CONNECTIVITY

Why connectivity? – To link our Micro to other resources, such as mainframes, databases, and info services, or for info transfer like e- mail. –This is called Data Communications.

CONNECTIVITY Types of Data Communications – FAX (facsimile) – Electronic Bulletin Boards open to all users controversy about what can be written/said – Electronic Mail confidentiality?

CONNECTIVITY Types of Data Communications – Voice Messaging like – Sharing Resources printers, storage, computers comms between different architectures – IBM vs. MAC

CONNECTIVITY Types of Data Communications – Databases – Commercial Services PRODIGY, COMPUSERV, American On-Line, Microsoft – Groupware a new kind of s/w allows real-time interaction

CONNECTIVITY How do we communicate? – Most common is over telephone lines ANALOG – But computers speak DIGITAL – To convert, use MODEM Modulator/Demodulator

CONNECTIVITY How do we communicate? – MODEMs rated in bits per second speed 9600, 14.1, 19.2, 28.8, 36.6, 57.6 kbps most services still use is most common ($ for fax/modem) PROCOMM operating at 19,600 w/ – MODEMs can be External or Internal

CONNECTIVITY Data Transmission - MEDIUM – twisted pair (TP) used in telephone lines – coaxial cable 80 times more data than TP

CONNECTIVITY Data Transmission - MEDIUM – fiber-optic cable 26,000 times more data than TP difficult to tap because no EM radiation not susceptible to EMI, so better results – microwave short distances (line of sight) UHF frequency range

CONNECTIVITY Data Transmission - MEDIUM – satellite microwaves used to achieve greater distances geo-synchronous orbit

CONNECTIVITY Data Transmission - FACTORS – bandwidth speed in bps – serial vs parallel

CONNECTIVITY Data Transmission - FACTORS – direction simplex half-duplex – most common for data links full-duplex – telephones

CONNECTIVITY Data Transmission - FACTORS – modes asynchronous – one byte at a time – slow, but cheap synchronous – many bytes at once (a block) – send/rcv must be in sync to differentiate different bytes – sync by a clock or control bits – much faster, but expensive

CONNECTIVITY Data Transmission - FACTORS – protocols rules for exchanging data – eg. speeds or modes adherence to standards

CONNECTIVITY Network Configurations – STAR many micros linked to a central host or file server all data goes via the central unit everybody gets a turn to speak (polling) – BUS no host or file server in charge a single, common line that all will try to use protocols define who speaks when every station sees all data, but ignores it if it is not addressed to that station.

CONNECTIVITY Network Configurations – RING no central host or server messages/data move around the ring until reaching addee best used when data sharing is minimal – HIERARCHICAL central host, like a star each node is like a smaller star

CONNECTIVITY Network Types – Local Area Networks (LAN) close physical proximity within the same building use physical media (cable) eg. 4 micros sharing a printer use a Gateway or Bridge to link to another LAN

CONNECTIVITY Network Types – Metropolitan Area Networks (MAN) links between buildings within a city – Wide Area Networks (WAN) geographically disbursed eg. DARPANET