Schmid Watson Przewodnik Instalacji Pobierz pdf (Strona 89)

LTU/NTU SZ-DOC-W5-1.pd

Operating Manual

ersion: 1.5

Revision: 2002-09-10 80

A multipoint LTU has two E1 interfaces (numbered 1 and 2) and four DSL interfaces (denoted A,

B, C and D). The LTU behaves like four single LTUs in a rack, i.e. it is addressable by four

addresses representing four systems. The address of the 1

system is given by the slot position

in the rack (like for a single LTU). The address of the 2

system is the 1

system’s address + 12,

the 3

and 4

addresses are calculated by adding 24 and 36. The two E1 interfaces are assigned

to the 1

and 3

system; the 2

and 4

system have only a DSL interface. When the multipoint

mode is switched off, the 1

and the 3

system work just like two E1 LTUs (the 1

system uses

E1 interface 1 and DSL loop A; the 3

system uses E1 interface 2 and DSL loop C); the 2

and 4

system are not used in this case. In multipoint mode, the time slots from the E1 interfaces can

be distributed freely to the available DSL loops, i.e. there is no more a fixed linkage between E1

and DSL interfaces. The assignment of the interfaces to systems is only relevant when

configuring the interfaces.

8.2 Configuration

The configuration of a point-to-multipoint system includes three steps:

• configure the E1 and DSL interfaces,

• assign the time slots from the E1 interfaces to the DSL loops,

• for each DSL loop, select the time slots, which are filled with the data from the E1

interfaces.

The following sections describe these three steps using the monitor’s configuration commands.

8.2.1 E1 and DSL Interface Configuration

For point-to-multipoint operation, the 32 time slots of an E1 frame are sent to different remote

modems. To structure the signal at the E1 interface into different time slots, the bit stream has to

be divided into frames, thus the E1 interface has to work in framed mode. When CRC4

multiframes are used, CRC4- and E-Bit insertion has to be switched on. The E1 interfaces at the

remote stations should work in the same mode.

The DSL interfaces used for point-to-multipoint operation must be in DSL master mode; the DSL

interfaces at the remote stations are slaves. The line rates have to be chosen to allow maximal

range first. Hence the number of time slots that can be carried is limited by: line rate - 16kbit/s

(a line rate of n ⋅ 64kbit/s + 16kbit/s can carry at most n time slots). DSL loops A and B must

have the same line rate (can be configured in the 1

system), and also DSL loops C and D must

have the same line rate (can be configured in the 3

system). So if you have two remote modems

which are connected by long loops and two other remote stations which are not that far away,

use loops A and B (or C and D) for the first two modems and the remaining two loops for the

other ones and select two appropriate line rates.

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