Bt8370/8375/8376
2.0 Circuit Description
2.4 Receiver
Fully Integrated T1/E1 Framer and Line Interface
Table 2-3. Criteria for Loss/Recovery of Receive Framer Alignment (1 of 2)
Mode
FAS
Description
Basic Frame Alignment (BFA) is recovered when the following search criteria are satisfied:
•
•
•
FAS pattern (0011011) is found in frame N.
Frame N+1 contains bit 2 equal to 1.
Frame N+2 also contains FAS pattern (0011011).
During FAS-only modes, BFA is recovered when the following search criteria are satisfied:
•
•
•
FAS pattern (0011011) is found in frame N.
No mimics of the FAS pattern are present in frame N+1.
FAS pattern (0011011) is found in frame N+2.
NOTE(S): If FAS pattern is not found in frame N+2, or if FAS mimic is found in frame N+1, the search restarts in
frame N+2.
Loss of FAS frame alignment (FRED) is declared when 1 of the following criteria is met:
•
Three consecutive FAS pattern errors are detected when the FAS pattern consists of a 7-bit (x0011011)
pattern in FAS frames, and if FS_NFAS is also active [addr 045], the FAS pattern includes bit 2 of NFAS
frames.
•
•
Loss of MFAS (MRED) is due to 915 or more CRC errors out of 1000.
Failure to locate two valid MFAS patterns within 8 ms after BFA.
NOTE(S): In all cases, FRED causes next search for FAS alignment to begin 1 bit after the current FAS location.
BSLIP
MFAS
FAS Bit Slip Enable. Applicable only for Dutch PTT national applications. If BSLIP is enabled, the online framer is
allowed to change RX timebase by ±1 bit when a 1-bit FAS pattern slip is detected. BSLIP does not affect the offline
framer's search criteria.
CRC4 Multiframe Alignment is recovered when the following search criteria are satisfied:
•
•
BFA is recovered, identifying FAS and NFAS frames.
Within 8 ms after BFA, bit 1 of NFAS frames contains two MFAS patterns (001011xx). The second MFAS
must be aligned with respect to first MFAS, but the second MFAS pattern is not necessarily received in
consecutive frames.
•
Within 8 ms after BFA, bit 1 of NFAS frames contains the second MFAS pattern (001011xx), aligned to first
MFAS.
Loss of MFAS alignment (MRED) declared when 1 of the following criteria is met:
•
•
915 or more CRC4 errors out of 1000 (submultiframe) blocks.
Loss of FAS (FRED).
NOTE(S): If Disable 915 CRC Reframe is set [RLOFD; addr 040], then MRED is activated only by FRED.
CAS
CAS Multiframe Alignment is recovered when the following search criteria are satisfied:
•
•
BFA is recovered, identifying TS0 through TS31.
MAS (0000xxxx) multiframe alignment signal pattern is found in the first 4 bits of TS16, and 8 bits of TS16
in preceding frame contains non-0 value.
Loss of CAS alignment (SRED) is declared when 1 of the following criteria is met:
•
•
•
Two consecutive MAS pattern errors are detected.
TS16 contains all 0s in 2 multiframes (32 consecutive frames).
Loss of FAS (FRED).
FT Only
Terminal frame alignment is recovered when the following occurs:
The first valid Ft pattern (1010) is found in 12 alternate F-bit locations (3 ms), where F-bits are separated by 193
bits.
During Ft-only mode, loss of frame alignment (FRED) is declared when the number of Ft bit errors detected meets
selected loss of frame criteria [RLOFA–RLOFC; addr 040].
N8370DSE
Conexant
2-23
CONEXANT [ CONEXANT SYSTEMS, INC ]
