
PEB 80900
Part I
’
NTC-T
’
: Functional Description
Data Sheet
31
2001-04-02
3.3
U-Transceiver
3.3.1
General
The U-interface performs full duplex data transmission and reception at the U-reference
point according to ETSI ETR 080 and FTZ 1TR 220. It applies the 4B3T block code
together with adaptive echo cancelling and equalization. Transmission performance is
such that it meets all ETSI and FTZ test loops with margin.
The U-interface is designed for data transmission on twisted pair wires in local telephone
loops, with basic access to ISDN and a user bit rate of 144 kbit/s.
The following information is transmitted over the twisted pair:
Bidirectional:
–
B1, B2, D data channels
–
120 kHz Symbol clock, 160 kbit/s Transmission rate
–
1 kHz Frame and 40 kHz block clock
–
Activation
From LT to NT side:
–
Power feeding
–
Deactivation
–
Remote control of test loops
From NT to LT side:
–
Indication of monitored code violations
On the U-interface, transmission ranges of 4.2 km on wires of 0.4 mm diameter and 8 km
on 0.6 mm wires are achieved without additional signal regeneration on the loop. The
transmission ranges can be doubled by inserting a repeater for signal regeneration.
3.3.2
Frame Structure of the U-Interface
1 ms frames are transmitted via the U-interface, each consisting of:
108 symbols: 144 bit scrambled and coded B1 + B2 + D data
11 symbols: Barker code for both symbol and frame synchronization (not scrambled)
1 symbol: Ternary maintenance symbol (not scrambled)
The 108 user data symbols are split into four equally structured groups. Each group
(27 ternary symbols, resp. 36 bits) contains the user data of two IOM-2 frames in the
same order (8B + 8B + 2D + 8B + 8B + 2D).
Different synchwords are used for each direction:
Downstream from LT to NT
+ + +
–
–
–
+
–
–
+
–
Upstream from NT to LT
–
+
–
–
+
–
–
–
+ + +
On the NT side, the transmitted Barker code begins 60 symbols after the received Barker
code and vice versa.