The Devine OSI Tragedy

The Devine OSI Tragedy

By: Ralph M. DeFrangesco

This paper is a geek’s version of Dante’s Inferno that takes the reader through the seven
OSI layers instead of to Hell. In that classic poem, Dante described the inferno as a
funnel shaped pit that was comprised of a series of staircases that descended into Hell. In
Dante’s time, numbers had mystical meaning. The number three represented the Holy
Trinity. Nine is three times three and thirty-three, a multiple of three. In addition, seven
was the number of days it took God to create the world, as we know it. It’s just a
coincidence that there are seven OSI layers. You will notice that there are twenty-one
paragraphs or seven times three in this paper.

In Dante’s poem Virgil Vergilius Maro, a classical Roman poet, was chosen to
accompany Dante on his epic journey through Hell and back out again. I have chosen
Vint Cerf, the father of the Internet, to accompany me through the journey of the OSI
layers.

Finally, although each paragraph is marked “CANTO”, they are not in the true Cantos
style.

CANTO 1

It was the night before Good Friday and I was on call. It was 2:00 a.m. when I received a
call to come into work to fix a problem. I arrived at work and headed immediately to the
server room to deal with a failed back up. As it turned out, the backup completed prior to
my arrival. I decided to go to my desk to check my email and phone messages. I put my
head down just for a moment when I must have fallen asleep. I started to dream that I was
in a server room when Vint Cerf, the father of the Internet, entered. He said that he was
there to take me on a journey. He was there to accompany me through the OSI layers. I
told him that I would go with him, but I was not that comfortable with the OSI model.

CANTO 2

We walked through two large doors that automatically opened when Mr. Cerf swiped his
card. 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 inventor
of HTTP, greeted us. Mr. Cerf explained why we were there. Tim volunteered to explain
what HTTP was and how it worked. In addition he said he would write us some HTML
code to help us get to the next layer.

CANTO 3

As he was explaining HTTP, a distinguished looking gentleman approached me. He
introduced himself as Paul Mockapetris. I immediately recognized him as being the
inventor of DNS. He asked me if I could deliver a message to someone on the outside
world. I told him that if he gave me a name, I would try. He asked me to locate Jon Postel
and to tell him that he has developed a better version of DNS. I told him I would do my
best.

CANTO 4

Here 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 5

As our pages were loading, Mr. Cerf explained that there were many other protocols used
at 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 that
protocol is in clear text. I should consider using Secure Telnet if I really need to use that
protocol. Our pages were fully loaded and we descended to the next layer.

CANTO 6

We approached another set of doors. This time they were a bit smaller. They opened
auto-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 was
old, probably from the 1960’s.

CANTO 7

There were some really strange character sets on one wall that I could not read. They
appeared to be in 8-bit character encoding. Mr. Cerf said that it was Extended Binary
Coded 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 that
had 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 for
me to come over. I did not recognize the gentleman. As I approached, he extended his
hand to shake mine. He introduced himself as Taher Elgamal. He explained that he was a
driving force behind the Secure Socket Layer (SSL). He said that he would be glad to
create an encrypted connection, helping us to get to the next layer securely. We accepted
his offer. He walked with us through a tunnel explaining what SSL was and how it could
help us travel securely. When we reached the end of the layer, he shook our hands again
and wished us luck.

CANTO 9

We used the encrypted connection to descend to the next layer. This door was even
smaller and had “Session” written above it. As we stepped through the door, I could feel
myself struggling to get through, almost like trying to connect to a session, but it kept
failing. A middle-aged male approached us. He said his name was Tatu Ylonen. He said
that 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 travel
any further”.

CANTO 10

Tatu 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 a
secure channel. Tatu escorted us to the edge of the protocol.

CANTO 11

We approached our fourth door. It said, “Transport” above it. As we passed through the
door, 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 David
Reed, the inventor of the User Datagram Protocol (UDP), the best protocol on the
Internet”. The other man stepped forward and introduced himself. “I am Bob Kahn, one
of the inventors of the Transmission Control Protocol (TCP)”. Just then another fight
broke out between them. Mr. Cerf pulled me aside and said that he agreed with Bob
Kahn, TCP was the better protocol and that the two of them were in constant
disagreement with David Reed. I asked why he defended the one man. He pulled a paper
out of his pocket and handed it to me. It was an IEEE publication that said, “A Protocol
for Packet Network Interconnection”, by Vinton G. Cerf and Bob Kahn. I asked if this
was 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 12

We were asked to wear a long-sleeved shirt over our t-shirts that read, “Segment” on it. It
was getting warm. We continued through the transport layer. There were many protocols
that I have never even heard of: CUDP, IL, SCTP, SST, and NFB. Mr. Cerf explained
them to me as we walked to the end of the Transport layer that coincidently was the end
of the TCP header. There was a sign on the wall that read, “Options (Variable 0-320
bits)”. Mr. Cerf explained that it was variable because it depended on the options that I
chose. I chose 128 bits worth of options and the wall slid open, we stepped through.

CANTO 13

We 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 walls
had RIP and RIPng written all over them. On the far back wall there was another sign that
said, “Router territory”. Packets were flying around, moving from one network to
another.

CANTO 14

We were asked to put on a hoodie that read, “Packets” on it. Mr. Cerf took out a box that
had two keys in it. He handed me one and said that we would need these because the
layer was encrypted and we each needed a key if we wanted to be able to talk to each
other. I put the key in my pocket.

CANTO 15

This door was the smallest so far. It had a really small sign above it that read, “Data
Link”. We struggled to push this door open. As we walked through, Mr. Cerf had a big
smile 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 active
layer in the OSI model. He said that we each had to put on a jacket. It read, “Frames” on
the back and would be the last one we had to put on. I was really hot and could barely
move with all of the clothing on.

CANTO 16

Mr. Metcalf explained that this layer was split into two sub-layers: the Logical Link
Control 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 was
the interface between the Media Access Control (MAC) sub-layer and the Network Layer

CANTO 17

The MAC layer plays a very important role in the OSI model. It provides physical
addresses. MAC addresses are assigned at the time a network device (a Network Interface
Card 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 18

Mr. Metcalf gave us an IP address and told us to report there. We shook hands with him
and left to find the address we were given. I asked Mr. Cerf how we find the physical
address of this IP address. He said that we could use Address Resolution Protocol (ARP)
to find the physical or MAC address.

CANTO 19

We approached the final layer. The door was barely big enough for us to fit through. It
said, “Physical” above it. As we transcended down to the final level, I could see stars all
around me. Mr. Cerf commented that they were not stars, but electrons. I could see open
pipes where thousands upon thousands of electrons were rushing out. I could feel my
body getting lighter. I was changing into a combination of zero’s and one’s. I looked like
the matrix. I too was rushing into the pipes, being carried along the river of binary data. It
became very dark. I was in the Ether. I could see the electrons sparkling all around me.

CANTO 20

I emerged out of the pipes and started to feel all of my clothing peeling off of me. I was
ascending upwards, but in a different place than where I started. As I reached the top, I
was becoming human again. I could feel myself waking up. My head hit the desk and I
jumped out of my seat. I was of course still in my office. I could see sunshine streaming
in the office windows; it was time to go home.

CANTO 21

I arrived back home very tired and confused about the dream I had. I walked in the door
at 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 liked
my 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 author

Mr. 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 Computer
Security program. He holds a BSCS, MBA, and is currently a PhD candidate. He has
written a technology based novel, a self-help book on time management and several
papers on various computer related topics. He gives presentations and lectures at various
conferences throughout the country when requested. He can be reached at
rdefrangesco@gmail.com

The Devine OSI Tragedy

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