1. 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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2. 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.
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
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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3. 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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4. 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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5. Internetwork LAN 1 LAN 4 WAN 1 WAN 2 MAN 1 WAN 3 LAN 2 LAN 3 LAN 5
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6. Network Hierarchies Access Networks Distribution Networks
Core Networks
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7. Access Networks Residential Institutional (Education or Business)
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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8. 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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9. 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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10. 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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11. 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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12. 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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13. Network Topologies Bus Ring Star Tree Mesh (Full or Partial) Hybrid
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14. 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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15. 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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16. 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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17. 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-to-multipoint circuit
Not resilient, but can be designed to minimise circuit lengths and hence cost
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18. 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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19. 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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20. 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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21. 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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22. 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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23. 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 star-bus or cascaded star network
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24. Star-Mesh Networks
The core network is partially- meshed and connects with the outlying nodes via star networks
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25. 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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26. London Metropolitan Network (LMN)
© London Metropolitan Network Ltd.
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27. KPN Qwest Network
© KPN Qwest
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28. Joint Academic Network (JANET)
© The JNT Association
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