MPC8280 datasheet(1150/1386 Pages) FREESCALE

1150 / 1386 page

Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

34-4

Freescale Semiconductor

34.1.4

PHY-Layer Devices Supported

The IMA microcode is primarily targeted at ATM’s primary application (i.e. IMA over multiple DS1/E1).

However, the IMA microcode supports any UTOPIA PHY device which (1) has a constant data rate and

(2) can be programmed not to screen out HEC-errorred cells. Most PHYs have this mode available for

IMA also.

34.1.5

ATM Features Not Supported

The following ATM features are not available for IMA links only, but are available for non-IMA links:

•

User-defined cells (UDC) (i.e. cells that are not 53 bytes and/or with customized headers)

•

Internal rate mode for APC scheduling

34.1.6

Additional Impact on MPC8280 Features

If the IDCR recovery feature is used, the following are true:

•

One of the IDMA channels are unavailable, and its resources are dedicated instead to the IDCR

master clock function. This can be any IDMA channel (1, 2, 3, or 4).

•

MPC8280 features sharing the IDMA channel’s parameter RAM page are unavailable.

For more detailed information, refer to Section 34.4.8.2, “IDCR FCC Parameter Shadow.”

34.2

IMA Protocol Overview

This section describes the IMA protocol, not the MPC8280’s IMA microcode.

34.2.1

Introduction

Inverse Multiplexing over ATM (IMA) provides a cost effective solution to carry high speed connections,

for example, T3/E3 and OC-3c/STM-1 links, over already installed low speed connections, for example,

T1/E1 links, in a flexible way by dynamically adding/removing links as required, depending on the

bandwidth required.

IMA is defined as transmitting a stream of data over multiple low speed links and recombining the stream

in the correct order at the end. IMA involves inverse multiplexing and de-multiplexing of ATM cells in a

cyclical fashion among links grouped to form a higher bandwidth logical link whose rate is approximately

the sum of the link rates. This is referred to as an IMA group. Figure 34-1 provides a simple illustration of

ATM Inverse Multiplexing technique in one direction. This technique applies in the opposite direction.

MPC8280 Datasheet(PDF) 1150 Page - Freescale Semiconductor, Inc