Interconnecting devies

INTRODUCTION
Inter connecting Devices:
 An Interconnecting device is any device that
can enable computers to exchange data on a
network.
 Backbone of a network.

INTERCONNECTING DEVICES
 Hubs
 Repeaters
 Bridges
 Switches
 Routers
 Gateways

HUBS
 A hub is basically a multiport repeater .Hubs
are a common connection point for devices in a
network and are commonly used to connect
segments of a LAN and have multiple ports.
 A hub takes the incoming data packet that
comes into a port and copies it out to all the
other ports in the hub.
 It doesn't perform any filtering or redirection of
data.
 It operates on physical layer of OSI model.

 Hubs cannot filter data, so data packets are sent to
all connected devices.

TWO TYPES OF HUBS
 PASSIVE HUB:
 A passive hub is just a connector, it simply
transmit and receive data from end devices
connected to the LAN.
 It does not amplify the signal.

 ACTIVE HUB:
 Active Hub is a hub which can amplify or
regenerate the information signal. This type of
hub has an advantage as it also amplifies the
incoming signal as well as forward it to multiple
devices.
 This hub is also known as Multiport Repeater.
 It strengthen the incoming signal before sending
them to destination.

ADVANTAGES:
 Hub is less expensive.
 Active hubs can extend maximum network
media distance.
 No processing is done at the hub to slow
down performance.

DISADVANTAGES:
 No intelligence to filter traffic.
 It will broadcast to all the ports which leads to
inefficiencies and wastage.

REPEATERS
 Repeater is a device used to regenerate the
signal over same network.
 A repeater connects segments of a LAN.
 A repeater is a device that operates only at the
Physical layer of OSI model.
 As the distance of the two segments increases,
the signal strength automatically keeps
decreasing due to attenuation (loss of energy due
to cable resistance and external noise factors). To
overcome this, devices like repeaters that span
long distances.

A REPEATER CONNECTING TWO SEGMENTS OF
A LAN

FUNCTION OF REPEATERS
 Repeaters receive signals from one network
segment and it regenerates, and retransmit those
signals to another network segment.
 When the signal becomes weak, they copy the
signal bit by bit and regenerate it at the original
strength.
 A repeater can extend only the physical length of
network.
 A repeater forwards every frame; it has no filtering
capability.

ADVANTAGES
 Extend length of network.
 It strengthen the weak signal.
 Remove the unwanted noise in an incoming
signal.

DISADVANTAGES
 It has no filtering capacity.
 It cannot connect two different architecture
such as token ring and Ethernet etc..
 Number of repeaters used must be least,
otherwise cause propagation delay.

BRIDGES
 Bridge is a device used to connect two
separate Ethernet networks into one extended
Ethernet that uses same protocol.
 Bridging occurs at the data link layer of the OSI
model, which means the bridge cannot read IP
addresses, but only the outermost hardware
address of the packet.
 The hardware address is also called the MAC
(media access control) address.

FUNCTION OF A BRIDGE
 When the frame enters it not only regenerates
the signal it receives.
 As a data link layer device it checks the source
and destination addresses in the frame.
 It maintains a table that maps addresses to ports.
 It send data frames only to the concerned
destination.
 If destination address is in the same segment as
the source address, stop transmit.
 Otherwise, forward to the other segment.

TYPES OF BRIDGES
BRIDGE
MULTIPORTLEARNINGSIMPLE

SIMPLE BRIDGES
 A simple bridge connects two segments and
contains table list of address of all the station
included in them.
 The table of host addresses verses segment
numbers entered manually.
 When new host added or existing deleted the
table has to be updated.
 These are cheapest but also are error prone.

LEARNING BRIDGE
 A learning bridge build its table of content on its
own, initially it is empty.
 When a frame comes to it, checks for the
addresses in the table. If it is not present adds
it to the table along with the segment number.
 The bridge continue checking and update its
mapping table, so the name learning bridge.

MULTI-PORT BRIDGE
 When a simple or
learning bridge
connects more than
two network
segments it is called
a multi-port bridge.
 It is a special case of
either the simple or
the learning bridge.

ADVANTAGES
 It minimizes unwanted traffic and it acts as a filter.
 It minimizes network congestion.
 Error links can be identified and then isolated.
 Bridges help to lower the data load over the data
link layer.

DISADVANTAGES
 The speed is slower than repeaters but it is fast than
that of the routers.
 Cost is expensive than repeaters but a bit cheaper
than routers.
 Not able to handle multiple paths.
 Bridges are unable to read specific IP address; they
are more concerned with the MAC addresses.

 A network switch is a networking device that
connects devices together on a computer
networks, by using packet switching to receive,
process and forward data to the destination
device.
 It process the data at the datalink layer and
network layer of the OSI model.
 Performs the datalink layer function, that is it
looks at each packets or data unit and determines
from a physical address(MAC address).
 Also called as Multilayer Switch because it works
on two different layers.

FUNCTIONS
 Allows more than one device connected to the
switch directly to transmit simultaneously.
 Can operates in Full-duplex mode(can send and
receive frames at the same time).
 Performs MAC address recognition and frame
forwarding in hardware.

Forwarding methods
 There are four forwarding methods
available.
1. Store-and-forward:
 Switch buffers and verifies each frame
before forwarding it. A frame is received
fully before it is forwarded.
 Buffering will cause some delay.

STORE-AND-FORWARD & CUT-THROUGH

Forwarding methods
2. Cut-through:
 Based on the destination address
appears at the beginning of the MAC
frame, the frame is directly sent to the
appropriate output line if the output
buffer is empty. If it is busy then, the
switch falls back to store-and-forward
operation.
 No error checking.

Forwarding methods
3. Fragment free
 A method that attempts to retain the
benefits of both store and forward and cut
through.
 Fragment free checks the first 64 bytes of
the frame, where addressing information
is stored.
 According to Ethernet, collisions should
be detected during the first 64 bytes of
the frame, so frames that are in error
because of a collision will not be
forwarded.

Forwarding methods
4. Adaptive Switching
 A method of automatically selecting
between the other three modes.
 In specialized applications like Storage area
networks, input and the output interfaces
are the same bandwidth, this is not always
general case in LAN’s.
 In LAN’s it is used for end user access that
is, lower bandwidth and uplinks into a
higher bandwidth.

SWITCH LEARNING PROCESS
 When the switch receives a frame, it compares
the source address of the frame with each entry
in the forwarding table.
 If No match is found, the bridge will add to the
table the frame source address and the
interface on which the frame was received.
 If the match is found, the bridge updates the
interface number on which the frame was
received if it is different from the one in the table
also it updates the record time.

 Then, the switch compares the destination
address of the frame with each entry in the
forwarding table (MAC table).
 If a match is found then,
The bridge compares the interface number on
which the frame was received and the
interface number in the table, if they are
different the bridge forwards the frame through
the interface number stored in the table.
Otherwise if they are same the switches
discards the frame.
 If no match found, the switch floods the
frame on all interfaces except the one on
which the frame was received.

TWO LAYER SWITCHES
 Two layer switch operate at data link layer.
 Bridge is an example of two-layer switch.
 Bridge with few port can connect a few LAN’s.
 Bridge with many port may be able to allocate
a unique port to each station, with each station
on its own independent entity. This means no
competing traffic.

THREE LAYER SWITCHES
 Three layer switch operates at network layer.
 Example for three-layer switch is router.
 Routes packets based on their logical
addresses (host to host addressing).
 A router normally connects LAN’s and WAN’s
in the internet and has a routing table that is
used for making decision about the route.
 The routing tables are normally dynamic and
are updated using routing protocols.

ADVANTAGES
 Only forwards frames as needed.
 Filters frames to avoid unnecessary load on
segments.
 Sends frames only to segments that need to
see them.
 Extends the geographical span of the
network.
 Separate segments allow longer distances.
 Improves privacy by limiting scope of
frames.

DISADVANTAGES
 While limiting broadcasts, switches are not as good
as a routers.
 Handling multicast packets needs configuration and
proper designing.
 It is difficult to reconfigure if any network error
occurs in multicast.
 If switches are in promiscuous mode they are
vulnerable to security attacks like spoofing IP
address or capturing of Ethernet Frames.
 Higher cost.

ROUTER
 A router is a three-layer device: It operates in the
physical, data link, and network layers.
 As a physical layer device:
It regenerates the signal it receives.
 As a data link layer device:
The router checks the physical addresses
(source and destination) contained in the packet.
 As a network layer device:
A router checks the network layer addresses
(addresses in the IP layer).

ROUTER
 A router can connect LANs together.
 A router can connect WANs together.
 A router can connect LANs and WANs together.
 In other words, a router is an internetworking device.
 It connects independent networks together to form an
internetwork. According to this definition, two networks
(LANs or WANs) connected by a router become an
internetwork or an internet.
A three-layer switch is a router

ROUTER
There are three major differences between a router and
a repeater or a bridge.
1. A router has a physical and logical (IP) address for
each of its interfaces.
2. A router acts only on those packets in which the
physical destination address matches the address of
the interface at which the packet arrives.
3. A router changes the physical address of the packet
(both source and destination) when it forwards the
packet.

COMPONENTS
 The router has four components :
1. Input ports
2. Output ports
3. Routing processor
4. Switching fabric

COMPONENTS
Input port:
1. An input port performs the physical and data link
layer functions of the router.
2. The bits are constructed from the received
signal.
3. The packet is decapsulated from the frame.
4. Errors are detected and corrected

COMPONENTS
Output ports:
1. An output port performs the same functions as the
input port, but in the reverse order.
2. First the outgoing packets are queued, then the
packet is encapsulated in a frame
3. And finally the physical layer functions are applied
to the frame to create the signal to be sent on the
line.

COMPONENTS
Routing processor:
1. The routing processor performs the functions of
the network layer .
2. The destination address is used to find the
address of the next hop.
3. This activity is sometimes referred to as table
lookup because the routing processor searches
the routing table.

COMPONENTS
Switching fabric:
1. The most difficult task in a router is to move the
packet from the input queue to the output queue.
2. The speed with which this is done affects the size
of the input/output queue and the overall delay in
packet delivery.
3. Routers use a variety of switching fabrics.
Some of the switching fabrics is ,
1) Crossbar Switch
2) Banyan switch

ADVANTAGES
 Easily Shared Internet.
 Security and Adaptability.
 Router limits the collision domain.
 Router can function on LAN & WAN.
 Router can connects different media & architectures.

DISADVANTAGES
 Router is more expensive than Hub, Bridge &
Switch.
 Routing updates consume bandwidth.
 Increase latency due to greater degree of
packet filtering.
 Complicated Setup.

A TYPICAL HOME / OFFICE WIRED ROUTER

EXAMPLE CONNECTIONS ON A ROUTER

 Gateway is a component that is part of two
networks, which use different protocols.
 It operates at all seven layers of OSI model.
 Unlike a router a gateway can forward packets
across different networks that may also use
different protocols.
 For example, If network A is token ring network
using TCP / IP and network B is in a Ethernet
network, a gateway can relay frames between
these two networks.
GATEWAY

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
G
A
T
E
W
A
Y
A
Physical layer
Data link layer
Network layer
Transport layer
Session layer
Presentation layer
Application layer
B
Gateway at all OSI layers

FUNCTIONS
 It has abilities to translate between different
frame formats and also between different
protocols.
 It is a very powerful computer system
compared with bridge.
 Used to connect huge and incompatible
networks.

ADVANTAGES
 The direct linking between internal and external
hosts are denied.
 In network gateway, the user level
authentication or protection is supported.
 Can connect or links two variant networks.
 The protocol conversion is done and it handles
the traffic problems.

DISADVANTAGES
 It is not an intellectual equipment.
 Protocol conversion is done so transmission
rate is slower.
 Expensive.
 Little hard to handle.
 Needs internal client to know about them.

REFERENCES
 “Data Communications and Networking”,
Behrouz A Forouzan.
 “Computer Networks -A Systems Approach”,
Larry L Peterson, Bruce S Davie.
 http://wikipedia.org/wiki/Networking_devices

Interconnecting devies

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