1. Common NetworkDevices
Network switches
Computernetworkingdevices are units that mediate data in a
computernetwork and are also called networkequipment.Units which
are the last receiver or generate data are called hosts or data terminal
equipment.
Hub[edit]
Hubs connect computers togetherin a star topology network. Due to
their design, they increase the chances for collisions.Hubs operate in
the physical layer of the OSI model and have no intelligence.Hubs flood
incomingpackets to all ports all the time. For this reason,if a network
is connected usinghubs,the chances of a collision increases linearly
with the numberof computers (assumingequal bandwidth use).Hubs
pose a security risk since all packets are flooded to all ports all the time.
If a userhas packet sniffing software, they can extract data from the
networkand potentiallydecode it and use it. Hubs make it easy to "spy"
on users on the same LAN as you.
Repeater[edit]

2. A wireless repeater.
A repeateris an electronicdevice that receives a signal and retransmits
it at a higherlevel and/orhigher power, or onto the other side of an
obstruction,so that the signal can cover longerdistances without
degradation.Becauserepeaters workwith 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.
Repeaters are majorlyemployed in long distance transmission to reduce
the effect of attenuation.It is important to note that repeaters do not
amplify the original signal but simply regenerate it.
Modem [edit]
Modem (from modulator-demodulator)is a device that turns the digital
1s and 0s of a personal computerinto sounds that can be transmitted
over the telephone lines of Plain Old Telephone Systems (POTS),and
once received on the other side, converts those sounds back into a form
used by a USB, Ethernet, serial,or network connection.Modemsare
generallyclassified by the amount of data they can send in a given time,
normallymeasured in bits per second,or "bps".
NIC (Network Interface Card) [edit]
A networkinterface card is a computerhardware componentdesigned
to allow computers to communicate overa computernetwork. It is both
an OSI layer 1 (physical layer) and layer 2 (data link layer) device, as it

3. provides physical access to a networkingmedium and provides a low-
level addressingsystem through the use of MAC addresses.It allows
users to connect to each other either by using cables or wirelessly.Most
motherboards todaycome equipped with a network interface card in the
form of a controller, with the hardware built into the board itself,
eliminatingthe need for a standalone card.
Media converters [edit]
Media converters are simple networkingdevices that make it possible to
connect two dissimilarmedia types such as twisted pair with fiber optic
cabling. Theywere introduced to the industrynearly two decades ago,
and are importantin interconnectingfiberoptic cabling-based systems
with existing copper-based,structured cablingsystems. Media
converters support many differentdata communication protocols
including Ethernet,T1/E1, T3/E3,as well as multiple cabling types
such as coaxial, twisted pair, multimode and single-mode fiberoptics.
When expandingthe reach of a Local Area Networkto span multiple
locations,media converters are useful in connectingmultiple LANs to
form one large "campus area network" that spans over a limited
geographicarea. As local networks are primarily copper-based,media
converters can extend the reach of the LAN over single-modefiberup to
130 kilometers with 1550 nm optics.
Basic switch [edit]
Switches are often confused with bridges because theyalso operate at
thedata link layer of the OSI model.Similar to a hub, switches provide
a central connection between two or more computers on a network, but
with some intelligence.Theyprovide traffic control for packets; rather
than forwardingdata to all the connected ports, a switch forwards data
only to the port on which the destination system is connected.Theyuse
a databaseof MAC addresses to determine where computers are located

4. and very efficiently send packets only where they need to go. The
database is created dynamicallyas computers communicate on the
network. The switch simply watches the incomingpackets and
memorizes the MAC address and port a packet arrives on. If a packet
arrives with a destination computerthat the switch does not have an
address for in its MAC address table, it will flood the packet out all
connected ports. A switch creates separate collision domains for each
physical connection.A switch will only create separate broadcast
domains if separate VLANs (Virtual Local Area Networks) are assigned
to different ports on the switch. Otherwise,a broadcastreceived on one
port will be flooded out all ports except the one it came in on.
Bridge [edit]
Bridges can be identified by the fact that they operate at the data link
layer of the OSI model.Bridges have intelligence and can "bridge" two
of their ports togetherat very high speed.Theyuse a database of MAC
addresses to determine where computers are located and very efficiently
send frames only where they need to go. The database is created
dynamicallyas computers communicate on the network. A bridge
simply watches the incomingframe and memorizes the MAC address
and port a frame arrives on. It uses this information to locate a
computerif a packet comes in that must be forwarded to it. If a frame
arrives at the bridge and the bridge does not know where to send it, the
bridge will flood the frame just like a hub does. Bridging is often
inaccuratelycalled switching.
Wireless access point [edit]

5. A wireless access point (WAP or AP) is a device that allows wireless
communicationdevices to connectto a wireless network usingWi-Fi,
Bluetooth or related standards.The WAP usuallyconnects to a wired
network, and can relay data betweenthe wireless devices (such as
computers or printers) and wired devices on the network.
A typical corporate use involves attaching several WAPs to a wired
networkand then providingwireless access to the office Local Area
Network. Within the range of the WAPs,the wireless end user has a
full networkconnection with the benefitof mobility. In this instance,
the WAP functions as a gatewayfor clients to access the wired network.
A Hot Spot is a common publicapplication of WAPs, where wireless
clients can connect to the Internetwithoutregard for the particular
networks to which they have attached for the moment.The concept has
become common in large cities, where a combination ofcoffeehouses,
libraries,as well as privately owned open access points, allow clients to
stay more or less continuouslyconnected to the Internet,while moving
around.A collection of connected Hot Spots can be referred to as a lily-
pad network.
Home networks generallyhave only one WAP to connectall the
computers in a home.Most are wireless routers, meaningconverged
devices that include a WAP,router, and often an Ethernetswitch in the
same device. Many also converge a broadband modem.In places where
most homes have their own WAP within range of the neighbors' WAP,

6. it's possible for technicallysavvy people to turn off their encryption and
set up a wireless communitynetwork, creating an intra-city
communicationnetworkwithoutthe need of wired networks.
Basic router [edit]
Routers operate at the networklayer of the OSI model and efficiently
route information between Local Area Networks. Since routers operate
in the third layer, the networklayer, they must understand layer3
addressing...such as TCP/IP.A router will divide a broadcastdomain by
not forwardingbroadcasts on one connected networkto another
connected network.Routers operate in two different planes:the control
plane,in which the router learns the outgoinginterface that is most
appropriate for forwardingspecific packets to specific destinations,and
the forwardingplane, which is responsiblefor the actual process of
sendinga packet received on a logical interface to an outbound logical
interface.
Basic firewall [edit]
A firewall is a part of a computer system or networkthat is designed to
block unauthorized access while permitting outward communication.It
is also a device or set of devices configured to permit, deny, encrypt,
decrypt, or proxy all computertraffic between differentsecurity
domains based upon a set of rules and other criteria.
Firewalls can be implemented in both hardware and software, or a
combinationof both. Firewalls are frequentlyused to prevent

7. unauthorized Internetusers from accessingprivate networks connected
to the Internet. All messages enteringor leavingthe Local Area
Network pass through the firewall, which examines each messageand
blocks those that do not meet the specified security criteria. Without
proper configuration,a firewall can often become worthless.Standard
security practices dictate a "default-deny"firewall ruleset,in which the
only networkconnections which are allowed are the ones that have been
explicitly allowed.
Basic DHCP (Dynamic Host ConfigurationProtocol)server [edit]
When a DHCP-configured client(be it a computeror any other network-
aware device) connects to a network,the DHCP client sends a broadcast
query requestingnecessaryinformation from a DHCP server. The
DHCP server manages a pool of IP addresses and information about
client configuration parameters such as the default gateway,the
domain name,theDNS (Domain Name System) servers, otherservers
such as time servers, and so forth. Upon receipt of a valid requestthe
server will assign the computeran IP address,a lease (the length of
time for which the allocation is valid), and other IP configuration
parameters,such as the subnetmask and the default gateway.The
query is typically initiated immediatelyafter bootingand must be
completed before the client can initiate IP-based communicationwith
other hosts.
Networking hardware
Networking hardware mayalso be known as network
equipment orcomputer networking devices.
Units which are the last receiver or generate data are
called hosts or data terminal equipment.[citationneeded]
All these terms refer to devices facilitating the use of a computer
network. Specifically, they mediate data in a computernetwork.[1]
Range

8. Typically, networkinghardware includes gateways,routers,network
bridges, switches,hubs,and repeaters.But it also includes hybrid
networkdevices such as multilayerswitches, protocol converters, bridge
routers, proxy servers, firewalls,networkaddress
translators,multiplexers,networkinterface controllers,wireless
networkinterface controllers,modems,ISDN terminal adapters,line
drivers, wireless access points, networkingcables and other related
hardware.
The most common kind of networkinghardware todayis a copper-
based Ethernetadapterbecause of its standard inclusion on most
modern computersystems. Wireless networking has,however,become
increasinglypopular,especiallyfor portable and handheld devices.
Other hardware prevalentin computernetworkingincludes data
center equipment(such as file servers, databaseserversandstorage
areas), networkservices (such as DNS, DHCP,email, etc.) as well as
devices which assure content delivery.
Takinga wider view, mobile phones,PDAs and even modern coffee
machines mayalso be considered networkinghardware.As technology
advances and IP-based networks are integrated into building
infrastructure and household utilities,networkhardware will becomes
an ambiguous term owingto the vastly increasingnumberof "network
capable"endpoints.
Specific devices
 Gateway:this device is placed at a networknode and interfaces with
anothernetworkthat uses different protocols.It works on OSI layers
4 to 7.
 Router: a specialized networkdevice that determines the next
networkpoint to which it can forward a data packet towards the
ultimate destination of the packet. Unlike a gateway,it cannot
interface differentprotocols. It works on OSI layer 3.
 Switch: a device that allocates traffic from one networksegmentto
certain lines (intended destination(s))which connectthe segmentto
anothernetworksegment.Unlike a hub,a switch splits the network
traffic and sends it to differentdestinations ratherthan to all
systems on the network.It works on OSI layer 2.

9.  Bridge: a device that connects multiple network segments along
the data link layer. It works on OSI layer 2.
 Hub: a device that connects multiple Ethernetsegments,making
them act as a single segment.When usinga hub, every attached
device shares the same broadcastdomain and the same collision
domain.Therefore,onlyone computer connected to the hub is able to
transmit at a time. Dependingon the networktopology,the hub
provides a basic level 1 OSI model connection amongthe network
objects (workstations,servers, etc.). It provides bandwidth which is
shared amongall the objects, in contrast to switches,which provide a
connection between individual nodes.It works on OSI layer 1.
 Repeater:a device which amplifies or regenerates digital signals
received while sendingthem from one part of a network into another.
It works on OSI layer 1.
Some hybrid network devices:
 Multilayerswitch: a switch which, in addition to switching on OSI
layer 2, provides functionalityat higherprotocol layers.
 Protocol converter: a hardware device that converts betweentwo
different types of transmission,such as asynchronous and
synchronoustransmissions.
 Bridge router (brouter): a device that combines routerand bridge
functionalityand therefore works on OSI layers 2 and 3.
Hardware or software components that typically sit on the connection
point of differentnetworks, e.g. betweenan internal network and an
external network:
 Proxy server: computernetwork service which allows clients to make
indirect network connectionsto other network services.
 Firewall:a piece of hardware or software put on the network to
prevent some communications forbiddenby the networkpolicy.
 Network address translator (NAT): networkservice provided as
hardware or software that converts internal to external network
addresses and vice versa.
Other hardware for establishingnetworks or dial-up connections:

10.  Multiplexer:a device that combines several electrical signals into a
single signal.
 Network interface controller: a device connectingthe attached
computerto a wire-based computernetwork.
 Wireless networkinterface controller:a device connectingthe
attached computer to a radio-based computernetwork.
 Modem:device that modulates an analog"carrier" signal (such as
sound)to encode digital information,and that also demodulates such
a carrier signal to decode the transmitted information,such as a
computercommunicatingwith anothercomputerover a telephone
network.
 ISDN terminal adapter (TA): a specialized gateway for ISDN.
 Line driver: a device to increase transmission distance byamplifying
the signal; used in base-band networks only.