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T7234

Compliance with the New ETSI PSD Requirement

Agere -> LSI Corporation 

T7256 Single-Chip NT1 (SCNT1) Transceiver

Data Sheet

January 1998

S/T-Interface Frame Structure

The S/T-interface transfers its subscriber line 2B+D

information as a 192 kbits/s full-duplex signal grouped

into frames of 48 bits with a period of 250 µs, as speci-

fied in the ITU-T I.430/ANSI T1.605 standard. Thirty-six

of the 48 bits sent in each direction convey user infor-

mation (two 8-bit occurrences of each of the two B

channels, and four D-channel bits). The remaining

12 bits per frame are used for framing, control, dc bal-

ance, and maintenance. The frame structures are

shown in each direction in Figure 6.

In the bit stream transmitted from the terminal endpoint

(TE) to the network termination (NT), 4 bits are used for

framing (F and FA, each with a dc balancing bit L),

eight additional L bits are used to balance the 32 B-

channel bits, and 4 bits are D-channel bits.

For the NT-to-TE transmission, 4 bits (F with dc balanc-

ing bit L, FA, and N) are used for framing, one M bit

marks the start of a 20-frame multiframe, four E bits

form an echo channel for retransmission of the D-chan-

nel bits received from the TE, one additional L bit is

used to balance the contents of the entire frame, and

1 bit (A) is set to one when bit synchronization is

achieved between TE and NT as part of the INFO 4

state. One S bit is used for transmitting S subchannel

messages in an NT-to-TE multiframe.

The framing procedure uses bipolar line-code viola-

tions to establish synchronization. Since the last binary

0 of any frame is a positive pulse and the F bit is also

defined to be a positive pulse (see Figure 7), the first bit

of each frame represents a coding violation. In addi-

tion, the second bit of each frame, a balance bit, is a

negative pulse, and the next binary 0 in the frame is

forced to be negative, causing another violation. Both

bipolar violations allow framing and provide dc balance.

All other pulses follow the alternating convention.

ONE FRAME = 48 bits IN 250 µs

NT-TO-

TE

FRAME

FL

EIGHT

B1 BITS

E D A FA N

EIGHT

B2 BITS

EIGHT

E D M B1 BITS

E DS

EIGHT

B2 BITS

ED L

TE-TO-

NT

FRAME

FL

EIGHT

B1 BITS

L D L FA L

EIGHT

B2 BITS

L DL

EIGHT

B1 BITS

L DL

EIGHT

B2 BITS

LDL

BANDWIDTH = 192 kbits/s

Figure 6. Frame Structures of NT and TE Frames

5-2479 (C)

14

Lucent Technologies Inc.

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