Describe the functions and practical applications of network topologies

• Network topology is the arrangement of devices (nodes) and connections (links) in a network.
• Topology can be:
  • physical topology
    • the actual arrangement of cables, routers, switches, and hardware
  • logical topology
    • how data flows across the network, regardless of physical layout

Star topology

• In a star topology, each device connects directly to a central device, usually:
  • a switch
  • a hub
  • a router
• Characteristics
  • all communication passes through the central device
  • the network has a star-like shape
• Reliability
  • reliability is generally high
  • if one cable or one end device fails, the rest of the network usually continues working
  • however, if the central device fails, the whole network may fail
• Transmission speed
  • usually fast
  • direct links between devices and the centre reduce delays
  • modern switches also reduce collisions effectively
• Scalability
  • good scalability
  • adding or removing a device is relatively easy
  • limited by the number of available ports on the central device
• Cost
  • can be expensive
  • each device needs its own dedicated connection to the centre
• Practical applications
  • home networks with a router or wireless access point in the centre
  • business LANs using central switches
  • school and office networks where centralized management is needed

Bus topology

• In a bus topology, all devices are connected to a single main communication line called the backbone cable (主干电缆).
• Characteristics
  • all devices share the same communication line
  • data travels along the backbone
  • terminators are needed at both ends to reduce signal reflection
• Reliability
  • reliability is lower than star or mesh
  • if the backbone cable fails, the whole network may fail
  • faults can be harder to locate
• Transmission speed
  • can be acceptable in small networks
  • performance drops as more devices send data at the same time
  • collisions are more likely because devices share one channel
• Scalability
  • limited scalability
  • adding more devices increases traffic and reduces performance
• Cost
  • relatively low cost
  • requires less cabling than star topology
• Practical applications
  • small or simple networks
  • older LAN designs
  • environments where low cost is more important than performance

Mesh topology

• In a mesh topology, devices connect directly to many other devices.
• Types of mesh:
  • full mesh
    • every node connects to every other node
  • partial mesh
    • nodes connect to some, but not all, other nodes
• Reliability
  • reliability is very high
  • if one connection or node fails, data can often be rerouted through another path
  • there is no single point of failure like a central switch
• Transmission speed
  • can be fast because multiple paths are available
  • however, speed depends on:
    • number of hops
    • traffic load
    • connection quality
• Scalability
  • can scale well in some wireless mesh systems
  • in fully connected mesh networks, adding nodes may greatly increase complexity
• Data collisions
  • collisions are uncommon
  • intelligent routing and multiple paths reduce traffic conflicts
• Cost
  • can be expensive, especially in full mesh systems
  • more links and more sophisticated hardware may be required
• Practical applications
  • modern Wi-Fi mesh systems in homes
  • community mesh networks providing internet in areas with limited infrastructure
  • manufacturing and warehousing systems where redundancy is important
  • sensor networks and industrial networks requiring resilience

Ring topology

• In a ring topology, each device is connected to two other devices, forming a closed loop.
• Characteristics
  • data travels around the ring from device to device
  • each device acts as a link in the path
• Reliability
  • reliability is moderate
  • if one device or connection fails, the ring may be disrupted unless the network has redundancy
• Transmission speed
  • can be efficient because data follows a structured path
  • collisions can be reduced in controlled ring systems
  • delay may increase as data passes through more nodes
• Scalability
  • moderate scalability
  • adding or removing devices may interrupt the network
• Cost and complexity
  • more complex than bus
  • usually less common in modern LAN design than star
• Practical applications
  • token ring style networks
  • specialized industrial or communication systems
  • situations where controlled access is important

Hybrid topology

• A hybrid topology combines features of two or more different topologies.
• It is designed to take advantage of the strengths of each topology used.
• Characteristics
  • can combine, for example:
    • star + mesh
    • star + bus
    • star + ring
  • different parts of the network can be designed for different needs
• Reliability
  • usually high
  • reliability depends on the topologies being combined
  • redundant paths from mesh-like sections can improve resilience
  • centralized sections can still support control and management
• Transmission speed
  • speed depends on the design
  • direct connections in some sections may improve performance
  • centralized sections may simplify traffic management
• Scalability
  • usually flexible
  • networks can be expanded by adding devices or segments in the most suitable topology
• Cost and complexity
  • may be more complex to design and manage
  • cost depends on the specific topologies and hardware involved
• Practical applications
  • large organizations where different departments need different network structures
  • enterprise networks with a star-based core and more redundant peripheral sections
  • environments where both resilience and centralized control are needed

Quick comparison

Topology	Advantages	Disadvantages	Common applications
Star	Fast, easy to manage, easy to expand, one device failure usually does not affect others	Central device is a single point of failure, more cabling needed	Home networks, offices, school LANs
Bus	Cheap, simple, uses less cabling	Backbone failure affects whole network, collisions, weak scalability	Small or older networks
Ring	Orderly transmission, can reduce collisions in controlled systems	A break can disrupt the network, harder to expand	Token ring and specialized systems
Mesh	Very reliable, redundant paths, strong fault tolerance	Expensive, complex, more links required	Mesh Wi-Fi, industrial and resilient networks
Hybrid	Flexible, combines strengths of multiple topologies	More complex to design and manage	Enterprise and large-scale networks