PXB4340E Datasheet, PDF (35/185 Pages) Infineon Technologies AG – ICs for Communications

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There are three possibilities for specifying the loopback point of an LB cell:
• End-to-end LB processing
• Segment LB processing
• End Point LB processing
The loopback function determines which loopback activities are executed dependent on ATM
layer configuration of the network element (originating segment/end point, terminating segment/
end point, intermediate point) and the received F4/F5 LB cell at the AOPE (upstream,
downstream). Loop of LB cells including reset of the LB indication bit in the cell is done without
microprocessor interaction at the respective segment or connection end points. The VPC
consistency flag (see VHFWLRQ  page 39) indicates the availability of the VPC to the
microprocessor at the loopback port.
The loopback processing selects the loopback actions dependent on the loopback state and the
loopback location/source ID flag of the F4/F5 flow and the content of the received F4/F5 LB cell
payload (LB indication, LB location ID, LB source ID) at the AOPE (upstream or downstream).
The evaluation of the LB location/source ID of the LB cell payload is switchable via the LB
location/source ID flag. The correlation tag of the LB cell payload is supported by SW.
If the connection is in loopback state (LB state = 1) then an LB cell can be copied or dropped
from cellstream into the cell buffer of the µP.
If the LB location/source ID flag is set a compare has to be done between the LB location/source
ID and the network element ID (see VHFWLRQ  page 98).
At the originating segment/end point, the F4/F5-LB cell can be inserted into the cellstream in
upstream or downstream direction. The insertion of the LB cell is done by SW via the transmit
cell buffer of the µP (see marker € in ILJXUH , ILJXUH  and ILJXUH ). If a looped F4/F5 LB
cell arrived at the originating segment/end point, this cell is dropped to the cell receive buffer of
the µP (see marker ö in ILJXUH , ILJXUH  and ILJXUH ).
Cell insertion and extraction functions are described in VHFWLRQ  page 49.
The ATM layer configuration, the loopback state of a connection and the LB location/source ID
flag are VP and VC connection specific data. This data is located in external RAMs for upstream
and downstream direction (see VHFWLRQ  page 98).
Note that the automatic loop function assumes identical connection identifiers for both forward
and backward connections.
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If the LB indication bit of an LB cell is equal to 1 the LB cell is forwarded to the terminating end
point. At the terminating end point the LB indication flag is set to 0 and the LB cell is looped back
(loopback point, see ILJXUH , marker ó).
If the LB indication is equal to 0 (LB cell already looped) and the connection is in LB state (LB
state = 1) and the LB source ID of the LB cell is equal the network element ID (LB source ID
match) then the LB cell is copied to the receive cell buffer of the µP and the LB cell is also
forwarded to the terminating end point (see ILJXUH , marker ì).
If the LB source ID flag of this connection is disabled the same loopback actions are done.
If the connection isn’t in LB state (LB state = 0) or an LB source ID mismatch occurs the LB cell
is forwarded to the terminating end point (see ILJXUH , marker ).
Data Sheet
2-35
04.2000