THE INTERNET'S GROWTH HAS BECOME EXPLOSIVE AND IT SEEMS IMPOSSIBLE TO ESCAPE THE BOMBARDMENT OF "WWW.COM" SEEN CONSTANTLY ON TELEVISION , HEARD ON RADIO , AND SEEN IN MAGAZINES.BECAUSE THE INTERNET HAS BECOME SUCH A LARGE PART OF OUR LIVES, A GOOD UNDERSTANDING IS NEEDED TO USE THIS NEW TOOL MOST EFFECTIVELY.
THIS WHITEPAPER EXPLAINS THE UNDERLYING INFRASTRUCTURE AND TECHNOLOGIES THAT MAKE THE INTERNET WORK.IT DOES NOT GO INTO GREAT DEPTH, BUT COVERS ENOUGH OF EACH ARES TO GIVE A BASIC UNDERSTANDING OF THE CONCEPTS INVOLVED.
WHERE TO BEGIN?INTERNET ADDRESSES
BECAUSE THE INTERNET IS A GLOBAL NETWORK OF COMPUTERS EACH COMPUTER CONNECTED TO THE INTERNET MUST HAVE A UNIQUE ADDRESS.INTERNET ADDRESSES ARE IN THE FORM NN.NNN.NNN.NNN WHERE MUST BE A NUMBER FROM 0-255. THIS ADDRESS IS KNOWN AS AN IP ADDRESS.
THE PICTURE BELOW ILLUSTRATES TWO COMPUTERS CONNECTED TO THE INTERNET, YOUR COMPUTER WITH IP ADDRESS 1.2.3.4 AND ANOTHER COMPUTER WITH IP ADDRESS 5.6.7.8. THE INTERNET IS REPRESENTED AS AN ABSTRACT OBJECT IN-BETWEEN. ( AS THIS PAPER PROGRESS , THE INTERNET PORTION OF DIAGRAM 1 WILL BE EXPLAINED AND REDRAWN SEVERAL TIMES AS THE DETAILS OF THE INTERNET ARE EXPOSED.)
IF YOU CONNECT TO THE INTERNET THROUGH AN INTERNET SERVICE PROVIDER (ISP), YOU ARE USUALLY ASSIGNED A TEMPORARY IP ADDRESS FOR THE DURATION OF YOUR DIAL-IN SESSION .IF YOU CONNECT TO THE INTERNET FROM A LOCAL ARE NETWORK(LAN) YOUR COMPUTER MIGHT HAVE A PERMANENT IP ADDRESS OR IT MIGHT OBTAIN A TEMPORARY ONE FROM A DHCP (DYNAMIC HOST CONFIGURATION PROTOCOL) SERVER.IN ANY CASE ,IF YOU ARE CONNECTED TO THE INTERNT ,YOUR COMPUTER HAS A UNIQUE IP ADDRESS.
PROTOCOL STACKS AND PACKETS
SO YOUR COMPUTER IS CONNECTED TO THE INTERNET AND HAS A UNIQUE ADDRESS.HOW DOES IT "TALK TO OTHER COMPUTERS CONNECTED TO THE INTERNT?AN EXAMPLE SHOULD SERVE HERE: LET'S SAY YOUR IP ADDRESS IS 1.2.3.4 AND YOU WANT TO SEND A MESSAGE TO THE COMPUTER 5.6.7.8. THE MESSAGE YOU WANT TO SEND IS "HELLO COMPUTER" 5.6.7.8!". OBVIOSULY, THE MESSAGE MUST BE TRANSMITTED OVER WHATEVER KIND OF WIRE CONNECTS YOUR COMPUTER TO THE INTERNET .KET'S SAY YOU'VE DIALED INTO YOUR ISP FROM HOME AND THE MESSAGE MUST BE TRANSMITTED OVER THE PHONE LINE.THEREFORE THE MESSAGE MUST BE TRANSLATED FROM ALPHABETIC TEXT INTO ELECTRONIC SIGNALS,TRANSMITTED OVER THE INTERNET, THEN TRANSLATED BACK INTO ALPHABETIC TEXT.HOW IS THIS ACCOMPLISHED? THROUGH THE USE OF A PROTOCOL STACK. EVERY COMPUTER NEEDS ONE TO COMMUNICATE ON THE INTERNET AND IT IS USUALLY BUILT INTO THE COMPUTER'S OPERATING SYSTEM.(I.E. WINDOWS , UNIX ,ETC.). THE PROTOCOL STACK USED ON THE INTERNET IS REFERED TO AS THE TCP/IP PROTOCOL STACK BECAUSE OF THE TWO MAJOR COMMUNICATION PROTOCOL USED.THE TCP/IP STACK LIKE THIS:
PROTOCOL LAYER COMMENTS
APPLICATION PROTOCOL LAYER PROTOCOL SPECIFIC TO APPLICTION
SUCH AS WWW,E-MAIL,FTP,ETC.
TRANSMISSION CONTROL TCP DIRECT PACKETS TO A
PROTOCOL LAYER APPLICATION ON A COMPUTER USING A PORT NUMBER.
INERNET PROTOCOL LAYER IP DIRECT PACKET TO A SPECIFIC
COMPUTER USING AN IP ADDRESS.
HARDWARE LAYER CONVERT BINARY PACKET DATA TO
NETWORK SIGNALS AND BACK
(E.G. ETHERNET NETWORK CARD ,MODEM
FOR PHONE LINES,ETC.)
IF WE WERE TO FOLLOW THE PATH THAT THE MESSAGE "HELLO COMPUTER 5.6.7.8!" TOOK FROM OUR COMPUTER TO THE COMPUTER WITH IP ADDRESS 5.6.7.8, IT WOULD HAPPEN SOMETHING LIKE THIS:
1. THE MESSAGE WOULD START AT THE TOP OF THE PROTOCOL STACK ON YOUR COMPUTER AND WORK IT'S WAY DOWNWARD.
2. IF THE MESSAGE TO BE SENT IS LONG, EACH STACK LAYER THAT THE MESSAGE PASSESS THROUGH MAY BREAK THE MESSAGE UP INTO SMALLER CHUNKS OF DATA. THIS IS BECAUSE DATA SENT OVER THE INTERNET (AND MOST COMPUTER NETWORKS) ARE SENT IN MANAGEABLE CHUNKS.ON THE INTERNET, THESE CHUNKS OF DATA ARE KNOWN AS PACKETS.
3. THE PACKETS WOULD GO THROUGH THE APPLICATION LAYER AND CONTINUE TO THE TCP LAYER.EACH PAKCET IS ASSIGNED A PORT NUMBER. PORTS WILL BE EXPLAINED LATER, BUT SUFFICE SAY THAT MANY PROGRAMS ON THE DESTINATION COMPUTER NEEDS TO RECEIVE THE MESSAGE BECAUSE IT WILL BE LISTENING ON A SPECIFIC PORT.
4. AFTER GOING THROUGH THE TCP LAYER, THE PACKETS PROCEED TO THE IP LAYER.
THIS IS WHERE EACH PACKET RECEIVES IT'S DESTINATION ADDRESS 5.6.7.8.
5. NOW THAT OUR MESSAGE PACKETS HAVE A PORT NUMBER AND AN IP ADDRESS, THEY ARE READY TO BE SENT OVER THE INTERNET. THE HARDWARE LAYER TAKES CARE OF TURNING OUR PACKETS CONTAINING THE ALPHABETIC TEXT OF OUR MESSAGE INTO ELECTRONIC SIGNALS AND TRANSMITTING THEM OVER THE PHONE LINE.
6. ON THE OTHER END OF THE PHONE LINE YOUR ISP HAS A DIRECT CONNECTION TO THE INTERNET .THE ISPs ROUTE EXAMINES THE DESTINATION ADDRESS IN EACH PACKET AND DETERMINES WHERE TO SEND IT.OFTEN, THE PACKET'S NEXT STOP IS ANOTHER ROUTER.
7. EVENTUALLY,THE PACKETS REACH COMPUTER 5.6.7.8. HERE,THE PACKETS START AT THE BUTTON OF THE DESTINATION COMPUTER'S STACK AND WORK UPWARDS.
8.AS THE PACKETS GO UPWARDS THROUGH THE STACK,ALL ROUTIN DATA THAT THE SENDING COMPUTER'S STACK ADDED (SUCH AS IP ADDRESS AND PORT NUMBER) IS STRIPPED FROM THE PACKETS.
9. WHEN THE DATA REACHES THE TOP OF THE STACK, THE PACKETS HAVE BEEN RE-ASSEMBLED INTO THEIR ORIGINAL FROM, "HELLO COMPUTER 5.6.7.8!."
NETWORKING INFRASTRUCTURE
SO NOW YOU KNOW HOW PACKETS TRAVEL FROM ONE COMPUTER TO ANOTHER OVER THE INTERNET. BUT WHAT'S IN-BETWEEN? WHAT ACTUALLY MAKES UP THE INTERNET?LET'S LOOK AT ANOTHER DIAGRAM:
HERE WE SEE DIAGRAM 1 REDRAWN WITH MORE DETAIL.THE PHYSICAL CONNECTION THROUGH THE PHONE NETWORK TO THE INTERNET SERVICE PROVIDER MIGHT HAVE BEEN EASY TO GUESS,BUT BEYOND THAT MIGHT BEAR SOME EXPLANATION.
THE ISP MAINTAINS A POOL OF MODEMS FOR THEIR DIAL-IN CUSTOMERS. THIS IS MANAGED BY SOME FROM OF COMPUTER (USUALLY A DEDICATED ONE) WHICH CONTROLS DTA FLOW FROM THE MODEM POOL TO A BACKBONE OR DEDICATED LINE ROUTER.THIS SETUP MAY BE REFERED TO AS A PORT SERVER,AS IT 'SERVER' ACCESS TO THE NETWORK.BILLING AND USAGE INFORMATION IS USUALLY COLLECTED HERE AS WELL.
AFTER YOUR PACKETS TRAVERS THE PHONE NETWORK AND YOUR ISP's LOACL EQUIPMENT , THEY ARE ROUTED ONTO THE ISP;s BACKBONE OR A BACKBONE THE ISP BUYS BANDWIDTH FROM.FROM HERE THE PACKETS WILL USUALLY JOURNEY SEVERAL ROUTERS AND OVER SEVERAL BACKBONE,DEDICATED LINES, AND OTHER NETWORKS UNTIL THEY FIND THEIR DESTINATION , THE COMPUTER WITH ADDRESS 5.6.7.8. BUT WOULDN'T IT WOULD BE NICE IF WE KNEW THE EXACT ROUTE OUR PACKETS WERE TAKING OVER THE INTERNET?AS IT TURNS OUT,THERE IS A WAY...
IF YOU USE TRACEROUTE, YOU'LL NOTICE THAT YOUR PACKETS MUST TRAVEL THROUGH MANY THINGS TO GET TO THEIR DESTINATION .MOST HAVE LONG NAMES SUCH AS SJC2-CORE1-H2-0-0.ATLAS .DIGEX.NET AND FDDI0-0.BR4.SJC.GLOBALCENTER.NET. THESE ARE INTERNET ROUTERS THAT DECIDE WHERE TO SEND TO YOUR PACKETS.SEVERAL ROUTERS ARE SHOWN IN DIAGRAM , BUT ONLY A FEW .DIAGRAM IS MEANT TO SHOW A SIMPLE NETWORK STRUCTURE .THE INTERNET IS MUCH MORE COMPLEX.
INTERNET INFRASTRUCTURE
THE INTERNET BACKBONE IS MADE UP OF MANY LARGE NETWORKS WHICH INTERCONNECT WITH EACH OTHER.THESE LARGE NETWORKS ARE KNOWN AS NETWORK PROVIDERS OR NSP's.SOME OF THE LARGE NSP's ARE UUNET,CERFNET, IBM,BBN PLANET , SPRINTNET, PSINET, AS WELL AS OTHERS. THESE NETWORKS PEER WITH EACH OTHER TO EXCHANGE PACKET TRAFFIC.EACH NSP IS REQUIRED TO CONNECT TO THREE NETWORK ACCESS POINTS OR NSP's. BACKBONE TO ANOTHER NSP's BACKBONE.NSPs ALSO INTERCONNECT AT METROPOLITAN ARE EXCHANGE OR MAEs. MAEs SERVE THE SAME PURPOSE AS THE NAPs BUT ARE PRIVATELY OWNED. NAPs WERE THE ORIGINAL INERNET INTERCONNECT POINTS.BOTH NAPs AND MAEs ARE REFERRED TO AS BANDWIDTH TO SMALLER NETWORKS, SUCH AS ISPs ANS SMALLER BANDWIDTH PROVIDERS. BELOW PICTURE SHOWING THIS HIERARCHICAL
INFRASTRUCTURE.
THIS IS NOT TRUE REPRESENTATION OF AN ACTUAL PIECE OF THE INTERNET .DIAGRAM ONLY MEANT TO DEMONSTRATE HOW THE NSPs COULD INTERCONNECT WITH EACH OTHER AND SMALLER ISPs.NONE OF THE PHYSICAL NETWORK COMPONENTS ARE SHOWN IN DIAGRAM AS THEY ARE IN DIAGRAM 3. THIS IS BECAUSE A SINGLE NSP's BACKBONE INFRASTRUCTURE IS A COMPLEX DRAWING BY ITSELF.MOST NSPs PUBLISH MAPS OF THEIR NETWORK INFRASTRUCTURE ON THEIR WEN SITES AND CAN BE FOUND EASILY .TO DRAW AN ACTUAL MAP OF THE INTERNET WOULD BE NEARLY IMPOSSIBLE DUE TO IT's SIZE, COMPLEXITY ,AND EVER CHANGING STRUCTURE.
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