
82
Agere Systems Inc.
Data Sheet
May 2001
155/622/2488 Mbits/s Data Interface
TDAT042G5 SONET/SDH
Functional Description
(continued)
Data Engine (DE) Block
(continued)
Over-Fiber Modes
In addition to the support of the normal SONET/SDH modes for different payload types such as HDLC, PPP, ATM
(X
43
or X
31
), and SDL as shown in Figure 2 on pa ge45, this device is capable of supporting the over-fiber modes
for two payload types, SDL or ATM (X
31
). In the over-fiber mode, a 3% payload increase can be realized because
the data stream contains no SONET/SDH overhead bytes.
In the over-fiber modes, it is possible to utilize the whole bandwidth (155 Mbits/s for OC-3, 622 Mbits/s for OC-12,
or 2.5 Gbits/s for OC-48) of the optical fiber for SDL packets or ATM cells.
As can be seen in Figure 21, for over-fiber modes the device is provisioned as follows:
I
The line termination (OHP) and path termination (PT) blocks of the device need to be provisioned in the
passthrough mode.
I
The payload termination (DE) block needs to be set to the bit synchronization mode in the payload control regis-
ter.
I
The transparent mode in the transmit and receive sequencers (addresses 0x102E and 0x102F; see register
description, page 223).
I
Bit 12 of the mode register (address 0x0010) needs to be set to 0 so that the received clock drives the entire
receive data path. In this way, there is no need to cross the clock domain boundary. As a result, only a single
channel is allowed for OC-3, OC-12, or OC-48 when the device is operated in the over-fiber modes. In contrast,
the device is capable of supporting four OC-3/OC-12 channels or one OC-8 channel in the SONET/SDH modes.
5-6680(F).cr.1
Figure 21. TDAT042G5 Over-Fiber Modes: SDL, ATM (X
31
)
PASSTHROUGH
L
LINE
TERMINATION
PATH
TERMINATION
PAYLOAD
TERMINATION
PACKET/CELL
PROCESSOR
-BIT SYNC
-DECAPSULATION
-UNSCRAMBLING
-CRC VERIFICATION
SINGLE OC-48
SINGLE OC-12
SINGLE OC-3
CONTROL
μ
P INTERFACE
ENHANCED
UTOPIA I/O
PACKET/CELL
PROCESSOR
-ENCAPSULATION
-SCRAMBLING
-CRC GENERATION
PASSTHROUGH
PASSTHROUGH
PASSTHROUGH