Network Components
Internetworking
• Internetworking is a comprehensive term for all the
concepts, technologies, and generic devices that
allow people and their computers to communicate
across different kinds of networks
• Some Internetworking Devices are:
• Repeaters
• Bridges
• Switches
• Routers
• Gateways
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Repeater
• Repeaters work at the OSI physical layer to regenerate the
network’s signal and resend them to other segments
• A Repeater is the simplest and the least expensive
internetworking device. It copies every messages it hears on
LAN #1 to LAN #2, sometimes unnecessarily.
• Used when you need to go farther distances than the cabling will
allow
• Usually has 2 ports (IN/OUT)
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Hub
• Primitive hub can be viewed as a multiport repeater
• It regenerates data and broadcasts them to all ports
• A central point of a star topology
• Allows the multiple connection of devices
• Functions in a similar manner to a Repeater
• Works at the Physical Layer of the OSI model
• Propagates each incoming signal to all connections
• Does not understand packets
• Multiple stations share one network connection
Hubs connecting segments
Bridge
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Like a Repeater or Hub it connects segments
Works at Data Layer – not Physical
Uses Mac address to make decisions
Acts as a ’filter’, by determining whether or not to forward
a packet on to another segment
Bridges
A bridge can be used to connect two similar LANs, such as two
CSMA/CD LANs.
A bridge can also be used to connect two closely similar LANs,
such as a CSMA/CD LAN and a token ring LAN.
The bridge examines the destination address in a frame and
either forwards this frame onto the next LAN or does not.
The bridge examines the source address in a frame and places
this address in a routing table, to be used for future routing
decisions.
Bridge
• Builds a Bridging Table, keeps track of devices on each
segment
• Filters packets, does not forward them, by examining
their MAC address
• It forwards packets whose destination address is on a
different segment from its own
• It divides a network in to multiple collision domains – so
reducing the number of collisions
• Bridges help to localize network traffic by only forwarding
data onto other segments as required (unlike repeaters)
A bridge interconnecting two dissimilar LANs
Bridge interconnecting two identical LANs
Illustration of a Bridge
• Bridge uses source address to learn location of computers
• Learning is completely automated
Illustration of a Bridge
Routing procedure for a transparent bridge:
1. If the destination and source LANs are the same, discard
the frame.
2. If the destination and source LANs are different, forward
the frame.
3. If the destination LAN is unknown, use flooding.
Remote Bridges
A remote bridge is capable of passing a data frame from one
local area network to another when the two LANs are separated
by a long distance and there is a wide area network connecting
the two LANs.
A remote bridge takes the frame before it leaves the first LAN
and encapsulates the WAN headers and trailers.
When the packet arrives at the destination remote bridge, that
bridge removes the WAN headers and trailers leaving the
original frame.
Two LANs with intervening frame relay network
Switches
•A switch is a combination of a hub and a bridge.
•A multiport Bridge, functioning at the Data Link Layer
•Each port of the bridge decides whether to forward data packets
to the attached network
•Keeps track of the Mac addresses of all attached devices (just
like a bridge)
•A switch improves network performance
•Each port on a Switch is a collision domain
When a frame arrives at a switch, the switch examines the
destination address and forwards the frame out the one necessary
connection.
•Workstations that connect to a hub are on a shared segment.
•Workstations that connect to a switch are on a switched
segment.
Switch
• A multiport Bridge, functioning at the Data Link Layer
• Each port of the bridge decides whether to forward data packets
to the attached network
• Keeps track of the Mac addresses of all attached devices (just
like a bridge)
• Similarly priced to Hubs – making them popular
• Acts like a Hub, but filters like a Bridge
• Each port on a Switch is a collision domain
Workstations connected to a shared segment of a LAN
Workstations connected to a dedicated segment of a LAN
A Switch with Two Servers Allowing Simultaneous Access to
Each Server
A server with two NICs and two connections to a switch
A pair of remote bridges and switch combination
designed to isolate network traffic
Switch providing multiple access to an e-mail server
Routers
A “router” is a device that operates at the network layer of
the OSI model
It supports multiple protocols (such as TCP/IP, IPX), and
can be used to link LANs together locally or remotely as
part of a WAN
Router
• Can connect different network segments, if they are in
the same building or even on the opposite side of the
globe
• Work in LAN and WAN environments
• Allows access to resources by selecting the best path
• Can interconnect different networks – Ethernet with
Token Ring
• Changes packet size and format to match the
requirements of the destination network
Characteristics of Routers
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Expensive piece of hardware
Comes with its own administrative burden
Can slow down the network
Have a lower packet-filtering-and-forwarding rate as
compared to switches
• Protocol-dependent and cannot handle protocols
that are not routable
• The move now is towards implementing “switching
routers”
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Router
• Two primary functions – to determine the ‘best path’ and
to share details of routes with other routers
• Routing Table – a database which keeps track of the
routes to networks and the associated costs
• Static Routing – routes are manually configured by a
network administrator
• Dynamic Routing – adjust automatically to changes in
network topology, and information it receives from other
routers
• Routing Protocol – uses a special algorithm to route data
across a network eg RIP
Gateway
• A Gateway is an inter-networking device that connects two or
more computer networks that use different communications
architectures
• Allows different networks to communicate by offering a
translation service from one protocol stack to another
• They work at all levels of the OSI model – due to the type of
translation service they are providing
• Address Gateway – connects networks using the same
protocol.
• Protocol Gateway – connects network using different protocols.
Translates source protocol so destination can understand it
• Application Gateway – translates between applications such as
from an Internet email server to a messaging server