MT9074 Просмотр технического описания (PDF) - Mitel Networks

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MT9074

T1/E1/J1 Single Chip Transceiver

Mitel Networks 

MT9074

Advance Information

appropriate mode and Jitter attenuation capability of

the MT9074

The Digital Interface

T1 Digital Interface

In T1 mode DS1 frames are 193 bits long and are

transmitted at a frame repetition rate of 8000 Hz,

which results in an aggregate bit rate of 193 bits x

8000/sec= 1.544 Mbits/sec. The actual bit rate is

1.544 Mbits/sec +/-50 ppm optionally encoded in

B8ZS format. The Zero Suppression control register

(page 1, address 15H,) selects either B8ZS

encoding, forced one stuffing or alternate mark

inversion (AMI) encoding. Basic frames are divided

into 24 time slots numbered 1 to 24. Each time slot is

8 bits in length and is transmitted most significant bit

first (numbered bit 1). This results in a single time

slot data rate of 8 bits x 8000/sec. = 64 kbits/sec.

It should be noted that the Mitel ST-BUS has 32

channels numbered 0 to 31. When mapping to the

DS1 payload only the first 24 time slots and the last

(time slot 31, for the overhead bit) of an ST-BUS are

used (see Table 6). All unused channels are tristate.

When signalling information is written to the MT9074

in T1 mode using ST-BUS control links (as opposed

to direct writes by the microport to the on - board

signaling registers), the CSTi channels

corresponding to the selected DSTi channels

streams are used to transmit the signalling bits.

Since the maximum number of signalling bits

associated with any channel is 4 (in the case of

ABCD), only half a CSTi channel is required for

sourcing the signaling bits. The choice of which half

of the channel to use is selected by the control bit

MSN (page 01H address 14H). The same control bit

selects which half of the CSTo channel will contain

receive signaling information (the other nibble in the

channel being tristate). Unused channels are tristate.

The most significant bit of an eight bit ST-BUS

channel is numbered bit 7 (see Mitel Application

Note MSAN-126). Therefore, ST-BUS bit 7 is

synonymous with DS1 bit 1; bit 6 with bit 2: and so

on.

Frame and Superframe Structure in T1 mode

Multiframing

In T1 mode, DS1 trunks contain 24 bytes of serial

voice/data channels bundled with an overhead bit.

The frame overhead bit contains a fixed repeating

pattern used to enable DS1 receivers to delineate

frame boundaries. Overhead bits are inserted once

per frame at the beginning of the transmit frame

boundary. The DS1 frames are further grouped in

bundles of frames, generally 12 (for D4 applications)

or 24 frames (for ESF - extended superframe

applications) deep. Table 7 and 8 illustrate the D4

and ESF frame structures respectively.

For D4 links the frame structure contains an

alternating 101010... pattern inserted into every

second overhead bit position. These bits are

intended for determination of frame boundaries, and

they are referred to as Ft bits. A separate fixed

pattern, repeating every superframe, is interleaved

with the Ft bits. This fixed pattern (001110), is used

to delineate the 12 frame superframe. These bits are

referred to as the Fs bits. In D4 frames # 6 and #12,

the LSB of each channel byte may be replaced with

A bit (frame #6) and B bit (frame #12) signalling

information.

For ESF links the 6 bit framing pattern 001011,

inserted into every 4th overhead bit position, is used

to delineate both frame and superframe boundaries.

Frames #6, 12, 18 and 24 contain the A, B, C and D

signalling bits, respectively. A 4 kHz data link is

embedded in the overhead bit position, interleaved

between the framing pattern sequence (FPS) and the

transmit CRC-6 remainder (from the calculation done

on the previous superframe), see Table 8.

DS1 Timeslots

Voice/Data Channels

(DSTi/o and CSTi/o)

Ds1 Timeslots

Voice/Data Channels

(DSTi/o and CSTi/o)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0 1 2 3 4 5 6 7 7 9 10 11 12 13 14 15

17 18 19 20 21 22 23 24 - - - - - - - -

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

xxxxxxxS

bit

Table 6 - STBUS vs. DS1 to Channel Relationship(T1)

14

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