This document provides an overview of various networking devices used for interconnecting local area networks (LANs). It describes the functions of repeaters, hubs, bridges, routers, gateways, and switches. Repeaters operate at the physical layer to amplify and extend signals. Hubs operate at the physical layer, copying and broadcasting packets to all ports. Bridges operate at the data link layer and learn MAC addresses to forward packets between connected segments. Routers operate at the network layer, using network addresses and routing tables to path packets between different networks. Gateways can translate between incompatible networks, operating across multiple OSI layers. Switches provide bridging functionality with greater efficiency than hubs.

1. STIJ3053 NETWORK
DESIGN
CHAPTER 3.1
Network Design With Internet Tools
(INTERNETWORKING)
1

2. Learning Objectives
• After completing this chapter you will be able
to:-
– Explain the function of commonly used network
devices such as
repeaters, bridges, routers, brouters, hubs and
gateways.
– Determine when and how to use those devices
– Describe what OSI layer or layers correspond to the
function of each device.
2

3. Chapter Outline
• Introduction
• Repeater
• Hubs
• Bridge
• Router
• Gateway
• Multiprotocol Routers
• Brouter
• Switches
3

4. Introduction
• Internetworking is the art and science of connecting
LANs to create WANs, and connecting WANs to form an
even larger WANs.
• Internetworking can be extremely complex because it
generally involves connecting networks that use
different protocols.
• Connecting networks requires repeaters, hubs or
bridges
• Internetworking is accomplished with routers and
gateways.
4

5. Connecting Devices
5

6. Introduction (cont…)
• Each of the devices interacts with protocols at different layers of
the OSI model.
• Repeaters act only upon the electrical components of a signal
and active only at the physical layer.
• Bridges utilize addressing protocols and can affect the flow
control of a single LAN; they are most actives at the DLL.
• Routers provide links between two separate but same-type LANs
and are most active at that network layer.
• Gateways provide translation services between each
incompatible LANs or applications and are active in all of the
layers.
6

7. Connecting Devices & OSI
7

8. REPEATER
• Also known as generator, is an electronic device that operates on
only physical layer of the OSI model.
• Signals that carry information within a network can travel a fixed
distance before attenuation endangers the integrity of data.
• A repeater amplifies, retimes and reproduces a packet-carrying
signal so it can be sent along all cable segments.
• It is an inexpensive solution that enables a network to reach
users in distant portions of building that are beyond IEEE
specifications for a single cable to run.
8

9. REPEATER
9

10. REPEATER (cont…)
• The location of the repeater is vital.
• A repeater must be placed so that a signal reaches it
before any noise changes the meaning of any of its bits.
• A repeater placed on the line before the legibility of the
signal becomes lost can still read the signal well enough
to determine the intended voltages and replicate them
in their original form.
10

11. REPEATER (cont…)
11

12. REPEATER (cont…)
• Repeaters are used to:
– Extend a cable segment, such as beyond 185 meters for a
10Base2 segment.
– Increase the number of nodes beyond the limit of one
segment, such as to over 200 nodes for 10Base5.
– Sense a problem and shut down a cable segment
– Amplify and retime a signal in other network devices such as
hub.
12

13. REPEATER (cont…)
• Repeaters can be divided as:
– Simple repeater ~ offers an inexpensive way to extend
older bus topology coaxial-based networks.
– Multiport repeater ~ when a repeater retransmits a signal
along more that one additional cable segment.
13

14. Hub
• Also known as concentrator, is a center of activity.
• It is a common wiring point for networks that are based
around a star topology.
• ARCNET, 10BaseT and 100BaseF, as well as many other
proprietary network topologies, all rely on the use of
hubs to connect different cable runs and to distribute
data across the various segments of a network.
• Hubs are commonly used to connect segments of a
LAN.
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15. Hub (cont…)
• A hub contains a multiple ports.
• When a packet arrives at one port, it is copied to the other ports
so that all segments of the LAN can see all packets.
• Hubs basically act as a signal splitter.
• They take all of the signals they receive in through one port and
redistribute it out through all ports.
• Some hubs actually regenerate weak signals before re-
transmitting them.
• Other hubs retime the signal to provide true synchronous data
communication between all ports.
• Hubs with multiple 10BaseF connectors actually use mirrors to
split the beam of light among the various ports.
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16. Hub (cont…)
• Token Ring networks also have devices on them (MSAU)
that can be referred to as hubs.
• A multi-station Access Unit (MSAU) can also be
considered a type of hub, because it serves a similar
purpose of an Ethernet hub.
• However, MSAUs use mechanical switches and relays to
reroute packets to each active device in serially – not in
parallel like Ethernet hubs.
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17. Types of Hubs
• Hubs provide a crucial function on networks with a star topology.
• There are many different types of hubs, each offering specific
features that allow you to provide varying levels of service.
• Types of the hubs that can be found include:
– Passive hubs
– Active hubs
– Intelligent hubs.
• Most of them use some of the standard features, and some have
additional features that can be found in high-performance hub.
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18. Standard Features
• All hubs have a basic set of features that is determined in part by
the types of cabling that run to the hub.
• Most hubs are connected through RJ-45 jacks that rely on
twisted-pair cabling.
• Some other requirement that since hubs are electronic devices
that take signal and broadcast it to multiple ports, hubs need a
power source.
• Most hubs have LEDs, that can be used to monitor various
conditions.
• The two most common are LEDs to monitor power and active
connections at particular ports.
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19. Advanced Features
• There are many additional features supported by some high-end
hubs from various manufacturers.
– Redundant AC power supplies ~ If one fails, the other takes over – and is
fully capable of powering the entire unit.
– Built-in DC power supplies to function in the event of power outage.
– Redundant fans ~ provide cooling of the hub in the event that either fan
fails.
– Automatic termination for coaxial connections.
– Redundant configuration storage ~ assigning various properties to various
ports.
– Redundant clocks ~ allow any hub with an onboard clock on the network
to act as a master to help in timing packet delivery.
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20. Passive Hubs
• Do not do very much to enhance the performance of LAN and
assist in troubleshooting faulty hardware or finding performance
bottlenecks.
• They simply take all of the packets they receive on a single port
and rebroadcast them across all ports.
• Commonly have one 10Base2 port in addition to the RJ-45
connectors that connect each LAN device.
• This 10Base2 port can be used as a network backbone.
• In some advance passive hubs, have AUI ports that can be
connected to transceiver to form a backbone (10Base5).
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21. Active Hubs
• Generally, they have all the features of passive hubs, with the added
bonus of actually watching the data being sent out.
• Implementing “store & forward” ~ hubs actually look at the data they
are transmitting before sending it.
• They repair some certain “damaged” packets and will retime the
distribution of other packets.
• If a signal received is weak but still readable, they restore a signal to a
stronger state before rebroadcasting it.
• They provide certain diagnostic capabilities ~ malfunction devices on
the network.
• Help diagnose bad cables ~ by showing which port needs
retransmission or retiming.
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22. Intelligent Hubs
• Contain all of the features found inside the active hubs.
• Some additional features include:
– Ability to manage the network from one central location ~ if
problems develop with any device on a network that is connected
to intelligent hubs, it can easily identify, diagnose, and remedy the
problem using the management information provided by the hubs.
– Ability to offer flexible transmission rates to various devices.
– Flexible use of the media ~ media can be mixed such as twisted pair
with fiber optics.
9/23/2012 22

23. Switches
• Traditionally, a switch is a device that provides bridging
functionality with greater efficiency.
• It may act as a multiport bridge to connect devices or segments
in a LAN.
• The switch may normally has a buffer for each link (network) to
which it is connected.
• When it receives a packet, it stores the packet in the buffer of the
receiving link and checks the address to find the out-going link.
• If out-going link is free, the switch sends the frame to that
particular link.
9/23/2012 23

24. Switches (cont…)
• Switches are made based on two different strategies:
– Store-and-forward switch ~ stores the frame in the
input buffer until the whole packet has arrived.
– Cut-through switch ~ forwards the packet to the
output buffer as soon as the destination is received.
9/23/2012 24

25. Bridge
• It operates in both physical
and the data link layers of the
OSI model.
• It can divides a large network
into smaller segments.
• It can also relay frames
between two originally
separate LANs.
9/23/2012 25

26. Bridge (cont…)
It contains logic that allows them to
keep the traffic for each segment
separate.
It filters traffic and makes them
useful for controlling congestion and
isolating the problem links.
It also provides security through
partitioning the traffic.
9/23/2012 26

27. Bridge (cont…)
• It operates at DLL, giving it access to the physical address of all
stations connected to it.
• When a frame enters a bridge, the bridge not only regenerates
the signal but checks address of the destination and forwards the
new copy only to the segment to which the address belongs.
• As a bridge encounters a packet, it reads the address contained
in the frame and compares that address with a table of all the
stations on both segments.
• When it finds a match, it discovers to which segment the station
belongs and relays the packet only to that segment.
9/23/2012 27

28. Bridge (Example)
• A packet from station A addressed to
station D arrives at the bridge.
• Station A is on the same segment as
station D; therefore the packet is blocked
from crossing into the lower segment.
• Instead the packet is relayed to the entire
upper segment and received by station D.
• A packet generated by station A is
intended for station G.
• The bridge allows the packet to cross and
relays it to the entire lower
segment, where it is received by station G.
9/23/2012 28

29. Types of Bridge
• To select between segment, a bridge must have a look-up table
that contains the physical address of every station connected to
it.
• The table indicates to which segment each station belongs.
• There are three types of bridge:
– Simple bridge
– Multiport bridge
– Transparent bridge
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30. Simple Bridge
• The most primitive and least expensive type of bridge.
• It links two segments and contains a table that lists the addresses
of all the stations included in each of them.
• What makes it primitive is that theses addresses must be entered
manually.
• Before a simple bridge can be used, an operator must sit down
and enter the addresses of every station.
• Whenever a new station is added, the table must be modified.
• If a station is removed, the address must be deleted.
• Installation and maintain simple bridge is time-consuming.
9/23/2012 30

31. Multiport Bridge
• It can be used to connect
more than two LANs.
• If the bridge connects 3
LANs, it must have three
tables, each one holding
the physical address of
stations reachable
through the
corresponding port.
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32. Transparent Bridge
• Also known as learning bridge, builds its table of station
addresses on its own as it performs its bridge functions.
• When the transparent bridge is first installed, its table is empty.
• As it encounters each packet, it looks at both the destination and
source addresses.
• It checks the destination to decide where to send the packet.
• If it does not yet recognize the destination address, it relays the
packet to all of the stations on both segments.
9/23/2012 32

33. Transparent Bridge (cont…)
• It uses the source address to build its table.
• As it reads the source address, it notes which side the packet
came from and associates that address with the segment it
belongs.
• With the first packet transmitted by each station, the bridge
learns the segment associated with that station.
• Eventually it has a complete table of station addresses and their
respective segment stored in its memory.
• By continuing this process even after the table is complete, a
transparent bridge is also self-updating.
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34. Spanning Tree Algorithm
• Bridges are normally installed redundantly, which
means that two LANs may be connected by more than
one bridge.
• If the bridge is transparent bridge, it may create a
loop, which means a packet may be going round and
round, from one LAN to another and back again to the
first LAN.
• To avoid this situation, bridge use what is called
“spanning tree algorithm”.
9/23/2012 34

35. Source Routing
• Another solution to prevent loops in the LANs
connected by bridges.
• In this method, the source of the packet defines the
bridges and the LANs through which the packet should
go before reaching the destination.
9/23/2012 35

36. Router
• An internetworking device operating at
the first three OSI layers
(physical, DLL, network).
• A router is attached to two or more
networks and forwards packets from
one network to another.
• It has access to network layer
addresses and contain software that
enables them to determine which of
several possible paths between those
addresses is the best for a particular
transmission.
9/23/2012 36

37. Router
• It connects any number of LANs.
• It uses headers and a forwarding table
to determine where packets go, and
they use ICMP to communicate with
each other and configure the best
route between any two hosts.
• Very little filtering of data is done
through routers ~ do not care about
the type of data they handle.
• It connects LANs at the network layer
of the OSI model, which enables them
to interpret more information from
frame traffic than bridges.
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38. Router
• Types of routers:
– Local router ~ joins networks in the same building or between
buildings.
– Remote router ~ joins networks across large geographic
areas, such as between cities, state and countries.
– Multiprotocol router ~ a router that can handle packets from
different protocols.
– Brouter ~ a device that functions as both a bridge and a
router.
9/23/2012 38

39. Multiprotocol Routers
• Usually, at the network layer, a router by default is a single-
protocol device.
• In other words, if two LANs are to be connected through a
router, they should use the same protocol at the network layer.
• E.g. both should use IP (the network layer protocol of the
internet) or IPX (Novell).
• The reason is that the routing table should use one single
addressing format.
• Multiprotocol routers have been designed to route packets
belonging two or more protocols.
9/23/2012 39

40. Multiprotocol Routers (cont…)
• E.g. A two-protocol router (IP and IPX) can handle packets
belonging to either of the two protocols.
• It can receive, process, and send a packet using the IP protocol or
it can receive, process and send a packet using the IPX protocol.
• In this case, the router has two routing tables: one for IP and one
for IPX.
9/23/2012 40

41. Brouters
• A brouter (bridge/router) is a single-protocol or
multiprotocol router that sometimes acts as a router
and sometimes as a bridge.
• When a brouter receives a packet belonging to the
protocol for which it is designed, it routes the packet
based on the network layer address; otherwise it acts
as a bridge and passes the packet using the DLL
address.
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42. Functions of Routers
• Routers are used for:
– Segment network traffic
– Limit certain types of packets from leaving a specific network segment
– Control which network nodes are able to reach a segment that contains
sensitive information.
– Efficiently direct packets from one network to another, reducing excessive
traffic.
– Join neighboring or distant networks.
– Connect dissimilar networks.
– Prevent network bottlenecks by isolating portions of a network.
– Secure portions of a network from intruders.
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43. Routing
• Routing can be performed in two ways:
– Static routing
– Dynamic routing
• Static Routing
– Accomplished by the network administrator setting up the network tables
so there are fixed paths between any two routers.
– The network administrator also intervenes to update routing tables when
a network device fails.
– A static router can determine that a network link is down, but it cannot
automatically reroute traffic without intervention from the network
administrator.
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44. Dynamic Routing
• It occurs independently of the network administrator.
• Dynamic routers monitor the network for changes, update their
routing tables, and reconfigure network paths as needed.
• When a network link fails, a dynamic router automatically
detects the failure and establishes the most efficient new paths.
• The new paths are configured based on the lowest cost as
determined by network load, line type and bandwidth.
• Routers maintain information about node addresses and the
network status in databases.
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45. Dynamic Routing (cont…)
• The routing table databases contain the addresses of other
routers and of each end node.
• Dynamic routers automatically update the routing table by
regularly exchanging address information with other routers and
network nodes.
• Routers also regularly exchange information about network
traffic, topologies and the status of network links.
• The information is kept inside a network status database in each
router.
9/23/2012 45

46. Gateways
• Operate in all seven layers of the
OSI model.
• It is a protocol converter.
• A router by itself
transfers, accepts, and relays
packets only across networks using
similar protocols.
• A gateway can accept packet
formatted for one protocol (e.g.
AppleTalk) and convert it to a
packet formatted for another
protocol (e.g. TCP/IP) before
forwarding it.
9/23/2012 46

47. Gateways (cont…)
• A gateway is generally a software installed within a router.
• The gateway understands the protocols used by each network
linked into the router and is therefore able to translate from one
to another.
9/23/2012 47

48. Gateways Functions
• Convert commonly used protocols (e.g. TCP/IP) to a
specialized protocol (e.g. SNA)
• Convert message formats from one format to another
• Translate different addressing schemes
• Direct e-mail to the right network destination
• Connect networks with different architecture
(SNA, TCP/IP, Novell, OSI etc).
• Connecting LAN to WAN
9/23/2012 48

49. Summary
• Introduction
• Repeater
• Hubs
• Bridge
• Router
• Gateway
• Multiprotocol Routers
• Brouter
• Switches
9/23/2012 49