Topologies
The physical dimensions and structure that defines a network is also known as its topology. Besides design and physical characteristics, you can also have a ‘logical’ dimension to the network that also forms part of its topology. The logical component is the part you don’t see, such as in a MAU or (Multi-Station Access Unit) that supports a logical ring within itself that you cannot physically see.
Bus Topology
The bus topology is a legacy standard that is in limited use and somewhat out-dated. It has all
nodes connect to the one cable, which is referred to as the ‘trunk’ or backbone, sometimes called the linear bus. The bus topology operates on the IEEE 802.3 standard. It has the advantage of being cheap to implement, but also incurs a distinct disadvantage, in that if the cable breaks, you lose connectivity.
The cabling used for the bus is usually coaxial or, 'COAX' for short. This cable must be terminated at each end to prevent signal reflectionand each joins via a BNC T-connector.
The bus topology is a legacy standard that is in limited use and somewhat out-dated. It has all
nodes connect to the one cable, which is referred to as the ‘trunk’ or backbone, sometimes called the linear bus. The bus topology operates on the IEEE 802.3 standard. It has the advantage of being cheap to implement, but also incurs a distinct disadvantage, in that if the cable breaks, you lose connectivity.
The cabling used for the bus is usually coaxial or, 'COAX' for short. This cable must be terminated at each end to prevent signal reflectionand each joins via a BNC T-connector.
The bus topology with terminators at each end.
Star Topology
A star topology has all nodes connect through a central device such as a hub or switch. Each node has its own line and should one fail, it will not disrupt the entire topology. In the physical sense, the star resembles the hub of a bicycle wheel and all the spokes are cables. At the end of each spoke
resides a node and all their communication goes through the central hub which resides in the middle.
The star topology is expensive to implement since it requires extra cabling, but it also easily accommodates expansion. The disadvantages are that everything connects via a central point, which is a single point of failure should the hub or switch fail. Obviously this would down the entire network.
Star topology with all nodes connected via a central hub.
Ring Topology
The ring topology is similar to the star topology in a physical sense but it is actually set around a ‘logical ring’ using a MAU or MSAU (multi-station access unit.) The MAU is serves as the
ring with each node connecting to it via ports on the MAU. The RI (ring-in) ports on the MAU are connected to the RO (ring-out) ports on another MAU forming the logical ring.
The IEEE 802.5 standard corresponds to the Token Ring network where the MAU circulates a logical token with-in the ring. As the token is circulated, it passes from node to node, this token piggy-backs the data, if the token is not destined for a node it will pass it on to the next node in the logical ring. This process continues until the destination node is reached.
In some cases it is possible to have a dual-ring topology where redundancy is offered because there are two rings, if one encounters a failure the other takes over. This configuration is also known as the 'self-healing ring.' Ring topologies are used in MANs (metropolitan area networks) but are fast becoming obsolete.
A cable break in the ring network may down the entire network.
In some cases it is possible to have a dual-ring topology where redundancy is offered because there are two rings, if one encounters a failure the other takes over. This configuration is also known as the 'self-healing ring.' Ring topologies are used in MANs (metropolitan area networks) but are fast becoming obsolete.
A cable break in the ring network may down the entire network.
Logical ring topology
Mesh Topology
The mesh topology offers the greatest amount of redundancy since it incorporates several redundant paths for communication. Being the most fault-tolerant network, also means having more cabling and equipment than any other network topology, this significantly increases costs.
There are two kinds of mesh topology, the full mesh and the partial mesh. The full mesh has more data paths and is extremely difficult to implement and troubleshoot. The partial mesh has less data paths and is often a simple combination of other topologies.
Hybrid Topology
A hybrid topology is a combination of other topologies. It is most common in enterprise networks where there is a requirement for scalability and some redundancy. Examples may include the star-ring and star-bus topology.