Topology Using Coaxial Cable

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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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