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  1. Durga,
    OSI and TCP/IP are both models, and TCP/IP is a currently implemented model. An interesting fact is that there was, at one time, an actual OSI protocol that followed the 7 layer model of OSI. The OSI protocol (obviously) lost out to TCP/IP.

  2. Hi Rene\Andrew,

    So are you saying both OSI and TCP\IP models were introduced as a reference models(theoretical model) by 2 different organizations and later TCP\IP became popular to implement in real world . Couldn’t they try to implement OSI stack ? I see only TCP\IP stack in all the computers in today’s world.

  3. Hello guys,

    I’ve read in the ICND1 100-105 book that the TCP/IP model has an updated version, with Internet layer becoming Network layer and Link layer split in Data Link and Physical layer (just like in the OSI model)

    Is this new version became a de facto or we can still consider the original TCP/IP model (RFC 1122) ?
    I’m just wondering if in the exam they refer to the original or updated version?


  4. Hello Sorin

    Yes, this is Cisco’s attempt to promote this new TCP/IP model in their curriculum, and to be honest, it’s not a bad idea. When we talk about networking, we usually use the OSI model layer names and numbers. We talk about a L2 or L3 switch, or L2 functionality as switching and L3 functionality as routing, and L4 operation as TCP sessions and UDP datagrams. The problem is that all of these technologies are not actually modeled around the OSI model but around the TCP/IP model. So according to the TCP/IP model, switching is L1, routing is L2 and TCP sessions are L3. However, we never refer to the layers of the TCP/IP model with numbers so that we don’t get confused with those of the OSI model.

    Now Cisco is attempting to normalize the TCP/IP model with the OSI model by splitting the Link layer into the Data Link and Physical layers and renaming the Internet layer as the Network layer as shown below.

    In my opinion this is a good idea because it clarifies the role of the various parts of Ethernet and IP communications by using the actual model after which they have been standardized, which is the TCP/IP model. And this clarifies its relationship with the OSI model as well.

    Now this has not generally been adopted by the telecom industry at large nor has it been defined in any RFC, but for the time being it is restricted to Cisco courses and documentation. I’m hoping that it will overflow into the more widespread conscience of the networking world as a whole. For the exams however, not to worry as any indication of layers of models will make it quite clear as to what they are asking for, whether it’s the updated TCP/IP model, the original or the OSI.

    I hope this has been helpful!


  5. @lagapides,

    Thank you for your explanation, make sense of what you say.
    I just hope I won’t get confused. There are three network models (ISO, TCP/IP, TCP/IP updated) that more or less look the same and they were supposed to define a common standard.

    Anyway thanks again.


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