3 computer networks

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TYPES OF NETWORK

In the world of computers, networking is the practice of linking two or more

computing devices together for the purpose of sharing data. Networks are built

with a mix of computer hardware and computer software.

Networks can be categorized in several different ways. One approach defines the

type of network according to the geographic area it spans. Local area networks

(LANs), for example, typically reach across a single home, whereas wide area

networks (WANs), reach across cities, states, or even across the world.

The Internet is the world's largest public WAN.

Network Design

Computer networks also differ in their design. The two types of high-level

network design are called client-server and peer-to-peer. Client-server networks

feature centralized server computers that store email, Web pages, files and or

applications. On a peer-to-peer network, conversely, all computers tend to

support the same functions. Client-server networks are much more common in

business and peer-to-peer networks much more common in homes.


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TOPOLOGY

A network topology represents its layout or structure from the point of view of

data flow. In so-called bus networks, for example, all of the computers share and

communicate across one common conduit, whereas in a star network, all data

flows through one centralized device. Common types of network topologies

include bus, star, ring and mesh.

1. RING Topology

2. BUS Topology


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3. STAR Topology

4. MESH Topology


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5. TREE Topology

6. HYBRID Topology


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LAN: Local Area Network

Typically connects computer in a single building or campus.

Developed in 1970s.

Medium: optical fibers, coaxial cables, twisted pair, wireless.

Low latency (except in high traffic periods).

High speed networks (0.2 to 100 Mbps).

Speeds adequate for most distributed systems

Problems : Multi media based applications

Typically bus or ring topology

Ethernet, Token Ring


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MAN: Metropolitan Area Network

Generally covers towns and cities (50 km)

Developed in 1980s.

Medium: optical fibers, cables.

Data rates adequate for distributed computing applications.

A typical standard is DQDB (Distributed Queue Dual Bus).

Typical latencies: < 1 ms.

Message routing is fast.


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WAN: Wide Area Network

Developed in 1960s.

Generally covers large distances (states, countries, continents).

Medium: communication circuits connected by routers.

Routers forwards packets from one to another following a route from the

sender to the receiver. Store-and-Forward

Hosts are typically connected (or close to) the routers.

Typical latencies: 100ms - 500ms.

Problems with delays if using satellites.

Typical speed: 20 - 2000 Kbps.

Not (yet) suitable for distributed computing. New standards are changing the landscape.

3 computer networks

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