E1 port crossover detection – Quick Eagle Networks DL3800E User Manual
Page 31
Introduction
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2
When the incoming signal is framed on the inverse mux frame, the framer
will start loading its Dual Port RAM. The address to the Dual Port RAM is
derived from the 16-bit inverse mux frame. The software will ask all
framers to latch their Dual Port RAM addresses at the same time, and by
looking at the addresses, the software can determine which network has
experienced the greatest delay.
From the receive inverse IMUX framer, the incoming data will go to the
receive multiplexer. The net that is last in time will be enabled to tell the
receive multiplexer when to start unloading the Dual Port RAM to the DTE
interface. To allow for jitter and wander specifications, the read address
counter will be positioned approximately three frames behind the write
address for the network last in time.
E1 Port Crossover Detection
When the IMUX E1 circuits synchronize, they use the IMUX framing to
communicate to know the ports (1-8). A crossover is a situation where a
network line is connected to a port on the remote 3800E different from the
port it originates from on the local 3800E.(e.g. port 1 on the local unit is
connected to port 2 on the remote unit). This situation will cause DTE
traffic to be incorrectly multiplexed and, as a result, severely errored.
When a crossover is detected, the DL 3800E removes the crossed port from
the DTE data bundle and reduces the DTE data rate. The LED will change
to flashing green and the port status in the Alarms & Status menu read
“Line crossed”, and also (Crossed to port:x), where x is the port number
connected at the remote end. It also generates an SNMP alarm:
enCrossoverAlarm.
When the crossover is cleared, the port is restored to DTE bundle and the
LED restores to green. Port crossover status clears and the SNMP alarm
enCrossoverAlarm is idled.
An IMUX E1 circuit is reestablished as soon as the mismatched circuits are
disconnected and reconnected properly.
Figure 2-3
is a functional schematic of the DL3800E unit showing a unit
supporting four E1 lines.