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QuadFALC
TM
PEF 22554 E
Functional Description E1
Data Sheet
144
Rev. 1.2, 2006-01-26
4.4.3.1
Synchronization Procedure (E1)
Multiframe alignment is assumed to have been lost if doubleframe alignment has been lost (flagged on status bit
FRS0.LFA). The rising edge of this bit causes an interrupt.
The multiframe resynchronization procedure starts when Doubleframe alignment has been regained which is
indicated by an interrupt status bit ISR2.FAR. For Doubleframe synchronization refer to section Doubleframe
Format. It is also be invoked by the user by setting
Bit FMR0.FRS for complete doubleframe and multiframe resynchronization
Bit FMR1.MFCS for multiframe resynchronization only.
The CRC checking mechanism is enabled after the first correct multiframe pattern has been found. However, CRC
errors are not counted in asynchronous state.
In doubleframe asynchronous state, counting of framing errors, CRC4 bit errors and detection of remote alarm is
stopped. AIS is automatically sent to the backplane interface (can be disabled by bit FMR2.DAIS). Further on the
updating of the registers RSW, RSP, RSA(8:4), RSA6S and RS(16:1) is halted (remote alarm indication, S
a/Si-bit
access).
The multiframe synchronous state is established after detecting two correct multiframe alignment signals at an
interval of n x 2 ms (n = 1, 2, 3 …). The loss of multiframe alignment flag FRS0.LMFA is reset. Additionally an
interrupt status multiframe alignment recovery bit ISR2.MFAR is generated with the falling edge of bit FRS0.LMFA.
4.4.3.2
Automatic Force Resynchronization (E1)
In addition, a search for Doubleframe alignment is automatically initiated if two multiframe pattern with a distance
of n x 2 ms have not been found within a time interval of 8 ms after doubleframe alignment has been regained (bit
FMR1.AFR). A new search for frame alignment is started just after the previous frame alignment signal.
4.4.3.3
Floating Multiframe Alignment Window (E1)
After reaching doubleframe synchronization a 8 ms timer is started. If a multiframe alignment signal is found during
the 8 ms time interval the internal timer is reset to remaining 6 ms in order to find the next multiframe signal within
this time. If the multiframe signal is not found for a second time, the interrupt status bit ISR0.T8MS is set. This
interrupt usually occurs every 8 ms until multiframe synchronization is achieved.
4.4.3.4
CRC4 Performance Monitoring (E1)
In the synchronous state checking of multiframe pattern is disabled. However, with bit FMR2.ALMF an automatic
multiframe resynchronization mode can be activated. If 915 out of 1000 errored CRC submultiframes are found
then a false frame alignment is assumed and a search for doubleframe and multiframe pattern is initiated. The new
search for frame alignment is started just after the previous basic frame alignment signal. The internal CRC4
resynchronization counter is reset when the multiframe synchronization has been regained.
4.4.3.5
Modified CRC4 Multiframe Alignment Algorithm (E1)
The modified CRC4 multiframe alignment algorithm allows an automatic interworking between framers with and
without a CRC4 capability. The interworking is realized as it is described in ITU-T G.706 Appendix B.
If doubleframe synchronization is consistently present but CRC4 multiframe alignment is not achieved within
400 ms it is assumed that the distant end is initialized to doubleframe format. The CRC4/non-CRC4 interworking
is enabled by FMR2.RFS(1:0) = 11
B and is activated only if the receiver has lost its synchronization. If doubleframe
alignment (basic frame alignment) is established, a 400 ms timer and searching for multiframe alignment are
started. A research for basic frame alignment is initiated if the CRC4 multiframe synchronization cannot be
achieved within 8 ms and is started just after the previous frame alignment signal. The research of the basic frame
alignment is done in parallel and is independent of the synchronization procedure of the primary basic frame
alignment signal. During the parallel search all receiver functions are based on the primary frame alignment signal,
like framing errors, S
a-, Si-, A-bits, …). All subsequent multiframe searches are associated with each basic framing
sequence found during the parallel search.