Networking

What is a Network?

Computer network a set of computers using common

protocols to communicate over connecting transmission media.

Protocol a formal description of message formats

and the rules two or more machines follow to exchange messages.

Protocols

Hi

Hi

Got thetime?2:00

TCP connection req.TCP connectionreply.Get http://gaia.cs.umass.edu/index.htm

<file>time

Classifying Networks

Networks can be classified by size Local Area Networks (small)▪ privately-owned▪ cover a small area▪ high data rates

Wide Area Networks (large)▪ owned/operated by a network provider▪ large capacity▪ often have an irregular topology

Internetworks

An internetwork, or internet, is formed when two networks are connected together.

Two networks are joined using a computer that is directly connected to both networks.

A computer that joins two networks is called a gateway

An Internet

A NetworkA Network

Service Provider’sNetwork

The Internet

The Internet is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of networking technologies.

A Network of Networks

Enlarged Section

The Internet in the US

How Did It Get Started?

The Internet started as the ARPAnet Started in the mid 60s, working in early

70s Designed for the military Could only be used by the military

Applications of the ARPAnet included Electronic Mail Remote Access File Transfer

NSFNet

In the late 80s NSF supported the creation of 5 supercomputer centers.

NSF Decided to use ARPAnet technology to provide remote access, but could not use the ARPAnet to do this.

In 1985 NSF announced its decision to build the NSFnet.

NSFNet Backbone

Commercialization

During NSF's support of the Internet commercial use was forbidden by law.

On April 30th, 1995 NSF pulled the plug on the NSFnet and turned it over to the private sector.

Since that time commercial use of the Internet has grown dramatically.

Routers An internet consists of

a number of independent networks

Networks are connected by routers

Routers selectively interchanges messages between the networks they connect

Switches Like a network in a

box

Think of it like a “power strip” for a network

Also called a hub

Sometimes a router has a switch built into it

ISP

Most of us cannot afford to establish our own connection to the Internet

An Internet Service Provider (ISP) provides you a connection to the Internet for a fee

Some examples… Time Warner DSL

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Internet Cable Modem Router

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Network Network

The Glue

The TCP/IP Protocol Suite TCP/IP is a set of protocols that were

created specifically to allow development of network and internetwork communications on a global scale.

TCP/IP is the most commonly used protocols within the internet.

Standardization Who controls the TCP/IP protoocol suite?

The Internet Society (ISOC) a professional society to facilitate, support, and promote the evolution and growth of the Internet

The Internet Architecture Board (IAB) the technical oversight and coordination body

The Internet Engineering Task Force (IETF) is the near-term, standards-oriented group.

The Internet Research Task Force (IRTF) pursues long-term research projects.

RFCs

All official standards in the internet community are published as a Request for Comments, or RFC.

All RFCs are available at no charge through electronic mail, FTP, or the Web.

A nice place to get RFCs is at http://www.rfc-editor.org/

IP: Internet Protocol

IP is the workhorse protocol of the TCP/IP protocol suite.

IP provides an unreliable, connectionless, datagram delivery service.

RFC791 is the official specification of IP.

IP Addresses

Every host on the internet must have a unique Internet Address (an IP address)

IP addresses are 32-bit numbers and are divided into two components: the host address and the network address The number of bits assigned to the host

and network varies depending on the class of the address

Dotted Decimal Notation

IP addresses are normally written as four numbers, one for each byte of the address. 129.21.38.169

Class RangeA 0.0.0.0 to 127.255.255.255B 128.0.0.0 to 191.255.255.255C 192.0.0.0 to 223.255.255.255D 224.0.0.0 to 239.255.255.255E 240.0.0.0 to 247.255.255.255

DHCP

Protocol used to assign IP address to machines

In a normal home setup the router runs DHCP and assigns IP addresses as they are requested

Exactly what happens at RIT when you use the wireless network

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74.65.0.57 Assigned byTime Warner via DHCP

192.168.1.254

192.168.1.1

192.168.1.2

192.168.1.9

Transmission Control Protocol TCP provides a connection-oriented,

reliable, byte stream service (RFC793)

TCP is an independent, general purpose protocol that can be adapted for use with delivery systems other than IP.

TCP Ports

TCP uses protocol port numbers to identify the ultimate destination within a machine.

How does one determine the port to communicate with? Well-known Ports Randomly Assigned Ports

Client/Server Computing

Client sends request to server

Server sends results to client

The World Wide Web

Developed by Tim Berners-Lee at CERN Original system built in 1980 Designed to publish documentation

Uses Client-Server Computing Servers store documents Clients request documents from servers

Another Form of Poverty?

Basic Components

Basic Components of the Web Web Servers HTTP protocol▪ Used to send requests and transfer results

Web Browsers HTML▪ Hypertext markup language▪ Used to define the documents

Web Browsers Many to choose from

Some implement standards better than others

Another place for “religion”

Client side computing is done within the browser

Server side computing is done on the server

HTML HTML is the primary

language for building/creating web pages.

HTML uses markup tags to define the elements of a web page

Many online tutorials http://

www.w3schools.com/web/web_html.asp

<html>< body>

< h1>My First Heading</h1>

< p>My first paragraph.</p>

< /body>< /html>