MT90221 Просмотр технического описания (PDF) - Mitel Networks

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MT90221

Quad IMA/UNI PHY Device

Mitel Networks 

MT90221

The clocking mode and reference link are fixed once

an IMA Group is setup and should remain

unchanged so long as that group is operational. The

reference link should not change unless problems

are reported with the link.

2.4.4 Stuff Cell Rate

The Stuff event algorithm differs between CTC and

ITC modes. In CTC mode, the Stuff event is typically

fixed and appears in the same IMA frame on all IMA

Group links. In ITC mode, the Stuff event is

determined using an adaptive algorithm that relates

the level of the internal TX Link FIFO to that of the

TX link FIFO of the Reference link.

The MT90221 implements 2 different stuffing

algorithms: a fixed stuffing rate and an adaptive

stuffing rate. The Stuffing events do not happen

more frequently than once every five IMA frames.

TX Group Control Mode register bit 3 selects either

the adaptive or fixed algorithm. Bit 4 determines the

timing mode declared in the ICP cell.

There are three possible combinations:

• CTC Mode with internal Fixed algorithm

• CTC Mode with internal Adaptive algorithm

• ITC Mode with internal Adaptive algorithm

In CTC mode, when using the Fixed algorithm, the

Stuff event is periodic and will appear in the same

IMA frame, once every 2048 cells, on each link that

is part of the IMA Group.

In CTC mode, when using the Adaptive algorithm,

the Stuff event will occur at an average rate of once

every 2048 cells on each link and may not occur in

the same IMA Frame on all the links.

In ITC mode, the Stuff event is determined using the

adaptive algorithm that relates the level of the

internal TX Link FIFO with that of the TX Link FIFO

of the Reference link. The reference link has one

Stuff event every 2048 cells.

The state of bit seven in the TX IMA Control register

determines whether a Stuff indication is generated in

the first or first four frames preceding a Stuff event.

2.4.5 IMA Data Cell Rate

The MT90221 computes the internal TX IMA Data

Cell Rate (IDCR) for each IMA Group. The cell rate

for the IMA Group reference link, specified in the TX

Group Control Mode register, is integrated over a

programmable period of time. The preferred

integration period is programmed in the TX IDCR

Integration register and the value is indicated in

Table 1

PCM Mode

Preferred Value

TX IDCR Integration

register

T1 ISDN (23 channels)

T1 (24 channels)

E1 (30 channels)

0x09 (216 clocks)

0x0B (218 clocks)

0x0C (219 clocks)

Table 1 - IDCR Integration Register Value

2.4.6 IMA Controller (RoundRobin Scheduler)

The IMA controller produces the cell stream to be

sent to the PCM blocks using the following four cell

types:

• Data cells received from the UTOPIA port (User

cells)

• Filler cells

• IMA ICP cells with Link status information

• Stuff cells

At an IDCR clock tick, the RoundRobin scheduler

inserts either an ICP cell, a User cell or a Filler cell

into the TX Link FIFO of the next link of the IMA

group, based on ascending link ID numbers. An ICP

cell is inserted every M cells and a stuff event is

inserted when indicated by the stuffing algorithm.

If it is not time for an ICP cell and if the traffic is not

enabled for the link (see bit 6 of the TX Link Control

register), then a Filler cell is inserted in the TX Link

FIFO. If the traffic is enabled and there is a User cell

in the TX Utopia FIFO, then the User cell is

transferred from the TX UTOPIA FIFO to the TX Link

FIFO. If there is no User cell in the TX UTOPIA FIFO,

then a Filler cell is inserted in the TX Link FIFO.

2.4.7 ICP Cell Generator

Once per IMA frame, an ICP cell is transmitted on

each link of the IMA Group. The content of the ICP

cell is controlled both by MT90221 and software. The

software content of the ICP cell bytes is stored in

buffer RAM. A copy of the ICP cell for each group is

kept in the internal Transmitter Cell RAM.

The ICP cell to be transmitted on each link is

assembled on an as required basis under the control

of the internal RoundRobin scheduler and ICP Cell

Modifier.

Hardware controls the following bytes of the ICP cell:

• Byte 5 - the HEC is always calculated and

inserted by the MT90221

• Byte 6 - the TX OAM Label is defined by the

software and the value contained in this

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