Hybrid topology
A hybrid topology is a type of network topology that
uses two or more other network topologies,
including bus topology, mesh topology, ring topology, star topology,
and tree topology.
For example, if there exists a ring topology in one office
department while a bus topology in another department, connecting these two
will result in Hybrid topology. Remember connecting two similar topologies
cannot be termed as Hybrid topology. Star-Ring and Star-Bus networks are most
common examples of hybrid network.
Advantages of Hybrid Network Topology:
Advantages of Hybrid Network Topology:
Reliable: Unlike other networks, fault
detection and troubleshooting is easy in this type of topology. The part in
which fault is detected can be isolated from the rest of network and required
corrective measures can be taken, WITHOUT affecting the functioning of rest of
the network.
Scalable: Its easy to increase the size of network by
adding new components, without disturbing existing architecture.
Flexible: Hybrid Network can be designed according to the
requirements of the organization and by optimizing the available resources.
Special care can be given to nodes where traffic is high as well as where
chances of fault are high.
Effective: Hybrid topology is the combination of two or more
topologies, so we can design it in such a way that strengths of constituent
topologies are maximized while there weaknesses are neutralized. For example we
saw Ring Topology has good data reliability (achieved by use of tokens) and
Star topology has high tolerance capability (as each node is not directly
connected to other but through central device), so these two can be used
effectively in hybrid star-ring topology.
Disadvantages of Hybrid Topology
Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to design this type of architecture and its a tough job for designers. Configuration and installation process needs to be very efficient.
Disadvantages of Hybrid Topology
Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to design this type of architecture and its a tough job for designers. Configuration and installation process needs to be very efficient.
Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are different from usual hubs as they need to be intelligent enough to work with different architectures and should be function even if a part of network is down.
Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables, cooling systems, sophisticate network devices, etc.
Backbone
networks
A backbone network is a
larger transmission line that carries data gathered from smaller lines that
interconnect with it.
Backbone part of the
network is a core of the network with its high throughput capability and
significant bandwidth. It is made for the ability of network to communicate
with external networks (like Internet). It is a root of the network tree, that
has rest of the network growing from it.
At the local level, a backbone is a line or set
of lines that local area networks connect to for a wide area network connection
or within a local area network to span distances efficiently (for example,
between buildings).
On the
Internet or other wide area network, a backbone is a set of paths that local or
regional networks connect to for long-distance interconnection. The connection
points are known as network nodes or telecommunication data switching
exchanges (DSEs).
Serial Backbone
Serial
backbone is formed of two or more devices that are connected in a daisy chain
(linked series). It is a simplest kind of backbone. As the one can see from
Figure 1, serial backbone can be made not only from switches, but also from gateways
and routers.
While
designing the backbone, the one should consider the limit of the devices that
can be connected to the backbone in the repeating fashion. Exceeding the limit
would result in the unexpected errors and data loss in the network. Serial
backbone networks are not very fault tolerant and not very scalable, that make
them less commonly used that the distributed backbone.
Figure 1. Serial backbone.
Distributed Backbone
Distributed
backbone uses hierarchical design of the network, where number of intermediate
devices are connected to single or multiple connectivity devices. These central
connectivity devices could be switches or routers and shown with purple color
in Figure 2.
Figure 2. Simple distributed backbone.
This type of
backbone is easily scalable since new layers of devices can be added with no
troubles. Distributed backbone allows simple administration and management of
the network due to its segregation. This type of network can have daisy chain
linked devices for the backbone, however, designer should consider the same
limitations as for the serial backbone.
Figure 3
provides a view of more complicated distributed backbone that connects multiple
LANs together. LANs are interconnected with routers that form the backbone.
Figure 3. Distributed backbone that connects
multiple LANs.
Overall, it is cheap, easy, and quick to implement the distributed
backbone network.
Collapsed backbone
This type of
backbone uses single, powerful router as the central connection point for
multiple subnetworks. As Figure 4 shows, the central device is the highest
level of the backbone. It should have powerful computational power in order to
manage big traffic coming in. This is highly risky, since if the central device
fails, the whole network would be down. However, this type of backbone is
useful for the one who wants to interconnect two types of subnetworks, with
ability to manage and troubleshoot them.
Figure 4. Collapsed backbone.
Parallel backbone
Parallel
backbone is a variation of the collapsed backbone, where devices are having
more than one connection between them. As Figure 5 shows, there are multiple
connections between the high level routers and the network segments. Duplicate
connections ensure networks availability at anytime, higher speeds, and high
fault tolerance. Logical drawback of this solutions is the increased price,
since amount of required cabling is highly increased. It is not obligatory to
have duplicate connections between all the devices, selective implementation of
parallel structure would significantly lower the overall price and make
additional ports of the devices available.
Figure 5. Parallel backbone
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Switching
a switch determines from the physical device (Media Access Control or MAC)
address in each incoming message frame which output port to
forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip
to the intended destination.
Circuit Switching
In this
networking method, a connection called a circuit is set
up between two devices, which is used for the whole communication. Information
about the nature of the circuit is maintained by the network. The
circuit may either be a fixed one that is always present, or it may be a circuit that
is created on an as-needed basis. Even if many potential paths through
intermediate devices may exist between the two devices communicating, only one
will be used for any given dialog. This is illustrated in Figure 1.
Figure 1: Circuit Switching
In a circuit-switched network, before
communication can occur between two devices, acircuit is established between them. This is
shown as a thick blue line for the conduit of data from Device A to Device B, and a matching purple line from B back to A. Once set up, all communication
between these devices takes place over this circuit, even though there are other
possible ways that data could conceivably be passed over the network of devices
between them. Contrast this diagram to Figure 2.
Packet
Switching
In
this network type, no specific path is used for data transfer. Instead, the
data is chopped up into small pieces called packets and sent over the network. The packets
can be routed, combined or fragmented, as required to get them to their
eventual destination. On the
receiving end, the process is reversed—the data is read from the
packets and re-assembled into the form of the original data. A
packet-switched network is more analogous to the postal system than it is to
the telephone system (though the comparison isn't perfect.) An example is
shown in Figure 2.
Figure 2: Packet Switching
In
a packet-switched network, no circuit is set up prior to sending data
between devices. Blocks of data, even from the same file or
communication, may take any number of paths as it journeys from one device to
another.
Comparing
Circuit Switching and Packet Switching
A common
temptation when considering alternatives such as these is to ask which is
“better”—and as usually is the case, the answer is “neither”. There are places
where one is more suited than the other, but if one were clearly superior, both methods wouldn't
be used.
One important
issue in selecting a switching method is
whether the network medium is shared or dedicated. Your phone line can be used
for establishing a circuit because you are the only one who can use it—assuming you can keep that
pesky wife/husband/child/sister/brother/father/mother off the phone.
However, this
doesn't work well in LANs, which typically use a single shared medium and baseband signaling. If two devices were to
establish a connection, they would “lock out” all the other devices for a long
period of time. It makes more sense to chop the data into small pieces and send
them one at a time. Then, if two other devices want to communicate, their packets can be interspersed and
everyone can share the network.
The ability to
have many devices communicate simultaneously without dedicated data paths is
one reason why packet switching is becoming predominant today.
However, there
are some disadvantages of packet switching compared to
circuit switching. One is that since all data does not take the same, predictable path
between devices, it is possible that some pieces of data may get lost in
transit, or show up in the incorrect order. In some situations this does not
matter, while in others it is very important indeed.
While the
theoretical difference between circuit and packet switching is pretty
clear-cut, understanding how they are used is a bit more complicated. One of
the major issues is that in modern networks, they are often combined. For example, suppose you
connect to the Internet using a dial-up modem. You will be using IP
datagrams (packets) to carry higher-layer data, but it will be over the
circuit-switched telephone network. Yet the data may be sent over the telephone
system in digital packetized form. So in some ways, both circuit switching and
packet switching are being used concurrently.
Another
issue is the relationship between circuit and packet switching, and whether a
technology is connection-oriented or connectionless. The two concepts are related but not the same; the next
topic discusses this in much more detail.
