Chapter 42 Diagnostic
VMG8825-B Series User’s Guide
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42.6 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 VMG sends
an OAM F4 or F5 packet to the DSLAM or ATM switch and then returns it to the VMG. 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 192 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
Features Select Variable Retrieval so the VMG can respond to requests for information, such
as requests for Ethernet counters and statistics, about link events.
Select Link Events so the VMG can interpret link events, such as link fault and dying
asp.Link events are set in event notification PDUs (Protocol Data Units), and indicate
when the number of errors in a certain given interval (time, number of frames,
number of symbols, or number of errored frame seconds) exceeds a specified
threshold. Organizations may create organization-specific link event TLVs as well.
Select Remote Loopback so the VMG can accept loopback control PDUs to convert
VMG into loopback mode.
Select Active Mode so the VMG initiates OAM discovery, send information PDUs; and
may send event notification PDUs, variable request/response PDUs, or loopback
control PDUs.
Apply Click this button to save your changes.
Table 147 Maintenance > Diagnostics > 802.3ah
LABEL DESCRIPTION
• 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
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