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 12/10/10 03-Concepts

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) 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

Internetwork LAN 1 LAN 4 WAN 1 WAN 2 MAN 1 WAN 3 LAN 2 LAN 3 LAN 5 12/10/10 03-Concepts

Network Hierarchies Access Networks Distribution Networks Core Networks 12/10/10 03-Concepts

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) 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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! 12/10/10 03-Concepts

Network Topologies Bus Ring Star Tree Mesh (Full or Partial) Hybrid 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

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 12/10/10 03-Concepts

Star-Mesh Networks The core network is partially- meshed and connects with the outlying nodes via star networks 12/10/10 03-Concepts

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 12/10/10 03-Concepts

London Metropolitan Network (LMN) © London Metropolitan Network Ltd. 12/10/10 03-Concepts

KPN Qwest Network © KPN Qwest 12/10/10 03-Concepts

Joint Academic Network (JANET) © The JNT Association 12/10/10 03-Concepts