Product manual

Product Manual - DM991 Series V Family - 204.4092.08 20
When set up in synchronous mode, the line clock becomes the same as the data clock. The precision of
such clock gets to be, thus, the same as the precision of the clock that is selected as the equipment
synchronization clock. Recommendation G.991.2 states that the clock precision shall be within ± 32 ppm,
regardless of the clock scheme selected, so it is up to the user to set up a clock with such precision so as
to operate within the Recommendation bounds (or the user can use a less precise clock, operating out of
the Recommendation). In this way, the stb1 and stb2 stuff bits are always present, while stb3 and stb4 are
not transmitted.
In the automatic selection mode, the LTU will use the NTU-selected mode. If the NTU accepts any mode
(automatic configuration), the synchronous mode will be used.
3.5.3. Annex
The annexes determine slight variations on the Recommendation to better suit the equipment to the
employed line.
One of three annex options can be chosen: A, B or automatic selection.
Annex A describes those specifications that are unique to lines operating under conditions such as those
typically encountered within the North American network.
Annex B describes those specifications that are unique to lines operating under conditions such as those
typically encountered within European networks.
For the automatic selection mode, the LTU will employ the NTU-selected annex. If the NTU accepts any
type of annex, Annex B will be used.
3.6. Performance
The interface performance is directly related to the transmission line characteristics.
The gauge and the length of the line wire, the noise and the susceptibility to micro-interruptions to which
the line is subjected will determine the maximum transmission rate.
The range also diminishes if the line sports a great number of splices and stubs. The length of the stubs
also alters the line characteristics. This can increase the signal reflections and the line noise.
For a noise-free line using a 0.4-mm gage wire, with no seams or bifurcations, the range will be of 4,100
m for 2,304kbit/s, and with a modem set to 192kbit/s, the range can reach 7,100 m.
These tests were conducted with an artificial transmission line emulating the behavior of an actual line.
The table 9 includes the expected ranges for some rates on a noise-free artificial line.
192 7,1
256 6,7
384 6,1
512 5,9
768 5,5
1024 5,1
1536 4,3
2048 4,2
2304 4,1
Data Rate
[kbit/s]
0.4mm Wire [km]
Table 9. G.shdsl Interface Reach