Comparing Full Duplex & Half Duplex Connections

Are you planning to take the Network+ exam? If so, make sure you understand the difference between half duplex and full duplex connections. These are the most common modes used for computers and network devices communication. Additionally, you should understand how to configure a switch using proper features in different scenarios.

For example, can you answer this question?

Q. What is created by separate switch ports?

A. Collisison domains

B. Broadcast domains

C. VLAN

D. ACL

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Duplex Connections and Collisions

Computers and network devices can typically communicate using different modes. The most common modes are half duplex and full duplex, but simplex mode is used in some specialized connections.

  • Simplex. Data is sent over the connection in one direction only. For example, a computer can send data over a simplex connection but not receive data on the same connection.
  • Half duplex. The same connection supports both transmitting and receiving but only one at a time. For example, while a computer is sending data over the connection, it cannot receive data on the same connection. This is similar to how push-to-talk cellular phones or old-fashioned walkie-talkies operate.
  • Full duplex. The same connection supports both transmitting and receiving simultaneously. The connection has separate wires used for both transmitting and receiving. This eliminates the possibility of data colliding with each other on the same cable. Most twisted pair cables and network interface cards (NICs) support full duplex mode, but some legacy hardware does not support it.

Learn more about common network  components mentioned in the Network+ objectives.

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The following figure shows a switch with two computers connected. Computer A has a full duplex connection, so it can use the same connection to send and receive data at the same time. Computer B is connected with a half duplex connection. It can send data to the switch using this connection, or receive data back from the switch on this connection, but it cannot send and receive data at the same time with this connection.

Full duplex

Full duplex and half duplex connections

Most interfaces support auto-negotiation for the correct duplex mode and speed. If both devices can operate using full duplex mode, they automatically configure themselves using full duplex mode. If one of the devices can only operate at half duplex mode, the other device will configure itself to use the slower half duplex mode.

If you run across a connection running in half duplex mode, check to see if one of the interfaces is manually configured to use half duplex. If it is, you can often change it to full duplex to increase the speed of the connections.

The connection will not work if both devices are manually configured with different modes. For example, the connection fails if one device is manually configured with half duplex and the other device is manually configured with full duplex. The link light on the devices will show that they are connected, but they won’t be transferring data back and forth between each other.

Remember This

Auto-negotiation automatically configures interfaces with the fastest duplex mode and speed of the other device. When using manual settings, both devices must be manually configured with the same duplex mode and speed or the connection fails.

There is a subtle point worth mentioning here. If you look at the full duplex connection in the figure, you can see collisions are impossible. The only way a collision can occur is if the same line is used to send and receive data, but you can see that the computer sends data on one line and receives data on the other line.

However, even though collisions are impossible if both devices are using full duplex mode, you should still think of each port on a switch creating separate collision domains, especially when taking the Network+ exam.


 

Q. What is created by separate switch ports?

A. Collision domains

B. Broadcast domains

C. VLAN

D. ACL

Answer is A is correct. A switch creates separate collision domains between each port and the device connected to the switch’s port.

All devices connected to a switch are in the same collision domain, so separate switch ports do not create different collision domains.

You can create separate virtual local area networks (VLANs) with a switch, but not all switches support VLANs so this isn’t the best answer

An access control list (ACL) is a group of rules used on a router or firewall to define network access.

You might like to check out these posts too:

Network Segments and Domains
Broadcast Domains and Collision Domains

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Network+ and Safety Precautions

If you’re planning on taking the Network+ exam, you should have a basic understanding of safety precautions when working on computers and networks.

For example, can you answer this question?

Q. Your organization recently purchased another company. Several administrators have inspected the server room at the new company and raised safety concerns. Specifically they state that the server room has a system that can remove all oxygen from the room and threaten the lives of anyone in the room. What is the purpose of this system?

A. ESD prevention

B. Safety of personnel

C. Temperature control

D. Fire suppression

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Fire Suppression

Network+ and Safety Precautions

You can fight fires with individual fire extinguishers, with fixed systems, or both. Most organizations included fixed systems to control fires and place portable fire extinguishers in different areas around the organization. A fixed system can detect a fire and automatically activate to extinguish the fire. Individuals use portable fire extinguishers to suppress small fires.

The different components of a fire are heat, oxygen, fuel, and a chain reaction creating the fire. Fire suppression methods attempt to remove or disrupt one of these elements to extinguish a fire.

You can extinguish a fire using one of these methods:

  • Remove the heat. Fire extinguishers commonly use chemical agents or water to remove the heat. However, you should never use water on an electrical fire.
  • Remove the oxygen. Many methods use a gas, such as carbon dioxide (CO2) to displace the oxygen. This is a common method of fighting electrical fires because CO2 and similar gasses are harmless to electrical equipment. However, when used in server rooms or data centers, they threaten the lives of employees so additional precautions are needed to ensure personnel exit before activating the fire suppression system.
  • Remove the fuel. Fire-suppression methods don’t typically fight a fire this way, but the fire will go out after all burnable material is gone.
  • Disrupt the chain reaction. Some chemicals can disrupt the chain reaction of fires to stop them.

Remember This

Fire suppression systems attempt to detect and extinguish fires. Systems that remove or displace all the oxygen in the room can potentially threaten the lives of personnel in the room, so should be considered with caution.

HVAC

Heating, ventilation, and air conditioning (HVAC) systems enhance the availability of systems. Computing and networking devices can’t handle drastic changes in temperatures, especially hot temperatures. If devices overheat, the chips can actually burn themselves out. HVAC systems also control humidity to help prevent ESD damage.

The cooling capacity of HVAC systems is measured as tonnage. This has nothing to do with weight, but instead refers to cooling capacity. One ton of cooling equals 12,000 British thermal units per hour (Btu/hour), and typical home HVAC systems are three-ton units. Higher-tonnage HVAC systems can cool larger areas or areas with equipment generating more heat.


Learn more about common safety precautions mentioned in the Network+ objectives.

Sign up for the free Networking Components course here.


The amount of air conditioning needed to cool a massive data center is much greater than you need to cool your home, primarily because of all the heat generated by the equipment. If your home air conditioner fails in the middle of summer, you may be a little uncomfortable for a while, but if the data center HVAC system fails, it can result in loss of availability and a substantial loss of money.

It’s common to mount computing and networking devices in installation racks (sometimes called bays or cabinets). These racks usually have locking doors in the front and rear for physical security. The doors have perforations allowing cold air to come in the front, passing over and through the devices to keep them cool. Slightly warmer air exits out the rear. Additionally, a server room has raised flooring with air conditioning pumping through the space under the raised floor.


 

Q. Your organization recently purchased another company. Several administrators have inspected the server room at the new company and raised safety concerns. Specifically they state that the server room has a system that can remove all oxygen from the room and threaten the lives of anyone in the room. What is the purpose of this system?

A. ESD prevention

B. Safety of personnel

C. Temperature control

D. Fire suppression

Answer is D. This scenario describes a fire suppression system.

An electrostatic discharge (ESD) prevention system includes tools and techniques to prevent ESD damage, but does not include the ability to remove oxygen from a room.

Removing oxygen from a room does not preserve safety of personnel. A Material Safety Data Sheet (MSDS) provides personnel with safety information about potentially hazardous materials, such as cleaning agents.

The Material Safety Data Sheet (MSDS) for the cleaning agent will provide the best information, such as first aid treatment.

Heating and ventilation air conditioning (HVAC) systems maintain proper temperature and humidity. They do not remove oxygen from a room.

Practice Test Questions To Help You Pass the Network+ Exam (N10-006) The First Time You Take It.

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Setting Up a Small Office Network

If you’re planning on taking the Network+ exam, you should have a basic understanding of the devices required in setting up a small office network.

For example, can you answer this question?

Q. You are helping a business owner set up small office network. Employees have ten laptops, each with Wi-Fi capabilities. The office has a DSL line. What equipment needs to be purchased? (Choose TWO.)

A. ISP

B. Wireless router

C. Modem

D. DSL balancer

E. Ten cables for the ten computers

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Modem

A modem (modulator/demodulator) converts digital and analog signals and is commonly used to provide Internet access through an Internet service provider (ISP). There are several types of modems available.

  • Cable modem. Many telecommunications companies sell subscriptions for cable television and use the same cable to provide users with an Internet connection. Cable Internet access has fast speeds and is commonly called broadband access. Broadband cable access is widely available in metropolitan areas, but not always available in rural locations.
  • Dial-up analog phone modem. In locations where broadband cable isn’t available, some users still use a dial-up connection and a phone modem. The phone modem connects via plain old telephone service (POTS) lines, which are widely available. Unfortunately, these connections are painfully slow due to the amount of traffic that most users download.
  • Digital subscriber line (DSL) modem. DSL modems provide significantly faster speeds than older phone modems but still use telephone lines. A DSL router includes the capabilities of a DSL modem and a router. Most DSL lines are asymmetric (ADSL), with the download link significantly faster than the upload link.

Remember This

Modems are a popular method of connecting to the Internet through an ISP. This includes cable modems and DSL modems.


Learn more about common network components.

Sign up for the free Networking Components course here.


Access Point

Most wireless networks use an access point to provide wireless devices access to a wired network. You’ll often hear an access point referred to as an AP or a wireless access point (WAP). The AP acts as a switch and connects all the devices into the same network.

Many APs include routing capabilities and are sold as wireless routers. These typically have physical ports similar to any switch allowing you to connect wired devices in addition to supporting wireless devices. The switch portion of the access point connects the devices on the network, and the routing portion of the access point connects networks together.

The following figure shows a typical network configuration in a small network using an AP with routing capabilities. The devices connected with a solid line are using wired connections. The devices connected with a dotted line are using wireless connections. The access point connects to the Internet via a modem and an ISP and all devices connected to the access point have Internet access through it.

Small Office Network

Wireless access point with routing capabilities

Other access points topics include:

  • Wireless standards such as 802.11g, 802.11n, and 802.11ac.
  • How to install and configure a wireless network
  • How to implement appropriate wireless security measures
  • How to troubleshoot common wireless problems
  • Common wireless threats, vulnerabilities, and mitigation techniques

 

Q. You are helping a business owner set up small office network. Employees have ten laptops, each with Wi-Fi capabilities. The office has a DSL line. What equipment needs to be purchased? (Choose TWO.)

A. ISP

B. Wireless router

C. Modem

D. DSL balancer

E. Ten cables for the ten computers

Answers are B and C. You would need to have a modem (more specifically, a digital subscriber line (DSL) modem) to connect to the DSL line. Additionally, you would need to have a wireless router to connect the ten laptops to the wireless router using wireless capabilities. You would then connect the wireless router to the DSL modem.

A small business owner does not need to purchase an Internet service provider (ISP), but would subscribe to Internet access through an ISP.

There is no such thing as a DSL balancer.

The ten wireless laptops connect wirelessly, so cables are not needed.

Practice Test Questions To Help You Pass the Network+ Exam (N10-006) The First Time You Take It.

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Decimal and Binary Number Systems

If you’re planning on taking the Network+ exam, you need to have a basic knowledge of numbering systems such as decimal. While this is basic knowledge, it is still important. If you haven’t used these numbering system in a while, they might be a little foggy.

For example, see if you can convert the following decimal numbers to four binary bits:

  • 1
  • 3
  • 5
  • 9

The answer is available at the end of this post.

Decimal

When reviewing many topics, it’s worth reviewing what you know and then connecting it to new topics. In this case, you should have a good understanding of decimal. Decimal numbers use a base of ten and include the numbers 0 to 9. Because it’s a base of 10, the next number after 9 is 10.

This shouldn’t be a surprise to anyone reading this book. However, it’s important to understand the underlying details of base 10.

The position of each number within base 10 has a different value such as 1, 10, 100, 1000, and so on. For example, consider the number 2,478. It has four numbers (2, 4, 7, and 8) but these numbers have significantly different values based on their place.

  • 2 is in the thousands place so it has a value of 2,000 (2 × 1000)
  • 4 is in the hundreds place so it has a value of 400 (4 × 100)
  • 7 is in the tens place so it has a value of 70 (7 × 10)
  • 8 is in the ones place so it has a value of 8 (8 × 1)

I’ve had students in the classroom try to make this difficult, but it doesn’t need to be. Imagine I offered you the choice of receiving $2,478 or $8,742. Which would you choose?

If you’re like most people, you recognize the first number is over $2,000 but the second number is over $8,000. Clearly, you would take the $8,000. The math behind it is that the 8 is in the thousands place so it represents 8 thousand dollars.

The table shows the underlying details using the base 10 number 2,478.

decimal

Base 10 Table

Note: Exams often use the caret (^) character instead of superscript so I’m using the caret here. In other words, 10^2 is the same as 102.

  • Column A is 10^3 or 10 × 10 × 10 (1,000).
    • With a value of 2, it equates to 2 × 1,000 (2,000).
  • Column B is 10^2 or 10 × 10 (100).
    • With a value of 4, it equates to 4 × 100 (400).

Learn more about other number systems such as binary, hexadecimal and octal.

Sign up for the free Networking Components course here.


Here are two important rules to know for any numbering system:

  • Any number raised to the power of 1 is itself so 10^1 is 10.
    • Column C is 10 ^ 1 (10).
    • With a value of 7, it equates to 7 × 10 (70).
  • Any number raised to the power of 0 is 1 so 10^0 is 1.
    • Column D is 10 ^ 0 (1).
    • With a value of 8, it equates to 8 × 1 (8).

Binary

Binary numbers use a base of 2 and include only the numbers 0 and 1. If you were to count with binary, it would look like this:

  • 0
  • 1
  • 10
  • 11
  • 100
  • 101

Just as decimal numbers have different values depending on their place, binary numbers also have different values depending on their place.

As an example, 2 raised to the power of 2 is the equivalent of 4 decimal (2 squared or 2 × 2). Most people know that 2 × 2 = 4. Similarly, 2 raised to the power of 3 is 8 (2 × 2 × 2). Table 1.2 shows several values for base 2, along with a binary number of 0000 1001.

Just as in base 10, base 2 follows these two rules:

  • Any number raised to the power of 0 is 1 so 2^0 is 1.
  • Any number raised to the power of 1 is itself so 2^1 is 2.
  A B C D E F G H
Base 2  2^7  2^6    2^5  2^4  2^3  2^2  2^1  2^0
Decimal Values 128 64 32 16 8 4 2 1
Binary Number 0 0 0 0 1 0 0 1
Binary Values 0 0 0 0 8 0 0 1

 Base 2 Table

  • The binary number 0000 1001 has four leading zeros (Columns A, B, C, and D), which can be ignored when calculating the binary value.
    • Similarly, the number 5 is the same as 0005. With 0005, we ignore the leading zeros.
  • Column E is 2^3 or 2 × 2 × 2 (8).
    • With a binary number of 1, it equates to 1 × 8 (8).
  • Columns F and G have 0 as the binary number so have a value of zero.
  • Column H is 2^0 or 1.
    • With a value of 1, it equates to 1 × 1 (1).

From a simpler perspective, the binary number of 0000 1001 equates to a decimal of number 9 (8 + 1).


Try This:

See if you can convert the following decimal numbers to four binary bits:

  • 1
  • 3
  • 5
  • 9

Answer. The following decimal numbers converted to four binary bits are:

  • 1 is 0001
  • 3 is 0011
  • 5 is 0101
  • 9 is 1001

Practice Test Questions To Help You Pass the Network+ Exam (N10-006) The First Time You Take It.

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Topology Using Coaxial Cable

If you’re planning on taking the Network+ exam, you should have a basic understanding of common network topologies such as a topology that uses coaxial cable.

For example, can you answer this question?

Q. You are a network technician for a small company. Another technician accidentally cut one of the cables effectively separating the network into two networks. Of the following choices, what type of network topology is this?

A. Bus

B. Mesh

C. Ring

D. Star

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Note that coaxial cable was once prevalent, but is rarely used in a commercial network today. However, you’ll still find it in some home Multimedia over Coax Alliance (MoCA) -based networks. MoCA networks connect devices using the same coaxial cable used to connect cable entertainment devices.

Bus Topology

A bus topology connects all devices together in a line. This is relatively easy to set up but is difficult to troubleshoot and rarely used as a primary network topology today. Bus topologies typically use coaxial cable. Thinner coaxial cable is used in ThinNet (10Base2) networks, and thicker coaxial cable is used in ThickNet (10Base5) networks.

One big difference with the bus topology compared with other topologies is that it requires a physical terminator at each end of the bus. Signals transmitted down the cable will reflect back if the terminator is missing, and the reflected signal interferes with all other transmissions. If one of the terminators is missing, it stops all network communications.

The following figure shows the logical layout of a bus topology. Each device has a “T” connector that connects into the NIC with a BNC and two open connections. On most devices in the bus, coaxial cable connects to these two open connections. On the last device at each end of the bus, the “T” connector includes a terminator. In the figure, the terminators and cable are disconnected from the “T” connectors so you can see the different components. You would see these connected in a live network.

 Coaxial Cable_1

Bus topology

One of the significant challenges with a bus topology is that it is difficult to troubleshoot when problems occur. If someone removes one of the terminators, disconnects any of the connectors, or accidentally cuts a cable within the network, the entire network fails. If your network has 100 computers, spread across three floors, you’d have to check each of them until you found the problem.

The following figure shows the result of a cable break in a bus topology. It effectively creates two separate bus networks and each network has only one terminator. When you have four computers in a bus topology, it won’t take too much time to locate this cable break. However, if you have dozens or even hundreds of computers, it becomes very difficult to identify the location of the break. As technicians are searching for the problem, none of the users will have access to any network resources.

 Coaxial Cable_2

Two non-functioning bus topologies due to a cable break

Remember This

A single break in the cable for a bus topology takes down the entire network. The break creates two networks and each network has only one terminator.


Learn more about  several common network topologies.

Sign up for the free Networking Components course here.


 

Q. You are a network technician for a small company. Another technician accidentally cut one of the cables effectively separating the network into two networks. Of the following choices, what type of network topology is this?

A. Bus

B. Mesh

C. Ring

D. Star

Answer: A is correct. Of the given choices, the only type of topology that separates a network into two networks is the bus topology. This cable break results in all devices on the network losing connectivity because of the two networks has only a single terminator.

A mesh network includes multiple redundant connections so a single break would not affect the network.

In a ring network, the devices are connected in a circle so a single break doesn’t create two networks.

Devices connect to a central device such as a hub or a switch in a star network and a single break does not create two networks.

Practice Test Questions To Help You Pass the Network+ Exam (N10-006) The First Time You Take It.

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Planning Networks

If you’re planning on taking the Network+ exam, you should have a good understanding of how to plan a network. For example, can you answer this question?

Q. A business owner hired you to help her create a basic network. Of the following choices, what would you do FIRST?

A. Purchase a switch and access point supported by the ISP

B. Identify the operating systems used within the network

C. Create a list of requirements and constraints

D. Upgrade computers within the network

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Planning Networks Lists

One of the first steps you’ll need to take when planning a basic network is to create a list of requirements for the network, and a list of devices to meet these requirements. You’ll consider the owner’s needs and desires, along with any constraints such as environmental or equipment limitations when creating this list. One of the first things that you’ll need to determine is if the business owner wants to use a wired network, a wireless network, or a combination of the two.

Remember This

One of the first things you’ll need to do when planning a basic network is to create a list of requirements and constraints. You should complete this list prior to making any purchases.


For a basic wired network, you would typically use the following devices:

  • Switch. The switch provides connectivity for all the devices in the network.
  • Router. The router connects the basic network to the Internet.
  • Firewall. The firewall provides a layer of protection for the internal network. For small networks, you will often use a device that functions as both a router and a firewall.
  • Internet access device. This might be a DSL or cable modem or another device depending on the ISP requirements.
  • Cables for wired connections. This includes cables from desktop PCs to a switch, a switch to a router, and a router to the Internet connection such as a cable modem. These are typically twisted pair cables with RJ-45 connectors.
  • NICs. While most computers have built-in NICs, you’ll need to ensure they meet the equipment requirements of the network. For example, if a desktop PC has a slower NIC, you might need to replace it with a newer, faster NIC.

Planning Networks

Remember This

A basic wired network needs at least one switch and cables to connect each device to the switch. If the basic network will connect to the Internet, you’ll also need at least one router, a cable to connect the switch to the router, and a cable to connect the router to the ISP device.


 

Q. A business owner hired you to help her create a basic network. Of the following choices, what would you do FIRST?

A. Purchase a switch and access point supported by the ISP

B. Identify the operating systems used within the network

C. Create a list of requirements and constraints

D. Upgrade computers within the network

Answer is C is correct. One of the first steps when creating any network, including a basic network, is to identify the requirements and constraints.

You should not purchase equipment until you identify what equipment is needed.

Most network devices are operating system independent so the type of operating systems running on the computers might not be relevant, and certainly isn’t as important as creating a list of requirements and constraints.

The computers probably don’t need to be upgraded but if they do, you would identify this in your list of requirements and constraints.

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CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

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