ATL TELECOM USER GUIDE
AM2048A OS/OM
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10
the end of the download. This minimises the interruption of payload traffic. Also, if
programming is interrupted, the previous version of software will remain intact. A new
application program may also be downloaded via the ELU to the remote NTU over the line.
10.4
ALARM INTERFACE
A 13 pin circular DIN connector provides access to 6 alarm inputs that are used to detect
metallic contact closure. For example, they can be used to sense a cabinet door open or
temperature sensors. The priority of these auxiliary alarms may be programmed through the
“Alarms>Severity Level Settings” screen.
There are also relay contact outputs to indicate urgent and non-urgent alarms. This allows the
system to be easily integrated into the alarm systems of other equipment.
10.5
USER INTERFACE MODULES
The user interface is provided by a plug-in module of which there are five types:
•
G.703, with software selectable 75ž or 120ž ports
•
X.21 MK II (with tail buffer)
•
V.35 MK II (with tail buffer)
•
e-PIM 10BaseT/USB
•
e-PIM2 10/100 BaseT/USB
The existing interface module can be changed out using a pluggable replacement unit.
These can be ordered separately using the part numbers detailed below. For part numbers and
order codes see Appendix B.
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ATL TELECOM USER GUIDE
AM2048A OS/OM
10.2
DSL TRANSMISSION FRAME
Both of the above transmission systems operate in a bit pump mode. The DSL frame is sent
over this ‘data pipe’. The DSL frame contains the following:
•
Sync word
•
Stuff bits
•
Stuff control bits
•
EOC channel
•
Customer data
The nominal DSL frame is always 6ms long, regardless of the transmission rate of the
individual channels.
The DSL frame length is adjusted slightly by the use of stuff bits. There may be 4 stuff bits or
2 stuff bits per frame. The stuff bits are used to adjust the effective payload bandwidth of the
DSL frame.
If the user rate clock is slightly quicker than the line rate clock then less stuff bits are sent.
Alternatively, if the user rate clock is slightly slower than the line rate clock then more stuff
bits are sent. This mechanism allows the line rate bandwidth to be adjusted to match the user
rate bandwidth.
At the receive end, the rate at which the stuff bits arrive is used to recover the user clock.
The transmit and receive paths may be operated independently from one another so that
when a G.703 user interface is present, the transmit and receive clocks are allowed to vary
independently by +50ppm. (
Note
: When operating with X.21 or V.35 interfaces, there is only
a single clock at each user interface.)
The Embedded Operation Channel (EOC) is carried in spare overhead bits in the transmission
frame. Packetised SNMP SET and GET messages are passed over the link from the ELU to the
NTU, which answers with the appropriate SNMP response.
10.3
CONTROL CIRCUIT
The control circuit is based on a micro-controller and determines the operational status of the
unit according to the state of the transmission system, the data interface and the
configuration information received from the terminal.
Configuration data and two copies of the application are stored internally in FLASH memory.
On power-up the application program is copied from FLASH to RAM from where it is
executed. The main application program is backed up so that if a corruption occurs it can be
corrected. This also enables the programming of a new application while the equipment is
operating normally. Control is transferred to the new application after an automatic restart at
