PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
requests by large numbers of low rate requests. To achieve this, each request is
placed into a priority FIFO. The priority of the request is based upon its rate.
There are a total of 5 rate-based FIFOs. When a service request is accepted by
the Transmit IMA processor (TIMA) or the Receive IMA Data Processor (RDAT),
the next request to be presented is taken from the highest priority FIFO that has
an entry. In this manner, the higher rate requests get higher priority than the
lower rate requests. Since the S/UNI-IMA-8 can always service all of the
requests, this algorithm limits the CDV experienced by any service request to
approximately one inter-arrival time of the service request for each group.
Rate changes are restricted to IMA frame boundaries. An IMA frame boundary
occurs once every (M-1)*N service requests. When a request is received to
change the rate(Non), the request is saved until the next IMA frame boundary, at
which point it takes effect. By restricting rate changes to frame boundaries, the
rate accuracy is preserved preventing FIFO underflows/overflows. Since rate
changes are not instantaneous, a vector that represents the active Link IDs
(LIDs) in the group is passed with the service request. In this manner, the entity
receiving the service requests is informed of the change in rate and of which links
should currently be in the round robin for servicing.
All IMA-based rate changes are internally managed by the S/UNI-IMA-8; no user
interaction is necessary for correct scheduling.
The IDCC is also used for scheduling the TC data flow. In this case, the rate
generated is simply the cell rate of the TC link and is not modified for IMA ICP
cells or stuff cells according to the following equation:
IDCR = TRLCR
For all TC connections, the IDCC must be configured in TC mode for the physical
link.
10.2.3 Transmit IMA Processor (TIMA)
The TIMA is responsible for the transmit IMA functions. This consists of
distributing the cells arriving from the ATM layer to links in a group and for
inserting ICP cells, filler cells, and stuff cells as required by the IMA protocol.
Additionally, the TIMA can support cell transmission on connections using only
the Transmission Convergence (TC) sublayer without the use of the IMA protocol
sublayer.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
