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In some sites , It is given that tcp/ip has 4 layers,network access,internet,transport,application. But in some other references , it is given that it has 5 layers (instead of network access, physical and link). What is the standard actually??? Somebody knows well tell me pls.

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    What does your own research suggest? This is now the second question you've posted which shows no research effort at all.
    – Dave
    Sep 18 '13 at 13:55
  • @DaveRook See,I haven't posted without any try. I am googling with my team with no luck. We know both 4 and 5 layers are same. But we want to be clarified with the exact standard ! Sep 18 '13 at 14:01
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    @JustinPearce, I don't think it is. The OSI Model has neither 4 nor 5 layers, it has 7. See the image in this answer for a good comparison.
    – heavyd
    Sep 18 '13 at 14:19
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    Just so everyone is clear, the OSI Model and TCP/IP Model actually have differences outlined on Wikipedia and in several other places.
    – dotVezz
    Sep 18 '13 at 14:24
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    I'd strongly encourage you to post questions about specific problems you're facing, or – if you'd like something explained – to clearly describe what your research has told you and what part you don't understand. Your research effort should be more than stating that googling didn't help. If you continue to post questions that are downvoted you might be banned from asking any further ones, so please take this advice seriously. Thanks!
    – slhck
    Sep 18 '13 at 15:10
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It seems like a combination of circumstances here has led to some confusion. Just so everyone is clear, The TCP/IP Model has a slightly different set of layers when compared to the OSI Model.

To be clear, the OSI Model's top three layers - that is: Application, Presentation, and Session - are essentially collapsed into the Application layer in TCP/IP. Additionally, the bottom two layers - Physical and Data Link - are combined into the Network Access layer for TCP/IP.

Therefore, there are 4 layers in the TCP/IP Model. Specifically, they are the Network Access Layer, Internet Layer, Transport Layer, and Application Layer.

You can find some (Difficult to read) technical information in RFC 1122, and some better-presented educational information provided by the University of Pittsburgh.

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I believe you are conflating the DOD\DARPA stack for IP with the OSI model

see here for how the layers of each model map to each other.

http://netcert.tripod.com/ccna/internetworking/dod.html

keep in mind, there are aspects of protocol modeling that are purely conceptual, and don't necessarily mimic analog reality. for instance in modern networking, the osi L1 and L2 are implemented in the network card's circuitry and in its driver code, but there's no good way to tell where one ends and the other begins. afterall the task of sending a media-compliant frame across the network cannot be separated from the task of constructing a 802.3 frame with all the correct data structures.

The layers are not necessarily concrete (especially when viewed from app perspectives), and as such there may not be a "correct" answer. A protocol can have as many layers as as you choose to slice it up into, regardless of the architecture of the code and the circuitry.

Models are often just how you think about a problem, and in this case, both models are valid for different analytic purposes.

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  • Oh well darn. Your answer already says everything that mine does. Good show. I should have read a bit deeper before posting my own.
    – dotVezz
    Sep 18 '13 at 14:38
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Not sure if this helps but.

The original TCP/IP Network Model started with 4 Layers

  1. Application

  2. Transport

  3. Internet

  4. Link Layer

The second version of TCP/IP became 5 layers: changed the name of Internet Layer to Network layer and divided the link Layer to 2 layers

  1. Application

  2. Transport

  3. Network

  4. Data-Link

  5. Physical

References

Daou, I. (n.d.). Why we should understand TCP/IP and OSI Models? Retrieved from CCNA Hub: http://www.ccnahub.com/ip-fundamentals/understanding-tcp-ip-and-osi-models/

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  • Note that the numbering of the layers in this answer is wrong. It should go down from 4 to 1 and 5 to 1 respectively.
    – href_
    Nov 25 '19 at 7:27
  • @href_ - That is due to a limitation of the formatting we have available on this network. There isn't anything we can do to make it present the correct values. The order would have to be reversed in order to have each layer be the correct numerical value.
    – Ramhound
    Nov 29 '19 at 4:23
  • Actually, I think the layers could just be written as code using triple back-ticks. Not ideal, but better than wrong numbers and still in the order that layers are usually presented.
    – href_
    Nov 30 '19 at 8:26
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It can be argued that there are 4 layers, even in the 5-layer model, as it seems that in the 5-layer model they are merely splitting the Link Layer into 2 layers: hardware and link.

The TCP/IP model (4-layer model) that is being talked about is the RFC 1122, which aligns with Cisco Academy: the important player here

Here is a picture of the various layered models, I'm unable to embed it yet.

reference: Internet protocol suite - Wikipedia

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I was taught they were 4 in TCP/IP mapped as follows over "iso/osi" layers, example of protocols between square brackets:

ISO/OSI          TCP/IP (extended)       Data unit's name (ISO-OSI)
Application   -> Application [telnet]        => Packet   (APDU)
presentation  -> Application                 => Packet   (PPDU)
Session       -> Application (Security) [TLS]=> Packet   (SPDU)
Transport     -> Transport [TCP/UDP]         => Segment  (TPDU)
----------Above this line the communication is end to end-------------
Network       -> Network [IP]                => Datagram (Packet)
DataLink      -> Host To Network             => Frame    (Frame)
Physical      -> Host To Network                         (Bit)

Answering your question the TCP/IP model has 5 layers: Application, tansport, network and host-to-network. But I'd add the 6th layer as now more and more common TLS security because it has it's own identifiers and is a layer between TCP and application.

I can remember this by finding the "identifiers" for each data unit relatively to more used connections:

 Application has application defined ID  
(TLS         has [implicit] message sequence number)  
 TCP         has segment sequence number  
 Network     has IP address  
 H2N         has MAC address

This makes, in my opinion, HTTPS as an example of "session" level (I'd call it "security" level because there is where most security operations could be bundeled) because each TLS connection has its own identifiers and is incapsulated into TCP segments.

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