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Advance Data Sheet
May 1998
T7633 Dual T1/E1 3.3 V Short-Haul Terminator
63
Lucent Technologies Inc.
Frame Formats
(continued)
T1 Frame Recovery Alignment Algorithms
When in a loss of frame alignment state, the receive framer searches for a new frame alignment and forces its
internal circuitry to this new alignment. The receive framer’s synchronization circuit inhibits realignment in T1 fram-
ing formats when repetitive data patterns emulate the T1 frame alignment patterns. T1 frame synchronization will
not occur until all frame sequence emulating patterns disappear and only one valid pattern exists. The loss of
frame alignment state will always force a loss of superframe alignment state. Superframe alignment is established
only after frame alignment has been determined in the D4 and SLC-96 frame format. Table 26 gives the require-
ments for establishing T1 frame and superframe alignment.
Table 26. T1 Frame Alignment Procedures
Frame Format
D4: Frame
Alignment Procedure
Using the F
T
frame position as the starting point, frame alignment is established when
24 consecutive F
T
and F
S
frame bits, excluding the twelfth F
S
bit, (48 total frames) are
received error-free. Once frame alignment is established, then superframe alignment is
determined.
After frame alignment is determined, two valid superframe bit sequences using the F
S
bits must be received error-free to establish superframe alignment.
Using the F
T
frame position as the starting point, frame alignment is established when
24 consecutive F
T
frame bits (48 total frames) are received error-free. Once frame
alignment is established, then superframe alignment is determined.
After frame alignment is determined, superframe alignment is established on the first
valid superframe bit sequence 000111000111.
Using the F
T
frame position as the starting point, frame alignment is established when
six consecutive F
T
/F
S
frame bits and the DDS FAS in time slot 24 are received error-
free. In the DDS format, there is no search for a superframe structure.
Frame and superframe alignment is established simultaneously using the F
E
framing
bit. Alignment is established when 24 consecutive F
E
bits are received error-free. Once
frame/superframe alignment is established, the CRC-6 receive monitor is enabled.
D4: Superframe
SLC-96: Frame
SLC-96: Superframe
DDS: Frame
ESF