MH89760B
Preliminary Information
False Candidate
Hunt Mode
False
Candidate
Forced
Reframe
Candidate
Out of
Sync.
False
Candidate
Verify
Candidate
Candidate
CRC
Check
*
Candidate
In sync
Maintenance
Valid Candidate
Valid Candidate
New Frame Position
Resync
Receiver
* Note: Only when in ESF mode and CRC
option is enabled.
Figure 8 - Off-Line Framer State Diagram
The chart shows the results for ESF mode with CRC
check, and D3/D4 modes of operation. The average
reframe time with random data is 24 ms for ESF, and
13 ms for D3/D4 modes. The probability of a
reframe time of 35 ms or less is 88% for ESF
mode, and 97% for D3/D4 modes. In ESF mode it is
recommended that the CRC check be enabled
unless the line has a high error rate. With the CRC
check disabled the average reframe time is greater
because the framer must also check for mimics.
detected a valid frame position. When the framer
exits maintenance mode the receive counters remain
where they are until the framer has found a new
frame position. This means that if the user forces a
reframe when the device was really in the right
place, there will not be any disturbance in the circuit
because the framer has no effect on the receiver
until it has found synchronization. The out of
synchronization criterion can be controlled by bit 0 in
Master Control Word 2. This bit changes the out of
frame conditions for the maintenance state.
The out of sync threshold can be changed from 2 out
of 4 errors in FT (or FPS) to 4 out of 12 errors in FT
(or FPS). The average reframe time is 24 ms for ESF
mode, and 12ms for D3/D4 modes.
Figure 9 is a bar graph which shows the probability
of achieving frame synchronization at a specific time.
4-70
MITEL [ MITEL NETWORKS CORPORATION ]
