chapter extension 7 how the internet works © 2008 prentice hall, experiencing mis, david kroenke

Chapter Extension 7

How the Internet Works

© 2008 Prentice Hall, Experiencing MIS, David Kroenke

CE 7-2 © 2008 Prentice Hall, Experiencing MIS, David Kroenke

Study Questions

How does e-mail travel? What is a communications protocol? What are the functions of the five TCP/IP OSI

layers? How does the Internet work? How does www.PrenHall.com become

192.52.0.34.65?


How Does E-mail Travel?

Messages and attachments sent from first computer– Broken down into pieces– Pieces called packets

Routers determine the best way to move messages through Internet

System employed to ensure all pieces are received– Packets resent if necessary

Messages and attachments reassembled at recipient’s computer


What Is a Communications Protocol?

Protocol– Standardized means– Used for coordinating activities– Sequence of ordered steps

Communications protocol– Means for coordinating activities between

communicating computers Computers agree on protocol to use

– Broken down into layers


Layered Protocol Schemes

Protocol architectures– Reference Model for Open Systems

Interconnection (OSI) Developed by International Organization for

Standardization (ISO)

– Transmission Control Program/Internet Protocol (TCP/IP)

Developed by the Internet Engineering Task Force (IETF)

– TCP/IP-OSI architecture is blend


TCP/IP-OSI Architecture

Figure CE7-3


Terminology

Architecture– Arrangement of protocol layers

Each layer performs specific tasks

Protocol– Exist at each layer of architecture– Set of rules that accomplish tasks at that layer

Program– Specific computer product – Implements a protocol


Layer 5

Protocols– Simple Mail Transfer Protocol (SMTP)

Standard e-mail protocol

– Hypertext Transfer Protocol (HTTP) Processes Web pages

– File Transfer Protocol (FTP) Used to copy files from one computer to another


Layer 4

Transmission Control program (TCP)– Converts from one data representation to another– Breaks e-mail into segments

Adds identifying segments to beginning of pieces

– Provides reliability Checks to see if all packets are received


Layer 3

Internet Protocol– Interacts with TCP in Layer 4– Routers send messages across Internet

Works through IP Special purpose computers

– Packages messages into packets Places IP data in front of TCP data


Layers 1 and 2

Switches facilitate data communications Layer 2 protocols

– Program packages packets into frames

Basic computer connectivity accomplished at layers 1 and 2


Network Addresses: MAC and IP

MAC addresses– Physical addresses– Implemented by programs that use Layer 2 protocols– Each NIC card given an address by manufacturer– Address only shared within network or segment

IP addresses– Logical addresses– Written as series of dotted decimals

192.68.2.28– Not permanently associated with hardware device

Can be reassigned as necessary


IP Addresses

Two kinds of IP addresses:– Public

Used on Internet Assigned by ICANN Each address is unique

– Private Used within private networks Controlled by company operating network


Dynamic Host Configuration Protocol

DHCP Distributes temporary IP address to

computers– Address loaned while computer connected to LAN– When computer disconnected, IP address made

available to others


Private IP addresses

Assigned manually by network administrator Usually given to:

– Web servers– Shared devices

Most users are given addresses by DHCP


Networks

Figure CE7-1


Using TCP/IP-OSI Protocols Within the Hotel

Hotel has private Web server– IP address of server assigned by network administrator

Guest computer signs into Web server– Guest browser constructs request for server– Uses HTTP

TCP breaks request into segments, adds additional data

TCP program hands segments to program that implements IP


Using TCP/IP-OSI Protocols Within the Hotel (continued)

IP program adds header into packet Passes on to program that implements

Ethernet Ethernet program translates IP address into

MAC address Ethernet wraps packet into frame

– Sends packet through switch


Switches and Routers

Switches– Switch table

Table of data– Entries for every device on network– Work with frames in Layer 2– Use MAC addresses

Routers– Routing tables

Directs packet traffic on Internet Work with packets in Layer 3 Use IP addresses


Accessing Hotel Web Server

Figure CE7-6



Switch consults switch table Directs frame to router Ethernet unpacks frame, send packet to IP Router consults routing table, sends packet one hop

down Internet Ethernet determines MAC address needed

– Ethernet packages packet into frame addressed to appropriate MAC address

– Sends frame to switch



Switch sends frame to destination Ethernet unpacks frame, send packet to IP program IP program strips off header Sends segment to program that implements TCP TCP sends acknowledgement back to guest

computer indicating receipt When both segments received, sent to Web server

program– Processes HTTP request


Network Address Translation

Internet traffic uses public IP addresses– Assigned in blocks

Routers may have two IP addresses– Private one assigned by organization for local traffic– Public one assigned by ISP for Internet traffic

Network Address Translation– Process of changing public IP addresses into private

addresses and reverse– Routers receive packets on Internet and redirects them to

individual computers on local network


Your E-mail

You enter e-mail address of recipient– E-mail program works at application layer

Implements SMTP to send email Uses domain name system to get public IP address

E-mail message sent to router– Sends message to TCP

Breaks into segments, placed in packets Sent to router

Packets sent to Ethernet program – Placed in frame– Sent to switch, sent to router


Your E-mail (continued)

Packets arrive at router– Implements NAT– Replaces private IP address with public IP address

Router consults table, sends to gateway router of recipient

Segments unpacked from packets, sent to TCP program

Program waits for all segments, then sends to program that implements SMTP

Program operates at Layer 5, puts message in mailbox


E-mail System

Figure CE7-7


Domain Name System

DNS– Converts user-friendly names into public IP

address– Resolves domain name

ICANN manages resolution system

Domain name– Registered name

Uniform Resource Locator (URL)– Document’s Web address


Domain Name Resolution

ICANN manages root servers– 13 computers across the world– Maintain lists of IP addresses of servers

Domain name resolvers– Cache name and IP address on local file– Used instead of going through entire resolution

process


Active Review

How does e-mail travel? What is a communications protocol? What are the functions of the five TCP/IP OSI

layers? How does the Internet work? How does www.PrenHall.com become

192.52.0.34.65?

chapter extension 7 how the internet works © 2008 prentice hall, experiencing mis, david kroenke

Documents

protocol slide

david kroenke slide

david kroenke ce

prentice hall

specific tasks protocol

tcp data slide

data communications

tcpip osi layers