Network topologies
Contents
 Network Repeaters
 Network Hubs
 Network Bridge
 Network Switches
 Wireless Access Points
 Network Interface Cards (NIC)
 Routers

Repeater
• A repeater is an electronic device that receives a signal and
retransmits it at high level and/or higher power.
• Repeaters can only be used to regenerate signals between
similar network segments.
• For example, we can extend an Ethernet 10Base2 network
to 400 meters with a repeater.
o But can’t connect an Ethernet and Token Ring network
together with one.
 Regenerate analog or digital signals distorted by
transmissions loss.
 Works on Layer 1 of OSI Model

• Analog Repeater only amplify the signal
• Digital repeater can reconstruct a signal to near its original
quality
Repeater

Network Hubs
• Hubs are one of the most basic pieces of networking equipment
available.
o In general, hub is the central part of a wheel where the spokes come
together.
• Hubs are devices used to link several computers together.
• They repeat any signal that comes in on one port and copy it to the
other ports (a process that is also called broadcasting).
• Physically a hub is a box with a number of RJ45 ports (typically
between 4 and 32) that allows you to connect several networking
devices together using twisted pair (CAT 5) network cables.
• A hub does not perform any type of filtering or routing of the data. A
hub is a junction that joins all the different nodes together.
• Hubs are used on a small networks where data transmission is not
very high.
• The device is form of multiport repeater
• A hub works on Layer 1 (Physical Layer) of the OSI model

Types of Hubs
• Passive Hubs
o A passive hub serves simply as a channel for the data, enabling it to go
from one device to another
o No amplification or regeneration of the signal
o Doesn’t required electricity
• Active Hubs
o Active hubs use electronics to amplify and clean up the signal before it
is broadcast to the other ports.
o Required electricity
• Intelligent Hubs
o In the category of active hubs, there is also a class called “intelligent”
hubs, which are hubs that can be remotely managed on the network.
o Enables an administrator to configure each port in the hub
o Intelligent hubs are also called manageable hubs.

Network Hub Working
• Hubs repeats all the information it receives and forward it
to all PC terminals attached to it.
• This repetition of data results in the unnecessary data
traffic being sent to the network.
• The data is sent in bulk without the identification of its
destination.

Bridges
• Bridges are devices that allow you to segment a large
network into two small, more efficient networks.
• A bridge monitors the information traffic on both sides of
the network so that it can pass packets of information to the
correct location.
• The bridge can inspect each message and, if necessary,
broadcast it on the other side of the network.
• Bridges can be used to connect different types of cabling as
long as both networks are using the same protocol.
• Works at the Data link layer or Layer 2 of the OSI model
• A bridge is sometimes combined with a router in a product
called a Brouter.

Network Bridge
• Filters traffic on the LAN by looking at the Media Access
Control (MAC) address, thus a bridge is more complex than a
hub
• A bridge looks at the destination of the packet before
forwarding unlike a hub.
• Bridges reduce the amount of traffic on a LAN by dividing it
into two segments
• Filters data traffic at a network boundary.
o For example, with 200 people on one Ethernet segment, the performance
will be mediocre, because of the design of Ethernet and the number of
workstations that are fighting to transmit. If you divide the segment into
two segments of 100 workstations each, the traffic will be much lower on
either side and performance will increase.
• The main disadvantage to bridges is that they can’t connect
dissimilar network types or perform intelligent path selection.
For that function, you would need a router.

Network Bridge Working
• Bridges inspect incoming traffic and decide whether to
forward or discard it.
• An Ethernet bridge, for example, inspects each incoming
Ethernet frame including the source and destination MAC
addresses in making the individual forwarding decisions.

Network Switch
• A network switch is a computer networking device that
connects network segments or network devices.
• When compared to bridge, a switch has multiple ports.
• Switches can support both layer 2 (based on MAC address)
and layer 3 (based on IP address) depending on the type of
switch.
• Allow different nodes of a network to communicate
directly with each other.
• Usually, large networks use switches instead of hubs to
connect computers within the same subset

Network Switch Working
• Network switches are capable of inspecting data packets as they
are received, determining the source and destination device of
that packet, and forwarding it appropriately.
• By delivering each message only to the connected device it was
intended for, a network switch conserves network bandwidth and
offers generally better performance than a hub.
• Allow several users to send information over a network at the
same time without slowing each other down that is a vital
difference between a hub and a switch is that all the nodes
connected to a hub share the bandwidth among themselves,
while a device connected to a switch port has the full bandwidth
all to itself.
o For example, if 10 nodes are communicating using a hub on a 10-
Mbps network, then each node may only get a portion of the 10
Mbps if other nodes on the hub want to communicate as well. .
o But with a switch, each node could possibly communicate at the full
10 Mbps.
• Integral part in most modern Ethernet LANs.

Network Switch Working
• An Ethernet switch creates a separate collision domain for
each switch port
• For example;
o With 4 computers (e.g., A, B, C, D) on 4 switch ports, A
and B can transfer data back an forth, while C and D
also do so simultaneously, and the two conversations
will not interfere with one a other.

Forwarding Table
or
MAC Address Table

Network Switch Benefits
• A few of the benefits provided by switching include:
o High-speed data exchange
o Full-duplex communication
o Low latency
o Dedicated communication between devices

Types of Network Switch
or Switching
• There are four forwarding methods a switch can use
1. Store and forward
2. Cut through
3. Fragment free
4. Adaptive switching

Store and forward
• Do error checking on each frame after the entire frame
has arrived into the switch
o If the error checking algorithm determines there is no error, the
switch looks in its MAC address table for the port to which to
forward the destination device
• Highly reliable because doesn’t forward bad frames
• Slower than other types of switches because it holds on to
each frame until it is completely received to check for
errors before forwarding

Cut through
• Faster than store and forward because doesn’t perform
error checking on frames
• Reads address information for each frame as the frames
enter the switch
• After looking up the port of the destination device, frame is
forwarded
• Forwards bad frames
o Performance decreases because bad frames can’t be used and
replacement frames must be sent which creates additional traffic

Fragment free
• Combines speed of cut through switch with error checking
functionality
• Fragment free checks the first 64 bytes of the frame,
where addressing information is stored.
• According to Ethernet specifications,
o Collisions should be detected during the first 64 bytes of the
frame, so frames that are in error because of collision will not be
forwarded.
o This way the frame will always reach its intended destination.
o Error checking of the actual data in the packet is left for the end
device.

Adaptive Switching
• A method of automatically selecting between the other
three modes.

Types of Network
Switches
• The second through fourth method were performance-
increasing methods when used with the same input and
output bandwidths.
o But compromise with error checking
• While in first one, the performance is comparatively slow
but flow of data is error free.

Wireless Access Points
• In a wireless local area network (WLAN), an access point is a
station that transmits and receives data (sometimes referred to
as a transceiver).
• An access point connects users to other users within the network
and also can serve as the point of interconnection between the
WLAN and a fixed wire network.
o Each access point can serve multiple users within a defined network area;
as people move beyond the range of one access point, they are
automatically handed over to the next one.
• A small WLAN may only require a single access point; the
number required increases as a function of the number of
network users and the physical size of the network.
• The term base station is sometimes used to refer to wireless
access points, particularly those used in cellular networking.

Network Interface Card
(NIC)
• NIC is an expansion card that enables a computer to connect to a
network.
• It provides the physical interface between computer and cabling.
• It prepares data, sends data, and controls the flow of data. It can also
receive and translate data into bytes for the CPU to understand.
• Each NIC has a unique serial number. This number is used to identify
the computer on the network.
o If two cards have the same hardware addresses, neither one of them will be
able to communicate.
• A network interface card must be installed on each computer on the
network.
• It is the NIC’s job to translate the data from the computer into signals
that can flow easily along the cable.
o It does this by translating digital signals into electrical signals (and in the
case of fiber-optic NICs, to optical signals).

Router
• A router is a device or a software in a computer that
determines the next network point to which a packet should
be forwarded toward its destination
• Allow different networks to communicate with each other
• A router creates and maintain a table of the available routes
and their conditions and uses this information along with
distance and cost algorithms to determine the best route for
a given packet
• A packet will travel through a number of network points with
routers before arriving at its destination
• Routers are normally used to connect one LAN to another.
• Typically, when a WAN is set up, there will be at least two
routers used.
• Routers operate at the Network Layer or Layer 3 of the OSI
Model.

• Router forwards packets based on address just like a
switch.
• Routers usually use the IP address to forward packets,
which allow the network to go across different protocols.
• Routers support different Wide Area Network (WAN)
technologies but switches do not.
• The advantage of using a router over a bridge is that
routers can determine the best path that data can take to
get to its destination.
• Like bridges, they can segment large networks and can
filter out noise.
• However, they are slower than bridges because they are
more intelligent devices; as such, they analyze every
packet, causing packet-forwarding delays. Because of this
intelligence, they are also more expensive.
Routers

Assignment#1
What is OSI Model? What are the functions of the Seven
layers of OSI Model.
Written Assignment…
Last Date to be submitted:
06-11-2015

Network hardware essentials Lec#3

Network hardware essentials Lec#3

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