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Page 266 / 327 Scroll up to view Page 261 - 265
VMG3926-B10A User’s Guide
266
C
HAPTER
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 267
).
• The
802.1ag
screen lets you perform CFM actions (
Section 39.5 on page 268
).
• 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 268
).
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.
Page 267 / 327
Chapter 39 Diagnostic
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267
39.3
Ping & TraceRoute & NsLookup
Use this screen to ping, traceroute, or nslookup an IP address. Click
Maintenance > Diagnostic >
Ping&TraceRoute&NsLookup
to open the screen shown next.
Figure 164
Maintenance > Diagnostic > Ping &TraceRoute&NsLookup
The following table describes the fields in this screen.
39.4
802.1ag
Click
Maintenance > Diagnostic
>
8.2.1ag
to open the following screen. Use this screen to
perform CFM actions.
Table 123
Maintenance > Diagnostic > Ping & TraceRoute & NsLookup
LABEL
DESCRIPTION
URL or IP
Address
Type the IP address of a computer that you want to perform ping, traceroute, or nslookup in
order to test a connection.
Ping
Click this to ping the IP address that you entered.
TraceRoute
Click this button to perform the traceroute function. This determines the path a packet
takes to the specified computer.
Nslookup
Click this button to perform a DNS lookup on the IP address of a computer you enter.
Page 268 / 327
Chapter 39 Diagnostic
VMG3926-B10A User’s Guide
268
Figure 165
Maintenance > Diagnostic > 802.1ag
The following table describes the fields in this screen.
39.5
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
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.
Table 124
Maintenance > Diagnostic > 802.1ag
LABEL
DESCRIPTION
802.1ag Connectivity Fault Management
Maintenance
Domain (MD)
Level
Select a level (0-7) under which you want to create an MA.
Destination
MAC Address
Enter the target device’s MAC address to which the VMG performs a CFM loopback test.
802.1Q VLAN
ID
Type a VLAN ID (0-4095) for this MA.
VDSL Traffic
Type
This shows whether the VDSL traffic is activated.
Loopback
Message (LBM)
This shows how many Loop Back Messages (LBMs) are sent and if there is any inorder or
outorder Loop Back Response (LBR) received from a remote MEP.
Linktrace
Message (LTM)
This shows the destination MAC address in the Link Trace Response (LTR).
Set MD Level
Click this button to configure the MD (Maintenance Domain) level.
Send Loopback
Click this button to have the selected MEP send the LBM (Loop Back Message) to a specified
remote end point.
Send Linktrace
Click this button to have the selected MEP send the LTMs (Link Trace Messages) to a
specified remote end point.
Page 269 / 327
Chapter 39 Diagnostic
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269
ATM sets up virtual circuits over which end systems communicate. The terminology for virtual
circuits is as follows:
Figure 166
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 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.
•
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
Page 270 / 327
Chapter 39 Diagnostic
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270
Figure 167
Maintenance > Diagnostic > OAM Ping
The following table describes the fields in this screen.
Table 125
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.
F5 segment
Press this to perform an OAM F5 segment loopback test.
F5 end-end
Press this to perform an OAM F5 end-to-end loopback test.

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