• Network protocols– Nodes of a network must obey some rules if they want to

communicate with each other. The set of rules is called network protocol.

– The set of programs or modules that implement the protocol is called protocol architecture.

– Example of protocol architecture, TCP/IP.

• Network interface cards (NIC) & protocols– Also called LAN adapter.– Can be plugged into the PCI slot.– Makes the physical connection between the computer and the

network.– It converts parallel data of the computer’s bus into serial data for

LAN.– It boosts the strength of a signal so that it can flow through the

transmission link.– Only one node is allowed to transmit in a LAN otherwise signals

will interfere.– LAN needs MAC scheme to prevent interference.– NIC determines the access method used by the network.– Example, Ethernet, Token Ring, FDDI, Arcnet etc.

• Client: A client computer uses, does not provide. Runs client OS. Example, Windows 98.

• Server: A server computer provides network resources. Runs network OS. Example, Windows NT server.

• Client/Server network– It’s a hierarchical strategy where all the nodes share

resources provided by one or more central servers.– This arrangement requires specialized software for both the

individual nodes and the server node.– Commonly used model in the Internet.– Example, Yahoo Web Server and Internet Explorer Web

Client.

• Peer-to-peer network– All the nodes have equal role in the network.– All have similar types of software.– Commonly used in small organizations. Example, your lab.– Primary benefit is sharing of files, printers etc.

The Internet• Largest network in the world.• It is owned by everyone. • It is the key platform for all kinds of services like

entertainment, business etc.• It evolved from ARPANET – a research network

developed by United States Defense Department in 1969. Initially created to help academic and government researchers to use e-mail and share files.

• The Internet is growing very fast and eventually will connect all the computers and networks in the world together.

• The Internet is based on the TCP/IP protocol suit which is used to identify every computer uniquely in the Internet.

• Internet services– Popular Internet applications are: e-mail, browsing,

news.– Some protocols supported by the Internet for various

services are:• HTTP (Hyper Text Transfer Protocol) – Web browsing.• SMTP (Simple Mail Transfer Protocol) – Sending e-mail.• POP (Post Office Protocol) – Receiving e-mail.• FTP (File Transfer Protocol) – Transferring data files.

• Internet address– Every computer on the Internet is identified by a 4 part

address called IP address.– Each of the 4 part is a number between 0 to 255.

– Example, 203.160.6.23.– Hard for humans to deal with IP address.– DNS addresses are also used for user

convenience which uses words instead of numbers.

• DNS addresses have 2 parts: machine name + domain name.

• Example, www.yahoo.com– www = machine/computer name.

– yahoo.com = domain name.

• Domains identify the type of institution that uses the address. Example, .edu for educational institution.

• Large companies may divide their domain into smaller sub-domains for their convenience.

• Outside USA domains usually identify the country in which the system is located called geographic domain. Example, .jp for Japan.

• Example, www.times.ac.uk

Internet Access

• There are 2 ways to access the Internet:– Dial-up telephone access: uses a modem.

Normally used by PC users at home. Data transfer rate is low.

– Leased line access: uses LAN card. Normally used by large companies. They have to pay a monthly rent to use the line. Connection is dedicated and any one in the company can access the Internet any time. More costly and more faster than dial-up scheme.