lecture # 35 internet organization. internet networking communicating between two or more computers...

Lecture # 35

Internet Organization

Internet

Networking

• Communicating between two or more computers

• Bits -> voltage ->wire->voltage->Bits

Network

• More than two computers

Network switch

• More than two computers

Switch

Network• Who is talking to who?

Switch

Network

• Who is talking to who?• Give each computer an

address (integer)

Switch

0

1

2

75

4243

Network

• Who is talking to who?• Give each computer an

address (integer)• Add the address to the

message– Computer with that

address takes the message

– All others ignore the message

Switch

0

1

2

75

4243

messageaddress

Internet

messageaddress

net

net

net

net

Internet

messageaddress

net

net

net

net

net ID host ID

Internet and WWW

Internet

• A way to send an array of bytes from any machine to any other machine

Internet

How to identify the machine to send to

• By address (IP Address - 4 bytes)

Internet

128.78.22.32233.21.1.45

117.211.23.22 233.12.32.111

How to identify the machine to send to

• By name (domain name)

Internet

Croatian.cs.byu.eduIcie.cs.byu.edu

Myhome.isp.com Yahoo.com

Domain Name - a pathname in a tree

EDU COM GOV

BYU

CS

WWW ICIE

EE

MIT Utah Microsoft

research

Yahoo

whitehouse

LOC

Icie.cs.byu.edu

EDU COM GOV

BYU

CS

WWW ICIE

EE

MIT Utah Microsoft

research

Yahoo

whitehouse

LOC

Servers

• Computers that store information or services

Internet

Icie.cs.byu.edu

Yahoo.com

Clients

• Programs that help users get access to info

Internet

Netscape

Instant messenger

Protocol

• Language for computers to talk with each other

Internet

Netscape

Instant messenger

HTTP

IRC

Review

• Internet– Array of bytes between computers– By address 128.23.12.1– By name icie.cs.byu.edu

• Server - delivers info on request• Client - helps user access server info• Protocol - language for computers to talk with

each other

URL (Uniform Resource Locator)

• http://www.yahoo.com/

• http://www.espn.com/nba

• http://icie.cs.byu.edu/cs100/schedule.html

URL - Protocol

• http://icie.cs.byu.edu/cs100/schedule.html

• ftp://netscape.com/downloads/msng.exe

• mailto:george.w.bush@whitehouse.gov

URL - Domain Namename of the server to access

• http://icie.cs.byu.edu/cs100/schedule.html

• ftp://netscape.com/downloads/msng.exe

URL - page name

• http://icie.cs.byu.edu/cs100/schedule.html

• ftp://netscape.com/downloads/msng.exe

URL - page name

• http://icie.cs.byu.edu/cs100/schedule.html• http://icie.cs.byu.edu/cs100/Lectures/server.gif• http://icie.cs.byu.edu/cs100/Lectures/L1.ppt• http://icie.cs.byu.edu/cs456/Homework/Program1• http://icie.cs.byu.edu/cs456/Homework/Program2

– -

URL - page name

• http://icie.cs.byu.edu/cs100/schedule.html• http://icie.cs.byu.edu/cs100/Lectures/server.gif• http://icie.cs.byu.edu/cs100/Lectures/L1.ppt• http://icie.cs.byu.edu/cs456/Homework/Program1• http://icie.cs.byu.edu/cs456/Homework/Program2

– Page names are pathnames in a tree

URL - page name

• cs100/schedule.html

• cs100/Lectures/ server.gif

• cs100/Lectures/L1.ppt

• cs456/Homework/Program1

• cs456/Homework/Program2

cs100

schedule.html

Lectures

server.gif L1.ppt

cs456

Homework

Program1

Program2

Hypertext

• How to link together many documents so that users can get whatever information they want.

IP address

messageaddress

net ID host ID

128.187.172.236

BYU

Computer Science

a computer

Internet Protocol (IP)

• Computer sends an IP “packet”• Other computers (routers) send it on until it

reaches the destination computer – (IP address)

• Each packet might get lost, may arrive in any order, may get delayed

messageIP Address

32 bits - 4 bytes

TCP/IP

• Uses IP to send packets

• Keeps track of which packets have been sent – Resends packets that get lost

• Keeps track of the correct order of packets– Reorders packets when they come in the wrong

order

Domain names vs. IP address

• students.cs.byu.edu

• www.byu.edu

• ee.utah.edu

• yahoo.com

• software.microsoft.com

• research.microsoft.com

Domain names

• students.cs.byu.edu

• www.byu.edu

• ee.utah.edu

• yahoo.com

• software.microsoft.com

• research.microsoft.com

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

Domain names

• If you have a domain name, how do you find the IP address of that computer?

• Maybe one computer has a list of all domain names and their IP addresses– If there are millions of computers– Who enters the data?– Who fixes the data?– Millions of requests will swamp that computer– If that computer goes down nothing works

• How do we get this to scale?

Domain names - scale

• Use a tree!

• Every node knows IP address of its parent

• Every node knows the IP/domain name of its direct children

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

DNS - domain name service

• If a node doesn’t know the IP address of some domain name:– If the domain name is

one of its own, ask the correct child

– If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

students asks cs

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

cs asks byu

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

BYU asks edu

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

edu asks com

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

com asks microsoft

DNS - domain name service

• If the domain name is one of its own, ask the correct child

• If the name is not one of its own, ask the parent

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

students.cs.byu.edu wants software.microsoft.com

microsoft knows and gives the answer

DNS - making it fast

• Each node remembers the most common requests for a day or two

• Doesn’t need to ask again

• Called “caching”

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

DNS - managing the data

• Each node can manage and change its own children without consulting anyone else

• Within 2 days of the changes, everyone’s cache has been updated

edu com

byu utah yahoo

microsoftcs www

students

software research

ee

Other protocols

• Use TCP/IP– WWW– Email– Instant messenger– FTP

WWW

• URL - “students.cs.byu.edu/index.html”

– Send a message to DNS - “what is students.cs.byu.edu?”

– Use IP address to send a message to “students.cs.byu.edu”• “GET index.html”

Email - uses TCP/IP

• send a message to “bill_gates@microsoft.com”• find my mail server “mail.cs.byu.edu”• message to “mail.cs.byu.edu”

to: bill_gates@microsoft.com

from: olsen@cs.byu.edu

subject: Hi there

• mail server forwards the message to “microsoft.com”– if no answer it will keep trying for about a week

Networking Review

• Sending bytes between computers• IP - sends a packet to a particular IP address• TCP - guarantees that packets are in correct

order and not lost• DNS - uses a tree to convert domain names

into IP addresses• WWW - uses TCP/IP• Email - uses TCP/IP