MT90710 Просмотр технического описания (PDF) - Mitel Networks

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MT90710

High-Speed Isochronous Multiplexer

Mitel Networks 

MT90710

Preliminary Information

Frame Pulse

255 0 1 2 3 4

Fiber Timeslot

5 6789

..........

246 247 248 249 250 251 252 2

Channel Assignment

ST7 Ch0 ST6 Ch0 ST5 Ch0 ST4 Ch0 ST3 Ch0 ST2 Ch0 ST1 Ch0 ST0 Ch0 ST7 Ch1 ST6 Ch1

Bit 9 Bit 8

Bit 7

4B/5B Encoded Data Bit Assignment

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Figure 3 - Fiber Timeslot Assignment

The MT90710 provides 15.808 Mb/s clear channel,

user bandwidth in both transmit and receive

directions. In addition, two 8 kHz sampled signals

and one 32 kHz sampled signal are encoded and

transported over the loop as additional user

bandwidth. These asynchronous signals, in

combination with overhead information and clear

channel bandwidth produce an aggregate data rate

of 16.384 Mb/s. After encoding (4B/5B) the final

transmitted baud rate is 20.48 Mbaud.

Once compiled, the contents of the transmit data

bandwidth is first 4B/5B encoded, then NRZI

encoded before it is applied to the transmit fiber

interface driver via TxDATA. 4B/5B ensures that the

NRZI encoded data will contain a minimum of two

transitions per baud. This is sufficient to allow the far

end to extract the embedded clock information. As a

result of 4B/5B encoding the information bandwidth

of 16.384 Mb/s increases to a total baud rate of

20.48 MBaud/s at the fiber interface.

Transmit

The transmit data interface consists of nine ST-BUS

input links and three asynchronously sampled input

signals. These are STi0 - STi5, STi6A and STi6B,

STi7, DIN8K0, DIN8K1 and DIN32K. Six ST-BUS

input links, STi0-5, each provide 2.048 Mb/s

transparent transmission bandwidth. With ST6MUX

Mode disabled STi6A is also a 2.048 Mb/s link while

STi6B is not used (see ST6MUX description). The

first nine channels of the STi7 input are ignored

leaving the remaining 23 channels for user

bandwidth. This allows a total of 15.808 Mb/s clear

bandwidth for application use. The first nine (576

kb/s) channels of STi7 are made available for

transmitting the three asynchronous signals

combined with fiber overhead information. This

overhead is automatically compiled in the transmit

interface and inserted into these timeslots for

transmission over the fiber interface.

Incoming ST-BUS link data is latched at the mid-bit

position of the internal timeslot. Since there is a

phase difference between the internal and external

timeslots, due to the operation of the PLL, latching

occurs at approximately the 3/4 bit position of the

external timeslot when in Controller mode. In

Peripheral mode data is latched at the midpoint of

the timeslot. Asynchronous signals DIN8K0-1 are

sampled once per frame (8,000 times per second)

and are intended to convey relatively static

information where a state transition is not time

critical enough that a resolution of one frame is

detrimental. Asynchronous signal DIN32K is

sampled four times per frame (32,000 times per

second) and may be used to transport data at a

higher rate than the other two asynchronous inputs.

As an example, this sampling rate is sufficient to

support 19.2K Baud RS-232 signals (TTL levels) so

that remote programming or loop maintenance may

be performed.

Overhead information includes a frame

synchronization byte, an error count and a checksum

calculated on the previous frame of transmitted data.

5-8

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