Home > Articles > Cisco Certification > CCNA Routing and Switching > CCNA Self-Study: Network Media (The Physical Layer)

CCNA Self-Study: Network Media (The Physical Layer)

Chapter Description

To determine what transmission media is right for particular networking enviornment you must consider organization's required throughput, cabling distance, noise resistance, security, flexibility and plans for growth.In this article Steve McQuerry highlights the concepts and procedures for assembling and cabling Cisco routers.

Upon completion of this chapter, you will be able to perform the following tasks:

  • Describe the primary types of network cabling, including shielded and unshielded twisted-pair, coaxial, fiber optics (multimode and single-mode), and wireless communications

  • Describe types and characteristics of cabling and connectors used in an Ethernet LAN

  • Describe the necessary components for enabling WAN connectivity over serial or ISDN BRI, local loop using DSL, and a cable connection for a Cisco router

This chapter examines several types of network media, including twisted-pair cable, coaxial cable, fiber-optic cable, and wireless. It highlights the concepts and procedures for assembling and cabling Cisco routers. This chapter also covers cabling and connectors used to interconnect switches and routers in a LAN or WAN. Finally, it presents factors that you should consider when selecting network devices.

Cabling and Infrastructure

Media is the actual physical environment through which data travels as it moves from one component to another, and it connects network devices. The most common types of net-work media are twisted-pair cable, coaxial cable, fiber-optic cable, and wireless. Each media type has specific capabilities and serves specific purposes.

Understanding the types of connections that can be used within a network provides a better understanding of how networks function in transmitting data from one point to another.

Twisted-Pair Cable

Twisted-pair is a copper wire-based cable that can be either shielded or unshielded. Twisted- pair is the most common media for network connectivity.

Unshielded twisted-pair (UTP) cable, as shown in Figure 4-1, is a four-pair wire. Each of the eight individual copper wires in UTP cable is covered by an insulating material. In addition, the wires in each pair are twisted around each other. The advantage of UTP cable is its ability to cancel interference, because the twisted-wire pairs limit signal degradation from electromagnetic interference (EMI) and radio frequency interference (RFI). To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies. UTP, as well as shielded twisted-pair (STP) cable, must follow precise specifications as to how many twists or braids are permitted per meter.

Figure 1Figure 4-1 Unshielded Twisted-Pair Cable

UTP cable is used in a variety of networks. When used as a networking medium, UTP cable has four pairs of either 22- or 24-gauge copper wire. UTP used as a networking medium has an impedance of 100 ohms, differentiating it from other types of twisted-pair wiring such as that used for telephone wiring. Because UTP cable has an external diameter of approximately 0.43 cm (0.17 inches), its small size can be advantageous during installation. Also, because UTP can be used with most of the major networking architectures, it continues to grow in popularity.

Several categories of UTP cable exist:

  • Category 1—Used for telephone communications; not suitable for transmitting data

  • Category 2—Capable of transmitting data at speeds of up to 4 Mbps

  • Category 3—Used in 10BASE-T networks; can transmit data at speeds up to 10 Mbps

  • Category 4—Used in Token Ring networks; can transmit data at speeds up to 16 Mbps

  • Category 5—Capable of transmitting data at speeds up to 100 Mbps

  • Category 5e—Used in networks running at speeds up to 1000 Mbps (1 Gbps)

  • Category 6—Consists of four pairs of 24-gauge copper wires that can transmit data at speeds up to 1000 Mbps

Shielded twisted-pair (STP) cable, as shown in Figure 4-2, combines the techniques of shielding and the twisting of wires to further protect against signal degradation. Each pair of wires is wrapped in a metallic foil. The four pairs of wires are then wrapped in an overall metallic braid or foil, usually 150-ohm cable. Specified for use in Ethernet network installations, STP reduces electrical noise both within the cable (pair-to-pair coupling, or crosstalk) and from outside the cable (EMI and RFI). Token Ring network topology uses STP.

Figure 2Figure 4-2 Shielded Twisted-Pair Cable

When you consider using UTP and STP for your network media, consider the following:

  • Speed of either media type is usually satisfactory for local-area distances.
  • Both are the least-expensive media for data communication. UTP is less expensive than STP.

  • Because most buildings are already wired with UTP, many transmission standards are adapted to use it to avoid costly rewiring with an alternative cable type.

Twisted-pair cabling is the most common networking cabling in use today; however, some networks still use older technologies like coaxial cable, as discussed in the next section.

Coaxial Cable

Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire conducting element. This section describes the characteristics and uses of coaxial cable.

As shown in Figure 4-3, the single inner wire located in the center of a coaxial cable is a copper conductor, surrounded by a layer of flexible insulation. Over this insulating material is a woven copper braid or metallic foil that acts both as the second wire in the circuit and as a shield for the inner conductor. This second layer, or shield, can help reduce the amount of outside interference. An outer jacket covers this shield. The BNC connector shown looks much like a cable-television connector and connects to an older NIC with a BNC interface.

Figure 3Figure 4-3 Coaxial Cable

Coaxial cable supports 10 to 100 Mbps and is relatively inexpensive, although more costly than UTP. Coaxial cable can be laid over longer distances than twisted-pair cable. For example, Ethernet can run approximately 100 meters using twisted-pair cable, but 500 meters using coaxial cable.

Coaxial cable offers several advantages for use in LANs. It can be run with fewer boosts from repeaters, which regenerate the signals in a network so that they can cover greater distances between network nodes than either STP or UTP cable. Coaxial cable is less expensive than fiber-optic cable, and the technology is well known. It has been used for many years for all types of data communication.

When you work with cable, consider its size. As the thickness, or diameter, of the cable increases, so does the difficulty in working with it. Cable must often be pulled through existing conduits and troughs that are limited in size. Coaxial cable comes in a variety of sizes. The largest diameter, frequently referred to as Thicknet, was specified for use as Ethernet backbone cable because historically it had greater transmission length and noise rejection characteristics. However, Thicknet cable can be too rigid to install easily in some environments because of its thickness. Generally, the more difficult the network media is to install, the more expensive it is to install. Coaxial cable is more expensive to install than twisted-pair cable, and Thicknet cable is almost never used except for special-purpose installations, where shielding from EMI or distance requires the use of such cables.

In the past, coaxial cable with an outside diameter of only 0.35 cm, sometimes referred to as Thinnet, was used in Ethernet networks. It was especially useful for cable installations that required the cable to make many twists and turns. Because Thinnet was easier to install, it was also cheaper to install. Thus, it was also referred to as Cheapernet. However, because the outer copper or metallic braid in coaxial cable comprised half the electrical circuit, special care needed to be taken to ground it properly, by ensuring that a solid electrical connection existed at both ends of the cable. Installers frequently failed to make a good connection. Connection problems resulted in electrical noise, which interfered with signal transmission. For this reason, despite its small diameter, Thinnet is no longer commonly used in Ethernet networks.

Although coaxial cable offers some distance advantages over twisted-pair, the disadvantages far outweigh the benefits. If a communications signal needs to travel a greater distance at high rates of speed, it is more common to use fiber-optic cable.

Fiber-Optic Cable

Fiber-optic cable is a networking medium capable of conducting modulated light trans-mission. This section describes the types, characteristics, and uses of fiber-optic cable.

Fiber-optic cable used for networking consists of two fibers encased in separate sheaths. Viewing it in cross section in Figure 4-4, you can see that each optical fiber is surrounded by layers of protective buffer material: usually a plastic shield, then a plastic such as Kevlar, and finally, an outer jacket that provides protection for the entire cable. The plastic conforms to appropriate fire and building codes. The purpose of the Kevlar is to furnish additional cushioning and protection for the fragile, hair-thin glass fibers. Where buried fiber-optic cables are required by codes, a stainless steel wire is sometimes included for added strength. Several connectors can connect fiber to the networking device; the most common is a SC connector, which has two optics, one connecting to transmit and the other connecting to receive.

Figure 4Figure 4-4 Fiber-Optic Cable

The light-guiding parts of an optical fiber are called the core and the cladding. The core is usually very pure glass with a high index of refraction. When a cladding layer of glass or plastic with a low index of refraction surrounds the core glass, light can be trapped in the fiber core. This process is called total internal reflection, and it allows the optical fiber to act like a light pipe, guiding light for long distances, even around bends. Fiber-optic cable is the most expensive of the three types discussed in this lesson, but it supports higher rate line speeds.

Fiber-optic cable does not carry electrical impulses as copper wire does. Instead, signals that represent bits are converted into pulses of light. Two types of fiber-optic cable exist:

  • Single-mode—Single-mode fiber-optic cable allows only one mode (or wavelength) of light to propagate through the fiber. This type of cable is capable of higher band-width and greater distances than multimode and is often used for campus backbones. Single-mode cable uses lasers as the light-generating method and is more expensive than multimode cable. The maximum cable length of single-mode cable is 60+ km (37+ miles).

  • Multimode—Multimode fiber-optic cable allows multiple modes of light to propa-gate through the fiber. Multimode cable is often used for workgroup applications, using light emitting diodes (LEDs) as light-generating devices. The maximum length of multimode cable is 2 km (1.2 miles).

The characteristics of the different media have a significant impact on the speed of data transfer. Although fiber-optic cable is more expensive, it is not susceptible to EMI and is capable of higher data rates than any of the other types of networking media discussed here. Fiber-optic cable is also more secure because it does not emit electrical signals that could be received by external devices.

NOTE

Even though light is an electromagnetic wave, light in fibers is not considered wireless because the electromagnetic waves are guided in the optical fiber. The term wireless is reserved for radiated, or unguided, electromagnetic waves.

In some instances, it might not be possible to run any type of cable for network communi-cations. This situation might be the case in a rented facility or in a location where you do not have the ability to install the appropriate infrastructure. In these cases, it might be useful to install a wireless network, as discussed in the next section.

Wireless Communications

Wireless networks are becoming increasingly popular, and they utilize a different type of technology. Wireless communication uses radio frequencies (RFs) or infrared waves to transmit data between devices on a LAN. For wireless LANs, a key component is the wireless hub, or access point, used for signal distribution. To receive the signals from the access point, a PC or laptop needs to install a wireless adapter card, or wireless network interface card (NIC). Figure 4-5 shows a number of wireless access points connected to an Ethernet backbone to provide access to the Internet.

Figure 5Figure 4-5 Wireless Access Points

Wireless signals are electromagnetic waves that can travel through the vacuum of outer space and through a medium such as air. No physical medium is necessary for wireless signals, making them a versatile way to build a network. They use portions of the RF spectrum to transmit voice, video, and data. Wireless frequencies range from 3 kHz to 300 GHz. The data-transmission rates range from 9 kbps to 54 Mbps. Figure 4-6 shows the electromagnetic spectrum chart.

Figure 6Figure 4-6 Electromagnetic Spectrum

You can differentiate electromagnetic waves by their frequency. Low-frequency electro-magnetic waves have a long wavelength (the distance from one peak to the next on the sine wave), while high-frequency electromagnetic waves have a short wavelength.

Some common applications of wireless data communication include the following:

  • Accessing the Internet using a cellular phone

  • Home or business Internet connection over satellite

  • Beaming data between two handheld computing devices

  • Wireless keyboard and mouse for the PC

Another common application of wireless data communication is the wireless LAN (WLAN), which is built in accordance with Institute of Electrical and Electronic Engineers (IEEE) 802.11 standards. WLANs typically use radio waves (for example, 902 MHz), microwaves (for example, 2.4 GHz), and infrared (IR) waves (for example, 820 nm) for communication. Wireless technologies are a crucial part of the future of networking.

Comparing Media Types

The choice of media type affects the type of network interface cards installed, the speed of the network, and the ability of the network to meet future needs. Table 4-1 compares the features of the common network media, including UTP, STP, coaxial cable, fiber-optic, and wireless connections.

Table 4-1 Comparing Media Types

Media Type

Maximum Segment Length

Speed

Comparative Cost

Advantages

Disadvantages

UTP

100 meters

10 Mbps

100 Mbps

Least expensive

Easy to install, widely available, widely used

Susceptible to interference; can cover only a limited distance

STP

100 meters

10–100 Mbps

More expen-sive than UTP

Reduced crosstalk, less susceptible to EMI than UTP or Thinnet

Difficult to work with; can cover only a limited distance

Coaxial

500 meters (Thicknet)

185 meters (Thinnet)

10–100 Mbps

Relatively inexpensive, but more costly than UTP

Less susceptible to EMI than other types of copper media

Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network

Media Type

Maximum Segment Length

Speed

Comparative Cost

Advantages

Disadvantages

Coaxial

500 meters (Thicknet)

185 meters (Thinnet)

10–100 Mbps

Relatively inexpensive, but more costly than UTP

Less susceptible to EMI than other types of copper media

Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network

Fiber-optic

3 km and further (single-mode)

2 km and further (multimode)

10–1000 Mbps (single-mode)

100 Mbps–9.92 Gbps (multimode)

Expensive

Cannot be tapped easily, so security is better; can be used over great distances; not susceptible to EMI; higher data rate than coaxial and twisted-pair

Difficult to terminate

Wireless

50 km—global

1–54 Mbps

Expensive

Does not require installation of media

Susceptible to atmospheric conditions


The media you choose has an important impact on the network's capabilities. You should consider all the factors before making your final selection.

2. Cabling and Infrastructure Section Quiz | Next Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020