CONFIDENTIAL
CY7C9537B
Protocol / Frame Types
"Clear Channel Transport"
ATM Framer
ATM Deframer
HDLC
Framer
SONET/
SDH
Framer
Frame
Tagger
SPI-3/
UTOPIA
HDLC
Deframer
Generic Protocol
Framer
SPI-3/
UTOPIA
SONET/
SDH
Framer
Generic Protocol
Deframer
"Clear Channel Transport"
Note: Only one protocol type can be active
Figure 2. Protocol Framers
.
The HDLC decapsulator descrambles the incoming byte
stream and searches the flag sequence. Upon finding the
boundary, the decapsulator performs destuffing and ACCM
demapping before passing the packets to the Programmable
Frame Tagging Engine.
Generic Frame Encapsulation/Decapsulation
POSIC2G supports a variety of protocols/packets/frames to
transport over a SONET/SDH link. For clarity of reference, in
this document, framing of packets/cells into these protocols is
called “encapsulation,” and the engine performing encapsu-
lation is called an “encapsulator.” Similarly, deframing is called
“decapsulation,” and the engine performing decapsulation is
called a “decapsulator.”
The Generic Protocol Encapsulator/Decapsulator supports all
the protocols with delineation based on length-CRC pair
header construct. In the transmit direction, it computes a 16-bit
header CRC based on 2-byte length value received from the
link layer device. The length and CRC fields are inserted as
header of the frame ahead of the packet. Scrambling of the
payload and 32-bit payload CRC computation and insertion
are optional.
Three different encapsulator and decapsulator engines are
integrated into POSIC2G.
The ATM encapsulator computes and adds the HEC field,
scrambles the cells and passes on to the SONET/SDH block.
In case of underflow, ATM encapsulator also creates program-
mable idle cells.
In the receive direction, frames are delineated based on the
length-CRC construct pair header, integrity verified, payload
extracted, optionally descrambled and sent to the Program-
mable Frame Tagging Engine.
The ATM decapsulator checks for HEC and integrity of the cell.
It descrambles the cells, isolates and discards idle cells, and
passes ATM cells to the Programmable Frame Tagging
Engine.
The Generic Protocol Encapsulator/Decapsulator can support
many protocols with length-CRC pair header construct as the
frame delineation mechanism. For example, Simple Data Link
(SDL), Generic Framing Procedure (GFP) in Data Over
SONET (DOS) and Cypress Hybrid Data Transport (HDT)
have frame structure supporting length-CRC construct based
delineation.
The HDLC encapsulator performs Asynchronous Control
Character Mapping (ACCM), stuffing, flag sequence insertion,
and scrambling. Optionally, up to 16 bytes of header is inserted
ahead of the packet while framing the packet. The host CPU
can program this 16-byte header through register
programming. Such programmable header insertion enables
encapsulation of PPP, frame relay, or other protocol.
Any selected channel can be programmed to become a clear
channel. The encapsulator and decapsulator remain in trans-
parent mode for the clear channel and data passes through
without any modification. This feature can be used to transport
any raw data streams on a portion of bandwidth while the rest
of the bandwidth is utilized for protocol traffic.
Document #: 38-02079 Rev. *F
Page 4 of 43
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