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I read that "TCP/IP protocol suite contains relatively independent protocols which can be mixed and matched which is not possible in OSI". What is the meaning of mix and match over here ? Can we mix transport layer and network layer protocols ?

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No, you can't mix transport and network protocols. But you can use different transport protocols (TCP and UDP) with the network layer, IP. They're considered independent because IP doesn't know or care what transport protocol you're using (Fun fact: there are about 150 transport layer protocols defined).

Remember that network models are just that: models. They don't always depict what people actually use. Also remember that no protocol suite in use today follows the OSI model.

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  • Even in OSI they are independent because we define different layers right ? Then what's the difference. – Zephyr Aug 24 '17 at 18:36
  • You can't mix freely with TCP/IP but other than - theoretical OSI - various protocols can be used in a very flexible fashion. There are numerous variants for tunneling, e.g. - essentially putting lower layer protocols on top of higher layer protocols. – Zac67 Aug 24 '17 at 19:31
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This could mean that you can have differing combinations of protocol headers (and trailer) stacked on the data during the encapsulation process. Some application layer services require TCP (FTP, HTTP) and some require UDP on the transport layer. The network layer is always IP when we are talking about the TCP/IP stack (not to confuse with OSI). The data link has different options as well: ethernet, ppp, hdlc, frame relay.

So you can have different header combinations: ETH-IP-TCP-data, ETH-IP-UDP-data, PPP-IP-TCP-data, HDLC-IP-UDP-data...etc.

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  • Same can be the case with OSI right ? Then what's the difference ? – Zephyr Aug 25 '17 at 4:56
  • There's no other network layer protocol except IP on TCP/IP. – wildHoneyPieWalrus Aug 25 '17 at 6:31
  • It has other network layer protocols like ARP, RARP etc. – Zephyr Aug 25 '17 at 6:33
  • I agree with Ron too. OSI is just a model. TCP/IP is found in Android, IOS, Linux, Windows and is widely adopted. ARP is layer 2. – wildHoneyPieWalrus Aug 25 '17 at 6:45
  • Actually on network layer you have 2 protocols: IPv4 and IPv6 ;) Otherwise I agree it is the more likely explanation, but then I cannot understand why the book states it is not possible with the OSI model, since the whole point of separating layers is to allow to replace a protocol by another at any layer, and as such allowing such a mix of protocol. – JFL Aug 25 '17 at 7:04
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The best way to look at these suites, be it OSI or TCP/IP is as a "frame of reference" when looking at implementations, but they are not strictly "fixed" settings in real life. An understanding of the interactions is the key here, the suites themselves is probably less important, as long as you understand the relationship between the sets of data that you are implementing or exploring.

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