Physical Interfaces and Cabling Types

This chapter ensures that you are ready for questions related to these topics in the Network Fundamentals section of the CCNA 200-301 exam blueprint from Cisco Systems. Remember that this is just a portion of the Network Fundamentals section. The other chapters in Part I, “Network Fundamentals,” also provide information pertinent to the Network Fundamentals section.

As you can see, it is time to get physical in our discussion of networking technologies! As in all other areas of information technology, there have been many advancements in this regard. As our networks have had to deal with more and more data (including audio and video data), we have needed faster and faster physical solutions to move that data.

This chapter covers the following essential terms and components:

• ▸ Ethernet

• ▸ Copper media

• ▸ Unshielded twisted pair (UTP)

• ▸ Fiber media

• ▸ Cat 5e

• ▸ Cat 6

• ▸ Auto MDI-X

• ▸ PoE

Topic: Single-mode fiber, multimode fiber, copper

Ethernet is king today, including when it comes to cabling. Ethernet is no longer made up of just copper at its core. Fiber options also exist within the standards and permit blazing speeds over relatively long distances.

Ethernet continues to evolve and get faster. Table 3.1 list some of the forms you should be aware of.

Table 3.1 Examples of Ethernet Technologies

The most popular forms of Ethernet use unshielded twisted pair (UTP). There are many categories of UTP, abbreviated as follows: Cat 1, Cat 2, Cat 3, Cat 4, Cat 5, Cat 5e, Cat 6, Cat 6a, and Cat 7. Each of the UTP cable categories is technologically advanced compared to its predecessor. For example, Cat 5e is capable of 1 Gbps Ethernet, whereas Cat 6 is capable of carrying 10 Gbps Ethernet.

Multimode Versus Single-Mode Fiber

If an Ethernet cable does not have copper in its core, it uses fiber optics. The signals pass through a fiber-optic cable using glass as the transmission medium. The signal is a light that transmits the 0s and 1s that systems use to communicate. While it is strange to think about glass being inside a network cable, keep in mind that the glass used in the core of the cable is a long, thin, flexible “fiber” of glass—not the glass you look through when you drive a car! Even though fiber-optic cable is quite flexible, it is very important for a fiber-optic cable plant installation never to exceed the fiber-optic cable’s bend radius.

There are two extremely popular variations of fiber-optic media: multimode fiber and single-mode fiber. Multimode fiber permits multiple angles of light waves, called modes, to propagate through the core.

Single-mode fiber has a much smaller diameter core for the network cable. To use this much smaller fiber-optic strand, a laser-based transmitter sends the light at a single angle through the core.

Ethernet Shared Media Versus Point-to-Point

Thankfully, using Ethernet in a “shared media” environment is a thing of the past. Shared media refers to Ethernet designs that use hubs (or a coaxial cable run) as networking devices. Hubs force the network devices to operate in half-duplex mode and use CSMA/CD to deal with collisions that occur.

Modern networks use switches with Ethernet and permit the creation of point-to-point links that function independently from each other at L1, making collisions extremely rare (or even impossible if all the devices are healthy and configured properly). It is possible to run a system in full-duplex mode with such a configuration. Systems enjoy sending and receiving data at the same time as other systems in the infrastructure, which makes for a wonderful, worry-free, and collision-less network.

Power over Ethernet (PoE)

Your phone calls are not transmitted over a dedicated phone (voice) network the way they were when I was making calls in high school (1983). Today, most voice traffic is transmitted over the same network as data. Wouldn’t it be nice if you could plug your voice over IP (VoIP) phone into a switch using an Ethernet cable and not only allow the phone to communicate but also allow it to receive the power it needs to operate? That is exactly what Power over Ethernet (PoE) makes possible!

Like the standards for all our other tech today, the PoE standards have evolved over time. Here is a quick recap for you:

• ▸ IEEE 802.3af: This is the original 2003 standard, which provides up to 15.4 W of DC power per port.

• ▸ IEEE 802.3at: This 2009 standard (called PoE+) provides 25.5 W of power.

• ▸ IEEE 802.3bu: This 2016 amendment introduces single-pair Power over Data Lines (PoDL) and is used for industrial applications; power can be set from .5 W to 50 W.

• ▸ IEEE 802.3bt: This 2018 standard provides up to 100 W of power; such great power needs are required by some wireless access points and sophisticated surveillance cameras.

Various network equipment vendors have also deployed their own proprietary PoE implementations, with Cisco leading the pack. These early proprietary implementations drove adoption of PoE and put pressure on the IEEE to standardize it.

Serial Connections

Serial connections are legacy connections for device communication, and you will not see serial connections deployed in new installations today. However, you may still find them in use in data centers to make certain types of WAN connections. Unfortunately, selecting the correct serial cable can be a complicated business. Here are just some of the questions you must answer:

• ▸ Is the router being connected to a data terminal equipment (DTE) or data communications equipment (DCE) device?

• ▸ Is a male or female connector required on the cable?

• ▸ What signaling standard does the device require?

Although it is not necessary to review the dozens of serial cables you might encounter in a data center, please pay attention to the next ExamAlert.

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