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

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 messageaddress

Internet message address net

Internet message address net net IDhost ID

IP address message address net IDhost ID 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 message IP 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 ee.utah.edu yahoo.com software.microsoft.com research.microsoft.com

Domain names icie.cs.byu.edu ee.utah.edu yahoo.com software.microsoft.com research.microsoft.com edu com byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cs 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 microsoft cs 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 microsoft cs 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 microsoft cs 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 microsoft cs 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 byuutah yahoo microsoft cswww 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 byuutah yahoo microsoft cswww icie software research ee

Other protocols Use TCP/IP –WWW – –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”

- uses TCP/IP send a message to find my mail server “mail.cs.byu.edu” message to “mail.cs.byu.edu” to: from: 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 - uses TCP/IP