Transcript 03-Concepts File

Networks
• A network is a collection of interconnected
systems that, typically, exchange information with
one another and share resources that may be
distributed among the systems.
• A computer network is a collection of terminals,
computers, servers and components (usually
owned and managed together) which allows for
the easy flow of data and use of resources between
one another
• A host or host computer is a computer that runs
(or hosts) end-user applications
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Subnetworks or Subnets
•
This term is used in respect of Computer Networks,
but it has two very different meanings which must be
determined from the context.
1. The subnetwork or subnet (sometimes also called the
communications subnetwork or subnet) is the part of
Computer Network left after all the hosts have been
excluded
2. The subnetwork or subnet can also mean an individual
network (such as an Ethernet) with a separate network
addressing range that forms part of an internetwork (such
as the Internet)
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Types of Network
• Personal Area Networks (PANs)
– Local to a person or personal computer (E.g. Bluetooth)
• Local Area Networks (LANs)
– Within a building (E.g. Ethernet)
• Metropolitan Area Networks (MANs)
– Between a group of buildings. (E.g. a campus network)
– Within a metropolitan area (city) E.g. Cable TV
• Wide Area Networks (WANs)
– Between cities, countries or continents
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Internetwork or Internet
• An internetwork or internet is a collection of
interconnected computer networks (a network of
networks).
Sometimes these networks incompatible (running
different protocols and addressing schemes and
must be interconnected by Gateways which
translate between the different protocols
NOTE: This is a generic term and the worldwide
Internet (with a capital I) is a specific example of
an internetwork
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Internetwork
LAN 1
LAN 2
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WAN 1
WAN 2
MAN 1
WAN 3
LAN 3
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Network Hierarchies
• Access Networks
• Distribution Networks
• Core Networks
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Access Networks
• Residential
– The Local Loop (Telco Exchange Line)
– Cable TV Networks
– Internet Service Provider Networks
• Institutional (Education or Business)
– LANs
• Mobile
– Wireless LANs
– Personal Area Networks (E.g. Bluetooth)
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Distribution Networks
• Provide no direct access for end-users
• Main function is to concentrate traffic from
the access network and pass it on to the core
network
• Provide limited resilience
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Core Networks
• Provide high performance and high capacity
to support large volumes of traffic
• Provide high level of resilience as failure of
the core will affect all users
• Topology of core should be kept stable.
Existing nodes and circuits should be
upgraded rather than adding new nodes to
the core
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Intranets
• An intranet is an internetwork which uses Internet
technology but is owned and managed by an
organisation (usually a company) for its the own
exclusive use to share information amongst its
employees
• Because intranets use the same technology as the
Internet, they are cheap to implement and operate
• An intranet is often connected to the public Internet
via firewalls which prevent unauthorised access
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Extranets
• An extranet is an extension of an intranet
that allows outsiders restricted access to an
organisation’s intranet
• Companies often allow their supplies,
partners and customers to access to some of
the information held on their intranets via
the Internet
• Usernames and password are used to
determine what information can be accessed
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Network Topologies
• Topology is a branch of Mathematics
• It is concerned with how things are
connected
• Spatial positions and distances are irrelevant
• It can be thought of as “rubber band
geometry”
• In topology, a cup is equivalent to a
doughnut!
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Network Topologies
•
•
•
•
•
•
Bus
Ring
Star
Tree
Mesh (Full or Partial)
Hybrid
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Bus Networks
• Buses are often used for LANs,
but not MANs or WANs. E.g.
Thick or Thin Ethernet using
coaxial cables
• The nodes all share access to the
same physical medium
• They are not resilient to failures
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Ring Networks
• Rings are used for LANs,
MANs and WANs. E.g. IBM
Token Ring and modern wide
area transmission systems
• They can provide resilience to
single failures
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Star Networks
• Star Networks are used in both
LANs and WANs. E.g. Twisted
pair Ethernets and Mainframe
computer networks where
remote terminals access a
central site
• They are not particularly
resilient to failures, especially at
the hub or central site
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Tree Network
• Extended bus with branching
points in a single medium (no
nodes)
• Often used in terminal host
networks to connect remote
terminals to a single point-tomultipoint circuit
• Not resilient, but can be designed
to minimise circuit lengths and
hence cost
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Mesh Networks
Fully Meshed Networks
• Are only used in WANs and
then usually only for small
networks or in core networks
• They are extremely resilient to
multiple failures
• They are very expensive if
there are a large number of
nodes
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Mesh Networks
Partially Meshed Networks
• Only used in WANs
• They are resilient to multiple
failures depending on the
degree of connectivity
• They are not as expensive as
fully meshed networks
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Hybrid Networks
There are many different possibilities including:
• Star–Bus Networks
• Star-Ring Networks
• Cascaded Star (Star-Star) Networks
• Multiple Overlapping Ring (Ring-Ring)
Networks
• Star-Mesh Networks
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Star-Bus Networks
Often used in
buildings where
each floor has a
star-connected
Ethernet and the
hub on each floor
is connected to a
Fast Ethernet bus
which connects
all the floors
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Star-Star Networks
Similar to a Tree
Networks, also
known as Cascaded
Star networks.
Again, they are
often used in
buildings where
each floor has its
own Sub-hub with
one floor having a
Master-hub
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Star-Ring Networks
This network has an
inner ring as a core
and the outer nodes
are connected to the
ring via star networks.
This type of network
is commonly used in
buildings with the ring
connecting hubs on
each floor. It is more
resilient than a starbus or cascaded star
network
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Star-Mesh Networks
The core network
is partiallymeshed and
connects with the
outlying nodes
via star networks
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Ring-Ring Networks
Also known as
Multiple
Overlapping Ring
Networks or
Shared Protection
Ring Networks
(SPrings) They
are used by Telcos
for their long haul
transmission
networks. They
are very resilient
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London Metropolitan Network (LMN)
© London Metropolitan Network Ltd.
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KPN Qwest Network
© KPN Qwest
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Joint Academic Network (JANET)
© The JNT Association
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