PEF2091 Siemens Semiconductor Group, PEF2091 Datasheet - Page 187

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

Figure 80
Loop-backs #1, #1A and #2 are controlled by the exchange. Loop-back #3 is controlled
by the terminal. All four loop-back types are transparent. This means all bits that are
looped back will also be passed onwards in the normal manner.
The next sections describe how these loop-backs are closed and opened using the C/I-
and MON-commands available to the IEC-Q.
4.7.1
Both loop-back #1 and loop-back #3 are closed by the IEC-Q as near to the U-interface
as possible. For this reason they are also called analog loop-backs. Data transmitted to
the U-interface are looped back as well. Only this internal loop-back signal is processed;
signals received from the U-interface are ignored. Because all analog signals will still be
passed on to the U-interface the opposite station (NT in case of #1, LT in case of #3) will
be activated as well, if available.
States
Because signals received from the metallic line are ignored, the IEC-Q stays in LT
modes in the "Line Active" state for loops No.1 and No.1a (upstream ACT-bit cannot be
received, see "LT Modes State Diagram", page 147).
In LT-RP mode the device stays in the "Transparent" state (see "State Machine in
Repeater Modes", page 173).
In NT modes (No.3) the device stays in "Analog Loop-Back" (see "NT Modes State
Diagram", page 161).
Semiconductor Group
S-Bus
Analog Loop-Back (No. 1/No. 3)
Test Loop-Backs Supported by the IEC-Q
Loop 2
SBCX
ICC
ICC
PBX or TE
IOM
IOM
NT
R
R
Loop
Loop 2
Loop
IEC-Q
IEC-Q
IEC-Q
3
2
U
Loop
IEC-Q
187
Repeater (optional)
1a
IOM
R
IEC-Q
Operational Description
U
Exchange
IEC-Q
Loop 1
Data Sheet 01.99
IOM
ITD04218
PEB 2091
PEF 2091
R