ZyXEL Communications VMG4005-B50A, User Manual, Page: 63 / 86

Chapter 17 Diagnostic
VMG4005-B50A/B60A User’s Guide
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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 predefined 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 VMG is connected must also support ATM F4 and/or F5 to use
this test.
Note: This screen is available only when you configure an ATM layer-2 interface.
Figure 46 Maintenance > Diagnostic > OAM Ping
The following table describes the fields in this screen.
Table 27 Maintenance > Diagnostic > OAM Ping
LABEL DESCRIPTION
Select a PVC on which you want to perform the loopback test.
F4 segment Press this to perform an OAM F4 segment loopback test.
F4 end-end Press this to perform an OAM F4 end-to-end loopback test.