Lab 5.1: Identifying Network Topologies, Cables, and Connectors

Upon completion of this lab, you will be able to:

• Determine the local topology of your network

• Identify network cables and connectors

Before we begin, you need to know a few networking basics.

Topologies

A topology describes the general layout of the network connections. LANs use several types of physical topologies (cable connection variations) and logical topologies (how the network messages travel). You should be able to identify the following networking configurations:

Bus Topology The bus topology has a single cable that runs to every computer in the network. Hubs or switches are not needed; however, repeaters are used to extend network length.

Star Topology The star topology uses a hub or switch as a central connection device. Every computer in the network is connected to the central connection device. The star is cheap, easy to install, easy to reconfigure, and fault tolerant. Hubs and switches can be connected together to extend the network.

Ring Topology In a physical ring topology, each computer is connected to two other computers to form a circle. The physical ring is difficult to reconfigure, and the entire network goes down if any computer is removed from the ring.

Logical rings connect the computers to a central connection device called a multistation access unit (MAU or MSAU). The MAU creates the ring in its circuitry, thereby making the ring easier to configure and manage. MAUs can be connected using the Ring In and Ring Out ports to extend the network.

Mesh Topology In the mesh topology, each device is connected to every other device with a direct cable connection. The mesh is very difficult to construct and reconfigure. However, it is very fault tolerant.

Hybrid Topology A hybrid topology is a mixture of networks, each using its own topology. The hybrid topology uses the best features of each topology.

Media Access Methods

A media access method is the way the computer accesses the physical medium. It lays out the rules of when and how a computer can put packets onto the network. You should be able to identify the various media used to connect a network:

Ethernet Ethernet uses an access protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Carrier Sense means that the computer listens to see if anyone else is already talking when it wants to put a packet on the wire. Multiple Access allows all the computers to listen at the same time; and, all the computers have equal access to the media. Because all computers have equal access, two computers will frequently attempt to put packets on the media at the same time. When this happens, a collision occurs. Both computers listen to detect if a collision has occurred. If it has, both computers stop transmitting and time themselves out for a random period before they listen again to see if they are clear to transmit. The Ethernet media is the wire that carries the signal between computers. It is often called the wire even though some media is wireless.

Token Ring Token Ring uses a token on the network to control when and how computers are allowed to put a packet on the wire. A free token is passed on the network from one computer to the next in line. When a computer receives the free token, it either passes it to the next computer, if it has nothing to transmit, or it captures the token and then loads a packet into the token. As the loaded token is passed from computer to computer, each one looks at the token’s header to see if the token is for that computer. If the computer is not the destination computer, the token is retransmitted to the next computer in line. When the destination is reached, the destination computer places an acknowledgement on the token and sends it back to the source computer. When the source computer gets the acknowledgement back, the token is released by simply flipping the two bits on the token.

Thicknet 10Base5 Thicknet gets its name from the size of the wire that is used. It is a coaxial cable with a center core wire that is insulated and shielded to reduce the amount of electromagnetic interference (EMI). Its cable can extend 500 meters without needing a repeater. It is used primarily to create a bus topology frequently called a backbone, because of the distance the signal can travel and its immunity to interference. Thicknet is very rigid, which makes it difficult to work with. Computers connect to the cable using a vampire tap that pierces the insulation and shielding. The network adapter has an AUI connector.

Thinnet 10Base2 Thinnet also gets its name from the size of the wire used. It is a coaxial cable but thinner than the cable used in Thicknet. Its cable can carry a signal 185 meters. Computers use a BNC T-connector to attach themselves to the network. The network adapter also uses a BNC connector.

Twisted Pair 10/100BaseT The most popular type of cable in use today is twisted pair. It comes in two basic varieties: shielded and unshielded. Shielded twisted pair (STP) uses a wire mesh shield to help protect the wire from EMI. Unshielded twisted pair (UTP) uses the twists in the pairs to reduce the amount of cross talk. The network adapter uses an RJ-45 connector.

Fiber Optic 100BaseFL Fiber optic has two main advantages over copper cable. First, fiber can extend greater distances—up to 2,000 meters. Second, it is immune to EMI because it uses light pulses instead of electrical signals.

Set Up

For this exercise, you will need a network-ready computer.

Exercise

In this lab, you will explore the different types of topologies, cables, and connectors.

1. Draw an example of a bus topology.

2. Draw an example of a ring topology.

3. Draw an example of a star topology.

4. Examine the back of your computer and determine the type of network cable used. You will probably find an RJ-45 connector on Category 5, twisted pair cable. The RJ-45 connector looks much like a telephone connector, but it is larger. You may find a coaxial cable that looks like a cable television cable. The coaxial cable is commonly used in a 10Base2 (Thinnet) network. Record the type of cable found:

5. Trace the network wiring and try to determine the physical topology of your network. Record the topology.