Network Topologies
Bus, ring, star, and other types of network topology
In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.
Topology in Network Design
Think
of a topology as a network's virtual shape or structure. This shape
does not necessarily correspond to the actual physical layout of the
devices on the network. For example, the computers on a home
LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.Network topologies are categorized into the following basic types:
More complex networks can be built as hybrids of two or more of the above basic topologies.
Bus Topology
Bus
networks (not to be confused with the system bus of a computer) use a
common backbone to connect all devices. A single cable, the backbone
functions as a shared communication medium that devices attach or tap
into with an interface connector. A device wanting to communicate with
another device on the network sends a broadcast message onto the wire
that all other devices see, but only the intended recipient actually
accepts and processes the message.Ethernet bus topologies are
relatively easy to install and don't require much cabling compared to
the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both
were popular Ethernet cabling options many years ago for bus topologies.
However, bus networks work best with a limited number of devices. If
more than a few dozen computers are added to a network bus, performance
problems will likely result. In addition, if the backbone cable fails,
the entire network effectively becomes unusable.
Ring Topology
In a ring network, every device has exactly two
neighbors for communication purposes. All messages travel through a ring
in the same direction (either "clockwise" or "counterclockwise"). A
failure in any cable or device breaks the loop and can take down the
entire network.To implement a ring network, one typically uses FDDI,
SONET, or
Token Ring technology. Ring topologies are found in some office buildings or school campuses.
Star Topology
Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a
network hub,
switch or
router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.Compared
to the bus topology, a star network generally requires more cable, but a
failure in any star network cable will only take down one computer's
network access and not the entire LAN. (If the hub fails, however, the
entire network also fails.)
Tree Topology
Tree
topologies integrate multiple star topologies together onto a bus. In
its simplest form, only hub devices connect directly to the tree bus,
and each hub functions as the root of a tree of devices. This bus/star
hybrid approach supports future expandability of the network much better
than a bus (limited in the number of devices due to the broadcast
traffic it generates) or a star (limited by the number of hub connection
points) alone.
Mesh Topology
Mesh
topologies involve the concept of routes. Unlike each of the previous
topologies, messages sent on a mesh network can take any of several
possible paths from source to destination. (Recall that even in a ring,
although two cable paths exist, messages can only travel in one
direction.) Some
WANs, most notably the Internet, employ mesh routing.A
mesh network in which every device connects to every other is called a
full mesh. As shown in the illustration below, partial mesh networks
also exist in which some devices connect only indirectly to others.
Summary
Topologies
remain an important part of network design theory. You can probably
build a home or small business computer network without understanding
the difference between a bus design and a star design, but becoming
familiar with the standard topologies gives you a better understanding
of important networking concepts like hubs, broadcasts, and routes.
Comments
