1

I'm currently learning the reference models. It's said that TCP/IP supports only connectionless communication in the Internet Layer but both connectionless and connection-oriented in the Transport Layer.

So what happens when a TCP segment goes through the Internet Layer? Does the Internet Layer simply cares nothing about the sequence at the sender, and then handle all these stuff by the Transport Layer at the receiver?

I'm really confused. Any help will be appreciated.

2

When the TCP segment is passed to the lower level (IP) it does the following:

  • Packetize the segment (break it in chunks).

  • Check where is the IP destination address using ARP if the destination is in the same subnet or through the default gateway if it is on another subnet).

  • Form packets with the chunks of TCP segment putting correctly the source and destination IP address.

The Internet Layer doesn't understand or care if the original data is TCP, UDP, ICMP or other thing. It simply sends the data.

2

TCP is a layer-4 protocol. It breaks your application data into segments, and it applies headers to the segments.

Your layer-3 protocol (IP) will then encapsulate the segments into packets, and it applies the layer-3 headers.

Your layer-2 protocol (probably ethernet) will then encapsulate the packets into frames, and it will apply frame headers to the packets.

Layer-1 will the turn the resulting frames into bits on the wire.

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