Point-to-Point with Optical Regenerator

In this topology we will consider a straightforward point-to-point topology but with a regenerator (3R) inline. What we can see happening here is that all three layers have their respective trails terminated at the regenerator. This is because the regenerator is affecting the individual signals at the highest optical channel layer. By doing 2R or 3R regeneration on the entire signal requires disturbance and manipulation of the individual client signals at the OC layer. Consequently, these changes to the client signals require subsequent changes to be made at the lower OMS and OTC layers.

In this regeneration example, we can see that the trails in all of the layers are affected by performing, 2R or 3R regeneration of the signal. Consequently, all the OCh and OMS trails sink at the regenerator and new trails are spawned and sourced again at the regenerator’s line output. 

Again, if this equipment is going to be OTH (G.709) compliant it must have the capability to understand, process, analyze the OTH OH, and to act accordingly. 

Optical Fiber Testers

Optical fiber requires a unique class of cable testers. Just like copper-cable testers, optical fiber testers are specialized. Figure 1 shows a simple continuity tester that verifies light transmission through the cable.

Figure 1: An optical fiber continuity tester

Another type of optical fiber test device is the power meter (also known as an attenuation tester), such as the one shown in Figure 2. Like the continuity tester, the power meter tests whether light is making its way through the cable, but it also tests how much of the light signal is being lost. Anyone installing fiber-optic cable should have a power meter. Most problems with optical fiber cables can be detected with this tool. Good optical fiber power meters can be purchased for less than $1,000.

Figure 2: An optical fiber power meter

Note

An attenuation tester checks for how much signal is lost on the cable, whereas a continuity tester only measures whether light is passing through the cable.

Many high-end cable testers, such as those available from Hewlett-Packard, Microtest, and others, can test both optical fiber and copper cables (provided you have purchased the correct add-on modules). You need to know a few points when you purchase any type of optical fiber tester:

• The tester should include the correct fiber connectors (ST, SC, FC, LC, MT-RJ, etc.) for the types of connectors you will be using.
• The tester should support the type of fiber-optic cable you need to test (single-mode or multimode).
• A power meter should test the wavelength at which you require the cable to be used (usually 850 or 1,300nm).

Professional fiber-optic cable installers usually carry tools such as an OTDR that perform more advanced tests on optical fiber cable. OTDRs are not for everyone, as they can easily cost in excess of $30,000. However, they are an excellent tool for locating faults.

UTP, Optical Fiber, and Future-Proofing

The common networking technologies today (Ethernet, Token Ring, FDDI, and ATM) can all use either UTP or optical fiber cabling, and IT professionals are faced with the choice. MIS managers and network administrators hear much about "future-proofing" their cabling infrastructures. The claim is that installing particular grades of cable and components will guarantee that you won't have to ever update your cabling system again. However, you should keep in mind that in the early 1990s network managers thought they were future-proofing their cabling system when they installed Category 4 rather than Category 3 cabling.

Today, decision makers who must choose between Category 6 and 6A cabling components are thinking about future-proofing. Each category is an improvement in potential data throughput and therefore a measure of future-proofing. Deciding whether to use optical fiber adds to the decision. Here are some of the advantages of using optical fiber:

• It has much higher potential bandwidth, which means that the data throughput is much greater than with copper cable. Optical fiber cable has the potential for higher bandwidth, because it requires a transceiver to deliver the bandwidth. If the highest bandwidth optical transceiver currently available is 10GB, then its actual bandwidth is no better 10GBase-T, notwithstanding the distance capability.
• It's not susceptible to electromagnetic interference.
• It can transmit over longer distances, which is useful for centralized cabling topologies and backbone cabling, although distance is set at 100 meters for the run of cable from the TR to equipment outlets regardless of media, according to ANSI/TIA-568-C.
• Optical fiber also allows the use of telecommunications enclosures, since it can support longer backbone distances than UTP. This essentially places the switches closer to the equipment outlets and can provide savings of approximately 25 percent over the use of switches in TRs. (For more information, see the TIA Fiber Optics LAN Section at www.fols.org)
• Improved termination techniques and equipment make it easier to install and test.
• Cable, connectors, and patch panels are now cheaper than before.
• It's valuable in situations where EMI is especially high.
• It offers better security (because the cable cannot be easily tapped or monitored).

UTP cabling is still popular in a traditional hierarchical topology where an intermediate switch is used in a TR, and you may want to consider remaining with UTP cabling for the following reasons:

• The TIA estimates that the combined installation and hardware costs result in a finished centralized cabling fiber optic network that is 30 percent more expensive than a Category 5e or 6 copper cable network using a traditional hierarchical star topology. However, these cost differences are expected to decrease with time.
• If higher bandwidth (more than a gigabit per second) requirements are not an issue for you, you may not need optical fiber.
• Fiber optics is the medium of choice for security only if security concerns are unusually critical.
• EMI interference is only an issue if it is extreme.

Fiber-optic cabling and transmission media are likely to outpace copper for 100 meter links as speeds increase; however, when considering optical fiber cable, remember that you are trying to guarantee that the cabling system will not have to be replaced for a very long time, regardless of future networking technologies. Some questions you should ask yourself when deciding if fiber optic is right for you include the following:

• Do you rent or own your current location?
• If you rent, how long is your lease, and will you be renewing your lease when it is up?
• Are there major renovations planned that would cause walls to be torn out and rebuilt?

As network applications are evolving, better UTP and optical fiber cabling media are required to keep up with bandwidth demand. As you will see from standards, the end user has many options in a media category. There are many types of UTP and optical fiber cabling. Standards will continue to evolve, but it's always a good idea to install the best grade of cabling since the cost of the structured cabling systems (excluding installation cost) is usually only 5–10 percent of the total project cost. Therefore, making the right decisions today can greatly future-proof the network.