T7264 datasheet(21/54 Pages) AGERE

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Data Sheet

April 1998

T7264 U-Interface 2B1Q Transceiver

Lucent Technologies Inc.

U-Interface Description

Data is transmitted over the U-interface in 240-bit groups called U frames. Each U frame consists of an 18-bit syn-

chronization word (ISW or SW), 12 blocks of 2B+D data (216 bits), and six overhead bits (M). A U-interface super-

frame consists of eight U frames grouped together. The beginning of a U superframe is indicated by the inverted

sync word (ISW). The six overhead bits from each of the eight U frames, when taken together, form the 48 M bits.

The following diagram shows how U frames, superframes, and M bits are mapped.

5-5171

Figure 12. U-Interface Frame and Superframe

Of the 48 M bits, 24 bits form the embedded operations channel (eoc) for sending messages from the LT to the NT

and responses from the NT to the LT. There are two eoc messages per superframe with 12 bits per eoc message

(eoc1 and eoc2). Another 12 bits serve as control and status bits (UCS). The last 12 bits form the cyclic redun-

dancy check (crc) which is calculated over the 2B+D data and the M4 bits of the previous superframe. Figure 13

shows the different groups of bits in the superframe.

5-5172

Figure 13. U-Interface Superframe Bit Groups

ISW[18]

M[6]

(2B+D) X 12 [216 bits]

U-INTERFACE M BITS [48]

U-SUPERFRAME SPAN = 12 ms

U-FRAME SPAN = 1.5 ms

BIT #

1—18

19—234

235

236

237

238

239

240

FRAME #

Sync

12(2B+D)

ISW

CONTROL & STATUS (UCS)

eoc1

2B+D

eoc2

crc

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