The Devine OSI Tragedy By: Ralph M. DeFrangescoThis paper is a geek’s version of Dante’s Inferno that takes the reader through the sevenOSI layers instead of to Hell. In that classic poem, Dante described the inferno as afunnel shaped pit that was comprised of a series of staircases that descended into Hell. InDante’s time, numbers had mystical meaning. The number three represented the HolyTrinity. Nine is three times three and thirty-three, a multiple of three. In addition, sevenwas the number of days it took God to create the world, as we know it. It’s just acoincidence that there are seven OSI layers. You will notice that there are twenty-oneparagraphs or seven times three in this paper.In Dante’s poem Virgil Vergilius Maro, a classical Roman poet, was chosen toaccompany Dante on his epic journey through Hell and back out again. I have chosenVint Cerf, the father of the Internet, to accompany me through the journey of the OSIlayers.Finally, although each paragraph is marked “CANTO”, they are not in the true Cantosstyle.CANTO 1It was the night before Good Friday and I was on call. It was 2:00 a.m. when I received acall to come into work to fix a problem. I arrived at work and headed immediately to theserver room to deal with a failed back up. As it turned out, the backup completed prior tomy arrival. I decided to go to my desk to check my email and phone messages. I put myhead down just for a moment when I must have fallen asleep. I started to dream that I wasin a server room when Vint Cerf, the father of the Internet, entered. He said that he wasthere to take me on a journey. He was there to accompany me through the OSI layers. Itold him that I would go with him, but I was not that comfortable with the OSI model.CANTO 2We walked through two large doors that automatically opened when Mr. Cerf swiped hiscard. On the doors, there were pictures of people’s faces - users. Above the doors it read“Applications”. There were many people walking around. Tim Burners Lee, the inventorof HTTP, greeted us. Mr. Cerf explained why we were there. Tim volunteered to explainwhat HTTP was and how it worked. In addition he said he would write us some HTMLcode to help us get to the next layer.
CANTO 3As he was explaining HTTP, a distinguished looking gentleman approached me. Heintroduced himself as Paul Mockapetris. I immediately recognized him as being theinventor of DNS. He asked me if I could deliver a message to someone on the outsideworld. I told him that if he gave me a name, I would try. He asked me to locate Jon Posteland to tell him that he has developed a better version of DNS. I told him I would do mybest.CANTO 4Here is the code that Tim wrote for us:<html><body><h1>Tim’s code</h1><p>Help Vint and Ralph get to the next layer.</p></body></html>We loaded the code into a browser and ran it. We started to transform into HTML pages.CANTO 5As our pages were loading, Mr. Cerf explained that there were many other protocols usedat this layer including: FTP, NFS, NTP, SMTP, and Telnet, just to name a few. However,he warned that I should be careful when using Telnet since anything sent over thatprotocol is in clear text. I should consider using Secure Telnet if I really need to use thatprotocol. Our pages were fully loaded and we descended to the next layer.CANTO 6We approached another set of doors. This time they were a bit smaller. They openedauto-magically when we approached them. The sign above the door read, “Presentation”.We walked cautiously through the doors and into a large room. The paint on the wall wasold, probably from the 1960’s.CANTO 7There were some really strange character sets on one wall that I could not read. Theyappeared to be in 8-bit character encoding. Mr. Cerf said that it was Extended BinaryCoded Decimal Interchange Code or just EBCDIC, and old way of representing a
character set developed by IBM in the 1960’s. He then pointed to an adjacent wall thathad the more familiar 7-bit ASCII translation that I was able to read.CANTO 8 I could see an Egyptian looking gentleman standing alone in the corner. He motioned forme to come over. I did not recognize the gentleman. As I approached, he extended hishand to shake mine. He introduced himself as Taher Elgamal. He explained that he was adriving force behind the Secure Socket Layer (SSL). He said that he would be glad tocreate an encrypted connection, helping us to get to the next layer securely. We acceptedhis offer. He walked with us through a tunnel explaining what SSL was and how it couldhelp us travel securely. When we reached the end of the layer, he shook our hands againand wished us luck.CANTO 9We used the encrypted connection to descend to the next layer. This door was evensmaller and had “Session” written above it. As we stepped through the door, I could feelmyself struggling to get through, almost like trying to connect to a session, but it keptfailing. A middle-aged male approached us. He said his name was Tatu Ylonen. He saidthat he was the inventor of the Secure Shell (SSH) protocol. He asked us to put on a T-shirt that said “Data” on the back of it. He said, “You will need to put this on to travelany further”.CANTO 10Tatu explained that if we needed to do any system maintenance that we should use SSH.His protocol used public-key encryption and was a great way to exchange data over asecure channel. Tatu escorted us to the edge of the protocol.CANTO 11We approached our fourth door. It said, “Transport” above it. As we passed through thedoor, I began to feel a lot of tension. Ahead in the distance, I saw two men fighting. Mr.Cerf and I walked toward them and broke up the fight. We asked why they were fighting.One of the men stepped forward and said that the two were born enemies. “I am DavidReed, the inventor of the User Datagram Protocol (UDP), the best protocol on theInternet”. The other man stepped forward and introduced himself. “I am Bob Kahn, oneof the inventors of the Transmission Control Protocol (TCP)”. Just then another fightbroke out between them. Mr. Cerf pulled me aside and said that he agreed with BobKahn, TCP was the better protocol and that the two of them were in constantdisagreement with David Reed. I asked why he defended the one man. He pulled a paperout of his pocket and handed it to me. It was an IEEE publication that said, “A Protocolfor Packet Network Interconnection”, by Vinton G. Cerf and Bob Kahn. I asked if thiswas the reason why he was condemned to the OSI model. He said yes, because of the
paper and the protocol spilled over into the next layer that included the Internet Protocol(IP).CANTO 12We were asked to wear a long-sleeved shirt over our t-shirts that read, “Segment” on it. Itwas getting warm. We continued through the transport layer. There were many protocolsthat I have never even heard of: CUDP, IL, SCTP, SST, and NFB. Mr. Cerf explainedthem to me as we walked to the end of the Transport layer that coincidently was the endof the TCP header. There was a sign on the wall that read, “Options (Variable 0-320bits)”. Mr. Cerf explained that it was variable because it depended on the options that Ichose. I chose 128 bits worth of options and the wall slid open, we stepped through.CANTO 13We walked through a narrow hallway to a door. The door was again smaller than the last.It had a sign that read, “Network” above it. We entered through the doors and the wallshad RIP and RIPng written all over them. On the far back wall there was another sign thatsaid, “Router territory”. Packets were flying around, moving from one network toanother.CANTO 14We were asked to put on a hoodie that read, “Packets” on it. Mr. Cerf took out a box thathad two keys in it. He handed me one and said that we would need these because thelayer was encrypted and we each needed a key if we wanted to be able to talk to eachother. I put the key in my pocket.CANTO 15This door was the smallest so far. It had a really small sign above it that read, “DataLink”. We struggled to push this door open. As we walked through, Mr. Cerf had a bigsmile on his face. A man I recognized immediately came up to us. It was Bob Metcalf.He and Mr. Cerf shook hands. He introduced me and welcomed me to the most activelayer in the OSI model. He said that we each had to put on a jacket. It read, “Frames” onthe back and would be the last one we had to put on. I was really hot and could barelymove with all of the clothing on.CANTO 16Mr. Metcalf explained that this layer was split into two sub-layers: the Logical LinkControl and Media Access Control. The Logical Link (LLC) sub-layer was first. Mr.Metcalf explained that LLC provides multiplexing and flow control. In addition, it wasthe interface between the Media Access Control (MAC) sub-layer and the Network Layer
CANTO 17The MAC layer plays a very important role in the OSI model. It provides physicaladdresses. MAC addresses are assigned at the time a network device (a Network InterfaceCard for example) is manufactured. All MAC addresses must be unique on a network.MAC addresses make it possible for packets to be delivered within a network.CANTO 18Mr. Metcalf gave us an IP address and told us to report there. We shook hands with himand left to find the address we were given. I asked Mr. Cerf how we find the physicaladdress of this IP address. He said that we could use Address Resolution Protocol (ARP)to find the physical or MAC address.CANTO 19We approached the final layer. The door was barely big enough for us to fit through. Itsaid, “Physical” above it. As we transcended down to the final level, I could see stars allaround me. Mr. Cerf commented that they were not stars, but electrons. I could see openpipes where thousands upon thousands of electrons were rushing out. I could feel mybody getting lighter. I was changing into a combination of zero’s and one’s. I looked likethe matrix. I too was rushing into the pipes, being carried along the river of binary data. Itbecame very dark. I was in the Ether. I could see the electrons sparkling all around me.CANTO 20I emerged out of the pipes and started to feel all of my clothing peeling off of me. I wasascending upwards, but in a different place than where I started. As I reached the top, Iwas becoming human again. I could feel myself waking up. My head hit the desk and Ijumped out of my seat. I was of course still in my office. I could see sunshine streamingin the office windows; it was time to go home.CANTO 21I arrived back home very tired and confused about the dream I had. I walked in the doorat 7:15 a.m. My wife was in the kitchen making breakfast for her and my two children.She asked how my night was. I told her she wouldn’t believe it. Then she said she likedmy T-Shirt but why did it say “Data” on it? I told her that I didn’t have a T-shirt that had“Data” on it. She said I should go back to bed because I must have been really tired.I walked upstairs to go to bed. As I walked past the mirror I looked at the back of my T-shirt and it did say, “Data” on it. Fact was I never owned a T-shirt with the word “Data”printed on it.
About the authorMr. DeFrangesco works with fortune 500 companies developing security programs,assessments, strategic and enterprise architectures, and disaster recovery programs.He currently teaches for Drexel University as an Adjunct Professor in their ComputerSecurity program. He holds a BSCS, MBA, and is currently a PhD candidate. He haswritten a technology based novel, a self-help book on time management and severalpapers on various computer related topics. He gives presentations and lectures at variousconferences throughout the country when requested. He can be reached email@example.com