A broadband network consists of geographical parts. The topology of a network describes how the different parts of a network are connected. The most relevant topologies for the backbone and area networks are tree topologies, ring topologies and meshed topologies. For the first mile, two main basic topologies: point-to-multipoint (p2mp) and point-to-point (p2p).

A broadband network consists of geographical elements (horizontal dimension) which include 3 distinct parts:

  • Backbone network: Consists of a ring of fibre optic cable connecting different areas of the municipality or region. The ring topology has the advantage to be robust against single fibre cuts or other faults. More advanced topologies (e.g. meshed) are sometimes used in the backbone section of the network.
  • Area networks (i.e. backhaul): Connect several access nodes aggregating the local traffic further up in the network. Often implemented with a ring of optical fibre cable, although tree topologies can be used. If funds available for the moment are very limited the total end-users to be connected in the area are relatively few, microwave links may be used as a short- to medium-term solution.  
  • First-mile connections to the end-users: Links from the end users to the access nodes where the first traffic aggregation takes place. Each situation will present different logistic, economic and demographic conditions; hence different infrastructure solutions may be best suited.

Network infrastructure topologies

The topology of a network describes how the different parts of a network are connected. The most relevant topologies for the backbone and area networks are:

  • Tree: The traffic from each element is aggregated upwards in a hierarchical manner; a tree topology is generally cheaper, but less robust: in case of a fibre cut or other fault certain parts of the network will be disconnected for long periods of time; moreover for each step up the hierarchy, traffic originating from more nodes shares the same physical connection.
  • Ring: Each network element is connected to two elements in such a way that all connections form a ring. The ring topology has the advantage that any node is connected to two neighbouring nodes (this is sometimes referred as “redundancy”), so if a fibre cut or other fault occurs, traffic can be rerouted the other way often automatically, while the fault is repaired.<
  • Meshed: Each network element is connected to several other elements; this is the most robust but also most complex and most expensive topology.

Two main basic topologies for the first mile

  • Point-to-multipoint (p2mp): the first aggregation node is transmitting information to a number of end-users over the same shared medium, using one transmitter. This take place both in wireless communications but also in wired communications, if the physical medium is simply split along the way between the aggregation node and the end users (e.g. fibre point-to-multipoint used in PON, or coax cable TV networks): in this case the same physical signal is received by all end users, which are then sharing the bandwidth.
  • Point-to-point (p2p): the first aggregation node is transmitting information to a number of end-users over dedicated physical channels, using a corresponding number of transmitters. In wireless communications this can be achieved if the communication beams do not overlap with each other (radio links), while in wired communications a dedicated line connect the aggregation node with each end user (e.g. fibre point-to-point and telephone lines).

Published: 
23 April 2015
Last update: 
9 May 2017
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