Post on 03-Jan-2016
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
4243messageaddress
Internet
messageaddress
net
net
net
net
Internet
messageaddress
net
net
net
net
net ID host ID
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
• icie.cs.byu.edu
• www.byu.edu
• ee.utah.edu
• yahoo.com
• software.microsoft.com
• research.microsoft.com
Domain names
• icie.cs.byu.edu
• www.byu.edu
• ee.utah.edu
• yahoo.com
• software.microsoft.com
• research.microsoft.com
edu com
byu utah yahoo
microsoftcs www
icie
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
icie
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
icie
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
icie
software research
ee
icie.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
icie
software research
ee
icie.cs.byu.edu wants software.microsoft.com
icie 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
icie
software research
ee
icie.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
icie
software research
ee
icie.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
icie
software research
ee
icie.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
icie
software research
ee
icie.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
icie
software research
ee
icie.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
icie
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
icie
software research
ee
Other protocols
• Use TCP/IP– WWW– Email– Instant messenger– FTP
WWW
• URL - “icie.cs.byu.edu/dan.html”
– Send a message to DNS - “what is icie.cs.byu.edu?”
– Use IP address to send a message to “icie.cs.byu.edu”
• “GET dan.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
• 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