Computer Network
Computer network
- A computer network is a set of
devices connected through links. A node can be computer, printer, or any other
device capable of sending or receiving the data. The links connecting the nodes
are known as communication channels.
- Addresses are numeric quantities that are easy for computers to work with, but not for humans to remember.
Example:
204.160.241.98
1. Bus
Topology
- The
bus topology is designed in such a way that all the stations are connected
through a single cable known as a backbone cable.
- Each
node is either connected to the backbone cable by drop cable or directly
connected to the backbone cable.
- When
a node wants to send a message over the network, it puts a message over
the network. All the stations available in the network will receive the
message whether it has been addressed or not.
- The
bus topology is mainly used in 802.3 (Ethernet) and 802.4 standard
networks.
- The
configuration of a bus topology is quite simpler as compared to other
topologies.
Advantages of Bus topology:
- Low-cost: In bus
topology, nodes are directly connected to the cable without passing
through a hub. Therefore, the initial cost of installation is low.
- Easy Setup: the Bus topology is easy for setup
- Moderate data speeds: Coaxial or
twisted pair cables are mainly used in bus-based networks that support
upto 10 Mbps.
- Limited failure: A failure
in one node will not have any effect on other nodes.
- Familiar
technology: Bus
topology is a familiar technology as the installation and troubleshooting
techniques are well known, and hardware components are easily available.
Disadvantages
of Bus topology:
- Extensive cabling: A bus
topology is quite simpler, but still it requires a lot of cabling.
- Signal interference: If two
nodes send the messages simultaneously, then the signals of both the nodes
collide with each other.
- Reconfiguration
difficult: Adding
new devices to the network would slow down the network.
2. Ring
Topology
- Ring
topology is like a bus topology, but with connected ends.
- The
node that receives the message from the previous computer will retransmit
to the next node.
- The
data flows in one direction, i.e., it is unidirectional.
- The
data flows in a single loop continuously known as an endless loop.
- It
has no terminated ends, i.e., each node is connected to other node and
having no termination point.
- The
data in a ring topology flow in a clockwise direction.
- The
most common access method of the ring topology is token
passing.
Advantages of Ring topology:
- Product availability: Many
hardware and software tools for network operation and monitoring are
available.
- Cost: Twisted
pair cabling is inexpensive and easily available. Therefore, the
installation cost is very low.
- Reliable: It is a
more reliable network because the communication system is not dependent on
the single host computer.
Disadvantages of Ring topology:
- Difficult troubleshooting: It
requires specialized test equipment to determine the cable faults. If any
fault occurs in the cable, then it would disrupt the communication for all
the nodes.
- Failure: The
breakdown in one station leads to the failure of the overall network.
- Delay: Communication
delay is directly proportional to the number of nodes. Adding new devices
increases the communication delay.
3. Star
Topology
- Star
topology is an arrangement of the network in which every node is connected
to the central hub, switch or a central computer.
- The
central computer is known as a server, and the peripheral
devices attached to the server are known as clients.
- Coaxial
cable or RJ-45 cables are used to connect the computers.
- Hubs or Switches are mainly used as connection devices in a .
- Star
topology is the most popular topology in network implementation.
Advantages of Star topology
- Network control: Complex
network control features can be easily implemented in the star topology.
Any changes made in the star topology are automatically accommodated.
- Limited failure: As each
station is connected to the central hub with its own cable, therefore
failure in one cable will not affect the entire network.
- Easily
expandable: It
is easily expandable as new stations can be added to the open ports on the
hub.
- Cost effective: Star
topology networks are cost-effective as it uses inexpensive coaxial cable.
- High data speeds: It
supports a bandwidth of approx. 100Mbps. Ethernet 100BaseT is one of the
most popular Star topology networks.
Disadvantages of Star topology
- A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.
- Cable: Sometimes
cable routing becomes difficult when a significant amount of routing is
required.
4. Tree
topology
- Tree
topology combines the characteristics of bus topology and star topology.
- A
tree topology is a type of structure in which all the computers are
connected with each other in hierarchical fashion.
- The
top-most node in tree topology is known as a root node, and all other
nodes are the descendants of the root node.
Advantages
of Tree topology
- Easily expandable: We can add
the new device to the existing network. Therefore, we can say that tree
topology is easily expandable.
- Easily manageable: In tree
topology, the whole network is divided into segments known as star
networks which can be easily managed and maintained.
- Error detection: Error
detection and error correction are very easy in a tree topology.
- Limited failure: The
breakdown in one station does not affect the entire network.
- Point-to-point wiring: It has
point-to-point wiring for individual segments.
Disadvantages of Tree topology
- Difficult
troubleshooting: If any fault occurs in the node, then it
becomes difficult to troubleshoot the problem.
- High cost: Devices
required for broadband transmission are very costly.
- Failure: A tree
topology mainly relies on main bus cable and failure in main bus cable
will damage the overall network.
5. Mesh
topology
- Mesh
technology is an arrangement of the network in which computers are
interconnected with each other through various redundant connections.
- There
are multiple paths from one computer to another computer.
- It
does not contain the switch, hub or any central computer which acts as a
central point of communication.
- The
Internet is an example of the mesh topology.
- Mesh
topology is mainly used for WAN implementations where communication
failures are a critical concern.
- Mesh
topology is mainly used for wireless networks.
- Mesh
topology can be formed by using the formula:
Number of cables = (n*(n-1))/2;
There are Two Types of mesh Topology: -
1) Fully connected mesh topology
2) Partially connected mesh topology
Advantages
of Mesh topology:
Reliable: The
mesh topology networks are very reliable as if any link breakdown will not
affect the communication between connected computers.
Fast Communication: Communication
is very fast between the nodes.
Easier Reconfiguration: Adding
new devices would not disrupt the communication between other devices.
Disadvantages of Mesh topology
- Management: Mesh
topology networks are very large and very difficult to maintain and
manage. If the network is not monitored carefully, then the communication
link failure goes undetected.
- Efficiency: In this
topology, redundant connections are high that reduces the efficiency of
the network.
- Cost: A mesh
topology contains a large number of connected devices such as a router and
more transmission media than other topologies.
6. Hybrid
Topology
- The
combination of various different typologies is known as Hybrid topology.
- A
Hybrid topology is a connection between different links and nodes to
transfer the data.
- When
two or more different typologies are combined together is termed as Hybrid
topology and if similar typologies are connected with each other will not
result in Hybrid topology. For example, if there exist a ring topology in
one branch of State bank and bus topology in another branch of State bank,
connecting these two typologies will result in Hybrid topology.
Advantages of Hybrid Topology
- Scalable: Size of
the network can be easily expanded by adding new devices without affecting
the functionality of the existing network.
- Reliable: If a fault
occurs in any part of the network will not affect the functioning of the
rest of the network.
- Flexible: This
topology is very flexible as it can be designed according to the
requirements of the organization.
- Effective: Hybrid
topology is very effective as it can be designed in such a way that the
strength of the network is maximized and weakness of the network is
minimized.
Disadvantages of Hybrid topology
- Complex design: The major
drawback of the Hybrid topology is the design of the Hybrid network. It is
very difficult to design the architecture of the Hybrid network.
- Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other typologies.
- Costly infrastructure: The
infrastructure cost is very high as a hybrid network requires a lot of
cabling, network devices, etc.
Ports
An IP address identifies a host machine on the Internet.
-An IP port will identify a specific application running on an Internet host machine.
-A port is identified by a number, the port number.
-The number of ports is not functionally limited, in contrast to serial
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port numbers | |||
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Applications |
Port
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HTTP |
80 |
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FTP |
20 and 21 |
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Gopher |
70 |
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SMTP (e-mail) |
25 |
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POP3 (e-mail) |
110 |
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Telnet |
23 |
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Finger |
79 |
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IP Address
IP address stands for internet protocol address it is an identifying number that is associated with a specific computer or computer network. When connected to the internet, the IP address allows the computers to send and receive information.Working of IP address-
An IP address allows computers to send and receive data over the internet. Most IP addresses are purely numerical, but as internet usage grows, letters have been added to some addresses.There are four different types of IP addresses: public, private, static, and dynamic. While the public and private are indicative of the location of the network—private being used inside a network while the public is used outside of a network—static and dynamic indicate permanency.
A static IP address is one that was manually created, as opposed to having been assigned. A static address also does not change, whereas a dynamic IP address has been assigned by a Dynamic Host Configuration Protocol (DHCP) server and is subject to change. Dynamic IP addresses are the most common type of internet protocol addresses. Dynamic IP addresses are only active for a certain amount of time, after which they expire. The computer will either automatically request a new lease, or the computer may receive a new IP address.
Transmission Control Protocol (TCP)
-TCP provides by using IP packets a
basic service that does guarantee safe delivery:
→
error detection
→
safe data transmission
→
assurance that data are received in
the correct order
User Datagram Protocol (UDP)
-Datagram protocol also built on top of IP.
-Has the same packet-size limit (64Kb) as IP, but allows for port number specification.
-Provides also 65,536 different ports.
-Hence, every machine has two sets of 65,536 ports: one for TCP and the other for UDP.
-Connectionless protocol, without any error detection facility.
-Provides only support for data transmission from one end to the other, without any further verification.
-The main interest of UDP is that since it does not make further verification, it is very fast.
-Useful for sending small size data
in a repetitive way such as time information.
OSI (Open Systems Interconnection) Data Model
-ISO standard for computer networks design and functioning.
-Involves at least 7 layers, each playing a specific role when applications are communicating over the net.
-During the sending process, each layer (from top to down) will add a specific header to the raw data.
-At the reception, headers are
eliminated conversely until the data arrived to the receiving application.
1) Physical layer: ensures a safe and efficient travel of data; consists of electronic circuits for data transmission etc.
2) Data link layer: in charge of data encapsulation under the form of packets and their interpretation at the physical layer.
3) Network layer: in charge of packets transmission from a source A to a destination B.
4) Transport layer: in charge of the delivery of packets from a source A to a destination B
5) Session layer: in charge of the management of network access.
6) Presentation layer: determines the format of the data transmitted to applications, data compressing/decompressing, encrypting etc.
7) Application layer: contains the applications which are used by the
end-user, such as Java, Word etc. |
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