It doesn't seem to be going up and down. We just had some calls about intermittant connectivity - losing connection to mapped drives and the Exchange server. Any ideas on what I can check? Cabling should be fine if the telco can get to both CSUs without errors. Do the errors seem the same on both ends?
Log the numbers of errors and watch to see if they are increasing. If so, there is a line problem of some type. Unfortunately you may have to take the T1 down to have them run patterns thru the CSUs to really see the problems. Run a hardware and software loopback test on the router. You can search on Cisco. If all is well, it's most likely a problem with the cabling at some point.
I went through this for a good 4 or 5 months with SBC while they were trying to find the problem. They finally found that it was both a bad pair at the CO and insufficient grounding on their side of the smartjack at our location.
Improve this answer. Community Bot 1. YLearn YLearn Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. DECnet is an example of a protocol that meets both criteria.
Local-area transport LAT does not because it does not tolerate delays. The interface is very slow. Bandwidth is low or anticipated utilization is likely to sporadically exceed available bandwidth. Note: When you increase the number specified for an output hold queue, you may need to increase the number of system buffers.
The value used depends on the size of the packets associated with the traffic anticipated for the network. Priority queuing is a list-based control mechanism that allows traffic to be prioritized on an interface-by-interface basis.
Priority queuing involves two steps:. Both of these steps use versions of the priority-list global configuration command. In addition, further traffic control can be applied by referencing access-list global configuration commands from priority-list specifications. For examples of defining priority lists and for details about command syntax associated with priority queuing, refer to the Cisco IOS configuration guides and command references.
Note: Priority queuing automatically creates four hold queues of varying size. This overrides any hold queue specification included in your configuration.
Use priority queuing to prevent packets from being dropped and to improve serial link performance under the following conditions:.
When the interface is slow, there is a variety of traffic types being transmitted, and you want to improve terminal traffic performance. If you have a serial link that is intermittently experiencing very heavy loads such as file transfers occurring at specific times priority queuing will help select which types of traffic should be discarded at high traffic periods.
In general, start with the default number of queues when implementing priority queues. After enabling priority queuing, monitor output drops with the show interfaces serial EXEC command. If you notice that output drops are occurring in the traffic queue you have specified to be high priority, increase the number of packets that can be queued using the queue-limit keyword option of the priority-list global configuration command.
The default queue-limit arguments are 20 packets for the high-priority queue, 40 for medium, 60 for normal, and 80 for low. A high-priority queue depth of about specified with the queue-limit keyword is a typical working value when your router is dropping output packets and the serial lines are subjected to about 50 percent bandwidth utilization. If the router is dropping packets and is at percent utilization, you need another line. You can implement LAT compression with the interface configuration command bridge-group group lat-compression.
In addition to the basic diagnostic capabilities available on routers, a variety of supplemental tools and techniques can be used to determine the conditions of cables, switching equipment, modems, hosts, and remote internetworking hardware.
Perform the local loop test first, and then the remote test. Because there is no concept of a loopback in X. Listed below is a general procedure for performing loopback tests in conjunction with built-in system diagnostic capabilities:. In local loop mode, the use of the line clock from the T1 service is terminated, and the DSU is forced to use the local clock.
Use the show interfaces serial EXEC command to determine if the line status changes from "line protocol is down" to "line protocol is up looped ," or if it remains down. If the line protocol comes up when the CSU or DSU is in local loopback mode, this suggests that the problem is occurring on the remote end of the serial connection.
If the problem appears to be local, use the debug serial interface privileged EXEC command. When the line protocol is down, the debug serial interface command output will indicate that keepalive counters are not incrementing. This should cause the keepalive packets to begin to increment. Specifically, the values for mineseen and yourseen keepalives will increment every 10 seconds. This information will appear in the debug serial interface output.
If the keepalives do not increment, there may be a timing problem on the interface card or on the network. For information on correcting timing problems, see the section "Troubleshooting Clocking Problems," earlier in this chapter. Make certain that the cables are within the recommended lengths-no more than 50 feet Make certain the cables are attached to the proper ports. Swap faulty equipment as necessary. Figure shows the output from the debug serial interface command for an HDLC serial connection, with missed keepalives causing the line to go down and the interface to reset.
If you determine that the local hardware is functioning properly but you still encounter problems when attempting to establish connections over the serial link, try using the remote loopback test to isolate the problem cause. Note: This remote loopback test assumes that HDLC encapsulation is being used and that the preceding local loop test was performed immediately before this test.
The following steps are required to perform loopback testing:The following steps are required to perform loopback testing:. Using the show interfaces serial EXEC command, determine if the line protocol remains up with the status line indicating "Serial x is up, line protocol is up looped ," or if it goes down with the status line indicating "line protocol is down.
Perform both local and remote tests at the remote end to isolate the problem source. If the line status changes to "line protocol is down" when remote loopback mode is activated, make sure that ones density is being properly maintained. The following sub-sections cover the show interfaces serial command's parameters, syntax description, sample output display, and field descriptions. To display information about a serial interface, use the show interfaces serial privileged EXEC command:.
Displays the number of packets of each protocol type that have been sent through the interface. On the Cisco series with an NPM or a Cisco series with a MIP, specifies the T1 channel-group number in the range of 0 to 23, defined with the channel-group controller configuration command. T1 channels on the CT3IP are numbered 1 to 28 rather than the more traditional zero-based scheme 0 to 27 used with other Cisco products.
This is to ensure consistency with Telco numbering schemes for T1 channels within channelized T3 equipment. The following is sample output from the show interfaces command for a synchronous serial interface:. Table show interfaces serial Field Descriptions - this table describes significant fields shown in the output. This section describes the techniques and procedures for troubleshooting T1 circuits for dial-in customers. This command displays the controller status that is specific to the controller hardware.
The information displayed is generally useful for diagnostic tasks performed by technical support personnel only. Issue a show controller t1 command to display statistics about the T1 link. If you specify a slot and port number, statistics for each minute period will be displayed. The show controller t1 EXEC command provides information to logically troubleshoot physical layer and data link layer problems.
This section describes how to logically troubleshoot using the show controller t1 command. Most T1 errors are caused by misconfigured lines. Ensure that linecoding, framing and clock source are configured according to what the service provider recommends. The controller is administratively down when it has been manually shut down. You should restart the controller to correct this error. If the T1 controller and line are not up, check to see if one of the following messages appears in the show controller t1 EXEC output:.
Check to see if the framing format configured on the port matches the framing format of the line. You can check the framing format of the controller from the running configuration or the show controller t1 command output. Line build out LBO compensates for the loss in decibels based on the distance from the device to the first repeater in the circuit. A longer distance from the device to the repeater requires that the signal strength on the circuit be boosted to compensate for loss over that distance.
Make sure that the cable between the interface port and the T1 service provider's equipment or T1 terminal equipment is connected correctly. Check to see if the cable is hooked up to the correct ports. Correct the cable connections if necessary. Check cable integrity. Look for breaks or other physical abnormalities in the cable. Ensure that the pinouts are set correctly. If necessary, replace the cable. Check the cable connectors. A reversal of the transmit and receive pairs or an open receive pair can cause errors.
The pins on a RJ jack are numbered from 1 through 8. Pin 1 is the leftmost pin when looking at the jack with the metal pins facing you. Refer to the figure below. Run the show controller t1 EXEC command after each step to check if the controller exhibits any errors. Check to see if the line is in loopback mode from the show controller t1 output. A line should be in loopback mode only for testing purposes. To turn off loopback, use the no loopback command in the controller configuration mode as shown below:.
Check the show controller command output to see if there are alarms displayed by the controller. A received Alarm Indication Signal AIS means there is an alarm occurring on the line upstream of the equipment connected to the port. If not, change the framing format on the controller to match that of the line.
A received RAI means that the far-end equipment has a problem with the signal it is receiving from its upstream equipment. Insert an external loopback cable into the port. To create a loopback plug refer to the section "Creating a Loopback Plug," later in the chapter.
Check to see if there are any alarms. If you do not see any alarms, then the local hardware is probably in good condition. In that case:. Check the cabling. Connect the T1 line to a different port. Configure the port with the same settings as that of the line. If the problem does not persist, then the fault lies with the one port:.
If not change the framing format on the controller to match that of the line. A transmitted RAI at the interface indicates that the interface has a problem with the signal it is receiving from the far-end equipment.
If not, correct the mismatch. The show controller t1 EXEC command provides error messages that can be used to troubleshoot problems. We will now discuss several error messages and how to correct the errors. To see if the error counters are increasing, execute the show controller t1 command repeatedly. Note the values of the counters for the current interval. Consult your service provider for framing and linecoding settings. The presence of slips on a T1 line indicates a clocking problem.
Verify that the clock source is derived from the network. This can be ascertained by looking for Clock Source is Line Primary. Note: If there are multiple T1s into an access server, only one can be the primary, while the other T1s derive the clock from the primary. In that case verify that the T1 line designated as the primary clock source is configured correctly. Check to see if the linecoding configured on the port matches the framing format of the line.
Contact your service provider for correct values. If the error counters do not increase but the problem persists, verify that the signaling channel is up and configured correctly.
Run the show interface serial x command, where x should be replaced by the interface number. Check to see if the interface is up. If the interface is not up, use the no shutdown command to bring the interface up. Ensure that encapsulation is PPP. If the interface is not using PPP then use the encapsulation ppp command in the interface configuration mode to correct it. Check to see if loopback is set. Loopback should be set only for testing purposes. Use the no loopback command to remove loopbacks.
Whenever troubleshooting a PRI, you need to check to see if the T1 is running cleanly on both ends. If Layer 1 problems have been resolved, as described above, consider Layer 2 and Layer 3 problems. Gives the number of times that the controller was restarted because of errors.
Shows the status of G. This section describes the techniques and procedures to troubleshoot T1 circuits for dial-in customers. The show controller t1 exec command provides information to logically troubleshoot physical layer and data link layer problems. This section describes how to logically troubleshoot using the show controller t1 command.
This command displays the controller status that is specific to the controller hardware. The information displayed is generally useful for diagnostic tasks performed by technical support personnel. Issue a show controller t1 command to display statistics about the T1 link. If you specify a slot and port number, statistics for each minute period will be displayed. Most T1 errors are caused by misconfigured lines. Ensure that linecoding, framing, and clock source are configured according to what the service provider recommends.
The controller is administratively down when it has been manually shut down. You should restart the controller to correct this error. Step 1 Enter enable mode. Step 2 Enter global configuration mode. Step 3 Enter controller configuration mode. Step 4 Restart the controller. If the T1 controller and line are not up, check to see if you are seeing one of the following messages in the show controller t1 exec output:. Step 1 Check to see whether the framing format configured on the port matches the framing format of the line.
You can check the framing format of the controller from the running configuration or the show controller t1 command output. Step 2 Try the other framing format to see if the alarm clears. Line build out LBO compensates for the loss in decibels based on the distance from the device to the first repeater in the circuit.
A longer distance from the device to the repeater requires that the signal strength on the circuit be boosted to compensate for loss over that distance. To configure transmit and receive levels for a cable length line build out longer than feet for a T1 trunk with a channel service unit CSU interface, use the cablelength long controller configuration command. To configure transmit attenuation for a cable length line build out of feet or shorter for a T1 trunk with a DSX-1 interface, use the cablelength short controller configuration command.
Consult your service provider and the Cisco IOS command reference for details on buildout settings. Step 1 Make sure that the cable between the interface port and the T1 service provider's equipment or T1 terminal equipment is connected correctly. Check to see if the cable is hooked up to the correct ports. Correct the cable connections, if necessary. Step 2 Check cable integrity. Look for breaks or other physical abnormalities in the cable.
Ensure that the pinouts are set correctly. If necessary, replace the cable. Step 3 Check the cable connectors. A reversal of the transmit and receive pairs or an open receive pair can cause errors. Set the receive pair to lines 1 and 2; the transmit pair should be lines 4 and 5.
The pins on an RJ jack are numbered from 1 through 8. Pin 1 is the leftmost pin when looking at the jack with the metal pins facing you. Refer to Figure Step 4 Try using a rollover cable.
Run the show controller t1 exec command after each step to see whether the controller exhibits any errors. Check to see whether the line is in loopback mode from the show controller t1 output. A line should be in loopback mode only for testing purposes. To turn off loopback, use the no loopback command in the controller configuration mode, as shown here:. Check the show controller command output to see if there are alarms displayed by the controller.
We will now discuss various alarms and the procedure necessary to correct them. A received alarm indication signal AIS means that an alarm is occurring on the line upstream of the equipment connected to the port. The AIS failure is declared when an AIS defect is detected at the input and still exists after the loss of frame failure is declared caused by the unframed nature of the "all-ones" signal.
The AIS failure is cleared when the loss of frame failure is cleared. If not, change the framing format on the controller to match that of the line. Step 2 Contact your service provider to check for misconfiguration within the telco. A received remote alarm indication means that the far-end equipment has a problem with the signal that it is receiving from its upstream equipment.
For SF links, the far-end alarm failure is declared when bit 6 of all the channels has been zero for at least ms. The failure is cleared when bit 6 of at least one channel is not zero for a period usually less than 1 second and always less than 5 seconds. The far-end alarm failure is not declared for SF links when a loss of signal is detected. For ESF links, the far-end alarm failure is declared if the yellow alarm signal pattern occurs in at least seven out of ten contiguous bit pattern intervals.
The failure is cleared if the yellow alarm signal pattern does not occur in ten contiguous bit signal pattern intervals. Step 1 Insert an external loopback cable into the port. To create a loopback plug, refer to the section "Performing Hardware Loopback Plug Test," later in this chapter. Step 2 Check to see if there are any alarms. If you do not see any alarms, then the local hardware is probably in good condition.
In that case, do the following:. Step 3 Remove the loopback plug, and reconnect your T1 line. Step 4 Check the cabling. Refer to the section "Loss of Signal" for more information. Step 5 Power-cycle the router. Step 6 Connect the T1 line to a different port.
Configure the port with the same settings as that of the line. If the problem does not persist, then the fault lies with the one port:. A red alarm is declared when the CSU cannot synchronize with the framing pattern on the T1 line.
Step 2 Check the settings at the remote end, and verify that they match your port settings. Step 3 Contact your service provider. A transmitted remote alarm indication at the interface indicates that the interface has a problem with the signal it is receiving from the far-end equipment. Step 1 Check the settings at the remote end, and verify that they match your port settings.
If not, correct the mismatch. Step 2 Power-cycle the router. Step 3 Connect the T1 line to a different port. The show controller t1 exec command provides error messages that can be used to troubleshoot problems. We will now discuss several error messages and how to correct the errors. To see whether the error counters are increasing, execute the show controller t1 command repeatedly. Note the values of the counters for the current interval.
Consult your service provider for framing and linecoding settings. The presence of slips on a T1 line indicates a clocking problem. The T1 provider telco will provide the clocking that the customer premises equipment CPE will need to synchronize to. Step 1 Verify that the clock source is derived from the network. Note : If there are multiple T1s into an access server, only one can be the primary, while the other T1s derive the clock from the primary.
In that case, verify that the T1 line designated as the primary clock source is configured correctly. Step 2 Set the T1 clock source correctly from the controller configuration mode. Step 1 Check to see whether the linecoding configured on the port matches the framing format of the line.
Use the show running-config command to check if isdn switchtype and pri-group timeslots are configured correctly. Contact your service provider for correct values. If the error counters do not increase but the problem persists, verify that the signaling channel is up and configured correctly. Step 1 Run the show interface serial x command, where x should be replaced by the interface number.
Step 2 Check to see if the interface is up. If the interface is not up, use the no shutdown command to bring the interface up. Step 3 Ensure that encapsulation is PPP.
If the interface is not using PPP, then use the encapsulation ppp command in the interface configuration mode to correct it. Step 4 Check to see whether loopback is set. Loopback should be set only for testing purposes. Use the no loopback command to remove loopbacks. Whenever troubleshooting a PRI, you need to check whether the T1 is running cleanly on both ends.
If Layer 1 problems have been resolved, as described previously, we must look to Layer 2 and 3 problems. The show isdn status command is used to display a snapshot of all ISDN interfaces. It displays the status of Layers 1, 2, and 3. Step 1 Verify that Layer 1 is active. Refer to the previous section "Is the Controller Administratively Down? Also verify that the T1 is not administratively down.
Use the no shutdown command to bring up the T1 controller. Refer to the section "Troubleshooting Using the show controller t1 Command. Use debug isdn q to verify that Layer 2 is stable. The debug isdn q command displays data link layer Layer 2 access procedures that are taking place at the router on the D-channel. Ensure that you are configured to view debug messages by using the logging console or terminal monitor command as necessary.
Note In a production environment, verify that console logging is disabled. Enter the show logging command. If logging is enabled, the access server might intermittently freeze up as soon as the console port gets overloaded with log messages.
Enter the no logging console command. Note If debug isdn q is turned on and you do not receive any debug outputs, place a call or reset the controller to get debug outputs.
Step 1 Verify that Layer 2 is stable. You should observe the debug outputs for messages indicating that the service is not bouncing up and down. If you see the following types of debug outputs, the line is not stable:. If Layer 2 does not appear to be stable, refer to the section "Troubleshooting Error Events. This is usually seen when we are transmitting poll requests RRp and not getting a response from the switch RRf , or vice versa.
Step 4 Verify that the D-channel is up using the show interfaces serial x command. If the D-channel is not up, then use no shutdown command to bring it up:. Step 5 Check to see whether encapsulation is PPP. If not, use the encapsulation ppp command to set encapsulation. Step 6 Check to see whether the interface is in loopback mode.
For normal operation, the interface should not be in loopback mode. Step 7 Power-cycle the router. The hardware loopback plug test can be used to test whether the router has any faults. If a router passes a hardware loopback plug test, then the problem exists elsewhere on the line. Step 1 Use wire cutters to cut a working RJ or RJ cable so that there are 5 inches of cable and the connector attached to it. Step 2 Strip the wires. Step 3 Twist the wires from pins 1 and 4 together.
Step 4 Twist the wires from pins 2 and 5 together. Pin 1 is the left-most pin when looking at the jack with the metal pins facing you. Step 1 Insert the plug into the T1 port in question. Step 2 Save your router configuration using the write memory command. Step 4 Use the show running-config command to check whether the interface has an IP address.
If the interface does not have an IP address, obtain a unique address and assign it to the interface with a subnet mask of Step 5 Clear the interface counters using the clear counters command.
Step 6 Perform the extended ping test as described in the "Using Extended ping Tests" section, earlier in this chapter.
This section describes the techniques and procedures to troubleshoot E1 circuits for dial-in customers. The show e1 controller exec command provides information to logically troubleshoot physical layer and data link layer problems. This section describes how to logically troubleshoot using the show controller e1 command.
The information displayed is generally useful for diagnostic tasks performed by technical support personnel only.
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