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PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
PM7341 S/UNI-IMA-84
DATASHEET
PMC-2000223
ISSUE 4
INVERSE MULTIPLEXING OVER ATM
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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10.1.4 ANY-PHY/UTOPIA Loopback
For diagnostic purposes, the capability to loopback all Any-PHY/UTOPIA traffic
back to the Any-PHY/UTOPIA bus is provided. Cells are taken from the Transmit
group FIFOs and placed into the respective Receive Group FIFOs, or to a single
FIFO on a space available basis. If the receive interface is in Any-PHY or single
address UTOPIA L2 mode, all tx ports are looped back to the respective rx port.
If the receive Interface is in multiple port UTOPIA L2 mode and the transmit Any-
PHY is configured in 84-port Any-PHY mode, the 84 transmit ports will be aliased
onto the 31 receive ports. Transmit port numbers 31 and 63 will be blocked and
are not functional for loopback operations.
10.2 IMA Sub-layer
10.2.1 Overview
The IMA protocol provides inverse multiplexing of a single ATM stream over
multiple physical links and reassembles the original cell stream at the far-end.
The inverse multiplexing is performed on a cell basis; hence, the IMA protocol is
described as a cell-based protocol. See Figure 9 below.
The protocol is based upon the concept of an IMA frame. An IMA frame is
programmable in size and is delineated by an IMA Control Protocol (ICP) Cell. It
is recommended that the ICP cells of each link in the IMA group be offset from
each other to reduce the notification time of link/group status changes.
The transmitter is responsible for aligning the IMA frames on all links within a
group, and for ensuring that cells are transmitted continuously by adding filler
cells as necessary. To maintain frame alignment in the presence of independently
timed line clocks, a cell based stuffing algorithm is utilized.
Since the IMA frames are aligned on transmission, this allows the receive end to
recover the IMA frames and align them to remove any differential delay between
the physical links.