PM5366-PI datasheet(81/267 Pages) PMC

81 / 267 page

PRELIMINARY

PM5366 TEMAP-84

DATASHEET

PMC-2010672

ISSUE 1

HIGH DENSITY 84/63 CHANNEL VT/TU MAPPER

AND M13 MULTIPLEXER

PROPRIETARY AND CONFIDENTIAL

frames, and the debounced value of the Remote Alarm bit (bit 3 of NFAS frames)

is reported. Loss of frame alignment is declared if 3 consecutive FASs have

been received in error or, additionally, if bit 2 of NFAS frames has been in error

for 3 consecutive occasions. In the presence of a random 10-3 bit error rate the

frame loss criteria provides a mean time to falsely lose frame alignment of >12

minutes.

The E1 framer can be forced to initiate a basic frame search at any time when

any of the following conditions are met:

• the software re-frame bit, REFR, in the T1/E1 Framer Indirect Channel Data

registers is set to logic 1;

• the CRC Frame Find Block is unable to find CRC multiframe alignment; or

• the CRC Frame Find Block accumulates excessive CRC evaluation errors (≥ 915

CRC errors in 1 second) and is enabled to force a re-frame under that condition.

CRC Multiframe Alignment Procedure

The E1 framer searches for CRC multiframe alignment by observing whether the

International bits (bit 1 of TS 0) of NFAS frames follow the CRC multiframe

alignment pattern. Multiframe alignment is declared if at least two valid CRC

multiframe alignment signals are observed within 8 ms, with the time separating

two alignment signals being a multiple of 2 ms

Once CRC multiframe alignment is found, the INCMF register bit is set to logic 1,

and the E1 framer monitors the multiframe alignment signal (MFAS), indicating

errors occurring in the 6-bit MFAS pattern, errors occurring in the received CRC

and the value of the FEBE bits (bit 1 of frames 13 and 15 of the multiframe).

The E1 framer declares loss of CRC multiframe alignment if basic frame

alignment is lost. However, once CRC multiframe alignment is found, it cannot

be lost due to errors in the 6-bit MFAS pattern.

Under the CRC-to-non-CRC interworking algorithm, if the E1 framer can achieve

basic frame alignment with respect to the incoming PCM data stream, but is

unable to achieve CRC-4 multiframe alignment within the subsequent 400 ms,

the distant end is assumed to be a non CRC-4 interface. The details of this

algorithm are illustrated in the state diagram in Figure 7.

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