an impedance of 75 Ω unbalanced or 120 Ω balanced. User data can be unstructured or structured according to
the G.704 framing standard, and optionally CRC-4 multiframed according to the G.706 standard. Structured mode
is automatically invoked when 1 to 29 time slots are selected. Unstructured mode is invoked when 30, 31, or 32
time slots are selected.
The exchange office data terminal equipment (DTE) allocates the 2048 kbps E1 payload to the G.703 port in
time-slot increments of 64 kbps each. The number of G.703 time slots allocated by the DTE is determined by the
selected HDSL payload rate (the DTE and HDSL payloads must be set to the same rate). Time slots not allocated
to the G.703 port are replaced by idle codes at the G.703 output.
The UTU-701C and ETU-751C have HDSL payload rates ranging from 256 kbps to 2048 kbps. The desired
HDSL payload rate is selected in time slot increments of 64 kbps from the system settings menu of the
LTU-configured unit. The selected payload rate applies to both the receive and transmit directions. The
LTU-configured unit automatically configures the NTU-configured unit for the same payload rate. Table 1 lists
the characteristics of the rate selectable G.703 line and desktop units covered in this practice.
The G.703 units always transmit time slots 0 and 16, which results in 128 kbps being added to the user-selected
HDSL payload rate (when 1 to 30 time slots are selected). For example, the lowest-selectable HDSL rates, 64 and
128 kbps, are transmitted at 256 kbps. This 128 kbps increase in payload rate, however, does not affect the rate of
the G.703 data received at the customer or network DTE.
Figure 1 shows a single-pair, leased-line data application using 4 time slots for a 256 kbps HDSL payload rate.
Customer data is input to the remote G.703 port at the 256 kbps rate, transported over the HDSL loop at an
increased 384 kbps rate, and received by the exchange office DTE at the original 256 kbps rate. For more
information, see “Rate Selectable Application Modes and Options” on page 14 and “G.704 Framing and Rate
Selectable HDSL” on page 17.
Table 1. Rate Selectable G.703 Unit Characteristics
Model Interface
User Selected
HDSL Payload
Rates (kbps)
Actual
HDSL Payload
Rates (kbps)
LTU/NTU
Configurable
UTU-701C G.703 64 to 2048 256 to 2048 Yes
ETU-751C G.703 64 to 2048 256 to 2048 Yes