NETWORK
DEVICES
Inter networking devices
are products used to connect networks.
As computer networks grow in size and complexity, so do the
inter networking devices used to connect them. Network devices are components
used to connect computers or other electronic devices together so that they can
share files or resources like printers or fax machines. Devices used to
setup a Local Area Network (LAN) are the most common type of network devices
used by the public. A LAN requires a hub, router, cabling or radio technology, network cards, and if online access is
desired, a high-speed modem. Happily this is much less complicated than it might
sound to someone new to networking. In a network, one computer is designated as
the server, and the others, clients. The server is connected to an external
hub, which the clients are also connected to. Now that the computers each have
one foot in a common electronic door (the hub), they can use the hub to pass
signals back and forth. To direct these signals, the hub contains a device
known as a router. The router is the equivalent of an electronic traffic cop
that handles data traffic between the computers. Every type of network device
was developed to solve a problem. Network devices operate at different
layers of the OSI model.
The Purposes
of having devices
b
First, they allow a greater number of nodes to be connected to the
network.
b
Second, they extend the distance over which a network can extend.
b
Third, they localize traffic on the network.
b
Fourth, they can merge existing networks.
b
Fifth, they isolate network problems so that they can be diagnosed
more easily.
Network
Devices Types
Network devices are four
types .They are
1-Hubs 2- Rutter’s 3- Switches 4-Routers
Hub
A Hub is a multiport repeater. It is
normally used to create connections between stations in a physical star
topology.
Multi-port repeaters are often called
hubs. Hubs are very common internetworking devices. Generally speaking, the
term hub is used instead of repeater when referring to the device that serves
as the center of a star topology network
This is a hardware device that
is used to network multiple computers together. It is a central connection for
all the computers in a network, which is usually Ethernet-based. Information
sent to the hub can flow to any other computer on the network. If you need to
connect more than two computers together, a hub will allow you to do so. If you
only need to network two computers together, a simple crossover Ethernet cable
will do the trick.
Types of Hub
There are three types of
hubs. These hubs include active, passive hub, and intelligent hub.
Active hubs
Active hubs act
as a connector between two regions. Amplify or repeat signals that pass to correct data transmission errors or help troubleshoot
network problems. . This type of hub is quite similar to that of the passive
hub but can perform the additional tasks. Active hubs are those hubs that can
work as connector between two regions but also has ability to regenerate the
information with the help of strong electrical signals. It is also called as
the multi -port repeater. It helps in the communication and can upgrade the
properties of the signals before delivery.
Passive hub
Merely connects cables on a network and provides no signal regeneration.
Passive hubs act like a bridge allowing
information to be received. Passive hubs simply pass
on the data they receive on the
network. Passive hub does not perform any particular function but it
just behaves like a bridge between the cables of connection and just receives
the information and forwards it without any change in topology.
Intelligent hubs
Intelligent hubs are hubs that perform the tasks
of both an active hub and a passive hub. Intelligent hubs have the most features of
all. Intelligent hubs are very useful in managing larger .The third and the last type of the hub that can
perform the both functions of the active and the passive hub is generally
referred to as the intelligent hub. Basically this hub provides the opportunity
to increase the speed of networking and also make the performance of the
network efficient as compared to other devices. Addition to their specific work
intelligent hubs can also perform the different functions that of routing,
bridging etc.
PURPOSE of Hub
A hub is a word with several meanings. It can mean the
central part of a rectangular box whose work is to join network devices like
computers together thus forming a one network segment. This enables the
computers to directly communicate with each other. It can also be used to mean
the central part of the bicycle wheel which provides a surface for attaching
the spokes of bicycles. With the help of hubs we can create a home
network easily. Hubs can also monitor the whole network in a real inexpensive
way. It also provide the opportunity to the users to connect their old devices
with their hub drives. Network hub or repeater
hub is a device for connecting multiple twisted pair or fiber optic Ethernet
devices together and thus making them act as a single network segment. Hubs
work at the physical layer (layer 1) of the OSI model. The device is thus a
form of multiport repeater. Repeater hubs also participate in collision
detection, forwarding a jam signal to all ports if it detects a collision.
FUNCTION
The functions of a hub within a network is so they produce
packets to the location of the service required to load or view a webpage or
document. A hub is a
network device that connects multiple computers on a LAN so they can
communicate with one another, the rest of the network, and the Internet. All
users connected to a hub share the available network bandwidth (unlike a
switch, which provides full bandwidth to each computer). Hubs enable computers on a network to communicate. Each computer
plugs into the hub with an Ethernet cable, and information sent from one
computer to another passes through the hub. A hub can't identify the source or
intended destination of the information it receives, so it sends the
information to all of the computers connected to it, including the one that
sent it. A hub can send or receive information, but it can't do both at the
same time. This makes hubs slower than switches. Hubs are the least complex and
the least expensive of these devices.
Network with a hub
Switches
A network switch is a small hardware device that joins
multiple computers together within one local
area network (LAN). Ethernet switch
devices were commonly used on home networks before home routers became popular; broadband
routers integrate Ethernet switches directly into the unit as one of their many functions. High-performance network
switches are still widely used in corporate networks and data centers.
A Network Switch is a constituent
of computer network that connects two network slices and/or two network devices
(switches or routers) together. Switch can be termed as a network bridge with
multiple ports which helps to process and route packets at data link layer of
the OSI reference model. There are some switches which have capabilities to
process data at the upper layers (network layer and above). Those switches are
often termed as multilayer switches.
Two
layer switch
Layer 2 refers to the Data Link layer of the commonly-referenced multilayered communication model, Open
Systems Interconnection (OSI). The Data Link layer
is concerned with moving data across the physical links in the network. In a
network, the switch is a device that redirects data messages at the layer 2 level,
using the destination Media Access Control (MAC) address to determine where to
direct the message.
The Data-Link layer contains two sub-layers that are described in
the IEEE-802 LAN standards:
·
Media Access Control (MAC)
sub-layer
·
Logical Link Control (LLC)
sub-layer
The Data Link layer ensures that an initial connection has been
set up, divides output data into data frames, and handles the acknowledgements
from a receiver that the data arrived successfully. It also ensures that
incoming data has been received successfully by analyzing bit patterns at
special places in the frames
Layer
2 Functionality
- Store and
Forward: The switch
stores and verifies each packet before routing it.
- Cut through: The switch verifies the portion of the
packet header up to the hardware address of frame before it is forwarded.
They may have to stick to the store and forward procedure if the outgoing
port is engaged when the packet enters.
- Fragment free: It is the methodology that tries to
preserve the advantages of both cut through and store and forward
functionalities. Fragment free verifies the first 64 bytes of the packet,
wherein addressing details are saved. This is because; collisions should
be determined within the first 64 bytes of the packet frame, so erroneous
packet frames will not be routed.
- Adaptive
switching: This method
automatically selects one of the above three methods depending upon
traffic situation.
L
3 Switches
Network device that
forwards traffic based on layer 3 information at very high speeds.
Traditionally, routers, which inspect layer 3, were considerably slower than
layer 2 switches. In order to increase routing speeds, many
"cut-through" techniques were used, which perform an "inspect
the first packet at layer 3 and send the rest at layer 2" type of
processing. Ipsilon's IP Switch and Cabletron's SecureFast switches were
pioneers in cut-through switching.
A Layer 3 switch is a high-performance device for
network routing. Layer 3 switches actually differ very little from routers. A
Layer 3 switch can support the same routing protocols as
network routers do. Both inspect incoming packets and make dynamic routing
decisions based on the source and destination addresses inside. Both types of
boxes share a similar appearance. A hybrid device is the latest improvement in internetworking
technology. Combining the packet handling of routers and the speed of
switching, these multilayer switches operate on both layer 2 and layer 3 of the
OSI network model. The performance of this class of switch is aimed at the core
of large enterprise networks. Sometimes called routing switches or IP switches,
multilayer switches look for common traffic flows, and switch these flows on
the hardware layer for speed. For traffic outside the normal flows, the
multilayer switch uses routing functions. This keeps the higher overhead
routing functions only where it is needed, and strives for the best handling
strategy for each network packet.
Many vendors are working on high end multilayer switches, and the
technology is definitely a "work in process". As networking
technology evolves, multilayer switches are likely to replace routers in most
large networks.
Functions
The basic function that any switch is supposed to perform is to
receive information from any source connected to it and dispatch that
information to the appropriate destination only. This thing differentiates
switches from hubs. Hub gets the information and forwards that to every other
device in the network. This is the reason why switches are called intelligent
devices.
The network switch has become a crucial part of present local
area networks (LANs). LANs with medium to large sizes are established using a
number of inter-linked network switches. SOHO (Small Office/Home office)
networks generally consist of a single switch, or sometimes a multi-purpose
device like a residential gateway to utilize small office/home broadband
services such as Digital subscriber line (DSL) and cable Internet. Nowadays, we
have been using router-like components which interface to the particular
physical broadband technology. We may see some people using telephone
technology on internet using Voice over IP (VoIP).
As mentioned above, a switch is operated at the data link layer
to develop a distinct collision domain for each port of the switch. Let us
consider, there are four computers - A, B, C, and D connected to four ports of
the switch, then any pair , say A and B, may transfer data in either
directions, at the same time, the other pair, C and D, can exchange their
information simultaneously, and these two communications will not interrupt
each other. Using full duplex mode, pairs may get overlapped (A communicating
with B, B with C, and so on). Whereas in hubs, all of them have to share the
same bandwidth by running in half duplex mode, causing collisions, which will
result in unnecessary packet retransmissions.
Network Switching
The benefits of switching vary from network to network. Adding a
switch for the first time has different implications than increasing the number
of switched ports already installed. Understanding traffic patterns is very
important to network switching - the goal being to eliminate (or filter) as
much traffic as possible. A switch installed in a location where it forwards
almost all the traffic it receives will help much less than one that filters
most Network response times (the user-visible part of network performance)
suffers as the load on the network increases, and under heavy loads small
increases in user traffic often results in significant decreases in
performance. This is similar to automobile freeway dynamics, in that increasing
loads results in increasing throughput up to a point, then further increases in
demand results in rapid deterioration of true throughput. In Ethernet,
collisions increase as the network is loaded, and this causes retransmissions
and increases in load which cause even more collisions. The resulting network
overload slows traffic considerably.
Using network utilities found on most server operating systems
network managers can determine utilization and collision rates. Both peak and
average statistics should be considered.
PURPOSE OF
SWITCHES
Switches work the same way as hubs, but they can identify the
intended destination of the information that they receive, so they send that
information to only the computers that are supposed to receive it. Switches can
send and receive information at the same time, so they can send information
faster than hubs can. If your home network has four or more computers or you
want to use your network for activities that require passing a lot of
information between computers (such as playing network games or sharing music),
you should probably use a switch instead of a hub. Switches cost a little more
than hubs.
Rutter’s
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Routers
have access to network layer addresses and contain software that enables them
to determine which of several possible paths between those addresses the best
for a particular transmission is.
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Router’s operate in the physical, data link,
and network layers of the OSI model.
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Routers
are another type of internetworking device.
•
These
devices pass data packets between networks based on network protocol or layer 3
information. Routers have the ability to make intelligent decisions as to the
best path for delivery of data on the network.
Purpose of
Rutter’s
Rutter’s enable computers to communicate and
they can pass information between two networks—such as between your home
network and the Internet. This capability to direct network traffic is what
gives the router its name. Routers can be wired (using Ethernet cables) or
wireless. If you just want to connect your computers, hubs and switches work
well; however, if you want to give all of your computers access to the Internet
using one modem, use a router or a modem with a built-in router. Routers also
typically provide built-in security, such as a firewall. Routers are more
expensive than hubs and switches.
Network with a wired router
An optical communications repeater receives light as input and outputs light. The output signal power
source is external to the input power, but the output power may be driven by
input power.
Function of a Router
The main
function of a router is to enable the movement of data by a device from one
network to another. A router is actually a specialized computer connected to
one or more networks
MAIN FUNCTION OF ROUTER
Router has generally three main functions.
- Packet Forwarding
- Packet switching and
- Packet filtering
PACKET FORWARDING:
Router maintains a routing
table for all possible networks those can be reached. In the routing
table, a router maintains, subnet, Gateway, forwarding interface, timing etc
of the destination network. If multiple paths exist to reach the destination
network, only best path is maintained in the routing table .Once any packet is
received, it checks the destination IP network in the routing table. If
destination network is available in routing table, It forwards the packet
otherwise it drops.
PACKET SWITCHING:
To move packets from one
interface to another to get a packet to its destination.
PACKET FILTERING:
Packet filtering is such like
firewall. By which you can define which network can be entered and which
network can be dropped. In easy word, it filters the packet on the basis of IP
address, subnet, and port no and protocols.
Repeaters
A network repeater is a
computer hardware that is used to expand the boundaries of a wired or wireless
local area network (LAN). These repeaters normally amplify data signals before
sending them on to the uplinked segment, thereby countering signal decay that
occurs over extended lengths of wire.
A repeater
(or regenerator) is an electronic device that operates on only the physical
layer of the OSI model. A repeater installed on a link receives the signal
before it becomes too weak or corrupted, regenerates the original pattern, and
puts the refreshed copy back on the link.
A repeater
does not actually connect two LANS; it connects two segments of the same LAN. A
repeater forwards every frame; it has no filtering capability
•
Function of a Repeater
A repeater is used to
amplify signals carried by a network. The function of a repeater is to receive incoming
signals or a packet of data, regenerate the signals to their original strength
and retransmit them. When a repeater amplifies the electric signals in a
network, they allow transmissions to travel a greater distance. For a repeater
to work, both network segments must be identical
The function of a repeater
is to amplify signals that are carried by a network. The repeater receives
incoming signals, regenerates them to their original power and then retransmits
them to cover longer distances.
A repeater is the simplest facility used for network
interconnection, whose major function is to receive a network signal from one
LAN terminal cable segment and to regenerate and retransmit the signal as it is
in its original strength over a one or more other cable segment. Basically
repeater regenerates the strength of the signal before transmitting it
Repeaters operate in the OSI model Physical layer and are transparent to
all the protocols operating in the layers above the Physical layer.
A specific LAN implementation usually places a limit on the
physical size of a single cable segment. The limit is based on the physical
medium and transmission techniques used
Repeaters allow a network to be constructed to exceed the size
limit of a single, physical, cable segment. The number of repeaters that can be
used intandem is generally limited by a particular LAN implementation. Using a
repeater between two or more LAN cables segment requires that the same physical
layer protocol be used to send signal over all the cable segments
Example of how this work
Two LAN cable segment in an Ethernet LAN
that both use baseband transmission could be connected with a repeater. Different
types of physical transmission medium can be connected using a properly
designed repeater as long as they handle similar type of signal, as explained
below: Ethernet repeaters are available that allows all the various types of
baseband Ethernet transmission medium, including 10baseT, Coaxial cable,
10base2 and twisted pair cable segment to be interconnected in the same LAN
Purpose of Repeaters
Repeaters are used to increase
the range of a transmitted signal by re-transmission. For a conducted signal, an
amplifier is used. Optical systems don't amplify but all these devices give the
appearance of doing so.
Some of the energy traveling as
direct current through a conductor is converted to heat energy. This causes a
drop in potential energy (a voltage) across the ends of the conductor
proportional to the current times the inverse of the conductor's conductance.
Energy passing as alternating current is also lost as it travels but, since it
changes direction, there is an additional loss proportional to the capacitive
reactance times the current. Since alternating voltage and its current are out
of phase, total losses equal the vector sum (rather than linear sum) of the two
losses. Similarly, light, which consists of photons rather than electrons,
suffer attenuation due to scattering and absorption. And then retransmit it on
the same frequency. When providing a point-to-point telecom link using radio
beyond line of sight, one uses repeaters in a microwave radio relay. A reflector, often on a
mountaintop, that relays such signals around an obstacle, is called a passive
repeater.
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