Download Network topology models.

Network Topologies
Lesson overview.
In this lesson, we will cover:
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What is a topology?
Peer-to-peer vs. client-server networks.
Network topology models.
What is a topology?
A topology is basically a map that can describe how a network is laid out or how the network
functions. The network topology can be described by either its logical or physical properties.
A logical topology describes the theoretical signal path, while a physical topology describes the
physical layout of the network. Most often, when we discuss topologies, we are discussing the
physical topology.
Peer-to-peer vs. client-server networks.
Are peer-to-peer and client-server really examples of topologies? The answer is both no and
yes. The answer is no, because they don’t describe the signal path or the physical layout of the
network. And the answer is also yes, because they describe how the network functions.
Peer-to-peer topology.
In a peer-to-peer network, the nodes, or computers, control and grant access to the resources
on the network. No one node, or group of nodes, controls access to a specific type of resource.
There is no server present in a peer-to-peer topology. Each node acts as its own server and is
responsible for the resources that it is willing to share.
Highlights:
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Nodes control and grant access to resources on the network.
Each node is responsible for the resources it is willing to share.
Client-server topology.
In a client-server topology, access to a network's resources is controlled by a central server (or
servers) and that central server (or servers) determines what resources get shared, who is
allowed to use those resources, and even when those resources can be used.
Highlights:
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Access to a network’s resources is controlled by a central server (or servers).
A central server (or servers) determines what resources get shared, who is allowed to
use the resources, and even when the resources can be used.
Hybrid topology.
It is possible to have a hybrid topology, in which some aspects of a client-server topology and a
peer-to-peer topology are combined. An example of this could be seen in a network that
contains a network file server and a desktop printer that is shared with multiple users. The file
server creates a client-server type topology, while the shared printer uses a peer-to-peer
topology.
Highlights:
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A combination of peer-to-peer and client-server networking.
Network topology models.
The original Ethernet standards established a bus topology for the network—both logically and
physically. As time went on, the bus developed some mechanical problems. That led to the
development of different physical topologies; however, the logical topology remained the same
in order to maintain backward compatibility.
When discussing Ethernet networks, the logical topology is always a bus topology, while the
physical topology can be different.
Highlights:
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The original Ethernet standards established a bus topology for the network, both
logically and physically.
When describing Ethernet networks, the logical topology is always a bus topology, while
the physical topology may be different.
Bus.
In a physical bus topology, the signal traverses from one end of the network to the other, always
back and forth. It follows the same path. A break in the line breaks the network. The ends of the
line have to be terminated with special resisters in order to prevent signal bounce, so when the
signal gets to the end of the network, it is absorbed by the resisters. The network cable is the
central point of a physical bus topology.
Highlights:
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In a bus topology, a break in the line breaks the network.
The ends of the line must be terminated in order to prevent signal bounce.
The network cable is the central point.
Ring.
The ring topology is a bus line with the endpoints connected together to create a ring. A break in
the ring breaks the network. Ring topologies are often implemented with multiple rings, often
two, that counter rotate. That way, if one ring breaks, the network still works, even though it will
be slower. Ring topologies are no longer very common in the local area network (LAN);
however, they are still widely used in the metropolitan area network (MAN) and the wide area
network (WAN).
Highlights:
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A ring topology is a bus line with the endpoints connected together.
Ring topologies are often implemented with multiple rings (often two) that counter rotate.
Not very common in the LAN any longer, but they are still used in the MAN and the WAN
(SONET especially).
Star.
The star topology is where the nodes radiate out from a central point. When implemented with a
switch, a break in a segment only brings down that segment. The star physical topology is the
most common implementation of the modern LAN. The central device is the focus for network
traffic.
Highlights:
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In a star topology, nodes radiate out from a central point.
When implemented with a switch, a break in a segment only brings down the segment.
It is the most common topology used in the modern LAN.
Mesh.
In a mesh topology, there are multiple connections between the nodes on a network. A full
mesh means that every node has a physical connection to every other node. A full mesh
topology creates a great deal of redundancy in the network, but is expensive to install—because
of the amount of wiring and because of the number of network interfaces required. It is also
difficult to maintain a full mesh, because there are so many pieces involved.
Rather than a full mesh, a partial mesh is often implemented. With a partial mesh, there are
multiple paths between nodes; however, not all of the nodes are physically connected to every
other node.
Highlights:
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Mesh topologies involve multiple connections between nodes on the network.
A full mesh means that every node has a physical connection to every other node.
A partial mesh means that there are multiple paths between nodes.
Point-to-point.
The point-to-point topology is where two nodes, or systems, are connected directly together. An
example is when two PCs are connected with a crossover cable. That creates a point-to-point
topology. If two routers are connected via a serial link, that is a point-to-point topology. No
central device is required to manage and maintain that connection. The point-to-point topology
is a common topology when implementing a WAN connection.
Highlights:
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In a point-to-point topology, two nodes or systems are connected directly together.
No central device is required to manage the connection.
It is a common topology when implementing a WAN connection.
Point-to-multipoint.
A point-to-multipoint topology is where a central device controls the path to all other devices. It
is different from the star in that the central device is intelligent and actually makes decisions as
to what data it will accept and where that data is going to go.
Wireless networks often implement a point-to-multipoint topology with wireless access points
and wireless routers. When the WAP sends, all devices on the network can receive that data.
When the device sends, its data is only passed along to the WAP, which then sends it along to
its destination. The point-to-multipoint topology is also a common topology when implementing a
WAN connection between networks.
Highlights:
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In a point-to-multipoint topology, a central device controls the paths to all other devices.
It differs from a star in that the central device is intelligent.
Wireless networks often implement point-to-multipoint topologies.
It is also a common topology when implementing a WAN connection.
What was covered.
What is a topology?
A topology is a map that can be used to describe the signal path or physical layout of a network.
The logical topology will describe the signal path, while the physical topology is more of a wire
schematic.
Peer-to-peer vs. client-server networks.
In peer-to-peer networking, there is no central control of network resources. Each node
determines what it will share and what it will not share. In client-server networking, there is
central control of shared network resources with a server controlling access. A network can
have aspects of both and, when this occurs, it is considered a hybrid topology.
Network topology models.
Ethernet networks are logical bus networks, regardless of the physical layout. In bus topology,
the signal goes end-to-end. Ring topology is a bus with the ends connected. In a star topology,
the nodes radiate out. Mesh topology is multipath. Point-to-point topology is a direct connection.
Point-to-multipoint topology is a single point going to multiple nodes.