Network Topologies

Circuit Switching

A circuit is set up between two devices, which is used for the whole communication. The circuit may either be a fixed one that is always present, or it may be a circuit that is created on an as-needed basis. Even if many potential paths through intermediate devices may exist between the two devices communicating, only one will be used for any given dialog.

Network Host

A computer or other device connected to a computer network

MAU (Media Access Unit/Multistation Access Unit)

A device used to connect multiple networks (typically star) in a token ring network. Each device on the ring is known as an attaching device. Each attaching device is connected to a MAU. The cable between the MAU and the attaching device is known as a lobe

Ring

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the ring acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring. When a device sends data, it must travel through each device on the ring until it reaches its destination. Every node is a critical link/SPOF. there is no server computer present; all nodes work as a server and repeat the signal.

Single Point of Failure (SPOF)

A part of a system that, if it fails, will stop the entire system from working.

Point-to-Point (Permanent/Dedicated)

A permanent link between two endpoints.

Repeater

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.

Linear Bus

All nodes connected to a common cable with exactly two endpoints

Endpoint

An endpoint device is an Internet-capable computer hardware device on a TCP/IP network.

Bus SPOF

Because only one cable is utilized, it can be the single point of failure.

Bus Pros and Cons

Because the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network.

Logical Topology Examples

Broadcast (Ethernet) or Token Passing

Frame

Data travels through networks inside units called frames, with each frame containing source and destination addresses.

Star Bus

Distributed bus network with two or more star topology "branches" connected to the bus trunk/backbone.

Star

Each network host (node) is connected to a central hub (called hub or switch) with a point-to-point connection. All traffic that traverses the network passes through the central hub.

Mesh (Fully Connected)

Each of the nodes is connected to each other.

Tree Pros and Cons

Easy to extend/scalable. Easy to control and identify issues. Failure of the root node or the backbone will bring the whole network down. Difficult to configure and maintain in extensive networks.

Token Passing

Empty data frames circulate around the ring. If a station wants to transmit, it receives the free token, discards it and replaces it with its own data frame. When a station then receives that data addressed to it, it marks the frame as received and passes it back out onto the network. The frame is received back at the originating station where it discards it and then releases a new free token onto the network which circulates around the ring until another system needs to send a message. This was seen by proponents as more efficient than Ethernet in handling messages and ensuring fewer "collisions" between transmitted data.

Bus

In local area networks where bus topology is used, each node is connected to a single cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data.

Distributed Star

Multiple Stars connected together in a linear fashion with no central/top level connection point

Packet Switching

No specific path is used for data transfer. Instead, the data is chopped up into small pieces called packets and sent over the network. The packets can be routed, combined or fragmented, as required to get them to their eventual destination. On the receiving end, the process is reversed—the data is read from the packets and re-assembled into the form of the original data. Info may be lost, but is not confined to one path and is useful for a network with more than a single sending and receiving device pair.

Extended Star

One or more repeaters between the hub and the nodes

Network Topology

Physical and logical.

Physical Topologies

Physical topology defines how the systems are physically connected.

Physical Network Topology Examples (7)

Point-to-Point, Bus, Star, Ring (Circular), Mesh, Tree, and Hybrid

Mesh (Partially Connected)

Some of the nodes of the network are connected the other nodes in the network with a single point-to-point link- this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

Hybrid Examples

Star Ring and Star Bus

Mesh network example

The Internet

TCP (Transmission Control Protocol)

The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message.

Logical Topologies

The logical topology defines how the systems communicate across the physical topologies. The logical topology defines how the data should transfer. (A logical topology is a concept in networking that defines the architecture of the communication mechanism for all nodes in a network. )

IP (Internet Protocol)

The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination.

Star Pros and Cons

The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

Distributed Bus

There are "branches" on the bus/backbone/trunk

Tree

Tree is type of network topology that is based on a hierarchy of nodes. Tree topology is a combination of Bus and Star topology. Nodes are connected in groups of star-configured workstations that branch out from a single "root". The root node usually controls the network and sometimes network traffic flow. Requires three levels of hierarchy to be considered this.

Token Ring/Star Ring

Two or more star topologies connected in a ring using a multi-station access unit (MAU) as a centralized hub.

Point-to-Point (Switched)

Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically and dropped when no longer needed. This is the basic mode of conventional telephony.

Bus Terminator

When the electrical signal reaches the end of the bus, the signal "echoes" back down the line, causing unwanted interference. As a solution, the two endpoints of the bus are normally terminated with a device called a terminator that prevents this echo.

Broadcast (Ethernet)

With Ethernet, data travels through the network inside units called frames. If data from multiple computers are transmitted at the same time and a collision happens, both stations have to wait a random amount of time before retransmitting the data. Waiting for a random time allows one of the workstations to retransmit first.