19216811.liveChapter 36 Diagnostic
eircom F1000 Modem User’s Guide
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36.5
OAM Ping
Click
Maintenance > Diagnostic > OAM Ping
to open the screen shown next. Use this screen to
perform an OAM (Operation, Administration and Maintenance) F4 or F5 loopback test on a PVC. The
Device sends an OAM F4 or F5 packet to the DSLAM or ATM switch and then returns it to the
Device. The test result then displays in the text box.
ATM sets up virtual circuits over which end systems communicate. The terminology for virtual
circuits is as follows:
Figure 170
Virtual Circuit Topology
Think of a virtual path as a cable that contains a bundle of wires. The cable connects two points and
wires within the cable provide individual circuits between the two points. In an ATM cell header, a
VPI (Virtual Path Identifier) identifies a link formed by a virtual path; a VCI (Virtual Channel
Identifier) identifies a channel within a virtual path. A series of virtual paths make up a virtual
circuit.
F4 cells operate at the virtual path (VP) level, while F5 cells operate at the virtual channel (VC)
level. F4 cells use the same VPI as the user data cells on VP connections, but use different
predefined VCI values. F5 cells use the same VPI and VCI as the user data cells on the VC
connections, and are distinguished from data cells by a predefinded Payload Type Identifier (PTI) in
the cell header. Both F4 flows and F5 flows are bidirectional and have two types.
•
segment F4 flows (VCI=3)
•
end-to-end F4 flows (VCI=4)
•
segment F5 flows (PTI=100)
•
end-to-end F5 flows (PTI=101)
OAM F4 or F5 tests are used to check virtual path or virtual channel availability between two DSL
devices. Segment flows are terminated at the connecting point which terminates a VP or VC
segment. End-to-end flows are terminated at the end point of a VP or VC connection, where an ATM
link is terminated. Segment loopback tests allow you to verify integrity of a PVC to the nearest
neighboring ATM device. End-to-end loopback tests allow you to verify integrity of an end-to-end
PVC.
Note: The DSLAM to which the Device is connected must also support ATM F4 and/or F5
to use this test.
•
Virtual Channel (VC)
Logical connections between ATM devices
•
Virtual Path (VP)
A bundle of virtual channels
•
Virtual Circuits
A series of virtual paths between circuit end points