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Physical topologies for metro networks The wavelengths added and dropped, which
The physical topology of a network is
defined by how the nodes are physically
connected to each other. Many types of
architectures are considered for metro
networks, such as meshed, chains, and
horseshoes.
In figure 2, two usual topologies used in
metro networks, the ring and horseshoe
topologies, are represented.
The metro network infrastructure usually
comprises physical ring topologies
interconnecting the nodes, with one or two
nodes attached to the core.
Figure 2: Physical topologies examples.
Source: The author
Another topology, known as the horseshoe
topology, is also used for MAN networks. This
topology, represented with more detail in figure
3, is also referred to as an open ring topology,
since there are two nodes connected to the
core network, including several intermediate
metro-access node points, known as tributary
nodes and represented by N1, in figure 3.
Each node N1 usually includes a connection
leading to an array of local Transmitter (Tx) and
Receiver (Rx) and corresponds to the interface
between the access network (client) and the
metro network.
are necessary for the communication between
the network and clients, occur at these nodes.
In addition, these nodes are connected to
central nodes of the metro network, known as
hub nodes, that N2 represents in figure 3, which
are colocated with a transport network optical
node.
Figure 3: Example of a metro network composed by
6 horseshoe networks interconnected by a mesh
network, where DL stands for downlink and UL
stands for uplink (Source 1) .
The function of nodes N2 is to interface and
provide connections between the nodes N1
and the metro-core nodes and ensure the
downlink and uplink directions in the
horseshoe network. The downlink represents
the transmission from N2 to N1, and the uplink
direction represents the data transmission
from N1 to N2. Two unidirectional fibers are
typically used to implement these downlink
and uplink communications.
So, the network represented in figure 3,
comprises two metro-core edge nodes having
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