psf21911 ETC-unknow, psf21911 Datasheet - Page 44

• Manufacturer Part Number: psf21911
• Description: Isdn Echocancellation Circuit Terminal Applications Iec-q
• Manufacturer: ETC-unknow

PSB 21911
PSF 21911
U-Transceiver
2.5.1.1
Cyclic Redundancy Check
The cyclic redundancy check provides a possibility to verify the correct transmission of
data. The checksum of a transmitted U-superframe is calculated from the bits in the D-
channel, both B-channels, and the M4 bits according to the CRC polynominal
12
11
3
2
G (u) = u
+ u
+ u
+ u
+ u + 1
(+ modulo 2 addition)
The check digits (CRC bits CRC1, CRC2, …, CRC12) generated are transmitted at
position M5 and M6 in the U-superframe. At the receiving side this value is compared
with the value calculated from the received superframe.
In case these values are not identical a CRC-error will be indicated to both sides of the
U-interface. It is indicated as a NEBE (Near-end Block Error) on the side where the error
is detected and as a FEBE (Far-end Block Error) on the remote side. The FEBE-bit will
be placed in the next available U-superframe transmitted to the originator.
Far-end or near-end error indications increment the corresponding block error counters
of exchange and terminal side. The IEC-Q TE additionally issues a MON-1 message
every time a NEBE or FEBE has occurred (chapter 2.5.3, page 54). The block error
counters can be read via MON-8 commands (refer to chapter 2.5.5, page 59).
It is not possible to directly access the CRC-checksum itself. Hence the user cannot read
or write the checksum values.
Figure 17 illustrates the CRC-process.
Due to the scrambling algorithm described hereafter, a wrong bit decision in the receiver
automatically leads to at least three bit errors. Whether all of these are recorded by a bit
error counter depends on whether all faulty bits are part of the monitored channels
(2B+D, M4) or not.
Semiconductor Group
44
11.97