PC 106 PPT-05

Network Topologies
LAN topologies
WAN topologies

LAN topologies
 Physical
Describes the geometric arrangement of
components that make up the LAN
 Logical
Describes the possible connections
between pairs of networked end-points
that can communicate
2

LAN Topologies(Physical)
1) Bus
2) Star
3) Ring
4) Switched
5) Daisy chains
6) Hierarchies
3

Bus topology
 All networked nodes are
interconnected, peer to peer, using a
single, open-ended cable
 Both ends of the bus must be
terminated with a terminating resistor
to prevent signal bounce
4

Advantages of Bus topology
1) Easy to implement and extend
2) Well suited for temporary networks
that must be set up in a hurry
3) Typically the least cheapest topology
to implement
4) Failure of one station does not affect
others
6

Disadvantages of Bus
topology
1) Difficult to administer/troubleshoot
2) Limited cable length and number of
stations
3) A cable break can disable the entire
network; no redundancy
4) Maintenance costs may be higher in
the long run
5) Performance degrades as additional
computers are added
7

Ring topology
 started out as a simple peer-to-peer
LAN topology
 Each networked workstation had two
connections: one to each of its nearest
neighbors
 Data was transmitted unidirectionally
around the ring
 Sending and receiving of data takes
place by the help of TOKEN
8

Token Passing
 Token contains a piece of information
which along with data is sent by the
source computer
 This token then passes to next node,
which checks if the signal is intended
to it
If yes, it receives it and passes the empty
to into the network
otherwise passes token along with the
data to next node
9

Advantages of Ring topology
1) This type of network topology is very
organized
2) Performance is better than that of Bus
topology
3) No need for network server to control
the connectivity between workstations
4) Additional components do not affect the
performance of network
5) Each computer has equal access to
resources
11

Disadvantages of Ring
topology
1) Each packet of data must pass
through all the computers between
source and destination, slower than
star topology
2) If one workstation or port goes down,
the entire network gets affected
3) Network is highly dependent on the
wire which connects different
components
12

Star topology
 Have connections to networked
devices that “radiate” out form a
common point
 Each networked device in star
topology can access the media
independently
 Have become the dominant topology
type in contemporary LANs
 Stars have made buses and rings
obsolete in LAN topologies 13

Advantages of star topology
1) Compared to Bus topology it gives
far much better performance
2) Easy to connect new nodes or
devices
3) Centralized management. It helps in
monitoring the network
4) Failure of one node or link doesn’t
affect the rest of network
15

Disadvantages of star topology
1) If central device fails whole network
goes down
2) The use of hub, a router or a switch
as central device increases the
overall cost of the network
3) Performance and as well number of
nodes which can be added in such
topology is depended on capacity of
central device
16

Switched topology
 A switch is a multiport, Data Link Layer device
 A switch “learns” Media Access Control
addresses and stores them in an internal
lookup table
 Temporary, switched paths are created
between the frame’s originator and its
intended recipient, and the frames are
forwarded along the temporary path
 Switched topology features multiple
connections to a switching hub/Switch
 Each port, and the device to which it
connects, has its own dedicated bandwidth
17

Advantages/Disadvantages of a
Switched topology
 Advantage:
Can improve LAN performance:
increase the aggregate bandwidth
available throughout the network
reducing the number of devices forced
to share each segment of bandwidth
 Disadvantage:
Large switched implementations do not
isolate broadcasts
19

Daisy chains
 Developed by serially interconnecting
all the hubs of a network
 This simple approach uses ports on
existing hubs for interconnecting the
hubs
 Daisy chains are easily built and don’t
require any special administrative
skills
 Daisy chains were, historically, the
interconnection method of choice for 20

Disadvantage of Daisy chain
 Increases the number of connections,
and therefore the number of devices,
on a LAN. Too many devices
competing for the same amount of
bandwidth can create collisions and
quickly incapacitate a LAN
22

Hierarchies
 Hierarchical topologies consist of more
than one layer of hubs. Each layer
serves a different network function
 The bottom tier is reserved for user
station and server connectivity. Higher-
level tiers provide aggregation of the
user-level tier
 A hierarchical arrangement is best
suited for medium-to-large-sized LANs
that must be concerned with scalability
of the network and with traffic 23

Hierarchical rings
 Ring networks can be scaled up by
interconnecting multiple rings in a
hierarchical fashion
 User station and server connectivity can
be provided by as many limited size
rings as are necessary to provide the
required level of performance
 A second-tier ring, either Token Ring or
FDDI, can be used to interconnect all the
user level rings and to provide
aggregated access to the Wide Area
Network (WAN) 24

Hierarchical stars
 Star topologies, can be implemented
in hierarchical arrangements of
multiple stars
 Hierarchical stars can be implemented
as a single collision domain or
segmented into multiple collision
domains using switches, routers or
bridges
26

Hierarchical combinations
 Overall network performance can be
enhanced by not force-fitting all the
functional requirements of the LAN
into a single solution
 Today’s high-end switching hubs
enable you to mix multiple
technologies
28

WAN Topologies
 The topology of a WAN describes the
way the transmission facilities are
arranged relative to the locations that
they interconnect
 Numerous topologies are possible,
each one offering a different mix of
cost, performance and scalability
30

WAN Topologies
1) Peer-to-peer WANs
2) Ring WANs
3) Star WANs
4) Full-mesh WANs
5) Partial-mesh WANs
6) Two-tiered
7) Three-tiered
8) Hybrids
31

Peer-to-peer topology
 A peer-to-peer WAN can be
developed using leased private lines
or any other transmission facility
 This WAN topology is a relatively
simple way of interconnecting a small
number of sites
 Represents the least-cost solution for
WANs that contain a small number of
internetworked locations
32

Peer-to-peer
T1
T1
User Location A
User Location B
User Location C
33

Advantage/Disadvantage of
Peer-to-peer
 Advantage:
It is inexpensive relative to other options
 Disadvantages:
They don’t scale very well. As additional
locations are introduced to the WAN, the
number of hops between any given pair of
locations remains highly inconsistent and
has an upward trend
An equipment or facility failure anywhere
in a peer-to-peer WAN can split the WAN
34

Ring topology
 Can be developed fairly easily from a
peer-to-peer network by adding one
transmission facility and an extra port on
two routers
 A ring-shaped WAN constructed with
point-to-point transmission facilities can
be used to interconnect a small number
of sites and provide route redundancy at
a potentially minimal incremental cost
 Can use dynamic routing protocols
35

Ring topology
T1
T1
User Location A
User Location B
User Location C
T1 T1
User Location D
36

Advantages/Disadvantages of
Ring topology
 Advantages:
It provides alternative routes
It is less expensive than all but the peer-
to-peer WAN
 Disadvantages:
Depending on the geographic dispersion
of the locations, adding an extra
transmission facility to complete the ring
may be cost prohibitive
Rings are not very scalable
37

Star network Topology
 constructed by homing all locations
into a common location
 The star topology can be constructed
using almost any dedicated
transmission facility including frame
relay and point-to-point private lines
38

star topology
 Advantages:
More scalable than a peer-to-peer or ring
network
Improved network performance. Hop
count of three
 Disadvantages:
It creates a single point of failure
There is no route redundancy
39

Star topology
T1
T1
User Location A
User Location B
User Location C
T1
User Location D
40

Full-mesh topology
 This topology features the ultimate reliability and fault
tolerance
 Every networked node is directly connected to every
other networked node
 Redundant routes to each location are plentiful, hence
static routing impractical.
 Use dynamic routing protocols
 One application would be to provide interconnectivity
for a limited number of routers that require high
network availability
 Another potential application is to fully mesh just parts
of the WAN, such as the backbone of a multitiered
WAN or tightly coupled work centers
41

full-mesh
 Advantages:
Minimizes the number of hops between
any two network-connected machines
Can be built with virtually any
transmission technology
 Disadvantages:
These WANs can be fairly expensive to
build
A finite (although substantial) limit on the
scalability of the network
42

Full-mesh topology
T1
T1
User Location A
User Location B
User Location C
T1 T1
User Location D
T1
T1
43

Partial-mesh topology
 Partial meshes are highly flexible
topologies that can take a variety of very
different configurations
 The routers are much more tightly
coupled than any of the basic topologies
but are not fully interconnected, as
would be the case in a fully meshed
network
 A partially meshed WAN topology is
readily identified by the almost complete
interconnection of every node with every
44

Partial-mesh
T1
T1
User Location A
User Location B
User Location C
User Location D
T1
T1
45

Advantages of partial-mesh
 Partial meshes offer the capability to
minimize hops for the bulk of the
WAN’s users
 Unlike fully meshed networks, a partial
mesh can reduce the startup and
operational expenses by not
interconnecting low-traffic segments of
the WAN, hence more affordable and
scalable
46

Two-tiered topology
 A two-tiered topology is a modified
version of the basic star topology.
Rather than single concentrator
routers, two or more routers are used
 A two-tiered WAN constructed with
dedicated facilities offers improved
fault tolerance over the simple star
topology without compromising
scalability
47

Two-tiered topology
T1 T1
User Location B
User Location D User Location F
T1
User Location E
T1 T1
User Location A
User Location C
48

Three-tiered topology
 WANs that need to interconnect a very
large number of sites, or are built
using smaller routers that can support
only a few serial connections, may find
the two-tiered architecture
insufficiently scalable.
 Therefore, adding a third tier may well
provide the additional scalability they
require
49

Three-tiered
T1
T1
User Location A
User Location B
User Location D
T1
User Location C
56Kb T1
T1
56Kb T1
User Location E User Location F User Location G User Location H
User Tier
Concentrator tier
Backbone tier
50

Advantage/Disadvantage of
three-tiered
 Advantage:
A three-tiered WAN constructed with
dedicated facilities offers even greater
fault tolerance and scalability than the
two-tiered topology
 Disadvantage:
Three-tiered networks are expensive to
build, operate and maintain
51

Hybrid topologies
 Hybridization of multiple topologies is
useful in larger, more complex networks
 Multitiered networks, in particular, lend
themselves to hybridization. A multitiered
WAN can be hybridized by fully or
partially meshing the backbone tier of
routers
 An effective hybrid topology may be
developed in a multitiered WAN by using
a fully meshed topology for the
backbone nodes only 52

Hybrid topology
T1
T1
User Location B
User Location D
T1
User Location C
56Kb T1
T1
56Kb T1
User Location E User Location F User Location G User Location H
User Tier
Concentrator tier
Backbone tier
T3 T3
T3
53

PC 106 PPT-05

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PC 106 PPT-05