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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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This is to enable the IMA to perform a fast recovery from error conditions. An
OCD event will result in a loss of IMA frame sync to ensure differential delay
checking is performed.
10.5 Line Side Physical Layer
The S/UNI-IMA-84 must be configured to support one of either the SBI interface
or the 32 Clock and Data interface.
10.5.1 TX Clock/Data (TCAS)
The S/UNI-IMA-84 supports up to 32 2-pin Clock/Data serial interfaces to
interface with standard framers. Each link is independent and has its own
associated clock. To enable easier support of CTC, a common clock is also
supported using the CTSCLK pin. The S/UNI-IMA-84 responds to the active edge
of each transmit clock by generating a single bit.
When the external framer needs to insert transmission overhead (such as
framing bits) into the data stream provided by the S/UNI-IMA-84, the framer is
required to gap the transmit clock provided to the S/UNI-IMA-84. This will
prevent the S/UNI-IMA-84 from outputting data bits during the overhead bit
period(s).
The Transmit Channel Assigner block (TCAS) processes up to 32 virtual links.
Data for all links is sourced from a single byte-serial stream from the TC layer.
For each link, the TCAS provides a holding register. The TCAS also performs
parallel-to-serial conversion to form a bit-serial stream. When multiple links are in
need of data, TCAS requests data from upstream blocks on a fixed priority basis
with link TSDATA[0] having the highest priority and link TSDATA[31] the lowest.
Links containing a T1 or an E1 stream may be channelized. Data at each time-
slot may be assigned either: (1) to be sourced from the virtual link or (2) to be
unassigned. This mechanism of assigning timeslots enables support of fractional
links. The link clock should only be active during time-slots 1 to 24 of a T1 stream
and inactive during the frame bit. Similarly, the clock is only active during time-
slots 1 to 31 of an E1 stream and inactive during the framing byte. The first bit of
time-slot 1 of a channelized link is identified by noting the absence of the clock
and its re-activation. With knowledge of the transmit link and time-slot identity, the
TCAS performs a table look-up to identify which timeslots are in use.
Links may also be unchannelized. In that case, all data bytes on that link belong
to the virtual link. The TCAS performs a table look-up to identify the link to which