參數(shù)資料
型號： PSF21911
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)： 90/164頁
文件大小： 1401K
代理商： PSF21911
PSB 21911
PSF 21911
S/G Bit and BAC Bit in TE Mode
Semiconductor Group
90
11.97
2.7.1
Applications with ELIC on the Linecard (PBX)
The S/G bit on DOUT (downstream) and the BAC bit on DIN (upstream) can be used to
allow D-channel arbitration similar to the operation of the Upn interface realised with the
OCTAT-P and the ISAC-P TE. The basic function is as follows:
The PBX linecard using the ELIC assigns one HDLC controller to a number of terminals.
As soon as one terminal Trequests the D-channel, e.g. for signalisation, all other
terminals receive a message indicating the D-channel to be blocked for them. The
request is done with the BAC bit. At terminal Tthe BAC bit is set and the IEC-Q TE
transfers the need for the D-channel to the LT-side. There, the HDLC-controller is
assigned to the appropriate IOM-channel. Once this is done and indicated to the terminal
by means of the S/G bit, the terminal begins to send D-channel messages.
Note that this procedure is somewhat different from the operation of the OCTAT/ISAC-
P TE. There, the beginn of the upstream D-channel data transfer itself indicates the need
for the HDLC-controller. This implies that any other terminal, that incidentally sent a
HDLC-message the same time, can be stopped before the message is lost in case the
HDLC-controller is not available. The U-interface featured by the IEC-Q TE is not able to
transfer the available/blocked information often enough to ensure this. Hence, it is
necessary to indicate a D-channel access by the terminal in advance. "In advance"
actually means about 14 ms.
Giving MON-0 25
H
at the LT during transparent operation will cause the D-channel
access at the NT-side to be on "STOP". As one EOC-message is transmitted via the
EOC-channel once every 6 ms, the S/G bit on IOM-2 can be set in 6 ms intervals.
If the 4 channel LT chip set PEB 24911 (DFE-Q) is used in the LT, a PEB 20550 (ELIC)
can arbitrate the D-channel via the C/I command as known from the OCTAT-P and
QUAT-S devices. Please refer to the PEB 24911 Data Sheet for detailed information on
this.
The BAC bit together with the EOC-messages received from the LT control the S/G bit
and the upstream D-channel according to the
table 19.
Table 19
Control Structure of the S/G Bit and of the D-Channel
BAC bit of
last
IOM-frame
0
S/G bit
1 = stop
0 = go
reflects last received EOC
message after falling edge after
delay TD1 (1.5 ms and two EOC-
frames)
1
D-channel upstream
tied to "0"
1
set transparent with first "0" in D-
channel
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PDF描述
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