
QuadFALC
TM
PEF 22554 E
Functional Description E1
Data Sheet
136
Rev. 1.2, 2006-01-26
Figure 45
Automatic Handling of Errored Signaling Units
The SS7 protocol is supported by the following hardware features in transmit direction:
Transmission of flags at the beginning of each Signaling Unit
Bit stuffing (zero insertion)
Calculation of the CRC16 checksum: The transmitter adds the checksum to each Signaling Unit.
Each Signaling Unit written to the transmit FIFO (XFIFO) is sent once or repeatedly including flags, CRC
checksum and stuffed bits. After e.g. an MSU has been transmitted completely, the QuadFALC
TM optionally starts
sending of FISUs containing the forward sequence number (FSN) and the backward sequence number (BSN) of
the previously transmitted Signaling Unit. Setting bit CCR5.AFX causes Fill In Signaling Units (FISUs) to be sent
continuously, if no HDLC or Signaling Unit (SU) is to be transmitted from XFIFO. During update of XFIFO,
automatic transmission is interrupted and resumed after update is completed. The internally generated FISUs
contain FSN and BSN of the last transmitted Signaling Unit written to XFIFO.
If CCR5.AFX is set, continuous insertion of FISUs is done. Transmitting of only one FISU can be performed if
register bit CMDR2.XFISUI is set.
If continuous transmission of FISUs is disabled, setting bit CMDR2.XFISUI will cause exactly one FISU to be sent.
CMDR2.XFISUI is reset automatically as soon as the command has been acknowledged by the signalling
controller. If a second command CMDR2.XFISUI is asserted before the execution of the first command has
started, this second command will be ignored.
If a command is received and BSN/FSN for insertion is unknown, transmission of the FISU starts not before
BSN/FSN is known; in this case the command will not be ignored.
Reset Counter values
C
s := 0
su := 0
[CMDR2.RSUC = 1]
Idle
in service
SU in error?
C
s := Cs + 1
su := su + 1
C
s = T ?
su = 256 ?
su := 0
C
s = 0 ?
C
s := Cs -1
in service
Link failure
[ISR1.SUEX = 1]
Idle
Notes:
su: signaling units counter
C
s: errored signaling units
counter
T: error threshold (64 or 32),
selectable by CCR5.SUET
N
Y
F0071