MT9072 Zarlink Semiconductor, Inc., MT9072 Datasheet - Page 49

• Manufacturer Part Number: MT9072
• Description: Octal T1-E1-J1 Framer
• Manufacturer: Zarlink Semiconductor, Inc.

Advance Information
4.2.1
Timeslot 0 of every 125us frame is reserved for basic frame alignment and contains a Frame Alignment Signal
(FAS) or a Non-Frame Alignment Signal (NFAS). FAS and NFAS occur in consecutive basic frames as shown
in Table 12.
Bit one of the FAS can be either a CRC-4 remainder bit or an international usage bit.
Bit one of the NFAS can be either a CRC-4 multiframe alignment signal, an E-bit or an international usage bit.
Refer to national standards bodies for specific requirements.
Bit two of the FAS and NFAS is used to distinguish between FAS (bit two = 0) and NFAS (bit two = 1) frames.
Bits two to eight of the FAS are used for basic frame alignment. Basic frame alignment is initiated by a search
for the bit sequence 0011011 which appears in the last seven bit positions of the FAS, see the Frame Algorithm
section.
Bit three of the NFAS (designated as “A”), the Remote Alarm Indication (RAI), is used to indicate the near end
basic frame synchronization status to the far end of a link. Under normal operation, the A (RAI) bit should be
set to 0, while in alarm condition, it is set to 1.
Bits four to eight of the NFAS (i.e., Sa4-8) are additional spare bits which may be used as follows:
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4.2.2
The primary purpose for CRC-4 multiframing is to provide a verification of the current basic frame alignment,
although it can also be used for other functions such as bit error rate estimation. The CRC-4 multiframe
consists of 16 basic frames numbered 0 to 15, and has a repetition rate of 16 frames X 125 microseconds/
frame = 2 msec.
CRC-4 multiframe alignment is based on the 001011 bit sequence, which appears in bit position one of the first
six NFASs of a CRC-4 multiframe.
The CRC-4 multiframe is divided into two submultiframes, numbered 1 and 2, which are each eight basic
frames or 2048 bits in length.
Sa4-8 may be used in specific point-to-point applications (e.g. transcoder equipments conforming to
G.761).
Sa4 may be used as a message-based data link for operations, maintenance and performance
monitoring.
Sa5-Sa8 are for national usage but are also available from the Data link interface(TxDL,RxDL).
Note that for simplicity all Sa bits including Sa4 are collectively called national bits throughout this
document. See the Data Link section for accessing the national bits.
E1 Basic Framing (Timeslot 0)
E1 CRC-4 Multiframing (Timeslot 0)
MT9072
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