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Multi-Service Access Device For Channelized Interfaces
Telecom Standard Product Data Sheet
Production
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990823, Issue 4
99
11.26 Transmit Cell and Frame Processor (TCFP)
The Transmit Cell and Frame Processor (TCFP) performs both ATM and PPP processing. It has
the capability to process a single STS-12c/STM-4c channel or a single STS-48c/STM-16c
channel.
TCFP ATM Cell Processor
In ATM mode, the TCFP provides rate adaptation via idle/unassigned cell insertion, provides
HCS generation and insertion, performs ATM cell scrambling, and provides performance
monitoring functions. Details on each of these functions can be found in the TTDP description.
TCFP PPP Frame Processor
The TCFP provides rate adaptation by transmitting flag sequences (0x7E) between packets,
provides FCS generation and insertion, performs byte stuffing and packet data scrambling, and
provides performance monitoring functions. Details on each of these functions can be found in
the TTDP description. Details on each of these functions can be found in the TTDP description.
Note that the TCFP only generates byte synchronous PPP frames, not bit synchronous HDLC
frames.
The TCFP behavior differs from that of the TTDP in the behavior of counters for an aborted
packet due to under-run. The TCFP counters are not aware of the under-run condition, and thus
the Abort counter is not incremented for this condition, and all remaining bytes of the aborted
packet are counted.
11.27 Layer-to-PHY Decoupling FIFO (TXSDQ)
The TXSDQ provides FIFOs for each channel to separate the higher layer ATM system timing
from line-side timing. Each STS-1/STM-0 or DS3 channel is given a 256 byte (4 ATM cells)
FIFO by default. Channels of higher data rates can be given proportionately more FIFO space up
to a maximum of 3072 bytes in increments of 16 byte blocks.
The TXPHY provides either a Utopia Level 3 or a POS-PHY Level 3 interface to transfer data to
the FIFO.
ATM Transmit FIFO
The Transmit FIFO is responsible for holding cells provided through the Transmit System
Interface until they are transmitted. FIFO space can be allocated to different channels in blocks
of 16 bytes. The transmit FIFO holds a maximium of 768 blocks (192 ATM cells). For instance,
if the S/UNI-MACH48 is configured to carry one STS-12c and 36 STS-1s, the FIFO can allocate
space for 48 ATM cells (192 blocks) for the STS-12c channel and 4 ATM cells (16 blocks) for
each of the 36 STS-1s. This would fully utilize the entire FIFO storage space. The maximum
value that can be allocated to any single channel is 192 blocks (48 ATM cells).