CompTIA Network+ N10-008 Exam: Basics of Network Technologies, Topologies, and Types

This guide covers the following official Network+ objective:
- Explain the characteristics of network topologies and network types.

Topics:
Wired and Wireless Network Topologies
Bus Topology
Ring Topology
Star Topology (Hub-and-Spoke)
Mesh Topology
Hybrid Topology
Bringing Wireless to a Topology
Infrastructure Wireless Topology
Ad Hoc Wireless Topology
Wireless Mesh Topology
Network Types and Characteristics
To Server or Not
LANs
WLANs
WANs
MANs
CANs
SANs
PANs
SDWANs
MPLS
mGRE
Network Links and Concepts
DSL Internet Access
Cable Broadband
The Public Switched Telephone Network
Leased Lines
T3 Lines
Metro-Optical
Satellite Internet Access
Termination Points
Demarc, Demarc Extension, and Smart Jacks
CSUs/DSUs
Verify Wiring Installation and Termination
Virtual Networking

This guide covers CompTIA Network+ objective 1.2. 
A variety of physical and logical network layouts are in use today. As a network administrator, you might find yourself working on these different network layouts or topologies. Therefore, you must understand how they are designed to function.
This guide reviews general network considerations, such as the various topologies used on today’s networks, local-area networks (LANs), wide-area networks (WANs), and some of the Institute of Electrical and Electronics Engineers (IEEE) standards.

Wired and Wireless Network Topologies
- Explain the characteristics of network topologies and network types.

1. Which topology (star, bus, or ring) would utilize a switch?
2. With which topology does every node have a direct connection to every other node?

Answers:
1. Of the choices given, only a star topology would utilize a switch.
2. With a mesh topology, every node has a direct connection to every other node.

A topology refers to a network’s physical and logical layout. A network’s physical topology refers to the actual layout of the computer cables and other network devices. A network’s logical topology refers to the way in which the network appears to the devices that use it.

Several topologies are in use on networks today. Some of the more common topologies are the bus, ring, star, mesh, and wireless. The following sections provide an overview of each.

Bus Topology
A bus topology uses a trunk or backbone to connect all the computers on the network, as shown in the below figure. Systems connect to this backbone using T connectors or taps (known as a vampire tap, if you must pierce the wire). To avoid signal reflection, a physical bus topology requires that each end of the physical bus be terminated, with one end also being grounded. Note that a hub or switch is not needed in this installation.



Physical bus topology

Loose or missing terminators from a bus network disrupt data transmissions.
The most common implementation of a linear bus is the IEEE 802.3 Ethernet standard.

TABLE: Advantages and Disadvantages of the Bus Topology

Ring Topology
The ring topology is a logical ring, meaning that the data travels in a circular fashion from one computer to another on the network. It is not a physical ring topology. Figure 1.2 shows the logical layout of a ring topology. Note that a hub or switch is not needed in this installation either.



Logical design of a ring topology

In a true ring topology, if a single computer or section of cable fails, the signal is interrupted. The entire network becomes inaccessible. Network disruption can also occur when computers are added to or removed from the network, making it an impractical network design in environments where the network changes often.
As just mentioned, if a single system on the ring fails, the whole network fails. This is why ring networks can be set up in a fault-tolerant design, meaning that they have primary and secondary rings. If one ring fails, data can use the second ring to reach its destination. Naturally, the addition of the second ring adds to the cost of the network as well as the complexity.
Ring networks are most commonly wired in a star configuration. In a token ring network, a multistation access unit (MSAU) is equivalent to a hub or switch on an Ethernet network. The MSAU performs the token circulation internally. To create the complete ring, the ring-in (RI) port on each MSAU is connected to the ring-out (RO) port on another MSAU. The last MSAU in the ring is then connected to the first to complete the ring.
 

TABLE: Advantages and Disadvantages of the Ring Topology

Star Topology (Hub-and-Spoke)
In the star topology, all computers and other network devices connect to a central device called a hub or switch and, for that reason, is sometimes called a hub-and-spoke network. Each connected device requires a single cable to be connected to the hub or switch, creating a point-to-point connection between the device and the hub or switch.
Using a separate cable to connect to the hub or switch allows the network to be expanded without disruption. A break in any single cable does not cause the entire network to fail. 
Among the network topologies discussed in this guide, the star topology is the easiest to expand in terms of the number of devices connected to the network.



Star topology

The star topology is the most widely implemented network design in use today, but it is not without shortcomings. Because all devices connect to a centralized hub or switch, this creates a single point of failure for the network. If the hub or switch fails, any device connected to it cannot access the network. Because of the number of cables required and the need for network devices, the cost of a star network is often higher than other topologies.

TABLE: Advantages and Disadvantages of the Star Topology

Mesh Topology
The wired mesh topology incorporates a unique network design in which each computer on the network connects to every other, creating a point-to-point connection between every device on the network. Since this is often done physically, the term wired mesh or wired mesh topology is sometimes used. The purpose of the mesh design is to provide a high level of redundancy. If one network cable fails, the data always has an alternative path to get to its destination; each node can act as a relay.
The wiring for a mesh network can be complicated, as illustrated by the below figure . Furthermore, the cabling costs associated with the mesh topology can be high, and troubleshooting a failed cable can be tricky. As a result, the mesh topology is not the first choice for many wired networks but is more popular with servers/routers.



Mesh topology


Because of the redundant connections, the mesh topology offers better fault tolerance than other topologies.

TABLE: Advantages and Disadvantages of the Mesh Topology

Hybrid Topology
A variation on a true mesh topology is the hybrid or hybrid mesh. It creates a redundant point-to-point network connection between only specific network devices (such as the servers). The hybrid mesh is most often seen in WAN implementations but can be used in any network.
Another way of describing the degree of mesh implementation is by labeling it as either partial or full. If it is a true mesh network with connections between each device, it can be labeled full mesh, and if it is less than that—a hybrid of any sort—it is called a partial mesh network.
Many of the topologies found in large networking environments are a hybrid of physical topologies. An example of a hybrid topology is the star bus—a combination of the star topology and the bus topology.

The below figure shows how this might look in a network implementation.



A star bus topology

Another meaning: The term hybrid topology also can refer to the combination of wireless and wired networks. For the Network+ exam, however, the term hybrid most likely refers to the combination of physical networks.

Bringing Wireless to a Topology
When cabling is run from one office to another, you can easily look at the layout and see whether the topology is a star, mesh, bus, ring, or hybrid. When the wires are absent, however, then it may not be as readily apparent what is being deployed. Wireless networks typically are implemented using one of three wireless topologies:
- infrastructure, or managed, wireless topology
- ad hoc, or unmanaged, wireless topology
- mesh wireless topology
The following sections describe these three wireless topologies in greater detail.

Infrastructure Wireless Topology
The infrastructure wireless topology is commonly used to extend a wired LAN to include wireless devices. Wireless devices communicate with the wired LAN through a base station known as an access point (AP) or wireless access point. The AP forms a bridge between a wireless and wired LAN, and all transmissions between wireless stations, or between a system and a wired network client, go through the AP. APs are not mobile and have to stay connected to the wired network; therefore, they become part of the wired network infrastructure (thus the name). In infrastructure wireless networks, there might be several access points providing wireless coverage for a large area or only a single access point for a small area, such as a single home or small building.
WAP or AP? Notice that although we call it a wireless access point, it is commonly referred to as an AP. As you study for the exam, know that it can be called either an AP or a WAP, and—just to make matters confusing—WAP is also the acronym for the Wireless Application Protocol.

Ad Hoc Wireless Topology
In a wireless ad hoc topology, devices communicate directly among themselves without using an access point. This peer-to-peer network design is commonly used to connect a small number of computers or wireless devices. For example, an ad hoc wireless network may be set up temporarily between laptops in a boardroom or to connect systems in a home instead of using a wired solution. The ad hoc wireless design provides a quick method to share files and resources among a small number of systems. Connecting mobile devices together or to a printer using Bluetooth is an example of an ad hoc network.

The below figures show an ad hoc wireless network, and an infrastructure network using the AP.



Ad hoc wireless topology

The ad hoc, or unmanaged, network design does not use an AP. All wireless devices connect directly to each other.
In an infrastructure wireless network, devices use a wireless AP to connect to the network.



Infrastructure wireless topology

Wireless Mesh Topology
As discussed earlier, wired mesh networks are costly because of the cabling required to interconnect all computer systems. Wireless mesh networks obviously do not need cables running between systems, making wireless mesh networks fairly common in the networking world. In the wireless mesh network, as with the wired mesh, each network node is interconnected to other nodes on the network. With a wired mesh, the wireless signal starts at a wireless base station (access point) attached to a wired network. A wireless mesh network extends the transmission distance by relaying the signal from one computer to another. Unlike the wired mesh, in which a complex and expensive collection of physical cables is required to create the mesh, the wireless mesh is inexpensive to implement. Figure 1.8 shows a wireless mesh topology.
A wireless mesh network is created through the connection of wireless access points installed at each network user’s locale. Data signals in a wireless mesh rely on all nodes to propagate signals. Wireless mesh networks can be identified by the interconnecting signals between each node.




Network Types and Characteristics

1. True or false: The biggest difference between a LAN and a WAN is usually the size of the network.
2. What network type is essentially a LAN created to share data among devices associated with you?
3. In what networking type is consolidated, block-level data storage made available to networked devices?

1. True. A WAN is a network that spans more than one geographic location, often connecting separated LANs.
2. A personal-area network (PAN) is essentially a LAN created to share data among devices associated with you.
3. A storage-area network (SAN) makes block-level data storage available to devices on the network.
Networks are classified according to their geographic coverage and size. The two most common network classifications are local-area networks (LANs) and wide-area networks (WANs). Choosing between the two is often a matter of understanding the requirements.
For the exam, you should be able to differentiate between the various types of networks discussed here.

To Server or Not
Sometimes there is a tendency to take concepts that are simple and complicate them when there is no real need for it. The truth of the matter is that every network is either a peer-to-peer network or a client/server network and the difference between the two is whether or not there is a dedicated server. Any networking environment that does not have dedicated servers, and where communication occurs between similarly capable network nodes that act as both clients and servers, is a peer-to-peer network. Any network that has a dedicated server is a client/server network. Period.

LANs
A local-area network (LAN) is a data network that is restricted to a single geographic location and typically encompasses a relatively small area, such as an office building or school. The function of the LAN is to interconnect workstation computers for the purpose of sharing files and resources. Because of its localized nature, the LAN typically is high speed and cheaper to set up than a WAN. Figure 1.9 shows an example of a LAN.



A local-area network

WLANs
Instead of being wholly dependent on wiring for your local network, the wireless LAN (WLAN) provides a flexible and secure data communications system that augments an Ethernet LAN or, in some cases, replaces it altogether. Wireless transmissions send and receive data using radio frequency (RF) signals, freeing you from wired solutions, and are dependent on a hotspot. That hotspot can be in a coffee shop, a train station, a restaurant, or almost any public place. Security should be a prime concern of public hotspot users, and encryption should be used everywhere possible.
In a common wireless implementation, a wireless transceiver (transmitter/receiver), known as an access point, connects to the wired network from a fixed location using standard cabling. The wireless access point receives and then transmits data between the wireless LAN and the wired network infrastructure.
Client systems communicate with a wireless access point using wireless LAN adapters. Such adapters are built in to or can be added to laptops and other mobile devices or desktop computers. Wireless LAN adapters provide the communication point between the client system and the airwaves via an antenna.

WANs
A wide-area network (WAN) is a network that spans more than one geographic location, often connecting separated LANs. WANs are slower than LANs and often require additional and costly hardware, such as routers, dedicated leased lines, and complicated implementation procedures. Figure 1.10 shows an example of a WAN.



A wide-area network

MANs
Occasionally, a WAN will be called a metropolitan-area network (MAN) when it is confined to a certain geographic area, such as a university campus or city. No formal guidelines dictate the differences between a MAN and a WAN; technically, a MAN is a WAN. Perhaps for this reason, the term MAN is used less often than WAN. If any distinction exists, it is that a MAN is smaller than a WAN. A MAN is almost always bigger than a LAN and usually is smaller than or equal to a WAN. MANs utilize an Internet service provider (ISP) or telecommunications (telco) provider.

CANs
When it comes to terminology and definitions, a computer network in a defined area that links buildings and consists of multiple LANs within that limited geographical area is usually called a campus-area network (CAN). The CAN may encompass the whole college campus, or a portion of it. It may also have nothing to do with a college but consists of office buildings in an enterprise “campus,” industrial complex, military base, or anywhere else. In reality, a CAN is a WAN, but what makes it distinct is the confined geographic area it includes.

SANs
A storage-area network (SAN) consists of just what the name implies: networked/shared storage devices. With clustered storage, you can use multiple devices to increase performance. SANs are subsets of LANs and offer block-level data storage that appears within the operating systems of the connected devices as locally attached devices.
File systems built on top of SANs can provide file-level access, but the SAN itself does not provide file abstraction, only block-level operations.

PANs
A personal-area network (PAN) is essentially a LAN created to share data among devices associated with you. Wireless technologies have taken PAN further and introduced a new term—wireless personal-area network (WPAN). WPAN refers to the technologies involved in connecting devices in very close proximity to exchange data or resources, usually through the use of Bluetooth, infrared, or near-field communication (NFC). An example is connecting a laptop with a smartphone to synchronize an address book. Because of their small size and the nature of the data exchange, WPAN devices lend themselves well to ad hoc wireless networking. Ad hoc wireless networks are those that have devices connect to each other directly, not through a wireless access point.

SDWANs
A software-defined wide area network (SDWAN) is an extension of software-defined networking (SDN)—which is commonly used in telco and data centers—on a large scale. The concept behind it is to take many of the principles that make cloud computing so attractive and make them accessible at the WAN level. This is done by adopting a virtual WAN architecture leveraging a combination of transport services (MPLS, 5G, LTE, broadband, and so on) to connect users to applications.
Moving away from the router-centric WAN architecture that has always been used, SDWANs support applications hosted pretty much anywhere: public or private clouds, or on-premises data centers. As with an SDN, an SDWAN enables services on-demand, reduces operational costs, and is intended to improve network scalability and performance.
The SDWAN evolved from MPLS technology (which is explored next) and implements a centralized controller for setting and maintaining policies—managing the implementation.
For the exam, think of SDWAN as a software abstraction of MPLS technology
An SDN is a dynamic approach to computer networking intended to allow administrators to get around the static limitations of physical architecture associated with traditional networks. The goal of SDN is to not only add dynamic capabilities to the network but to also reduce IT costs through implementation of cloud architectures. SDN combines network and application services into centralized platforms that can automate provisioning and configuration of the entire infrastructure.

MPLS
Multiprotocol Label Switching (MPLS) is a WAN technology used in high-performance-based telco networks. MPLS is a technology that uses short path labels instead of longer network addresses to direct data from one node to another. These “labels” are used to identify shorter virtual links between nodes instead of endpoints. MPLS supports technologies such as ATM, Frame Relay, DSL, T1, and E1.
MPLS has been used for more than 20 years to provide secure, private connectivity, but it has limits to what it can do and is costly.
While SDWANs can utilizes MPLS technology, the goal is often to eliminate or minimize its usage due to cost. Administrators are often seeking lower-cost, higher-speed connectivity options (such as broadband and DSL).

mGRE
Multipoint Generic Routing Encapsulation (mGRE) is an extension of GRE (Generic Routing Encapsulation) that expands its capabilities. GRE can be configured as a point-to-point tunnel between two sites, and mGRE extends this capability from a limited number of sites by dynamically establishing tunnels without the need to explicitly configure mapping entries between each and every potential next-hop destination.
The exam objectives mix in a few protocols and technologies, such as mGRE and MPLS, with the network types and characteristics.

Network Links and Concepts
1. What is VHDSL commonly used for?
2. True or false: DSL using regular phone lines transfers data over the same copper wire.
3. What is the difference between a one-way and a two-way satellite system?
4. What hardware is located at the demarcation point?

1. VHDSL supports high-bandwidth applications such as VoIP and HDTV.
2. True. DSL using regular phone lines transfers data over the same copper wire.
3. A one-way satellite system requires a satellite card and a satellite dish installed at the end user’s site. This system works by sending outgoing requests on one link using a phone line, with inbound traffic returning on the satellite link. A two-way satellite system, in contrast, provides data paths for both upstream and downstream data.
4. The hardware at the demarcation point is the smart jack, also known as the network interface device (NID).
Internet access has become an integral part of modern business. You can obtain Internet access in several ways. Which type you choose often depends on the cost and what technologies are available in your area. This section explores some of the more common methods of obtaining Internet access.
The term broadband often refers to high-speed Internet access. Both DSL and cable modems are common broadband Internet technologies. Broadband routers and broadband modems are network devices that support both DSL and cable.

DSL Internet Access
Digital subscriber line (DSL) is an Internet access method that uses a standard phone line to provide high-speed Internet access. DSL was most commonly associated with high-speed Internet access, but is fading in popularity and availability. Because it is a relatively inexpensive Internet access, it is often found in homes and small businesses, but even there it is quickly being replaced by fiber. With DSL, a different frequency can be used for digital and analog signals, which means that you can talk on the phone while you upload data.
For DSL services, two types of systems exist: asymmetric digital subscriber line (ADSL) and high-rate digital subscriber line (HDSL). ADSL provides a high data rate in only one direction. It enables fast download speeds but significantly slower upload speeds. ADSL is designed to work with existing analog telephone service (POTS) service. With fast download speeds, ADSL is well suited for home-use Internet access where uploading large amounts of data isn’t a frequent task.
In contrast to ADSL, HDSL provides a bidirectional high-data-rate service that can accommodate services such as videoconferencing that require high data rates in both directions. A variant of HDSL is very high-rate digital subscriber line (VHDSL), which provides an HDSL service at very high data transfer rates.
DSL arrived on the scene in the late 1990s and brought with it a staggering number of flavors. Together, all these variations are known as xDSL:
- Asymmetric DSL (ADSL): Probably the most common of the DSL varieties is ADSL, which uses different channels on the line. One channel is used for POTS and is responsible for analog traffic. The second channel provides upload access, and the third channel is used for downloads. With ADSL, downloads are faster than uploads, which is why it is called asymmetric DSL.
ADSL2 made some improvements in the data rate and increased the distance from the telephone exchange that the line can run. ADSL2+ doubled the downstream bandwidth and kept all the features of ADSL2. Both ADSL2 and ADSL2+ are compatible with legacy ADSL equipment.
- Symmetric DSL (SDSL): A version that offers the same speeds for uploads and downloads, making it most suitable for business applications such as web hosting, intranets, and e-commerce. It is not widely implemented in the home/small business environment and cannot share a phone line.
- ISDN DSL (IDSL): A symmetric type of DSL commonly used in environments in which SDSL and ADSL are unavailable. IDSL does not support analog phones.
- Rate-adaptive DSL (RADSL): A variation on ADSL that can modify its transmission speeds based on signal quality. RADSL supports line sharing.
- Very high-bit-rate DSL (VHDSL or VDSL): An asymmetric version of DSL and, as such, can share a telephone line. VHDSL supports high-bandwidth applications such as VoIP and HDTV. VHDSL can achieve data rates up to approximately 10 Mbps, making it the fastest available form of DSL. To achieve high speeds, VHDSL uses fiber-optic cabling.
- High-bit-rate DSL (HDSL): A symmetric technology that offers identical transmission rates in both directions. HDSL does not allow line sharing with analog phones.
Why are there are so many DSL variations? The answer is quite simply that each flavor of DSL is aimed at a different user, business, or application. Businesses with high bandwidth needs are more likely to choose a symmetric form of DSL, whereas budget-conscious environments such as home offices are likely to choose an option that enables phone line sharing at the expense of bandwidth. In addition, some of the DSL variants are older technologies. Although the name persists, they have been replaced with newer DSL implementations. When you work in a home/small office environment where DSL is present, you are usually working with an ADSL system.


TABLE: DSL Speeds

*Speeds may vary greatly, depending on the technologies used and the quality of the connection.

For the exam, focus on ADSL as you study, but be able to put it in perspective with other varieties.
DSL using regular phone lines transfers data over the same copper wire. The data and voice signals are sent over different frequencies, but sometimes the signals interfere with each other. This is why you use DSL filters. A DSL filter works by minimizing this interference, making for a faster and cleaner DSL connection.
At the risk of being repetitive, it is worth pointing out again that DSL is fading in popularity as other technologies, such as cable and fiber, grow in marketplace adoption.

Cable Broadband
Cable broadband Internet access is an always-on Internet access method available in areas that have digital cable television. Cable Internet access is attractive to many small businesses and home office users because it is both inexpensive and reliable. Most cable providers do not restrict how much use is made of the access, but they do control the speed. Connectivity is achieved by using a device called a cable modem. It has a coaxial connection for connecting to the provider’s outlet and an unshielded twisted-pair (UTP) connection for connecting directly to a system or to a hub, switch, or router.
Cable providers often supply the cable modem, with a monthly rental agreement. Many cable providers offer free or low-cost installation of cable Internet service, which includes installing a network card in a PC. Some providers also do not charge for the network card. Cable Internet costs are comparable to DSL subscription.
Most cable modems offer the capability to support a higher-speed Ethernet connection for the home LAN than is achieved. The actual speed of the connection can vary somewhat, depending on the utilization of the shared cable line in your area.
A cable modem generally is equipped with a medium-dependent interface crossed (MDI-X) port, so you can use a straight-through UTP cable to connect the modem to a system.
One of the biggest disadvantages of cable access is that you share the available bandwidth with everyone else in your cable area. As a result, during peak times, performance of a cable link might be poorer than in low-use periods. In residential areas, busy times are evenings and weekends, and particularly right after school. In general, though, performance with cable systems is good, and in low-usage periods, it can be fast.
A debate between cable and DSL went on for many years. Although cable modem technology delivers shared bandwidth within the local neighborhood, its speeds are theoretically higher but influenced by this shared bandwidth. DSL delivers dedicated local bandwidth but is sensitive to distance that impacts overall performance. In recent years, DSL has faded in popularity as cable and fiber have grown.

The Public Switched Telephone Network
The public switched telephone network (PSTN), often considered a POTS, is the entire collection of interconnected telephone wires throughout the world. Discussions of the PSTN include all the equipment that goes into connecting two points, such as the cable, the networking equipment, and the telephone exchanges.
Although PSTN is not specifically listed as an exam objective, you need to know how it compares with other technologies. Know that if money is a major concern, the PSTN is the method of choice for creating a WAN.
The modern PSTN is largely digital, with analog connections existing primarily between homes and local phone exchanges. Modems are used to convert the computer system’s digital signals into analog so that they can be sent over the analog connection.
Using the PSTN to establish WAN connections is a popular choice, although the significant drawback is the limited transfer speeds. Transfer on the PSTN is limited to 56 Kbps with a modem and 128 Kbps with an ISDN connection, and it is difficult to share large files or videoconferencing at such speeds. However, companies that need to send only small amounts of data remotely can use the PSTN as an inexpensive alternative for remote access, particularly when other resources such as the Internet are unavailable.

Leased Lines
T-carrier lines are high-speed dedicated digital lines that can be leased from telephone companies. They create an always-open, always-available line between you and whomever you choose to connect to when you establish the service.
T-carrier lines can support both voice and data transmissions and are often used to create point-to-point private networks. Because they are a dedicated link, they can be a costly WAN option. Four types of T-carrier lines are available:
- T1: Offers transmission speeds of 1.544 Mbps and can create point-to-point dedicated digital communication paths. T1 lines have commonly been used for connecting LANs. In North America, DS (digital signal) notation is used with T-lines to describe the circuit. For all practical purposes, DS1 is synonymous with T1.
- T2: Offers transmission speeds of 6.312 Mbps. It accomplishes this by using 96 64-Kbps B channels.
- T3: Offers transmission speeds of up to 44.736 Mbps, using 672 64-Kbps B channels. Digital signal 3 (DS3) is a more accurate name in North America, but T3 is how most people refer to the link.
When you take the exam, think of DS3 and T3 as synonymous.
- T4: Offers impressive transmission speeds of up to 274.176 Mbps by using 4,032 64-Kbps B channels.
Of these T-carrier lines, the ones commonly associated with networks and the ones most likely to appear on the exam are the T1 and T3 lines.
Because of the cost of a T-carrier solution, you can lease portions of a T-carrier service. This is known as fractional T. You can subscribe and pay for service based on 64 Kbps channels.
T-carrier is the designation for the technology used in the United States and Canada. In Europe, they are called E-carriers, and in Japan, J-carriers.

TABLE: Comparing T/E/J Carriers

Ensure that you review the speeds of the T1, T3, E1, and E3 carriers.

T3 Lines
For a time, the speeds offered by T1 lines were sufficient for all but a few organizations. As networks and the data they support expanded, T1 lines did not provide enough speed for many organizations. T3 service answered the call by providing transmission speeds of 44.736 Mbps.
T3 lines are dedicated circuits that provide high capacity; generally, they are used by large companies, ISPs, and long-distance companies. T3 service offers all the strengths of a T1 service (just a whole lot more), but the cost associated with T3 limits its use to the few organizations that have the money to pay for it.

Metro-Optical
Metro-optical networks (also known as MONs) are optical networks that can span up to several hundred kilometers and are used to serve metropolitan areas in which there is a large, concentrated population. A metropolitan-area Ethernet (Ethernet MAN, or metro Ethernet network) is one form of a metro-optical network, with the typical service provider’s network including a collection of switches and routers connected through optical fiber.
Think of metro-optical as the “fiber to the home” connection. Many large metropolitan areas have undertaken initiatives to make this an affordable option for residents.
As a bit of background, in 1984, the U.S. Department of Justice and AT&T reached an agreement stating that AT&T was a monopoly that needed to be divided into smaller, directly competitive companies. This created a challenge for local telephone companies, which were faced with the task of connecting to an ever-growing number of independent long-distance carriers, each of which had a different interfacing mechanism. Bell Communications Research answered the challenge by developing Synchronous Optical Network (SONET), a fiber-optic WAN technology that delivers voice, data, and video at speeds starting at 51.84 Mbps. Bell’s main goals in creating SONET were to create a standardized access method for all carriers within the newly competitive U.S. market and to unify different standards around the world. SONET is capable of transmission speeds from 51.84 Mbps to 2.488 Gbps and beyond.
One of Bell’s biggest accomplishments with SONET was that it created a new system that defined data rates in terms of Optical Carrier (OCx) levels.

Be sure that you are familiar with OC-3 and OC-192 specific transmission rates.

TABLE: OCx Levels and Transmission Rates

Optical carrier (OCx) levels represent the range of digital signals that can be carried on SONET fiber-optic networks. Each OCx level defines the speed at which it operates.
Synchronous Digital Hierarchy (SDH) is the European counterpart to SONET.
When you take the exam, equate SDH with SONET.
A passive optical network (PON) is one in which unpowered optical splitters are used to split the fiber so it can service a number of locations, and it brings the fiber either to the curb, the building, or the home. It is known as a passive system because there is no power to the components and it consists of an optical line termination (OLT) at the split and a number of optical network units (ONUs) at the end of each run (typically near the end user). It can be combined with wavelength division multiplexing and is then known as WDM-PON.
A form of multiplexing optical signals is dense wavelength-division multiplexing (DWDM). This method replaces SONET/SDH regenerators with erbium-doped fiber amplifiers (EDFAs) and can also amplify the signal and enable it to travel a greater distance. The main components of a DWDM system include the following:
Terminal multiplexer
Line repeaters
Terminal demultiplexer

Make sure that you understand that DWDM works with SONET/SDH.
An alternative to DWDM is coarse wavelength-division multiplexing (CWDM). This method is commonly used with television cable networks. The main thing to know about it is that it has relaxed stabilization requirements; thus, you can have vastly different speeds for download than upload.
Make sure that you associate CWDM with television cabling.

Satellite Internet Access
Many people take DSL and cable Internet access for granted, but these technologies are not offered everywhere. Many rural areas do not have cable Internet access. For areas where cheaper broadband options are unavailable, a limited number of Internet options are available. One of the primary options is Internet via satellite. Recently, SpaceX has launched Starlink Internet satellites with the intent of increasing the number of low-cost global broadband capabilities.
Satellite access provides a viable Internet access solution for those who cannot get other methods of broadband. Satellite Internet offers an always-on connection with download speeds considerably faster than an old dial-up connection. Satellite Internet access does have a few drawbacks, though, such as cost and high latency. Latency is the time it takes for the signal to travel back and forth from the satellite.
Although satellite Internet is slower and costlier than DSL or cable, it offers some attractive features, the first of which is its portability. Quite literally, wherever you go, you have Internet access with no phone lines or other cables. For businesses with remote users and clients, the benefit is clear. But the technology has a far-reaching impact; it is not uncommon to see recreational vehicles (RVs) with a satellite dish on the roof. They have 24/7 unlimited access to the Internet as they travel.
Many companies offer satellite Internet services; a quick Internet search reveals quite a few. These Internet providers offer different Internet packages that vary greatly in terms of price, access speeds, and service. Some target businesses, whereas others aim for the private market.
Two different types of broadband Internet satellite services are deployed: one-way and two-way systems. A one-way satellite system requires a satellite card and a satellite dish installed at the end user’s site. This system works by sending outgoing requests on one link using a phone line, with inbound traffic returning on the satellite link. A two-way satellite system, in contrast, provides data paths for both upstream and downstream data. Like a one-way system, a two-way system uses a satellite card and a satellite dish installed at the end user’s site; bidirectional communication occurs directly between the end user’s node and the satellite.
Home satellite systems are asymmetric; that is, download speeds are faster than upload speeds. A home satellite system is likely to use a modem for the uplink traffic, with downloads coming over the satellite link. The exact speeds you can expect with satellite Internet depend on many factors. As with other wireless technologies, atmospheric conditions can significantly affect the performance of satellite Internet access. One additional consideration for satellite Internet is increased propagation time—how long it takes the signal to travel back and forth from the satellite. In networking terms, this time is long and therefore is an important consideration for business applications.

Termination Points
To work properly, a network must have termination points. These endpoints stop the signal and prevent it from living beyond its needed existence. For the exam, CompTIA wants you to be familiar with a number of termination-related topics, all of which are discussed in the sections that follow.

Demarc, Demarc Extension, and Smart Jacks
A network’s demarcation point is the connection point between the operator’s part of the network and the customer’s portion of the network. This point is important for network administrators because it distinguishes the portion of the network that the customer is responsible for from the section the owner is responsible for. For example, for those who have high-speed Internet, the boundary between the customer’s premises and the ISP typically is mounted on the wall on the side of the home. However, high-speed service providers support everything from the cable modem back to their main distribution center. This is why, if a modem fails, it is replaced by the ISP and not by the customer. This is true for the wiring to that point as well.
Knowing the location of the demarcation point is essential because it marks the point between where the customer (or administrator) is responsible and where the owner is. It also identifies the point at which the customer is responsible should a problem occur, and who should pay for that problem. The ISP is responsible for ensuring that the network is functional up to the demarcation point. The customer/administrator is responsible for ensuring that everything from that point is operational.
The demarcation point is the point at which the ISP places its services in your network. There is not always a choice of where this demarcation is placed. This means that a company might have six floors of offices, and the demarcation point is in the basement—impractical for the network. In this case you need a demarcation extension, which extends the demarcation point to a more functional location. This solution might sound simple, but it involves knowledge of cabling distances and other infrastructure needs. The demarcation extension might be the responsibility of the administrator, or for a fee, owners might provide extension services.
As you might imagine, you need some form of hardware at the demarcation point. This is the smart jack, also known as the network interface device (NID). The smart jack performs several primary functions:
- Loopback feature: The loopback feature is built in to the smart jack. Like the Ethernet loopback cable, it is used for testing purposes. In this case, the loopback feature enables remote testing so that technicians do not always need to be called to visit the local network to isolate problems.
- Signal amplification: The smart jack can amplify signals. This feature is similar to that of the function of repeaters in an Ethernet network.
- Surge protection: Lightning and other environmental conditions can cause electrical surges that can quickly damage equipment. Many smart jacks include protection from environmental situations.
- Remote alarms: Smart jacks typically include an alarm that enables the owner to identify if something goes wrong with the smart jack and therefore the connections at the demarcation point.
Demarcation point is the telephone company or ISP term for where their facilities or wires end and where yours begin.

CSUs/DSUs
A channel service unit/data service unit (CSU/DSU) acts as a translator between the LAN data format and the WAN data format. Such a conversion is necessary because the technologies used on WAN links are different from those used on LANs. Some consider a CSU/DSU a type of digital modem. But unlike a normal modem, which changes the signal from digital to analog, a CSU/DSU changes the signal from one digital format to another.
A CSU/DSU has physical connections for the LAN equipment, normally via a serial interface, and another connection for a WAN.
Traditionally, the CSU/DSU has been in a box separate from other networking equipment. However, the increasing use of WAN links means that some router manufacturers are now including CSU/DSU functionality in routers or are providing the expansion capability to do so.

Verify Wiring Installation and Termination
After a segment of network cable has been placed where it needs to go, whether run through the plenum or connecting a patch cable, the final task is wiring termination. Termination is the process to connect the network cable to the wall jack, plug, or patch panel. Termination generally is a straightforward process. You can quickly see if the wiring and termination worked if the LED on the connected network card is lit. Also, if you connect a client system, you can ping other devices on the network if all works.


Virtual Networking
Cloud computing is built on virtualization; it is the foundation on which cloud computing stands. At the core of virtualization is the hypervisor (the software/hardware combination that makes it possible to manage multiple virtual machines existing on one host). There are two methods of implementation: Type I (known as bare metal) and Type II (known as hosted). Type I is independent of the operating system and boots before the OS, whereas Type II is dependent on the operating system and cannot boot until the OS is up; it needs the OS to stay up so that it can operate. From a performance and scalability standpoint, Type I is considered superior to Type II.
Know that the hypervisor is used to manage multiple virtual machines (VMs) existing on one host.
The machine on which virtualization software is running is known as a host, and the virtual machines are known as guests.
Network function virtualization (NFV) is a method of virtualizing network services instead of running them on proprietary hardware: think routers, firewalls, and load balancers. These virtual services allow service providers to run their network on standard servers instead of proprietary ones—improving scalability, agility, and on-demand services without needing additional hardware resources.
Whereas once it was the case that hypervisors were the only way to have virtualization, now most people think of containers as their successor. You should know that the use of containers (a piece of software bundled with everything that it needs to run—code, runtime, system tools, system libraries, and so on) are becoming more common.
Cloud computing holds great promise when it comes to scalability, cost saving, rapid deployment, and empowerment. As with any technology where so much is removed from your control, however, risks are involved. Each risk should be considered and thought through to identify ways to help mitigate them. Data segregation, for example, can help reduce some of the risks associated with multitenancy. Common virtual network components include virtual network interface cards (vNICs), virtual routers and switches, shared memory, virtual CPUs, and storage (shared or clustered).
A NIC card within a machine can be either virtual or physical and will be configured the same. Existing on the virtual network, it must have an IP address, a MAC address, a default gateway, a subnet mask value, and can have a connection that is bridged or not. A vNIC is software only but allows interaction with other devices on the network. (The VLAN makes it possible for vNICs to communicate with other network devices.)
For the exam, you should be able to differentiate between the various virtualization concepts: hypervisor, network function virtualization (NFV), vNIC, and vSwitch.
In a discussion of virtual networking, it is important to note that so much of what is discussed is software based. Never forget that the goal of virtualization is to emulate physical environments and devices without actually having those physical elements.
Just as physical routers establish communication by maintaining tables about destinations and local connections, a virtual router works similarly but is software only. Remember that a router contains information about the systems connected to it and where to send requests if the destination is not known. These routing tables grow as connections are made through the router. Routing can occur within the network (interior) or outside it (exterior). The routes themselves can be configured as static or dynamic.
A virtual switch (vSwitch), similarly, is a software program that allows one virtual machine (VM) to communicate with another. The virtual switch allows the VM to use the hardware of the host OS (the NIC) to connect to the Internet and can be configured through an interface similar to the one shown in the below figure.



Virtual switch configuration

Switches are multiport devices that improve network efficiency. A switch typically contains a small amount of information about systems in a network—a table of MAC addresses as opposed to IP addresses. Switches improve network efficiency over routers because of the virtual circuit capability. Switches also improve network security because the virtual circuits are more difficult to examine with network monitors. The switch maintains limited routing information about nodes in the internal network, and it enables connections to systems such as a hub or a router.