XRT74L73 Datasheet, PDF (438/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
FIGURE 200. THE RECEIVE E3 FRAMER BLOCK AND THE ASSOCIATED PATHS TO THE OTHER FUNCTIONAL BLOCKS
To Receive E3 HDLC
Buffer
Receive Overhead Data
Output Interface
Receive Payload Data
Output Interface
Receive
E3
Framer Block
From Receive E3
LIU Interface Block
Once the HDB3 (or AMI) encoded data has been de-
coded into a binary data-stream, the Receive E3
Framer block will use portions of this data-stream in
order to synchronize itself to the remote terminal
equipment. At any given time, the Receive E3 Fram-
er block will be operating in one of two modes.
• The Frame Acquisition Mode: In this mode, the
Receive E3 Framer block is trying to acquire syn-
chronization with the incoming E3 frame, or
• The Frame Maintenance Mode: In this mode, the
Receive E3 Framer block is trying to maintain
frame synchronization with the incoming E3
Frames.
Figure 201 presents a State Machine diagram that
depicts the Receive E3 Framer block’s E3/ITU-T
G.832 Frame Acquisition/Maintenance Algorithm.
6.3.2.1 The Framing Acquisition Mode
The Receive E3 Framer block is considered to be op-
erating in the Frame Acquisition Mode, if it is operat-
ing in any one of the following states within the E3
Frame Acquisition/Maintenance Algorithm per
Figure 201 .
• FA1, FA2 Octet Search State
• FA1, FA2 Octet Verification State
• OOF Condition State
• LOF Condition State
Each of these Framing Acquisition states, within the
Receive E3 Framer Framing Acquisition/Maintenance
State Machine are discussed below.
The FA1, FA2 Octet Search State
When the Receive E3 Framer block is first powered
up, it will be operating in the FA1, FA2 Octet Search
state. While the Receive E3 Framer is operating in
this state, it will be performing a bit-by-bit search for
the FA1 and FA2 Framing Alignment octets. FA1 is
assigned the value “0xF6”, and FA2 is assigned the
value of “0x28”. Figure 202 , which presents an illus-
tration of the E3, ITU-T G.832 Framing Format, indi-
cates that these two octets will occur at the beginning
of each E3 frame, and that the FA2 octet will appear
immediately after the FA1 octet.
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