Installation guide

SZ-DOC-W5-1.pdf LTU/NTU
Version: 1.5 Operating Manual
15 Revision: 2002-09-10
N
T2/TE
N
T1 LT ET
DSL
XVR
DSL
XVR
TV3 V3'
DSL Link
Figure 3-4: Reference Points of the PRA
Normally, the PRA-digital section (NT1 and LT) is configured as a digital link with CRC processing
in the NT1 (option 2, according to I.604). However, also the other subscriber access options
described in I.604 Annex A, can be configured. One of the DSL system units must be configured
as master and the other as slave. Normally, the LTU (or the NTU, respectively) at the exchange is
configured as the master on the DSL link, and the PRA-NTU as slave.
The equipment described above provides an access digital section for ISDN primary rate at
2048kbit/s. The 120Ω port (or optionally the 75Ω In/Out BNC) is the user/network-interface for
primary rate access, which is denoted as T reference point in ISDN terminology. The equipment
at the user side of the T reference point, which may be TE1, TA or NT2, is termed TE or NT2 in
the normative references. Therefore, it is denoted as NT2/TE in this document. The interface
towards the exchange, which will be abbreviated ET in the following, is the V3 reference point.
3.3.1 PRA Mode
The modem can work as NT1, LT or NT1 and LT combined.
3.3.2 CRC4 Processing Options
In addition to the usual PRA operation with CRC4 processing in both directions, the PRA interface
also offers other modes of operation. Following ITU-T Rec. I.604 Annex A, three subscriber
access options for a digital link are supported. The PRA interface can be configured to work
either as a digital link without CRC processing (option 1), a digital link with CRC processing in
the NT1 (option 2) or a digital link with CRC monitoring only in the NT1 (option 4). A digital link
with CRC processing in the LT and NT1 is possible by using a DSL link consisting of an NT1 and
an LT, both configured with CRC processing on.
3.3.2.1 Digital Link without CRC Processing (Option 1)
In this mode, transparent transmission between the ET and the NT2/TE is possible. There is no
CRC4 processing in the PRA-NTU; the CRC processing is only done in the ET and the NT2/TE.
When loss of incoming signal is detected on either side, AIS is transmitted at the opposite side.