PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
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DESCRIPTION
The PM7340 S/UNI-IMA-8 is a monolithic integrated circuit that implements the
Inverse Multiplexing for ATM (IMA 1.1) protocol with backward compatibility to
IMA 1.0 and the Transmission Convergence (TC) layer function.
IMA is a protocol designed to combine the transport bandwidth of multiple links
into a single logical link. The logical link is called a group. The S/UNI-IMA-8 can
support up to 4 independent groups with each group capable of supporting from
1 to 8 links. All links within an IMA group must be at the same nominal rate,
however the link rates within a group can be different across groups. The S/UNI-
IMA-8 can be programmed on a per link basis for cell delination or IMA.
The S/UNI-IMA-8 supports 8 T1, E1 or unchannelized links where each link is
dynamically configurable to support either IMA 1.1, backward compatible IMA
1.0, ATM over T1/E1, ATM over fractional T1/E1 or ATM HEC cell delination for
unchannelized links. Unchannelized links may be used to support applications
such as ADSL.
The S/UNI-IMA-8 supports a clock and data interface where eight 2-pin serial
clock and data interfaces are provided. Each clock and data interface can be
configured to simultaneously support combinations of either T1, E1, or
unchannelized links. Unchannelized links may be used to support applications
such as ADSL. Additionally, for cell delineation only, ATM over fractional T1/E1 is
supported by allowing individual DS0 timeslots to be configured as active or
inactive.
In the transmit direction, the S/UNI-IMA-8 accepts cells from the Any-
PHY/UTOPIA interface. As per the IMA specification, the cells, destined for a
group, are distributed in a round-robin fashion to the links within the group,
adding IMA Control Protocol (ICP) cells, filler cells, and stuff cells as needed. The
ICP cells convey state information to the far end and are used to format an IMA
Frame. The IMA Frame is used as a mechanism to synchronize the links at the
far end. Cell rate decoupling is performed at the IMA sub-layer via filler cells.
Filler cells are used instead of physical layer cells for cell rate decoupling, thus a
continuous stream of cells is sent to the TC layer. The stuff cells are used to
maintain synchronization between links in a group by absorbing the rate
differential that exists when links are running at slightly different rates.
The data from the IMA sub-layer is passed on to the TC layer. In the TC layer, the
HEC is calculated and inserted into the cell headers; optional scrambling of the
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
