A network topology describes the physical and logical layout of the network components. A physical network topology refers to the actual layout of computers, cables, and other networking devices. The network topology is determined by the connections between different components. A logical topology refers to the communication methods used by different components. The Network+ Exam covers the commonly used physical topologies: star, bus, mesh, ring, and wireless, described in the following sections.
(i) Star topology
In a star topology, computers (also called nodes) connect to each other through a central device, called a hub or a switch. Since each device is connected independently to the central device using a separate cable, the star network can be expanded at any time without affecting the operation of the network. Failure of one or more nodes also does not affect the network operation. The central device becomes the single point of failure because all nodes are connected to it. This topology is easy to implement, and its cost depends on the type of central device as well as the type of cable used to connect nodes. Figure shows a star network, and the advantages and disadvantages are described next.
(i) Star topology
In a star topology, computers (also called nodes) connect to each other through a central device, called a hub or a switch. Since each device is connected independently to the central device using a separate cable, the star network can be expanded at any time without affecting the operation of the network. Failure of one or more nodes also does not affect the network operation. The central device becomes the single point of failure because all nodes are connected to it. This topology is easy to implement, and its cost depends on the type of central device as well as the type of cable used to connect nodes. Figure shows a star network, and the advantages and disadvantages are described next.
Advantages
• A star network is easy to implement.
• It can be easily expanded without affecting the network operation.
• Failure of a single node or the connecting cable does not affect the entire net-work’s operation.
• It is easy to isolate nodes in order to troubleshoot problems.
Disadvantages
• Failure of the central device (hub or switch) can bring down the entire network.
• The length of cable required is much more than ring and bus networks because each node is connected separately.
• Cable length from the central device can be a limiting factor, depending on the type of cable used.
• A star network is easy to implement.
• It can be easily expanded without affecting the network operation.
• Failure of a single node or the connecting cable does not affect the entire net-work’s operation.
• It is easy to isolate nodes in order to troubleshoot problems.
Disadvantages
• Failure of the central device (hub or switch) can bring down the entire network.
• The length of cable required is much more than ring and bus networks because each node is connected separately.
• Cable length from the central device can be a limiting factor, depending on the type of cable used.
(ii) Bus topology
In a bus topology, all computers are connected to a shared communication line, called a trunk or a backbone. The computers are connected to the backbone using T-connectors. Both ends of the backbone use terminators in order to prevent reflection of signals. If the terminator is missing or is deliberately removed, the data transmissions are disrupted. There is no central device or any special configuration. Figure shows a bus network, and the advantages and disadvantages are described next.
In a bus topology, all computers are connected to a shared communication line, called a trunk or a backbone. The computers are connected to the backbone using T-connectors. Both ends of the backbone use terminators in order to prevent reflection of signals. If the terminator is missing or is deliberately removed, the data transmissions are disrupted. There is no central device or any special configuration. Figure shows a bus network, and the advantages and disadvantages are described next.
Advantages
• A bus network is the cheapest of all topologies.
• No special configuration is required.
• It is easy to install, and no special equipment is needed for installation.
• It needs less cable length than do other topologies.
Disadvantages
• A break in cable or a missing terminator can bring down the entire network.
• It is not possible to add or remove computers without disrupting the network.
• It is difficult to troubleshoot and administer.
• Addition of more computers degrades performance.
• A bus network is the cheapest of all topologies.
• No special configuration is required.
• It is easy to install, and no special equipment is needed for installation.
• It needs less cable length than do other topologies.
Disadvantages
• A break in cable or a missing terminator can bring down the entire network.
• It is not possible to add or remove computers without disrupting the network.
• It is difficult to troubleshoot and administer.
• Addition of more computers degrades performance.
(iii) Mesh topology
In a mesh topology, all computers in the network are connected to every other computer, forming a mesh of connections. Each computer makes a point-to-point connection to every other computer. This makes the network highly fault tolerant and reliable, as a break in the cable or a faulty computer does not effect network operation. Ad-hoc wireless networks fall into this category, as each connection is independent of the other. Data can travel from one computer to another using a number of paths. With the exception of wireless networks, mesh networks are very expensive in terms of the length of cable required to create multiple redundant connections. Figure shows a mesh network, and the advantages and disadvantages are described next.
In a mesh topology, all computers in the network are connected to every other computer, forming a mesh of connections. Each computer makes a point-to-point connection to every other computer. This makes the network highly fault tolerant and reliable, as a break in the cable or a faulty computer does not effect network operation. Ad-hoc wireless networks fall into this category, as each connection is independent of the other. Data can travel from one computer to another using a number of paths. With the exception of wireless networks, mesh networks are very expensive in terms of the length of cable required to create multiple redundant connections. Figure shows a mesh network, and the advantages and disadvantages are described next.
Advantages
•A mesh network is highly reliable because of redundant multiple paths between computers.
•The failure of a single computer or a cable fault does not affect network operations.
• Computers can be added or removed without affecting the network.
Disadvantages
• It is difficult to install and troubleshoot.
• It is very expensive because of the length of cable required to make multiple redundant connections.
• Only a limited number of computers can be connected in a mesh topology.
•A mesh network is highly reliable because of redundant multiple paths between computers.
•The failure of a single computer or a cable fault does not affect network operations.
• Computers can be added or removed without affecting the network.
Disadvantages
• It is difficult to install and troubleshoot.
• It is very expensive because of the length of cable required to make multiple redundant connections.
• Only a limited number of computers can be connected in a mesh topology.
(iv) Ring topology
In a ring topology, each computer is connected to its neighboring computer to form a logical ring. Data travels in the ring in a circular fashion from one computer to another, forming a logical ring. If one of the computers in the ring fails or if the cable is broken, the entire network becomes inaccessible. The addition or removal of computers also disrupts network transmissions. Ring networks are less efficient than star networks because of the fact that data must pass through each computer on the way to the destination. The physical layout of a ring network actually forms a star network. In a Token Ring network, a Multi Station Access Unit (MSAU),or Media Access Unit (MAU) acts as the central device or hub to process circulation of a special data packet called a Token. The MSAU has Ring In (RI) and Ring Out (RO) ports that facilitate connection of one MSAU to another MSAU for expanding the network. The last MSAU is connected to the first MSAU to complete the ring. Figure shows a ring network, and the advantages and disadvantages are described next.
In a ring topology, each computer is connected to its neighboring computer to form a logical ring. Data travels in the ring in a circular fashion from one computer to another, forming a logical ring. If one of the computers in the ring fails or if the cable is broken, the entire network becomes inaccessible. The addition or removal of computers also disrupts network transmissions. Ring networks are less efficient than star networks because of the fact that data must pass through each computer on the way to the destination. The physical layout of a ring network actually forms a star network. In a Token Ring network, a Multi Station Access Unit (MSAU),or Media Access Unit (MAU) acts as the central device or hub to process circulation of a special data packet called a Token. The MSAU has Ring In (RI) and Ring Out (RO) ports that facilitate connection of one MSAU to another MSAU for expanding the network. The last MSAU is connected to the first MSAU to complete the ring. Figure shows a ring network, and the advantages and disadvantages are described next.
Advantages
• A ring network is relatively easy to install.
• There are fewer collisions because only one computer transmits at a time.
Disadvantages
• A break-in cable or a faulty computer can bring down the entire network.
• It is not as efficient as a star network.
• It is difficult to troubleshoot a ring network.
• The addition or removal of computers can disrupt network operation.
(v) Wireless topologies
A wireless network connects two or more computers without using cables. To communicate with each other, these networks use spread spectrum technology, which is based on radio frequencies. Each device in the network is equipped with a wireless network adapter and is called a station. The area of communication is limited and is known as the basic service set. Wireless stations or clients can freely move within the basic service set. A wireless network can further be connected to a wired network with the help of wireless access Points (AP). The IEEE 802.11 standards define two main configurations of wireless communications: Ad-hoc and Infrastructure.
Ad-hoc wireless network. An Ad-hoc wireless network is also known as a peer-to-peer or an unmanaged wireless network. Two or more computers directly communicate to each other without using an access point. There is no central device (or hub), and these networks can be created spontaneously anywhere when two or more network devices fall within the range of each other. It provides the fastest way to temporarily connect computers and share resources. For example, two or more laptop computers can be connected in a conference room or in a cafeteria. Figure shows an ad-hoc network.
A wireless network connects two or more computers without using cables. To communicate with each other, these networks use spread spectrum technology, which is based on radio frequencies. Each device in the network is equipped with a wireless network adapter and is called a station. The area of communication is limited and is known as the basic service set. Wireless stations or clients can freely move within the basic service set. A wireless network can further be connected to a wired network with the help of wireless access Points (AP). The IEEE 802.11 standards define two main configurations of wireless communications: Ad-hoc and Infrastructure.
Ad-hoc wireless network. An Ad-hoc wireless network is also known as a peer-to-peer or an unmanaged wireless network. Two or more computers directly communicate to each other without using an access point. There is no central device (or hub), and these networks can be created spontaneously anywhere when two or more network devices fall within the range of each other. It provides the fastest way to temporarily connect computers and share resources. For example, two or more laptop computers can be connected in a conference room or in a cafeteria. Figure shows an ad-hoc network.
Infrastructure wireless networks. In an Infrastructure configuration, a central wireless device known as the access point (AP) is used to authenticate and configure wireless clients that fall within its range. Wireless clients communicate to each other through the AP. A special identifier known as a Service Set Identifier (SSID) must be configured on the AP and on each wireless client. All clients in one Infrastructure network use the same SSID. Different Infrastructure networks are identified by their unique SSIDs. The AP can further be connected to the wired local area network so that wireless clients can access the wired LAN also. Figure shows an infrastructure wireless network.
(vi) Tree Topology:
Tree topology is a LAN topology in which only one route exists between any two nodes on the network. The pattern of connection resembles a tree in which all branches spring from one root. Tree topology is a hybrid topology, it ie similar to tha star topology but the nodes are connected to the secondary hub, which in turn is connected to the central hub. Figure shows:
Tree topology is a LAN topology in which only one route exists between any two nodes on the network. The pattern of connection resembles a tree in which all branches spring from one root. Tree topology is a hybrid topology, it ie similar to tha star topology but the nodes are connected to the secondary hub, which in turn is connected to the central hub. Figure shows:
Advantages:
Installation and configuration of networks is easy
Less expensive when compared to mesh topology
Faults in the network can be detected traced
Supports multiple cable types like shielded twisted pair cable ordinary telephone cable etc.
Disadvantages:
Failure in the central hub brings the entire network to a halt
More cabling is required when compared to bus topology because each node is connected to the central hub.
Installation and configuration of networks is easy
Less expensive when compared to mesh topology
Faults in the network can be detected traced
Supports multiple cable types like shielded twisted pair cable ordinary telephone cable etc.
Disadvantages:
Failure in the central hub brings the entire network to a halt
More cabling is required when compared to bus topology because each node is connected to the central hub.
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