參數(shù)資料
型號: PSB21911
廠商: SIEMENS A G
元件分類: 數(shù)字傳輸電路
英文描述: ISDN Echocancellation Circuit for Terminal Applications IEC-Q TE
中文描述: DATACOM, ISDN ECHO CANCELLER
文件頁數(shù): 76/164頁
文件大小: 1401K
代理商: PSB21911
PSB 21911
PSF 21911
U-Transceiver
Semiconductor Group
76
11.97
2.5.9
Layer 1 Loop-Backs
Test loop-backs are specified by the national PTTs in order to facilitate the location of
defect systems. Four different loop-backs are defined. The position of each loop-back is
illustrated in
figure 23
.
Figure 23 Test Loop-Backs Supported by the IEC-Q TE
Loop-backs #1, #1A and #2 are controlled by the exchange. Loop-backs #3 is controlled
by the terminal. All loop-back types are transparent. This means all bits that are looped
back will also be passed onwards in the normal manner.
2.5.9.1
Normally loop-back #2 is controlled from the exchange via the EOC commands LBBD,
LB1 and LB2. In EOC auto mode the EOC commands are recognized and executed
automatically (see page 51). The single channel loop-backs (LB1, LB2) are closed in the
U-transceiver itself whereas the complete loop-back (LBBD) is closed in a connected S-
transceiver.
All loop-back functions are latched. This allows channel B1 and channel B2 to be looped
back simultaneously. All loop-backs are opened when the EOC command RTN is sent
by the LT.
Loop-Back (No. 2)
ITD10198
Loop 2
2
Loop
S-Bus
IOM
R
SBCX
IEC-Q TE
NT
ICC
R
IOM
Loop 2
3
Loop
ICC
PBX or TE
IEC-Q
IEC-Q
R
IOM
1a
Loop
U
U
Repeater (optional)
Loop 1
IEC-Q
IOM
R
Exchange
IEC-Q TE
IEC-Q TE
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