PM8313 datasheet(45/192 Pages) PMC

45 / 192 page

PM8313 D3MX

DATA SHEET

PMC-920702

ISSUE 5

M13 MULTIPLEXER

off-line framer, indicating both OOF and COFA events. Even if an OOF is

indicated, the framer will continue indicating performance monitoring information

based on the previous frame alignment.

Status signals such as the RED alarm, alarm indication signal, and the idle

signal are detected. The framer employs a simple integration algorithm (with a

1:1 slope) that is based on the occurrence of "valid" M-frame intervals. For the

RED alarm, an M-frame is said to be a "valid" interval if it contains a RED defect,

defined as an occurrence of an OOF or LOS event during that M-frame. For AIS

and IDLE, an M-frame is said to be a "valid" interval if it contains AIS or idle,

defined as the occurrence of less than 15 discrepancies in the expected signal

pattern ("1010" or "1111" for AIS; "1100" for idle) while valid frame alignment is

maintained. The discrepancy threshold ensures the detection algorithms operate

in the presence of bit error rates of up to 10-3. For AIS, the expected pattern

may be selected to be: the framed "1010" signal; the framed arbitrary DS3 signal

and the C-bits all zero; the framed "1010" signal and the C-bits all zero; the

framed all-ones signal (with overhead bits ignored); or the unframed all-ones

signal (with overhead bits equal to ones). Each "valid" M-frame interval causes

an associated integration counter to increment; "non-valid" M-frames cause a

decrement. With the slow detection option, RED, AIS, or idle is declared if the

associated count saturates at 127 which results in a detection time of 13.5 ms.

With the fast detection option, RED, AIS, or idle is declared if the associated

count saturates at 21 which results in a detection time of 2.23 ms. RED, AIS, or

idle declaration is deasserted when the associated interval count decrements

to 0.

Valid X-bits are extracted by the FRMR to provide indication of far end receive

failure. The FERF status is set to logic 1 if the extracted X-bits are equal and are

logic 0 (i.e. X1=X2=0); the status is set to logic 0 if the extracted X-bits are equal

and are logic 1(i.e. X1=X2=1). If the X-bits are not equal, the FERF status

remains in its previous state. The extracted FERF status is buffered for 2 M-

frames before being reported within the DS3 FRMR Status register or being

output on the RFERF pin. This buffer ensures a better than 99.99% chance of

freezing the FERF status on a correct value during the occurrence of an out of

frame. When an OOF occurs, the FERF value is held at the state contained in

the buffer location corresponding to the second to last M-frame. This location is

not updated until the OOF condition is deasserted. Meanwhile, the buffer

location corresponding to the last M-frame is continually updated every M-frame

based on the above FERF definition. Once correct frame alignment has been

found and OOF is deasserted, the buffer location corresponding to the last M-

frame will contain valid FERF status and the buffer location corresponding to the

second to last M-frame is enabled to be updated every M-frame.

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