S/UNI-IMA-4 Telecom Standard Product Data Sheet
Released
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.
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 10 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.
Figure 10 Inverse Multiplexing
Physical Link #0
IMA Group
IMA Group
PHY
PHY
PHY
PHY
Physical Link #1
PHY
PHY
Single ATM Cell Stream
from ATM Layer
Original Cell stream
passed to ATM Layer
Physical Link #2
IMA VirtualLInk
Tx direction cells distributed across links in round robin sequence
Rx direction cells recombined into single ATM stream
Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2020889, Issue 2
52
PMC [ PMC-SIERRA, INC ]
