Product Manual - DM991 Series V Family - 204.4092.08
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3.4.4. SNR Margin Defect
An SNR margin defect occurs when the signal-to-noise ratio falls below the specified margin, i.e., when
the signal quality is too poor. The standard signal-to-noise ratio for the DM991 G.shdsl interface is 6 dB.
3.4.5. LOSW Defect
An LOSW (Loss of Sync Word Defect) defect shall be declared when at least three consecutive received
frames contain one or more errors in the framing bits. The term framing bits shall refer to that portion of
Frame Sync Word, Stuff Bits and Stuff Bit Ids – see Table 8 -, which are used for G.shdsl frame
synchronization. An LOSW defect shall be cleared when at least two consecutive received frames contain
no errors in the framing bits. For the DM991, the error indication is activated for one second after the
reception of the two error-free consecutive frames.
When the interface is indicating LOSWD, the DSL interface status LED blinks four times per second (4
Hz).
3.4.6. LOSW Failure
An LOSW failure (Loss of Sync Word Failure) shall be declared after 2.5 ± 0.5 seconds of contiguous
LOSW defect. The LOSWF shall be cleared when the LOSW defect is absent for 20 seconds or less (i.e.
clear within 20 s). The minimum hold time for indication of LOSW failure shall be 2 seconds.
When the interface is indicating LOSWF, the DSL interface status LED blinks eight times per second (i.e.
at 4 Hz).
3.5. G.shdsl Interface Configurations
The operation modes are all configured by software.
The explanation of the configuration parameters of the G.shdsl interface is presented below.
3.5.1. Terminal Type
Indicates if the interface operates as LTU (central office) or as NTU (subscriber).
When the modem is configured as LTU, it will determine every connection parameters during handshake,
as the Annex to be used, the number of channels, the clock type (synchronous or plesiochronous), etc. It
is not possible to recover the system clock from the interface clock when it is set up in such a way.
When the modem is set up as NTU, it is mandatory that the settings of the annex and of the clock type
(Frame Mode) be automatic, for it accepts any settings determined by the LTU.
It is not possible to interconnect two equipments which are set up for the same type of terminal, for the
handshake happens between LTU and NTU only.
3.5.2. Frame Mode
This option determines the interface operating mode as synchronous or plesiochronous.
In plesiochronous mode, the transmission and receive clocks are independent of the line clock, which is
generated by the LTU. The line clock shall be accurate to within
±
32 ppm of the nominal frequency, as
defined by G.991.2. Periodically, four stuff bits are automatically inserted to adequate the data clock to the
line clock. This procedure is essential for equipment synchronization.
Summary of Contents for DM991C
Page 1: ...DM991 SERIES V DM991C DM991CE DM991S DM991SE PRODUCT MANUAL 204 4092 08 rev 08 Date 8 12 2008 ...
Page 66: ...Product Manual DM991 Series V Family 204 4092 08 66 Figure 31 LDL Test Converter Mode ...
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