Network Implementations

Hybrid Topologies

A hybrid topology is any topology that exhibits the characteristics of more than one standard topology. Each section of the network follows the rules of its own topology. Hybrid topologies can be complex to maintain because they typically incorporate a wide range of technologies. Most large networks consist of several smaller subnetworks, and each subnetwork may have a different topology.

Logical Bus Topology

A logical bus topology is a network topology in which nodes receive the data transmitted all at the same time, regardless of the physical wiring layout of the network. A common implementation is physical star-logical bus. In this topology, even though nodes connect to a central switch and resemble a star, data appears to flow in a single, continuous stream from the sending node to all other nodes through the switch. Because the transmission medium is shared, only one node can transmit at a time.N

Logical Ring Topology

A logical ring topology is a network topology in which each node receives data only from its upstream neighbor and retransmits data only to its downstream neighbor, regardless of the physical layout of the network. In a LAN, the logical ring topology has generally been implemented as a physical star (physical star-logical ring). In the days of token ring, a central hub (multistation access unit or MSAU) would connect the devices in a star shape, but the wiring was such that the electrical path was actually a never-ending loop, passing from the hub to a node, back to the hub, to another node, back to the hub, and so forth.

Physical Bus Topology

A physical bus topology is a network topology in which the nodes are arranged in a linear format, and a T-connector connects each node directly to the network cable.

Physical Mesh Topology

A physical mesh topology is a network topology in which each node is directly connected to every other node, similar to the physical point-to-point topology. This configuration allows each node to communicate with multiple nodes at the same time. All nodes have dedicated links with other nodes, so there is no congestion on the network and data travels very fast. Because no node can be isolated from the network, this topology is extremely reliable. It is also difficult to implement and maintain because the number of connections increases exponentially with the number of nodes. Mesh topologies typically provide reliable communications between independent networks.

Physical Ring Topology

A physical ring topology is a network topology in which each node is connected to the two nearest nodes: the upstream and downstream neighbors. The flow of data in a ring network is unidirectional to avoid collisions. All nodes in the network are connected to form a circle. There is no central connecting device to control network traffic, and each node handles all data packets that pass through it. Data moves in one direction through each node that scans data packets, accepts packets destined for it, and forwards packets destined for another node.

Physical Star Topology

A physical star topology is a network topology that uses a central connectivity device, such as a switch, with individual physical connections to each node. The individual nodes send data to the connectivity device, and the device then forwards data to the appropriate destination node. In legacy implementations, hubs were also used in physical star topologies, where nodes sent data to the hub, which simply passed it through to all attached nodes. Star topologies are reliable and easy to maintain, as a single failed node does not bring down the whole network. However, if the central connectivity device fails, the entire network fails.

Physical vs. Logical Topologies

A physical topology describes a network's physical wiring layout or shape, whereas a logical topology describes the paths through which data moves. The physical and logical topologies can be different for a network.

Star-ring

Connecting the central nodes of multiple star networks in a ring. The data flow between different subnetworks is through this ring. Data is sent in a circular pattern around the star configuration. Star-ring topologies are commonly found in metropolitan area networks (MANs).

Extended-star (or star-of-stars)

Connecting the central nodes of two or more star networks with a new common node. To move data from one subnetwork to another, it must be forwarded through the new common node. Extended star topologies are commonly found in LANs.

Star-bus

Linking the central nodes of several star networks by using a common bus, or network backbone. Inside each subnetwork, data flows as it would on a star network, and each of these star networks is treated as a node on the larger bus network. To move data from one subnetwork to another, it must be placed on the common bus. Star-bus topologies are commonly found in local area networks (LANs).

Termination

Termination is the application of a resistor or other device to the end of a cable. Adding a terminator ensures that the ends of the cable do not represent an abrupt change in impedance, causing signal reflections and noise. The electrical characteristics of a terminator must match those of the cable and other components.