Understanding Troubleshooting Basics


When you begin troubleshooting a problem, you are under the assumption that something in your phone system isn’t performing at an acceptable level. For example, you might have echo when you call your grandmother or static when you call work. You might not be able to get through to your girlfriend because someone in the world of telecom thinks that her number has been disconnected or is no longer in service. The issue can affect all of your calls, both inbound and outbound, or just outbound calls to a specific city or state. Before you can begin testing a specific issue, you have to narrow down the problem.

 Remember  When troubleshooting your issues, it’s not your responsibility to correct the problem. Your main responsibility is to accurately report the issue. You can speed the process along by doing some troubleshooting yourself, but generally only your carriers or your hardware vendor can fix a problem. By isolating the issue to a single source, either a carrier or a piece of hardware, you can reduce the troubleshooting time by hours or possibly days.

The first step in troubleshooting is to systematically isolate the potential causes and eliminate them one by one. You are aided in this process by simply observing whether the issue affects a variety of calls or just a small group of them. Every type of call, whether it’s inbound to your toll-free number or outbound to a local business, is handled by a different group of carriers. Any issue that isn’t intermittent is easy to track down and troubleshoot by checking a handful of call types. There are only six varieties of call, so by figuring out the characteristics of the issue, you can either eliminate or indicate the source of the problem.

Switched outbound long-distance call

A switched outbound long-distance call is one of the most basic calls that people make every day. You make this call from a regular phone line, just like the one at your house, to a phone number that is outside of your LATA (Local Access Transport Area), state, or country. The distilled version of the call is represented in Figure 11-1.

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Figure 11-1: A switched outbound long-distance call.

You can see in Figure 11-1 how the call starts with your phone system (your phone system may be as simple as a single phone attached to a jack), and then progresses from your local carrier, to your long-distance carrier, to the local carrier that handles the service for the person you are calling, and finally to the phone you are actually calling. This is one of the most basic calls that you make, and probably the type of call that experiences the greatest quantity of issues.

 Remember  Before you can pinpoint a problem to any variable in the diagram, you need to compare the call to at least one of the remaining five call types.

 Technical Stuff  The public switched telephone network, or PSTN, is a generic term for all the long-distance carrier (Points of Presence) POPs, and hardware that routes and directs phone calls, as well as the local carrier central offices (COs), and all of their hardware that routes and directs phone calls. While a call is being sent through the PSTN, it is aggregated onto circuits with other calls for part of the path it takes from origin to termination. Imagine the PSTN is like a huge freeway for phone calls. All calls use the same roads, sometimes only until the nearest offramp, and sometimes for hundreds of miles. If a problem on a call happens while it’s being routed through the PSTN, the issue is said to be in the switched network, even if the call originally started, or ended, on a dedicated circuit.

Switched inbound long-distance call

A switched inbound long-distance call is a very helpful call type because it eliminates your long-distance carrier as a potential cause of any issue. The long-distance portion of the PSTN is filled with hardware that routes and maintains the quality of your call. The greater the distance the call must travel through the PSTN, the more hardware is required to maintain the call. More hardware, of course, means that there are more potential points of failure, and so you are more likely to encounter a problem in the 28 or 2,800 miles where your long-distance carrier is handling your call.

As you can see in Figure 11-2, when someone calls directly into your phone system (not using a toll-free number), the caller doesn’t use your long-distance carrier. If you have a problem on both outbound long-distance calls and inbound long-distance calls, you can eliminate your long-distance carrier as the source.

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Figure 11-2: A switched inbound long-distance call.

Switched local call (inbound or outbound)

A switched local call uses the same carrier and interacts with the same hardware (carrier hardware and your phone system) for both outbound and inbound calls. It doesn’t matter if you call your friend across the street or if someone calls you; the only carrier that generally ever sees your call is the local carrier you both use. Figure 11-3 offers a visual representation of this call type.

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Figure 11-3: A switched local call.

You can see in Figure 11-3 that the call barely enters the PSTN and might pass through only one central office. If you have a problem with a local call, the possible sources are your phone system and the local carrier.

Dialing someone else’s toll-free number

When you dial someone else’s toll-free number, the only piece of the call that you have any responsibility for is your phone system. Your local carrier is responsible for identifying the carrier that receives the traffic, and then your local carrier forwards the call to that network. Figure 11-4 shows the path the call takes when you dial someone else’s toll-free number.

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Figure 11-4: Dialing someone else’s toll-free number.

If you have a problem calling someone else’s toll-free number, but all of your other calls work fine, the problem probably has something to do with either the carrier that handles the traffic of the toll-free number, or the local carrier that terminates the call. Identifying which carrier is the problem is covered in the step-by-step troubleshooting section for toll-free numbers in Chapter 12.

 Remember  Many companies use the same long-distance carriers. If you use Sprint for your long distance and you dial the toll-free number of a company that also uses Sprint for long distance, you can possibly see a similar problem on your outbound calls. In this case, you should focus on troubleshooting your out-bound long-distance calls on the Sprint network. When Sprint resolves your outbound issue, the toll-free problem for the company you are dialing to will probably also be fixed.

Someone is dialing your switched toll-free number

The last switched call type is an inbound call to your toll-free number. The diagram for this call, shown in Figure 11-5, looks quite a bit like Figure 11-1. It includes the same path.

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Figure 11-5: Someone dialing your switched toll-free number.

The main aspect that separates a toll-free issue from a regular outbound issue is the fact that the call is being sent to your long-distance carrier based on a database check done by the originating local carrier. Aside from how the call is sent to your long-distance carrier, the path the call takes encountersall the same carriers and hardware it would if you had made an outbound call to the origination number.

Dedicated calling

You can compare calls over your dedicated circuits with switched calls in order to eliminate your local carrier as a possible source of the problem. Figure 11-6 shows how the local loop of your dedicated circuit passes through your local carrier, but doesn’t really interact with it.

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Keeping the switched network in mind when you have a problem on a dedicated circuit

 Remember  When you report trouble on your dedicated circuit, keep in mind that the local loop is the dedicated section your calls pass through. If you have constant echo, static, dropped calls, or if the entire circuit is completely down, you should refer to your circuit when you open the trouble ticket. If you have any problems that you can duplicate by dialing out on a regular phone line over your carrier’s switched network, such as calls failing to a certain area code, fax completion problems, static, or echo, you should open a trouble ticket with your carrier based on the call from your regular phone line. If the problem exists on both your switched and dedicated calls, but you open the ticket as a dedicated issue, the problem will be harder to diagnose.

Carriers do assign greater priority to dedicated circuits, but they also push to intrusively test your circuit as the first step in troubleshooting. The intrusive testing process prevents you from using any channel on your circuit during the testing. If you can open the trouble ticket on a call from a regular phone line, your carrier won’t be distracted by your T-1 and waste time testing your local loop.

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Figure 11-6: Dedicated calling process.

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 Remember  There are only three elements that interact at the individual channel (DS-0) level on a dedicated circuit:

  • Your channel bank or multiplexer: This is the piece of hardware at your office that breaks the dedicated T-1 circuit down into 24 useable DS-0 circuits that transmit and receive your phone calls.

  • Your carrier’s switch: The one piece of hardware in your carrier’s switch that you should be concerned with is the section that functions like your multiplexer.

  • Echo cancellers: These pieces of hardware eliminate the echo on your phone calls. They may be in your long-distance carrier’s network between the POP and the local carrier, or within the local carrier network.

The next important area to note in the diagram is the point where the call enters your carrier’s network to the point where it’s delivered to the recipient’s phone. Figure 11-7 shows an expanded view of a dedicated call.

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Figure 11-7: Expanded view of a dedicated call.

In Figure 11-7, you can now see that the local loop begins at your building and ends at the CFA (Carrier Facilities Assignment) point where the local loop enters your long-distance carrier’s network within their POP. (Check out Chapter 8 if you have any question about the CFA point.) The majority of a dedicated call actually isn’t dedicated at all, but is handled by the PSTN, where it’s routed and handled with every other call in your carrier’s network.

Comparing call types

Call type diagrams are great tools when you are troubleshooting. You should record the types of calls you have made and note whether they experienced the problem. Then you can refer to the diagrams and begin eliminating variables. For example, if you have static on local calls and inbound calls, but not on dedicated calls, you can distill the variables in the following manner, as shown in Figure 11-8.

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Figure 11-8: Comparing the call types in diagram form.

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Keeping an open mind to the information

 Remember  The speed at which a problem is resolved is directly related to how well you accept the results of your testing. It’s not uncommon for people to place the calls side by side and have a good indication of where a problem is, but not troubleshoot that section first. This is very common when all the signs indicate that the issue is with your hardware. Open a technician assistance ticket (also called a tech assist ticket) with your carrier to schedule a time with their technician to walk you through testing and work with your hardware vendor. The help of your carrier’s technician aids your hardware vendor in isolating issues within your phone system, but your first call should be to your hardware vendor if you suspect that is the site of your issue.

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When troubleshooting, look for similar paths. For example, when you compare the diagrams of the inbound calls and the local calls, you see that there are only two variables in common: your phone system and the network of your local carrier. Local calls are commonly handled by your phone system, your local carrier, and the phone system of whomever you are calling. If you simply call another person in your local area and have the same problem, you can eliminate the hardware of the first person you called as the potential problem. The only two variables left for you to investigate are your phone system and your local carrier.

Every inbound long-distance call that comes from various companies in different sections of the world has its own local and long-distance carrier. Therefore, you can quickly eliminate the other long-distance carrier and the other phone system. The only variables that can possibly be causing a problem are either your phone system or your local carrier.

After you consider the call from your dedicated circuit that did not have the problem, you can eliminate your phone system as a possible source of the issue. As long as you are dialing out from the same phone system over both your dedicated circuit and your switched lines, it’s very unlikely that your phone system is the source of the problem. You have now reduced the possible sources of the problem to just one entity (your local carrier). The next step is to call the local carrier and open a trouble ticket. It’s helpful to let the local carrier know about the tests you have done and that the problem doesn’t affect calls on your dedicated circuit, where they don’t interact at DS-0 level.

Narrowing down carrier-level problems

If your problem persists on all your calls, but you’ve narrowed down the source to one of your carriers (eliminating hardware as a source), you can easily locate the issue and make sure that it gets repaired. If the problem doesn’t affect all of your calls, you might need to focus more on the pattern of failures within the carrier.

There are three additional bits of information that can help save time when you open your trouble ticket. Ask the following questions:

  • Is the issue specific to a time of day? Your carrier might be sending your calls over an overflow route that isn’t very stable at peak network times between 10 a.m. and 3 p.m. If this is the case, the issue might be with a route that isn’t used or monitored very often. If the problem happens intermittently during your peak times and not the peak times of your carrier, you might have a bottleneck in your own phone system. Time-of-day issues typically indicate a problem based on the volume of calls passing over a network, and identifying a problem this way can steer the technicians to a faster resolution. Share the information; it’s good for everyone.

  • Is the issue geographically specific? If you can call everywhere in America except the West coast, the state of South Carolina, LATA 730, the 305 area code, or any geographic region that you can identify in a telecom-based group, note this information to your carrier. If there has been a large outage affecting all calls to the West coast, your carrier might not know this until you call.

  • Is the issue intermittent? If the problem occurs randomly, regardless of time of day or geography, get ready to settle in for a long troubleshooting process. The first thing to do about intermittent issues is determine the percentage of calls affected. Issues that affect about 50 percent of your calls are not that difficult to find, because if your carrier watches 10 test calls, the problem is bound to show up in around half of them, making it easier to research and repair. If the problem affects 5 or 10 percent of your calls, you may make 10 or 20 test calls before one call is affected. When less than 10 percent of your calls are affected by a problem, you enter the world of the needle in the haystack. As long as both you and your carrier stay focused and have the time to devote to troubleshooting, you will eventually find the problem. If the issue is low on your priority list, it might persist for weeks or months.




Telecom for Dummies
Telecom For Dummies
ISBN: 047177085X
EAN: 2147483647
Year: 2006
Pages: 184

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