TFRA08C13-DB AGERE [Agere Systems], TFRA08C13-DB Datasheet - Page 51

• Manufacturer Part Number: TFRA08C13-DB
• Description: TFRA08C13 OCTAL T1/E1 Framer
• Manufacturer: AGERE [Agere Systems]

Preliminary Data Sheet
October 2000
Lucent Technologies Inc.
Lucent Technologies Inc.
Frame Formats
CEPT Loss of CRC-4 Multiframe Alignment
Recovery Algorithms
Several optional algorithms exist in the receive framer.
These are selected through programming of register
FRM_PR9.
CRC-4 Multiframe Alignment Algorithm with 8 ms
Timer
The default algorithm is as described in ITU Rec.
G.706 Section 4.2. The recommendation states that if a
condition of assumed frame alignment has been
achieved, CRC-4 multiframe alignment is deemed to
have occurred if at least two valid CRC-4 multiframe
alignment signals can be located within 8 ms, the time
separating two CRC-4 multiframe signals being 2 ms or
a multiple of 2 ms. The search for the CRC-4 multi-
frame alignment signal is made only in bit 1 of NOT
FAS frames. If multiframe alignment cannot be
achieved within 8 ms, it is assumed that frame align-
ment is due to a spurious frame alignment signal and a
new parallel search for basic frame alignment is initi-
ated. The new search for the basic frame alignment is
started at the point just after the location of the
assumed spurious frame alignment signal. During this
parallel search for basic frame alignment, there is no
indication to the system of a receive loss of frame align-
ment (RLFA) state. During the parallel search for basic
frame alignment and while in primary basic frame align-
ment, data will flow through the receive framer to the
system interface as defined by the current primary
frame alignment. The receive framer will continuously
search for CRC-4 multiframe alignment.
(continued)
CRC-4 Multiframe Alignment Algorithm with
100 ms Timer
The CRC-4 multiframe alignment with 100 ms timer
mode is enabled by setting FRM_PR9 to 0XXXX1X1
(binary). This CRC-4 multiframe reframe mode starts a
100 ms timer upon detection of basic frame alignment.
This is a parallel timer to the 8 ms timer. If CRC-4 multi-
frame alignment cannot be achieved within the time
limit of 100 ms due to the CRC-4 procedure not being
implemented at the transmitting side, then an indication
is given, and actions are taken equivalent to those
specified for loss of basic frame alignment, namely:
Optional automatic transmission of A = 1 to the line if
register FRM_PR27 bit 3 is set to 1.
Optional automatic transmission of E = 0 to the line if
register FRM_PR28 bit 5 is set to 1.
Optional automatic transmission of AIS to the system
if register FRM_PR19 bit 1 is set to 1.
TFRA08C13 OCTAL T1/E1 Framer
51