PEF2091 Siemens Semiconductor Group, PEF2091 Datasheet - Page 176

• Manufacturer Part Number: PEF2091
• Description: ICs for Communications(ISDN Echocancellation Circuit)
• Manufacturer: Siemens Semiconductor Group

Semiconductor Group
4.5
The basic tool for monitoring transmission quality is the cyclic redundancy check
procedure (see "Cyclic Redundancy Check (CRC)", page 64). Calculation verification
and insertion of the CRC bits are performed automatically by the IEC-Q and there is no
possibility to directly control this procedure, or access the CRC bits. Nevertheless, the
IEC-Q provides several methods for monitoring CRC failures and CRC procedure
function. This will be discussed in this chapter. For an overview of CRC violation
indications on both LT and NT sides, see Figure "CRC Violation Indications", page 184.
Definitions
NEBE: For the 2B+D and M4 bits received from the U-interface the check sum will be
calculated by the CRC processor and compared with the CRC bits received in the
successive superframe (see "U-Frame Structure", page 68, for definition of data position
in the U-interface). A "Near End Block Error" (NEBE) occurs If these two values are not
identical. In other words
– NEBE (LT side)
– NEBE (NT side)
If a NEBE has been detected the bit FEBE of the next U superframe available for
transmission is set to ’0’.
FEBE: A "Far End Block Error" (FEBE) is detected if the FEBE bit of the received from
the U-interface is set to ’0’. In other words
– FEBE (LT side)
– FEBE (NT side)
Note 48: Near-end block errors and far end block errors correspond to bit errors
occurred in the superframe preceding the last completed one. This is due to
the fact that the CRC sum of a superframe, say SF(1), is transmitted in the
next superframe SF(2), i.e. a comparison between the calculated sum and the
received sum can only be performed if the superframe containing the check
sum, SF(2), has been completely received. Figure 77 shows this relationship
for the CRC and the FEBE bits.
Monitoring Transmission Quality
error during transmission from NT to LT
error during transmission from LT to NT
error during transmission from LT to NT
error during transmission from NT to LT
176
Operational Description
Data Sheet 01.99
PEB 2091
PEF 2091