Network Topology and The Internet
By: Dave Amiana
Tags: Internet, Computer Science, Information Technology, Discrete Mathematics, Networking

1.1. Fundamental Elements of a Graphs: A brief overview of graph theory and network topologies

The abstraction of network topology is graph theory, that is, network topologies applies the notions established in graph theory.

What is graph theory: In discrete mathematics, graph theory is the study of graphs, which are mathematical structures used to model pairwise relations between objects. A graph in this context — does not pertain to a graph of a function (typically projected into some coordinate space) rather is made up of vertices (also called nodes or points) which are connected by edges (also called links or lines).

Whereas graph theory has a ton of stuff to offer into molding our basic knowledge of these topologies, our focus [in this article] is to build our understanding with some of the basic structures (topologies) of networks. So, this article will not discuss graph theory, in detail — if ever you are interested and want to build a deeper understanding with these networks I would recommend reading this article https://bit.ly/2yjWM5M.

Suffice to say, that the notion of vertices, edges, undirected (is a graph in which the two endpoints of each edge are not distinguished from each other.) and directed graphs (is one in which the edges have a distinguished direction, from one vertex to another) will help us understand the core concepts behind these topologies — introduced in the succeeding sections.

The very basic building block of the World Wide Web is built upon the concepts introduced here.

1.1.1. Bus topology (linear topology)

Bus Network Topology (source).

Bus topology is a network type in which every computer and network device is connected to a single cable. It transmits the data from one end to another in a single direction.

Note: No bidirectional feature is in a bus topology, meaning the data transmits only in one direction.

The Big Idea:

A host[2] on a bus network is called a station. In a bus network, every station will receive all network traffic, and the traffic generated by each station has equal transmission priority. A bus network forms a single network segment[3] and a collision domain[4]. In order for nodes to share the bus, they use a media access control technology such as carrier sense multiple access (CSMA) or a bus master.

Advantages

● It is easy to connect a computer or device and typically it requires less cable than a star topology.

○ Very easy to connect a computer or peripheral to a linear bus.

○ Requires less cable length than a star topology resulting in lower costs

○ The linear architecture is very simple and reliable

○ It works well for small networks

○ It is easy to extend by joining cable with connector or repeater

○ If one node fails, it will not affect the whole network

Disadvantages

● The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.

○ The entire network shuts down if there is a break in the main cable or one of the T-connectors break

○ A large number of packet collisions on the network, which results in high amounts of packet loss

○ This topology is slow with many nodes in the network

○ It is difficult to isolate any faults on the Network

1.1.2. Ring topology

Ring Network Topology (source).

Ring topology forms a ring connecting devices with its exactly two neighboring devices. Furthermore, a ring network (ring topology) is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node — a ring. Data travels from node to node, with each node along the way handling every packet.

Note: Rings can be unidirectional, with all traffic traveling either clockwise or anticlockwise around the ring, or bidirectional (as in SONET/SDH).

Advantages

● It can span larger distances than other types of networks, such as bus networks because each node regenerates messages as they pass through it.

○ A very orderly network where every device has access to the token and the opportunity to transmit

○ Performs better than a bus topology under heavy network load

○ Does not require a central node to manage the connectivity between the computers

○ Due to the point to point line configuration of devices with a device on either side (each device is connected to its immediate neighbor), it is quite easy to install and reconfigure since adding or removing a device requires moving just two connections.

○ Point to point line configuration makes it easy to identify and isolate faults.

○ Reconfiguration for line faults of bidirectional rings can be very fast, as switching happens at a high level, and thus the traffic does not require individual rerouting.

Disadvantages

● Aggregate network bandwidth is bottlenecked by the weakest link between two nodes.

○ One malfunctioning workstation can create problems for the entire network. This can be solved by using a dual ring or a switch that closes off the break.

○ Moving, adding and changing the devices can affect the network

○ Communication delay is directly proportional to the number of nodes in the network

○ Bandwidth is shared on all links between devices

○ More difficult to configure than a Star: node adjunction = Ring shutdown and reconfiguration

1.1.3. Star topology

Star Topology (source).

A star network is an implementation of a spoke–hub distribution paradigm[5] in computer networks. In a star network, every host is connected to a central hub. In its simplest form, one central hub acts as a conduit to transmit messages[6]. The hub can be passive ​in nature i.e., not intelligent hubs such as broadcasting devices, at the same time the hub can be intelligent known as active ​hubs. Active hubs have repeaters in them.

Advantages

● One malfunctioning node does not affect the rest of the network.

○ If one node or its connection breaks, it does not affect the other computers nor their connections

○ Devices can be added or removed without disturbing the network

○ Works well under heavy load

○ Appropriate for a large network

Disadvantage

● If the central computer fails, the entire network becomes unusable.

○ Expensive due to the number and length of cables needed to wire each host to the central hub

○ The central hub is a single point of failure for the network

1.1.4. Mesh topology

Partially connected Mesh Topology (source).

A mesh network (or simply meshnet) is a local network topology in which the infrastructure nodes (i.e. bridges, switches, and other infrastructure devices) connect directly, dynamically and non-hierarchically to as many other nodes as possible and cooperate with one another to efficiently route data from/to clients. This lack of dependency on one node allows for every node to participate in the relay of information. Mesh networks dynamically self-organize and self-configure, which can reduce installation overhead. The ability to self-configure enables the dynamic distribution of workloads, particularly in the event a few nodes should fail. This, in turn, contributes to fault-tolerance and reduced maintenance costs.

There are two types of mesh topology: Full mesh topology — which occurs when every node has a circuit connection it to every other node in a network — and partial mesh topology — which is less expensive to implement, and also yields less redundancy.

Note: Mesh topology may be contrasted with conventional star/tree local network topologies in which the bridges/switches are directly linked to only a small subset of other bridges/switches, and the links between these infrastructure neighbors are hierarchical. While star-and-tree topologies are very well established, highly standardized and vendor-neutral, vendors of mesh network devices have not yet all agreed on common standards, and interoperability between devices from different vendors is not yet assured

1.1.5. Hybrid topology

A hybrid topology is a collection of two or more topologies that are described above. This is a scalable topology that can be expanded easily. It is a reliable one but at the same time, it is a costly topology.