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`TCP/IP Protocol Fundamentals Explained
`with a Diagram
`
`by Himanshu Arora on November 2, 201 l
`
`Tweet
`
`Have you ever wondered how your computer talks to other computers on your local LAN or to
`other systems on the intemet?
`
`Understanding the intricacies of how computers interact is an important part of networking and is
`of equal interest to a sysadmin as well as to a developer. In this article, we will make an attempt
`to discuss the concept of communication from the very basic fundamental level that needs to be
`understood by everybody.
`
`TCP/IP PROTOCOL SUITE
`
`Communications between computers on a network is done through protocol suits. The most
`widely used and most widely available protocol suite is TCP/IP protocol suite. A protocol suit
`consists of a layered architecture where each layer depicts some functionality which can be
`carried out by a protocol. Each layer usually has more than one protocol options to carry out the
`responsibility that the layer adheres to. TCP/IP is normally considered to be a 4 layer system.
`The 4 layers are as follows :
`
`1. Application layer
`2. Transport layer
`3. Network layer
`4. Data link layer
`
`ALA11353476
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`Alacritech, Ex. 2043 Page 1
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`Alacritech, Ex. 2043 Page 1
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`

`

`1. Application layer
`
`This is the top layer of TCP/1P protocol suite. This layer includes applications or processes that
`use transport layer protocols to deliver the data to destination computers.
`
`At each layer there are certain protocol options to carry out the task designated to that particular
`layer. So, application layer also has various protocols that applications use to communicate with
`the second layer, the transport layer. Some of the popular application layer protocols are :
`
`0 HTTP (Hypertext transfer protocol)
`.
`FTP (File transfer protocol)
`.
`SMTP (Simple mail transfer protocol)
`.
`SNMP (Simple network management protocol) etc
`
`2. Transport Layer
`
`This layer provides backbone to data flow between two hosts. This layer receives data from the
`application layer above it. There are many protocols that work at this layer but the two most
`commonly used protocols at transport layer are TCP and UDP.
`
`TCP is used where a reliable connection is required while UDP is used in case of unreliable
`connections.
`
`TCP divides the data(coming fi'om the application layer) into proper sized chunks and then
`passes these chunks onto the network. It acknowledges received packets, waits for
`the acknowledgments of the packets it sent and sets timeout to resend the packets if
`acknowledgements are not received in time. The term “reliable connection’ is used where it is not
`desired to loose any information that is being transferred over the network through this
`connection. So, the protocol used for this type of connection must provide the mechanism to
`achieve this desired characteristic. For example, while downloading a file, it is not desired to
`loose any information(bytes) as it may lead to corruption of do wnloaded content.
`
`UDP provides a comparatively simpler but unreliable service by sending packets from one host
`to another. UDP does not take any extra measures to ensure that the data sent is received by the
`target host or not. The term ‘unreliable connection” are used where loss of some information
`does not hamper the task being fulfilled through this connection. For example while streaming a
`video, loss of few bytes of information due to some reason is acceptable as this does not harm
`the user experience much.
`
`3. Network Layer
`
`This layer is also known as Internet layer. The main purpose of this layer is to organize or handle
`the movement of data on network. By movement ol'data, we generally mean routing ol‘data over
`the network. The main protocol used at this layer is lP. While lCMP(used by popular ‘ping’
`command) and IGMP are also used at this layer.
`
`ALA11353477
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`Alacritech, Ex. 2043 Page 2
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`Alacritech, Ex. 2043 Page 2
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`

`

`4. Data Link Layer
`
`This layer is also known as network interface layer. This layer normally consists ofdevice
`drivers in the OS and the network interface card attached to the system. Both the device drivers
`and the network interface card take care of the communication details with the media being used
`to transfer the data over the network. In most of the cases, this media is in the form of cables.
`Some ofthe famous protocols that are used at this layer include ARP(Address resolution
`protocol), PPP(Point to point protocol) etc.
`
`TCP/IP CONCEPT EXAMPLE
`
`One thing which is worth taking note is that the interaction between two computers over the
`network through TCP/IP protocol suite takes place in the form of a client server architecture.
`
`Client requests for a service while the server processes the request for client.
`
`Now, since we have discussed the underlying layers which help that data flow from host to target
`over a network. Lets take a very simple example to make the concept more clear.
`
`Consider the data flow when you open a website.
`
`ALA11353478
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`Alacritech, Ex. 2043 Page 3
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`Alacritech, Ex. 2043 Page 3
`
`

`

`Host (your laptop)
`
`Target (webserver)
`
`
`
`Media for data transfer (eg. Ethernet)
`
`As seen in the above figure, the information flows downward through each layer on the host
`machine. At the first layer, since http protocol is being used, so an HTTP request is formed and
`sent to the transport layer.
`
`Here the protocol TCP assigns some more information(like sequence number, source port
`number, destination port number etc) to the data coming fiom upper layer so that the
`communication remains reliable i.e, a track of sent data and received data could be maintained.
`
`At the next lower layer, IP adds its own information over the data coming from transport layer.
`This information would help in packet travelling over the network. Lastly, the data. link layer
`makes sure that the data transfer to/from the physical media is done properly. Here again the
`communication done at the data link layer can be reliable or unreliable.
`
`This information travels on the physical media (like Ethernet) and reaches the target machine.
`
`Now, at the target machine (which in our case is the machine at which the website is hosted) the
`same series of interactions happen, but in reverse order.
`
`ALA11353479
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`Alacritech, Ex. 2043 Page 4
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`Alacritech, Ex. 2043 Page 4
`
`

`

`The packet is first received at the data link layer. At this layer the information (that was stuffed
`by the data link layer protocol of the host machine) is read and rest of the data is passed to the
`upper layer.
`
`Similarly at the Network layer, the information set by the Network layer protocol ofhost
`machine is read and rest of the information is passed on the next upper layer. Same happens at
`the transport layer and finally the HTTP request sent by the host applieation(your browser) is
`received by the target applieation(Website server).
`
`One would wonder what happens when information particular to each layer is read by the
`corresponding protocols at target machine or why is it required? Well, lets understand this by an
`example of TCP protocol present at transport layer. At the host machine this protocol adds
`information like sequence number to each packet sent by this layer.
`
`At the target machine, when packet reaches at this layer, the TCP at this layer makes note of the
`sequence number of the packet and sends an acknowledgement (which is received seq number +
`1).
`
`Now, ifthe host TCP does not receive the acknowledgement within some specified time, it re
`sends the same packet. So this way TCP makes sure that no packet gets lost. So we see that
`protocol at every layer reads the information set by its counterpart to achieve the functionality of
`the layer it represents.
`
`PORTS, SERVERS AND STANDARDS
`
`On a particular machine, a port number coupled with the IP address of the machine is known as a
`socket. A combination oflP and port on both client and server is known as four tuple. This four
`tuple uniquely identifies a connection. In this section we will discuss how port numbers are
`chosen.
`
`You already know that some ofthe very common services like FTP, telnet etc run on well known
`port numbers. While FTP server runs on port 21, Telent server runs on port 23. So, we see that
`some standard services that are provided by any implementation ofTCP/IP have some standard
`ports on which they run. These standard port numbers are generally chosen from 1 to 1023. The
`well known ports are managed by Internet Assigned Numbers Authority(IANA).
`
`While most standard servers (that are provided by the implementation of TCP/IP suite) run on
`standard port numbers, clients do not require any standard port to run on.
`
`Client port numbers are known as ephemeral ports. By ephemeral we mean short lived. This is
`because a client may connect to server, do its work and then disconnect. So we used the term
`‘short lived’ and hence no standard ports are required for them.
`
`Also, since clients need to know the port numbers ofthe servers to connect to them, so most
`standard servers run on standard port numbers.
`
`ALA11353480
`
`Alacritech, Ex. 2043 Page 5
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`Alacritech, Ex. 2043 Page 5
`
`

`

`The ports reserved for clients generally range from 1024 to 5000. Port number higher than 5000
`are reserved for those servers which are not standard or well known.
`
`If we look at the file ‘/etc/services’, you will find most of the standard servers and the port on
`which they run.
`
`$ cat /eLc/services
`systat
`ll/tcp
`daytime
`l3/udp
`netstat
`lS/tcp
`qotd
`l7/tcp
`msp
`l8/udp
`chargen
`l9/udp
`ftpedata
`20/tcp
`ftp
`Zl/tcp
`ssh
`22/tcp
`ssh
`22/udp
`telnet
`23/tcP
`
`users
`
`quote
`
`ttytst source
`
`As you see from the /etc/services file, FTP has port number 21, telent has port number 23 etc.
`You can use ‘grep’ command on this file to find any server and its associated port.
`
`As far as the standards are concerned, the following four organizations/groups manage the
`TCP/IP protocol suite. Both the IRTF and the IETF fall under the lAB.
`
` PP’Nt‘
`
`The Internet Society (ISOC)
`
`The Internet Architecture Board (IAB). The IAB falls under the ISOC.
`The Internet Engineering Task Force (IETF)
`The Internet Research Task Force (IRTF)
`
`Tweet
`
`> Add your comment
`
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`ALA11353481
`
`Alacritech, Ex. 2043 Page 6
`
`Alacritech, Ex. 2043 Page 6
`
`

`

`Wigglsalitks 3% h -
`
`wax’wamwm
`
`Sed & Awk
`101 Hacks
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`
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`“13de
`
`,fi} :3.
`
`Vim
`101 HACKS
`mm mwbm
`:wwhmnmnmnem
`
`Mural \’.:u-m~
`
`G
`
`{ 72 comments... m }
`
`. Devin November 2, 2011, 9:02 am
`
`You lefl out the most popular application layer protocol — HTTP!
`
`m
`
`o
`
`krishnan November 2, 2011, 9:09 am
`
`Excellent job. Short and informative
`
`@
`
`o
`
`jalal hajigholamali November 2, 2011, 12:10 pm
`
`Hi,
`
`very nice article
`thanks a lot. ..
`
`Link
`
`0
`
`Julio l-loffimann Mendes November 2, 2011, 1:52 pm
`
`Thank you for the clear explanation! I’ve always wanted to learn a little about TCP/IP.
`Keep the good work!
`
`Regards,
`Julio.
`
`Link
`
`- Walyonaire November 2, 2011, 3:l7 pm
`
`ALA11353482
`
`Alacritech, Ex. 2043 Page 7
`
`Alacritech, Ex. 2043 Page 7
`
`

`

`This reminds me of my Cisco Lessons, thanks for the “refresh”.
`Excellent Article.
`
`
`Link
`
`Narendra Kangralkar November 2, 201 l, 10:21 pm
`
`Very good explanation !!!
`Keep writing.
`
`Link
`
`Ramesh Natarajan November 2, 2011, 10:27 pm
`
`@Devin,
`
`Yes. HTTP is the most popular application layer protocol. This is why the “TCP/IP
`Concept Example” section explains it using the HTTP protocol.
`
`Anyway, thanks for pointing it out, HTTP is added to the “Application Layer” section to
`make the list complete.
`
`
`Link
`
`Joe November 3, 2011, 3:37 am
`
`Thank you for the effort.
`
`Well written.
`
`m V
`
`onskippy November 3, 2011, 2:54 pm
`
`Seems redundant to the 081 model.
`
`m A
`
`TUL KHACHANE November 4, 2011, 8:32 pm
`
`
`Yes. Vonskippy ,
`
`Great articles here always ................ this is one stop resource. . ...and you will find
`almost everything you need...
`
`Link
`
`ALA11353483
`
`Alacritech, Ex. 2043 Page 8
`
`Alacritech, Ex. 2043 Page 8
`
`

`

`Himanshu November 5, 2011, 12:48 pm
`
`Thank you all for your valuable comments.
`
`
`Link
`
`grouchO November 13, 2011, 9: 15 pm
`
`Some books say the 5000 upper limit for client (dynamic/ephemeral) ports was a Inisprint
`in W. Richard Stevens’ “TCP/IP Illustrated Vol. 1” and should have been 50000. The
`
`issue doesn’t seem to have affected the progress of the protocol in taking over the world.
`
`Link
`
`Himanshu November 13, 2011, 11:30 pm
`
`@grouchO
`OK. Can you provide some references?
`
`Link
`
`Devin November 28, 2011. 8:37 pm
`
`You forgot the physical layer.
`
`Link
`
`Himanshu November 29, 2011, 12:08 am
`
`Well, I think you are talking about the 081 model where physical layer is the last layer.
`In TCP/lP model Data link layer is the layer 1. Sometimes this layer is also referred to as
`“Network Interface Layer” as as to avoid confusion with the data link layer of the 051
`model. This Network interface Layer encapsulates physical layer also.
`
`Link
`
`Sravan December 15, 2011, 2:48 am
`
`Thanks. Short and informative article.
`
`m d
`
`eepak kumar January 3, 2012, 2:23 pm
`
`nice .....very helpfull
`tlmx
`
`ALA11353484
`
`Alacritech, Ex. 2043 Page 9
`
`Alacritech, Ex. 2043 Page 9
`
`

`

`% R
`
`eece April 17, 2012, 5:04 am
`
`thanks for the information, it helped me understand TCP/IP
`
`L'Ak
`
`Dharmesh May 13, 2012, 9:42 pm
`
`Thanks a lot!!!
`
`It was a very short and good explanation...
`
`
`Link
`
`AsifMay 13, 2012, 10:08 pm
`
`Simple nd Superbbbbbbbbbbb
`
`Link
`
`rohan June 16, 2012, 1:15 am
`
`an application uses ephemeral port and it uses http as application layer protocol. Now
`when the packet is sent to destination, will it contain both ephemeral destination port and
`standard http destination port no. How this packet will be handled by transport layer and
`application layer at destination?
`
`Link
`
`Tariq August 9, 2012, 3:02 pm
`
`Nice.
`
`A small demo with
`
`wireshark or any other tool could be used to show “how” this happens in real time.
`
`Link
`
`raju September 13, 2012, 8:54 am
`
`Thanks a pile
`It’s fabulous artical and very knowledgeable for me,
`
`Link
`
`ALA11353485
`
`Alacritech, Ex. 2043 Page 10
`
`Alacritech, Ex. 2043 Page 10
`
`

`

`malik usman October 3, 2012, 9:15 am
`
`Thanks a lot!!!
`
`It was a very short and good explanation...
`
`m s
`
`wathi November 24, 2012, 10:13 am
`
`Its is short but soooo ...... informativc,thank u very much
`
`Link
`
`Ritu Kushwaha January 26, 2013, 11:12 am
`
`Useful Information in Short. Well Done!!
`
`Keep Writing...
`
`m U
`
`mar Badu February 7, 2013, 10:28 am
`
`Useful information,i really appreciate this ...... Thanks
`
`mk
`
`poonguzhali February 14, 2013, 7:37 am
`
`Its very easy to understand.
`
`L'Ak
`
`Nagendra Bhat February 20, 2013, 8:20 pm
`
`Hi..
`
`Explanation is good and if there any blogs related to this subject please mention it or
`please mail me.
`
`Link
`
`monica March 15,2013, 3:10 am
`
`Very well explained in simple language
`
`Link
`
`ALA11353486
`
`Alacritech, Ex. 2043 Page 11
`
`Alacritech, Ex. 2043 Page 11
`
`

`

`pemo May 13, 2013, 2:13 am
`
`nice thanks a lot...
`
`
`Link
`
`Ameen June 12, 2013, 9:49 am
`
`tanx 4 ur explanation.
`
`m a
`
`nand July 31, 2013, 12:43 am
`
`very good to understand
`
`m b
`
`rig (retd) ashwani sharma August 20, 2013, 9:47 am
`
`An extremely clear, concise and lucid explanation of TCP/IP.
`Great effort. Keep it up.
`
`Best Wishes
`
`Link
`
`hana September 2, 2013, 12:05 am
`
`good understand
`thanks
`
`Link
`
`khanabusd Scptcmbcr 28, 2013, 6:00 am
`
`very helpful ....................................
`
`
`Link
`
`zug October 16, 2013, 10:29 pm
`
`We’ll written in a language that I find easy to read and understand, Thank you.
`
`Link
`
`ALA11353487
`
`Alacritech, Ex. 2043 Page 12
`
`Alacritech, Ex. 2043 Page 12
`
`

`

`o
`
`justauser October 27, 2013, 2:41 pm
`
`great article! the perfect balance of details and general View 1
`thanks!
`
`Lnk
`
`. maurice November 7, 2013, 2:51 am
`
`it very helpful ....... in simple language
`
`mk
`
`.
`
`jaeo November 8, 2013, 9:00 pm
`
`Thank u
`
`u manage to save me
`as i don’t yet have a text book to read
`this gave light into my understanding of TCP/IP im able to
`peruse my dreams U
`
`Link
`
`0 Mehbub November 19, 2013, 6:00 am
`
`very good explanation,u save me also ............................thank u vry much
`
`
`Link
`
`.
`
`arun mehta December 8, 2013, 8:28 pm
`
`thanks
`
`Link
`
`. Mintu Krishna December 12, 2013, 12:09 pm
`
`very nice, in short & informative explanation. Useful for those who have keen interest in
`lntemet.
`Thanks a lot.
`
`
`Link
`
`0 Ben January 24, 2014, 5:57 am
`
`
`I found this very useful! Thank you very much I
`
`ALA11353488
`
`Alacritech, Ex. 2043 Page 13
`
`Alacritech, Ex. 2043 Page 13
`
`

`

`fl
`
`. Karm Nath February 12, 2014, 3:23 am
`
`good explanation .......
`
`m
`
`.
`
`joe March 19, 2014, 2:22 am
`
`thanks for this articlc, Quite good.
`
`Link
`
`0
`
`amar March 24, 2014, 3:15 am
`
`Hi,
`Explanations are very easy to read and understand. I would like to know more depth
`about encapsulation and decapsulation process of pkts in source side and destination side.
`
`Thanks
`
`Link
`
`0
`
`kamal April 9, 2014, 9:29 am
`
`I really found useful article coz. . .before the exam usually I don’t read the book I just
`look and search the info. . .in the net. . ..
`
`m
`
`.
`
`raVi June 5, 2014, 6:25 am
`
`short n sweet 1
`
`fl
`
`-
`
`kul sidhu June 10,2014, 8:11 am
`
`P12 give difference between osi and tcp/ip with diagram
`
`Link
`
`- Asamoah Apau Daniel August 21, 2014, 6:55 am
`
`ALA11353489
`
`Alacritech, Ex. 2043 Page 14
`
`Alacritech, Ex. 2043 Page 14
`
`

`

`1. what is a transport protocol?
`a. explain with diagrams different between TCP and UDP
`2. Explain secure Protocol
`a. explain with diagrams different between FTP and SSH
`
`Link
`
`Anonymous October 22, 2014, 1:43 am
`
`Clearly explained
`
`Link
`
`Nasham November 24, 2014, 12:15 pm
`
`It very education tanks a lot
`
`Link
`
`lNADRAIEET KUMAR VERMA December 21, 2014, 9:45 pm
`
`Very good explanation !!!
`Keep writing.
`
`m A
`
`run May 16, 2015, 7:00 am
`
`vrh well explained in simple langu
`
`m A
`
`run May 16, 2015, 7:01 am
`
`thanks all
`
`m Z
`
`ubair Khalid May 25, 2015, 6:18 am
`
`well explained sir!
`
`most of my confusion is gone and my concepts are clear now. Thank your very much
`
`Link
`
`ALA11353490
`
`Alacritech, Ex. 2043 Page 15
`
`Alacritech, Ex. 2043 Page 15
`
`

`

`RVT May 25, 2015, 10:22 am
`
`Can you compare Modbus TCP and IEC 61850? What are the advantages and
`disadvantages between these two communication protocols?
`
`Lnk
`
`jagrati sharma June 3, 2015, 8:25 pm
`
`dear friend thanks a lot 11 helped me to understand .thanksV.
`
`m D
`
`anish June 7, 2015, 1:22 am
`
`awesome article. I had a 3 hour class yesterday but I learned more clearly from this
`article than I did in that class. So thanks a lot.. really appreciated”
`
`
`Link
`
`Hum Tum!! June 8,2015, 1:23 pm
`
`Can u just tell me the order of osi layer.
`
`1 > 7 or 7 <1 which 1 is correct?
`
`m V
`
`ignesh July 3, 2015, 4:25 am
`
`any possibility to increase the TCP/IP ports more than 65355.
`
`m A
`
`ravind Reddy Solipuram August 21, 2015, 11:11 pm
`
`vcry informativc.thanks a lot
`
`Link
`
`majulaliefAugust 23, 2015, 8:31 am
`
`Nice and clearly explained
`
`Link
`
`gopi September 14, 2015, 11:20 am
`
`ALA11353491
`
`Alacritech, Ex. 2043 Page 16
`
`Alacritech, Ex. 2043 Page 16
`
`

`

`I like this article. Now 1 undrstnd hw data is tmsfr through layer. Thnxxx
`
`Link
`
`Mitravinda September 23, 2015, 12:20 am
`
`The intemet model or TCP/IP reference model specifically applies to intemet worked
`systems, and has 4 layers. The movement of data packets across a network would be
`managed by which layer?
`A) The link layer
`B) The (inter) network layer
`C) The transport layer
`D) The application layer
`
`Link
`
`Abdul Mohsin December 30, 2015, 3:21 am
`
`Very nice explanation .ThankYou.
`
`Link
`
`Prakash January 25, 2016, 3: 10 am
`
`nicc details on TCP/IP basics.
`
`Link
`
`Carol February 18, 2016, 12:27 pm
`
`Thanks for the short cut TCP/IP lesson. I’m a bit of a hack with interoperability. Helped
`me to understand where to look when I’m stuck. Well done!
`
`fl
`
`DONA DILIGA DUKU March 17, 2016, 12:55 am
`
`very interesting. Thanks alot
`
`fl
`
`Mark Aguilar December 25, 2016, 11:26 pm
`
`Very informative and an excellent refresher.
`
`Link
`
`ALA11353492
`
`Alacritech, Ex. 2043 Page 17
`
`Alacritech, Ex. 2043 Page 17
`
`

`

`o
`
`basavaraj P April 20, 2017, 1:00 am
`
`nice explanation man, many thanks
`
`Link
`
`Cancel re 1
`
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`BEE! Linux 101 Hacks 2nd Edition eBook - Practical Examples to Build a Strong
`Foundation in Linux
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`Bash 101 Hacks eBook - Take Control of Your Bash Command Line and Shell Scripting
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`Sed and Awk 101 Hacks eBook — Enhance Your UNIX / Linux Life with Sed and Awk
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`Vim 101 Hacks eBook - Practical Examples for Becoming Fast and Productive in Vim
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`Nagios Core 3 eBook - Monitor Everything, Be Proactive, and Sleep Well
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`15 Essential Accessories for Your Nikon or Canon DSLR Camera
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`12 Amazing and Essential Linux Books To Enrich Your Brain and Library
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`50 UNIX / Linux Sysadmin Tutorials
`50 Most Frequently Used UNIX / Linux Commands (With Examples)
`How To Be Productive and Get Things Done Using GTD
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`30 Things To Do When you are Bored and have a Computer
`Linux Directog Structure (File System Structure! Explained with Examples
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`Linux Crontab: 15 Awesome Cron Job Examples
`Get a Grip on the Grep! — 15 Practical Grep Command Examples
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`Unix LS Command: 15 Practical Examples
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`15 Examples To Master Linux Command Line History
`Top 10 Open Source Bug Tracking System
`Vi and Vim Macro Tutorial: How To Record and Play
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`Mommy. I found it! -- 15 Practical Linux Find Ceimnand Examples
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`15 Awesome Gmail Tips and Tricks
`15 Awesome Google Search Tips and Tricks
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`RAID 0, RAID 1, RAID 5, RAID 10 Explained with Diagrams
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`Can You Top This? 15 Practical Linux Top Command Examples
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`Top 5 Best System Monitoring Tools
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`Top 5 Best Linux OS Distributions
`How To Monitor Remote Linux Host using Nagios 3.0
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`Awk Introduction Tutorial — 7 Awk Print Examples
`How to Backup Linux? 15 rsyne Command Examples
`The Ultimate Wget Download Guide With 15 Awesome Examples
`Top 5 Best Linux Text Editors
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`Packet Analyzer: 15 TCPDUMP Command Examples
`The Ultimate Bash Array Tutorial with 15 Examples
`3 Steps to Perform SSH Login Without Password Using ssh—keygen & ssh—copy—id
`Unix Sed Tutorial: Advanced Sed Substitution Examples
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`UNIX / Linux: 10 Netstat Command Examples
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`The Ultimate Guide for Creating Strong Passwords
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`6 Steps to Secure Your Home Wireless Network
`Turbocharge PuTTY with 12 Powerful Add—Ons
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`jMy name is Ramesh Natarajan. I will be posting instruction guides, how-to,
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