Comp Sci 2

Connectivity

Using computer networks to link people and resources

Communication system

Electronic systems that transmit data between locations

Four elements of communication system

Send and receiving, connection devices, data transmission specifications, communication channel

Sending and receiving devices

Originate (send) and accept (receive) messages as data, info, or instructions

Connection devices

Interface between sending and receiving devices and communication channel, convert outgoing messages into packers for travel, reverse process for incoming messages

Data transmission specifications

Rules and procedures that coordinate S and R devices, define how message will be sent across communication channel

Communication channel

Transmission medium that carries the message, can be physical or wireless

Cellular communication

Uses antennae (cell towers) to S and R data within cells

Cells

Small geographic regions

Bluetooth

Short range radio comm, transmits data over short distances, 33 feet

Wi-Fi (wireless fidelity)

Uses high frequency radio signals to transmit data

Microwave communication

Uses high frequency radio waves

Microwave communication, AKA  line-of sight communication because

Microwaves can only travel in straight line

WiMax (Worldwide Interoperability for Microwave Access)

Wireless standard, extends range of Wi-Fi networks using microwave connections

Satellite communication

Use satellites orbiting 22, 000 miles above earth as microwave relay stations

Intelsat

International Telecommunications Satellite Consortium, worldwide communication system

Uplink

Sending data to a satellite

Downlink

Receiving data from a satellite

Global positioning system (GPS)

Network of satellites continuously sends location info to earth to determine geo location of device

Infrared

Infrared light waves communicate over short distances, line-of-sight

Physical connections

Twisted pair, coaxial, fiber-optic

Fiber-optic

Transmits data as pulses of light through tiny glass tubes, 1 petabit per second, lighter, faster, more reliable

Coaxial cable

High frequency transmission cable, replaces wires with single solid copper core, 80x transmission capacity of twisted pair

Twisted-pair cable

Pairs of copper wire twisted together - used by telephone and Ethernet

Analog signals

Continuous electronic waves

Digital signals

Represent binary signals, sent and received by computers

Modulation

Converting from digital to analog

Demodulation

Converting from analogue to digital

Full length motion picture (700 MB) on 1.5Mbps vs 10Mbps

1 hour vs 9 mins

Digital Subscriber Line (DSL) modem

Uses phone lines to create high-speed connection from company to phone, connects through USB or Ethernet

Cable modem

Uses coaxial cable, creates high-speed connection using USB or Ethernet port

Wireless wide area network (WWAN) modem

Built-in to most modern computers, or wireless adapter cards for plug in

T1 Line

High-speed copper line, leased from phone company

T3/DS3 Lines

Combined T1 lines for higher capacity

Optical carrier (OC) Lines

Faster than T1 and T3 lines

Dial-up services

Using existing telephones and modems to connect to the Internet

Cellular service providers

Support voice and data transmission to wireless devices using cellular networks

1G

First generation, started in 1980s, transmit only analog signals for voice communication

2G

Second gen, Used radio signals for cellular calls, introduced texting

3G

Third gen, improved data speed, widespread Internet use on cell phones

4G

Fourth gen, uses Long Term Evolution (LTE) for faster Internet, better video/music streaming

5G

Fifth gen, speeds rival ISP

Digital Subscriber Line (DSL) service

Provided by phone companies, use existing lines to provide high-speed connection

Asymmetric digital subscriber line (ADSL)

One of most widely used DSL

Cable service

Provided by cable television, faster than DSL

Fiber-optic service (FiOS)

Faster than cable or DSL

Satellite connection services

Slower than DSL and cable but available almost anywhere with receiving disk

Bandwidth

Capacity of communication channel, how much info can move across in a time, four categories

Voiceband/ Low bandwidth

Used for landline telephone comms

Medium band

Special leased lines, connect midrange and mainframe computer, transmit over long distance, high speed

Broadband

Used for DSL, cable, satellite connections, can be used by several users at once for high speed transfer

Baseband

Connect computers located closer together, high speed, carries one signal at a time

Hypertext Transfer Protocol Secure (HTTPS)

Protects transfer of sensitive information

Transmission Control Protocol/Internet Protocol (TCP/IP)

Internet Protocol, identifies S and R devices, breaks information into packets for transmission

Identification

Uses IP address to deliver email and locate websites

Internet Protocol (IP) address

Unique numeric address for each computer on the Internet

Domain name server (DNS)

Converts text address to numeric IP address

Packetization

Message packetized, packets sent separately, sometimes over different routes, reassembled at common destination

Packet

Message reformatted or broken into smaller parts

Computer network

Communication system connecting two or more computers to exchange information and share resources

Node

Any device connected to a network

Client

Node that uses resources from other nodes

Server

Nodes that shares resources with other nodes, types of servers include: Application, communication, database, file, printer, web

Directory server

Special server, manages resources for entire network

Host

Any CS connected to network that provides resources

Router

Node that routes data packets from one network to destination network

Switch

Central node, coordinates flow of data, sends messages directly between sender and receiver nodes

Hub

Sends received messages to all connected nodes, not just intended

Network administrator

Manage LAN and WAN networks, responsible for design, implementation and maintenance of networks

Local area network (LAN)

Span less than a mile, close proximity, operated by individual organizations to link PCs and share resources

Network gateway

Allows one LAN to link to other LANs or larger networks

Ethernet

A standard to connect nodes to one another, how their communications are controlled in a LAN

Home network

Used by individuals in homes, allow resource sharing and common Internet connection

Wireless Local Area Network (WLAN)

Uses radio frequencies to connect devices

Wireless access point/Base Station

Centrally located, all communications pass through, interprets incoming radio frequencies, routes communication to devices

Hotspots

Wireless access points that provide Internet access

Personal area network (PAN)

Wireless network that works within a small area, immediate surroundings - ex Bluetooth, reaches 33 feet

Metropolitan area networks (MAN)

Span up to 100 miles, used as links between office buildings throughout a city, owned by group of organizations or single NSP

Wide area networks (WAN)

Country and worldwide networks, provide access to regional service provides, span more than 100 miles

Network architecture

How network resources are coordinated and shared

Network topology

Physical arrangement of the network

Bus network

Each device connected to bus/backbone (common cable), communications travel along bus

Ring network

Each device connected to two other devices, forming a ring, message passed along ring until intended destination

Star network

Each device connected to central network switch, messenger node routed to switch, switch passes message to recipient

Tree network AKA hierarchical network

Each device connected directly or indirectly to central node, central node connected to two or more subordinates, subords connected to two more subords and so on

Mesh network

Each node has more than one connection to other nodes, pattern forms mesh, path disruptions can be rerouted using an alternate path

Strategy

Way of coordinating info and resource sharing

Client/server

Use central servers to supply services to other network nodes, server provides access to resources - server nodes supply, client nodes request

Peer-to-peer (P2P) network

Nodes have equal authority, act as clients and servers, used to share media and entertainment, free and easy to use but lack security control

Intranet

Private network within organization, resembles Internet

Extranet

Private network to connect more than one organization, increases efficiency, reduces costs

Firewall

Security buffer between private and external networks, hardware and software that control access to intranet and internal networks

Proxy server

Firewall software, all communication between internal networks and outside world (source, content) evaluated before being let through

Intrusion detection system (IDS)

Work with firewalls to protect organization network, use statistics, pattern matching, and heuristics to analyse network traffic, recognize signs of attack and disable access to intruders

Virtual private network (VPN)

Secure private connection between remote user and organization network, dedicated line between PC and company server, heavily encrypted

Privacy

Collection and use of data about individuals

Three privacy issues:

Accuracy, property, access

Accuracy

Responsibility of those who collect data to ensure it is correct

Property

Who owns data

Access

Responsibility over who is able to use data