Computer network can be defined as the connecting of two or
more computer from one source server.
When computer are linked or joined in a network, the computer
resource like files, software, printers, are shared among the system
Ø Wired or
cable network
Ø Wireless
network
Ø Wired
network: is when two or more computers are linked together using cable
Ø Wireless
network: these does not involve the use of cable, but set of radio waves to
transmit data from one data to another
v LAN:
Local Area Network
v MAN:
Municipal Area Network
v WAN: Wide
Area Network
v GAN: Global
Area Network
v LAN: this
is the inter connection of two or more computer system, device within one
building or room
v MAN:
These are the network that covers a large area. e.g. L.G.A, City.
v WAN: Wide
area network are the network that covers a large area e.g. state & country
v GAN: This
is the inter connection across the whole world
Advantages
ü It makes
work easier & stress free
ü It iron
the issues of moving from one place to another
ü Files can
easily be shared from one system to another
ü It
reeducates the cost of buying many printer and server
ü It makes productivity
faster
ü There is
this likely hood that a virus that affect one system will automatically attack
another
ü A break
down of a server can paralyze the entire system
ü Hackers
can easily have access to it
Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network nodes,
such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and
Routers. In addition, some method of connecting these building blocks is
required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Network Interface Cards
Template:Main
A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
Repeaters
Template:Main
A repeater is an electronic device that receives a
signal and retransmits
it at a higher level or higher power, or onto the other side of an
obstruction, so that the signal can cover longer distances without
degradation.
Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the Physical layer, the first layer of the OSI model.
Hubs
Template:Main
A hub contains multiple ports. When a packet arrives at one port, it is
copied to all the ports of the hub. When the packets are copied, the
destination address in the frame does not change to a broadcast address.
It does this in a rudimentary way, it simply copies the data to all of
the Nodes connected to the hub. [4]
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
Switches
Template:Main
Switches are a marketing term that encompasses routers and bridges, as
well as devices that may distribute traffic on load or by application
content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.
Routers
Template:Main
Routers are the networking device that forward data packets along
networks by using headers and forwarding tables to determine the best
path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812)
This is accomplished by examining the Header of a data packet, and
making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols
to select the best route between any two subnets. A router is connected
to at least two networks, commonly two LANs or WANs or a LAN and its
ISP's network. Some DSL and cable modems, for home use, have been
integrated with routers to allow multiple home computers to access the
Internet.
Building a simple computer network
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable.
This type of network is useful for transferring information between two
computers that are not normally connected to each other by a permanent
network connection or for basic home networking applications.
Alternatively, a network between two computers can be established
without dedicated extra hardware by using a standard connection such as
the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to beuipped with. Examples of some of these special devices are hubs, switches and routers.
Ancillary equipment used by networks
To keep a network operating, to diagnose failures or degradation, and
to circumvent problems, networks may have a wide-ranging amount of
ancillary equipment.
Providing Electrical Power
Individual network components may have surge protectors - an
appliance designed to protect electrical devices from voltage spikes.
Surge protectors attempt to regulate the voltage supplied to an electric
device by either blocking or shorting to ground voltage above a safe
threshold.[5]
Beyond the surge protector, network elements may have uninterruptible power supplies (UPS), which can be anywhere from a line-charged battery to take the element through a brief power dropout, to an extensive network of generators and large battery banks that can protect the network for hours or days of commercial power outages.
A network as simple as two computers linked with a crossover cable has several points at which the network could fail: either network interface, and the cable. Large networks, without careful design, can have many points at which a single failure could disable the network.
When networks are critical the general rule is that they should have no single point of failure. The broad factors that can bring down networks, according to the Software Engineering Institute [6] at Carnegie-Mellon University:
Some network elements operate in a manner to protect themselves and shut down gracefully in the event of a loss of power. These might include noncritical application and network management servers, but not true network elements such as routers. UPS may provide a signal called the "Power-Good" signal. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present, the computer shuts down. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself
To help standardize approaches to power failures, the Advanced Configuration and Power Interface (ACPI) specification is an open industry standard first released in December 1996 developed by HP, Intel, Microsoft, Phoenix and Toshiba that defines common interfaces for hardware recognition, motherboard and device configuration and power management.
Monitoring and Diagnostic Equipment
Networks, depending on their criticality and the skill set available
among the operators, may have a variety of temporarily or permanently
connected performance measurement and diagnostic equipment. Routers and
bridges intended more for the enterprise or ISP market than home use,
for example, usually record the amount of traffic and errors experienced
on their interfaces.
Diagnostic equipment, to isolate failures, may be nothing more complicated than a spare piece of equipment. If the problem disappears when the spare is manually replaced, the problem has been diagnosed. More sophisticated and expensive installations will have spare elements that can automatically replace a failed unit. Failures can be made transparent to user computers with techniques such as the Virtual Router Redundancy Protocol (VRRP), as specified in RFC 3768.
LET HEAR HOW YOU FEEL IN THE COMMENT BOX
Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network nodes,
such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and
Routers. In addition, some method of connecting these building blocks is
required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Network Interface Cards
Template:Main
A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
Repeaters
Template:Main
A repeater is an electronic device that receives a
signal and retransmits
it at a higher level or higher power, or onto the other side of an
obstruction, so that the signal can cover longer distances without
degradation.
Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the Physical layer, the first layer of the OSI model.
Hubs
Template:Main
A hub contains multiple ports. When a packet arrives at one port, it is
copied to all the ports of the hub. When the packets are copied, the
destination address in the frame does not change to a broadcast address.
It does this in a rudimentary way, it simply copies the data to all of
the Nodes connected to the hub. [4]
Bridges
Template:Main A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do. but learns which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
SwitchesEdit
Template:Main
Switches are a marketing term that encompasses routers and bridges, as
well as devices that may distribute traffic on load or by application
content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.
Routers
Template:Main
Routers are the networking device that forward data packets along
networks by using headers and forwarding tables to determine the best
path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812)
This is accomplished by examining the Header of a data packet, and
making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols
to select the best route between any two subnets. A router is connected
to at least two networks, commonly two LANs or WANs or a LAN and its
ISP's network. Some DSL and cable modems, for home use, have been
integrated with routers to allow multiple home computers to access the
Internet.
Building a simple computer network
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable.
This type of network is useful for transferring information between two
computers that are not normally connected to each other by a permanent
network connection or for basic home networking applications.
Alternatively, a network between two computers can be established
without dedicated extra hardware by using a standard connection such as
the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to beuipped with. Examples of some of these special devices are hubs, switches and routers.
Ancillary equipment used by networks
To keep a network operating, to diagnose failures or degradation, and
to circumvent problems, networks may have a wide-ranging amount of
ancillary equipment.
Providing Electrical Power
Individual network components may have surge protectors - an
appliance designed to protect electrical devices from voltage spikes.
Surge protectors attempt to regulate the voltage supplied to an electric
device by either blocking or shorting to ground voltage above a safe
threshold.[5]
Beyond the surge protector, network elements may have uninterruptible power supplies (UPS), which can be anywhere from a line-charged battery to take the element through a brief power dropout, to an extensive network of generators and large battery banks that can protect the network for hours or days of commercial power outages.
A network as simple as two computers linked with a crossover cable has several points at which the network could fail: either network interface, and the cable. Large networks, without careful design, can have many points at which a single failure could disable the network.
When networks are critical the general rule is that they should have no single point of failure. The broad factors that can bring down networks, according to the Software Engineering Institute [6] at Carnegie-Mellon University:
- Attacks: these include software attacks by various miscreants (e.g., malicious hackers, computer criminals) as well as physical destruction of facilities.
- Failures: these are in no way deliberate, but range from human error in entering commands, bugs in network element executable code, failures of electronic components, and other things that involve deliberate human action or system design.
- Accidents: Ranging from spilling coffee into a network element to a natural disaster or war that destroys a data center, these are largely unpredictable events. Survivability from severe accidents will require physically diverse, redundant facilities. Among the extreme protections against both accidents and attacks are airborne command posts and communications relays[7], which either are continuously in the air, or take off on warning. In like manner, systems of communications satellites may have standby spares in space, which can be activated and brought into the constellation.
Dealing with Power Failures
One obvious form of failure is the loss of electrical power. Depending on the criticality and budget of the network, protection from power failures can range from simple filters against excessive voltage spikes, to consumer-grade Uninterruptible Power Supplies(UPS) that can protect against loss of commercial power for a few minutes, to independent generators with large battery banks. Critical installations may switch from commercial to internal power in the event of a brownout,where the voltage level is below the normal minimum level specified for the system. Systems supplied with three-phase electric power also suffer brownouts if one or more phases are absent, at reduced voltage, or incorrectly phased. Such malfunctions are particularly damaging to electric motors. Some brownouts, called voltage reductions, are made intentionally to prevent a full power outage.Some network elements operate in a manner to protect themselves and shut down gracefully in the event of a loss of power. These might include noncritical application and network management servers, but not true network elements such as routers. UPS may provide a signal called the "Power-Good" signal. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present, the computer shuts down. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself
To help standardize approaches to power failures, the Advanced Configuration and Power Interface (ACPI) specification is an open industry standard first released in December 1996 developed by HP, Intel, Microsoft, Phoenix and Toshiba that defines common interfaces for hardware recognition, motherboard and device configuration and power management.
Monitoring and Diagnostic Equipment
Networks, depending on their criticality and the skill set available
among the operators, may have a variety of temporarily or permanently
connected performance measurement and diagnostic equipment. Routers and
bridges intended more for the enterprise or ISP market than home use,
for example, usually record the amount of traffic and errors experienced
on their interfaces.
Diagnostic equipment, to isolate failures, may be nothing more complicated than a spare piece of equipment. If the problem disappears when the spare is manually replaced, the problem has been diagnosed. More sophisticated and expensive installations will have spare elements that can automatically replace a failed unit. Failures can be made transparent to user computers with techniques such as the Virtual Router Redundancy Protocol (VRRP), as specified in RFC 3768.
LET HEAR HOW YOU FEEL IN THE COMMENT BOX
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