Since, we are going to do a series of tutorials on packet tracer. In this manner, we need to have a familiarity of various networking components and devices. We are going to discuss some important devices which are going to be used in networking.
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 etc. These devices also need cables to connect them. In this tutorial, we are going to discuss these important devices.
Network
interface cards
A 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.The NIC provides the
transfer of data in megabytes.
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NIC
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Every device on a network that needs to transmit
and receive data must have a network interface card (NIC)
installed. They are sometimes called network adapters, and are
usually installed into one of the computer's expansion slots in the same way as
a sound or graphics card. The NIC includes a transceiver, (a
transmitter and receiver combined). The transceiver allows a network device to
transmit and receive data via the transmission medium. Each NIC has a unique
48-bit Media Access Control (MAC) address burned in to its ROM
during manufacture. The first 24 bits make up a block code known as the Organisationally
Unique Identifier (OUI) that is issued to manufacturers of NICs, and
identify the manufacturer. The issue of OUIs to organisations is administered
by the Institute of Electrical and Electronics Engineers (IEEE).
The last 24 bits constitute a sequential number issued by the manufacturer. The
MAC address is sometimes called a hardware address or physical address, and
uniquely identifies the network adapter. It is used by many data link layer
communications protocols, including Ethernet, the 802.11 wireless protocol and
Bluetooth. The use of a 48-bit adress allows for 248(281,474,976,710,656)
unique addresses. A MAC address is usually shown in hexadecimal format, with
each octet separated by a dash or colon,
For example: 00-60-55-93-R2-N7
Repeaters
A repeater is an electronic
device that receives a signal and retransmits
it at a higher power level, or to the other side of an obstruction, so that the
signal can cover longer distances without degradation. In most twisted pair
ethernet configurations, repeaters are required for cable runs longer than 100
meters away from the computer. As signals travel along
a transmission medium there will be a loss of signal strength i.e. attenuation.
A repeater is a non-intelligent network device that receives a signal on one of
its ports, regenerates the signal, and then retransmits the signal on all of
its remaining ports. Repeaters can extend the length of a network (but not the
capacity) by connecting two network segments. Repeaters cannot be used to
extend a network beyond the limitations of its underlying architecture, or to
connect network segments that use different network access methods. They can,
however, connect different media types, and may be able to link bridge segments
with different data rates.
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| Repeater |
Repeaters
are used to boost signals in coaxial and twisted pair cable and in
optical fibre lines. An electrical signal in a cable gets weaker the
further it travels, due to energy dissipated in conductor resistance and
dielectric losses. Similarly a light signal traveling through an optical
fiber suffers attenuation due to scattering and absorption. In long cable runs,
repeaters are used to periodically regenerate and strengthen the signal.
Hubs
A hub contains multiple ports. When a packet
arrives at one port, it is copied to all the ports of the hub for transmission. In a hub, a frame is passed along or
"broadcast" to every one of its ports. It doesn't matter that the
frame is only destined for one port. The hub has no way of distinguishing which
port a frame should be sent to. Passing it along to every port ensures that it
will reach its intended destination. This places a lot of traffic on the
network and can lead to poor network response times. Additionally, a 10/100Mbps hub must share
its bandwidth with
each and every one of its ports. So when only one PC is broadcasting, it will
have access to the maximum available bandwidth. If, however, multiple PCs are
broadcasting, then that bandwidth will need to be divided among all of those
systems, which will degrade performance.
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| Network Hub |
Bridges
A network bridge connects
multiple network segments
at the data link layer
(layer 2) of the OSI model. Bridges
do not copy traffic to all ports, as hubs do, but learn 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.
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| Network Bridge |
Bridges don't know anything about protocols, but
just forward data depending on the destination address in the data packet. This
address is not the IP address, but the MAC (Media Access Control) address that
is unique to each network adapter card. The bridge is basically just to connect
two local-area networks (LANs), or two segments of the same LAN that use the
same protocol. Bridges can extend the length of a network,
but unlike repeaters they can also extend the capacity of a network,
since each port on a bridge has its own MAC address. When bridges are powered
on in an Ethernet network, they start to learn the network's topology
by analysing the source addresses of incoming frames from all attached network
segments (a process called backward learning ). Over a period of
time, they build up a routing table .
The bridge monitors all traffic on the
segments it connects, and checks the source and destination address of each
frame against its routing table. When the bridge first becomes operational, the
routing table is blank, but as data is transmitted back and forth, the bridge
adds the source MAC address of any incoming frame to the routing table and
associates the address with the port on which the frame arrives. In this way,
the bridge quickly builds up a complete picture of the network topology. If the
bridge does not know the destination segment for an incoming frame, it will
forward the frame to all attached segments except the segment on which the frame
was transmitted. Bridges reduce the amount of traffic on individual segments by
acting as a filter, isolating intra-segment traffic. This can greatly improve
response times.
Switches
The switch is a relatively new network
device that has replaced both hubs and bridges in LANs. A switch uses an
internal address table to route incoming data frames via the port associated
with their destination MAC address. Switches can be used to connect together a
number of end-user devices such as workstations, or to interconnect multiple
network segments. A switch that interconnects end-user devices is often called
a workgroup switch. Switches provide dedicated full-duplex links for every
possible pairing of ports, effectively giving each attached device its own
network segment This significantly reduces the number of intra-segment and
inter-segment collisions. Strictly speaking, a
switch is not capable of routing traffic based on IP address (layer 3) which is
necessary for communicating between network segments or within a large or
complex LAN. Some switches are capable of routing based on IP addresses but are
still called switches as a marketing term. A switch normally has numerous
ports, with the intention being that most or all of the network is connected
directly to the switch, or another switch that is in turn connected to a
switch.
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| Network Switch |
Routers
Routers are
networking devices that forward data packets between networks using headers and
forwarding tables to determine the best path to forward the packets. A network environment that consists of several interconnected
networks employing different network protocols and architectures requires a
sophisticated device to manage the flow of traffic between these diverse
networks. Such a device, sometimes referred to as an intermediate system,
but more commonly called a router, must be able to determine how to get
incoming packets (or datagrams) to the destination network by the most
efficient route. Routers gather information about the networks to which they
are connected, and can share this information with routers on other networks.
The information gathered is stored in the router's internal routing table,
and includes both the routing information itself and the current status of
various network links. Routers exchange this routing information using
special routing protocols.
A router is connected to at least two
networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are
located at gateways, the places where two or more networks connect, and are the
critical device that keeps data flowing between networks and keeps the networks
connected to the Internet. When data is sent between locations on one network
or from one network to a second network the data is always seen and directed to
the correct location by the router. The router accomplishes this by using
headers and forwarding tables to determine the best path for forwarding the
data packets, and they also use protocols such as ICMP to communicate with each
other and configure the best route between any two hosts. The Internet itself
is a global network connecting millions of computers and smaller networks. There are various routing protocols which are helpful for various different environments and will be discussed later.
