NetworksThe Big Picture

Three Great Leaps of Civilization

Computer Network

Single Computer Network of Computers

Why Network?

• Access information• Exchange information• Networks help people work faster and

smarter by making information available when they need it, where they need it.

Makes distances between computers invisible.

Network Services and BenefitsSharing Information

You and other network users can have access to the same information.

Accessing remote information

You can use your personal devices to access information through a public information service.

CommunicatingYou can exchange messages with a local group or around the world in a quick and paperless form of communication.

Sharing ApplicationsYou and several other users can have access to the same application software; for example everyone in a work group can upgrade simultaneously.

Sharing Network ResourcesNetworks allow users to share connected devices (i.e. printers)

Overview of Computer Networks

• A network suggests a collection of related things or people that are somehow interconnected.

• In a computer network the interconnected parts are computers, peripherals and other devices that communicate with one another.

• A computer network may connect as few as two computers or as many as thousands even millions.

Computer Networks

This is a Network. This is not a Network.

Network Evolution

Host-Based computing

Decentralized computing

Peer-to-peer computing

Cloud computing

What is a computer network made of?

• Network Components– Hardware: clients and servers; shared devices

(peripherals); hubs, routers and switches– Software: applications and underlying control

software that allows the components to work together

– Network Media: fiber optics, wireless (infrared and radio)

Clients and Servers

Client computers•Regular desktop, laptop, or mobile devices that connect to a network to use its services.•When connecting to a network, clients normally have to authenticate themselves using a username and password.

Clients and Servers

Servers •Assigned responsibility for certain tasks for the whole network, provide services for other computers (clients)

– File servers– Application servers– Print servers– Database server– Authentication server (domain controller)– Firewall– Web server– Email server

Shared Devices

Hubs, Routers and Switches

All three allow multiple computers to be connected to them.

Difference: how each broadcasts data

Hubs

• Most basic and cheapest of these devices• Broadcasts to every connected device,

including the one that sent it• Lot of wasted bandwidth

Switches

• Smarter version of hubs• Inspect received data and forward to intended

recipient• Saves bandwidth compared to hubs

Routers

• Connect two or more separate networks• Gateway through which all data entering and

leaving the network passes

Network Architecture

Network architecture refers to the way computers are locally organized on a network, and the role each takes.

Network Architecture

Client/ Server Network Peer-to-Peer Networks (P2P)

Client/Server

Centralized on one or more computers that act as servers to the rest of the network

Centrally manage access control and provide a single location for file storage

Benefits Access from any client (not limited to one computer) Easier to backup files Better security (authenticate users and control access)

Client/ Server

P2P (Peer-to-Peer)

No central authority or control(all clients equal status)

User accounts have to be made on each machine for each use who wants access

Less security

Benefits Cost efficient

Peer-to-Peer File Sharing

Sharing files over the internet without a central server

Every user both downloads they need and uploads the data they have.

Quicker downloading from single server

Concern: A means to illegally spread copyrighted material(e.g. Napster)

Peer to Peer (P2P)

Firewalls

Determine which data is allowed to enter and leave a network

Secure a computer by preventing network access from external unauthorized access

Control user connection to external networks

Proxy Servers

Middle step between two computers(computer on LAN and web server on Internet)

All communication between the two passes through proxy

Caching, filtering, logging data

Types of Networks

Local Area Networks (LAN) Wireless LANs (WLAN) Personal Area Networks (PAN) Metropolitan Area Networks (MANs) Wide Area Networks (WAN) Storage Area Networks (SAN) Virtual Private Networks (VPN) Virtual LAN (VLAN)

Protocols

• Network protocols are the rules that network devices must follow to successfully interact with one another.

• Protocols define the actual steps that any device or program must take to communicate with another device or program on the network.

Protocols

TCP/ IP: Transmission Control Protocol

Internet Protocol

Network Connections

Cables and other carriers of a network’s transmission signals are called media. Wired Connections Wireless Connections

Wired Connections

Dialup Ethernet Cable Internet Access Fibre optic cables

Wireless Connections

Wi-Fi WiMax BlueTooth 3G and 4G

Network Media Characteristics

Transmission Speed

Maximum Length

Shielding Against Interference

Physical properties of different media types make them suitable for higher or lower rates of data transmission.

Signals transmitted cannot travel indefinitely. After a given distance, the signal begins to weaken, lose integrity, and experience severe distortion.

You can partially protect transmission by locating network cables away from potential sources of interference.

Signal interference and other factors can reduce media reliability, requiring transmission to be limited to lower speeds.

Distances can be amplified using devices such as repeaters, bridges, or by joining multiple networks.

Network cables are available with varying forms of shielding that can lessen the signal’s sensitivity to outside interference.

Network Media Comparisons

Network Media Comparisons

Measuring Network Speed

• Bandwidth: Network’s speed; the quantity of information that can be transmitted through a communication medium in a given amount of time.

• Broadband: an Internet connection (DSL or cable modem) that offers higher bandwidth , and therefore faster transmission speed.

• Units of measurement: bps, Kbps, Mbps, Gbps

Connecting Networks Together

• Routers: Hardware device used to connect two separate networks that decide the best “route” for Internet transmissions.

• Gateways: Computer which acts as a bridge between a local area network and the Internet.

Preventing Unauthorized Access