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VMG5313-B10A/-B30A Series User’s Guide
340
CHAPTER 39
Diagnostic
39.1 Overview
The Diagnostic screens display information to help you identify problems with the VMG.
The route between a CO VDSL switch and one of its CPE may go through switches owned by
independent organizations. A connectivity fault point generally takes time to discover and impacts
subscriber’s network access. In order to eliminate the management and maintenance efforts, IEEE
802.1ag is a Connectivity Fault Management (CFM) specification which allows network
administrators to identify and manage connection faults. Through discovery and verification of the
path, CFM can detect, analyze and isolate connectivity faults in bridged LANs.
39.1.1 What You Can Do in this Chapter
•The Ping & TraceRoute & NsLookup screen lets you ping an IP address or trace the route
packets take to a host (Section 39.3 on page 341).
•The 802.1ag screen lets you perform CFM actions (Section 39.5 on page 342).
•The OAM Ping screen lets you send an ATM OAM (Operation, Administration and Maintenance)
packet to verify the connectivity of a specific PVC. (Section 39.5 on page 342).
39.2 What You Need to Know
The following terms and concepts may help as you read through this chapter.
How CFM Works
A Maintenance Association (MA) defines a VLAN and associated Maintenance End Point (MEP) ports
on the device under a Maintenance Domain (MD) level. An MEP port has the ability to send
Connectivity Check Messages (CCMs) and get other MEP ports information from neighbor devices’
CCMs within an MA.
CFM provides two tests to discover connectivity faults.
• Loopback test - checks if the MEP port receives its Loop Back Response (LBR) from its target
after it sends the Loop Back Message (LBM). If no response is received, there might be a
connectivity fault between them.
• Link trace test - provides additional connectivity fault analysis to get more information on where
the fault is. If an MEP port does not respond to the source MEP, this may indicate a fault.
Administrators can take further action to check and resume services from the fault according to
the line connectivity status report.