Tcp

DerekAustin26

TCP we all know is what sets up the virtual circuit. It creates a connection oriented session before you actually send packets down the model, this virtual session is setup before anything so the 2 nodes can communicate flow control, sequencing etc..

What I dont understand is if IP is used via Router to connect or communicate to anything via remote networks, then how can TCP create a "Virtual Connection" prior to any traffic/messages to be sent over the internet?

It simply does not make sense. Hence the phrase "all roads lead to Rome" or "All roads lead to IP" - then how is TCP communicating before any "real communication" is done w/o IP? and if it uses IP howcome no book says this? I've read ALOT of material!

Anyone explain this?

dynamik

Which CCENT/CCNA resources are you using?

Higher-level protocols rely on lower-level protocols to deliver information. If you're using the OSI model, TCP is layer-4, so it will flow down to layer-3 (IP), layer-2, and finally layer-1. It will then go from layer-1 to layer-4 at the destination device.

DerekAustin26

I have been reading CCENT/CCNA by Todd Lammle and I've also half way through CCNA book by Richard Deal. I also have studied up on TCP through Examforce software. And the basics in A+ Books. No where does it say anything about TCP using IP to establish it's virtual connection prior to communication.

I am not trying to be difficult, but if these books aren't saying this, "assuming" is not a viable option to me.

dynamik

I heard decent things about the Lammle book, but maybe you should go with the Odom books. This is basic stuff that's detailed early-on; I'm surprised they haven't covered it.

Transmission Control Protocol - Wikipedia, the free encyclopedia

billscott92787

Dynamik does a great job of explaining it. I know on my first book that I started reading this was the first topic that was discussed. When data is "sent" it must first travel down the OSI stack. In that example, the data would travel just as he described.

dynamik

You can find some diagrams showing this here.

Kaminsky

Dynamik is a G.I.E - Google Internetwork Expert. The links he finds never cease to amaze me. So usefull.

The "Virtual Circuit" you are asking about is the SYN, SYN/ACK, ACK process. Once established, the two hosts are ready to speak whether they are right next to each other on a null modem cable or on the other side of the world.

Data goes out 7,6,5,4,3,2,1 then hops from router to router via layer 3 [ hop 1,2,3 route 3,2,1 hop 1,2,3 route 3,2,1 etc ] When it finally reaches it's host it can finally go 4,5,6,7 again.

The routes each individual frame takes may not necessarily be the same as it is routed across the network. (crashes, conjestion, etc) and the frames may arrive out of sequence. When they arrive at their destination and get to layer 4, that is when these frames / packets are then placed back in order and missing frames are re-requested if they were lost in transit or didn't arrive in time.

All the way through this, the two hosts are talking with the aid of the various flags attached to the data at each level of the OSI model before it encapsulates the previous layers "data". If you look at the actual make up of a Segment, Packet, Frame you will see these flags and can investigate what can be related to the other host about how to handle that actual bit of data.

So, not so much a circuit, but more an ongoing conversation.

Once all the data has been sent, the sender sends a FIN packet to the host to signify conversation end and the "circuit" is ended.


A bit of a rough and ready explanation but hope that explains it a bit more for you.