Q regarding Transport Layer

Dowima

Hi all, guys i'm reading the technotes about the 7-layer OSI model. They said there that the transport layer is responsible for the End-to-End ( also called source to destination) delivery.
But isn't that wrong. Transport layer only see ports not network addresses. That's why the can communicate with processes on the destination device. also we communicate with the same destination with different port numbers!! And just below it the network layer that can communicate with the destination's box thru his IP only. If we change the IP we may send the data to another device on the network.
Concluding :
1.Transport provide process-to-process connectivity or delivery.
2.Network provide end-to-end or source-to-destination delivery.

EdTheLad

Delivery is the process of picking goods from a warehouse and packing ready for transport by a means, any means of freight forwarding eg air, truck, train, courier. The exact route the plane, truck or train takes isn't important to the delivery process, once the goods arrive at the destination
the delivery process is complete.
Lets say one of the ships sunk due to a storm out at sea, the delivery process can send another shipment via air to ensure a reliable service to the end customer.

Now replace the delivery process with the transport layer and the route taken with the network layer and maybe you will form a new conclusion.

Dowima

I agree with what you are saying but it didn't answer my Q
the Q again :

Which is correct :
1. Transport provide process to process connectivity. (processes are identified by port numbers in each host).
2. Transport provide end to end connectivity.(host are identified by network address).

EdTheLad

Obviously you didn't get it, the transport layer is responsible for the delivery, the network layer is responsible for the path taken.Transport layer provides e2e delivery, network layer provides an e2e path.Why do you call the transport layer a process and why not consider the network layer as a process with its own end goals? What in your opinion is a process?

Dowima

You know i'm totally lost.

i remember that i have red this back when i was in college. I must get the book and read again.


Anyhow thanks for you help .
I post again soon regarding this issue.

tech-airman

Dowima wrote:

You know i'm totally lost.

i remember that i have red this back when i was in college. I must get the book and read again.


Anyhow thanks for you help .
I post again soon regarding this issue.

Dowima,

Questions:

1. Do you understand encapsulation of data from the Application Layer down to the Physical Layer from the point of view of a client host computer?
2. Do you understand decapsulation of data from the Physical Layer from the point of view of the receiving server?

Dowima

Yes I do dude

Pash

EdTheLad wrote:

Delivery is the process of picking goods from a warehouse and packing ready for transport by a means, any means of freight forwarding eg air, truck, train, courier. The exact route the plane, truck or train takes isn't important to the delivery process, once the goods arrive at the destination
the delivery process is complete.
Lets say one of the ships sunk due to a storm out at sea, the delivery process can send another shipment via air to ensure a reliable service to the end customer.

Now replace the delivery process with the transport layer and the route taken with the network layer and maybe you will form a new conclusion.

This is probably the best analogy of L4 i have ever heared. Hi5 at you.

ITdude

I was thinking pretty much the same thing, Pash! Very graphic analogy... Nice one EdTheLad!

darkuser

type netstat at a dos prompt
then you can watch layers 3 and 4 meet .....!!!!

kenny504

EdTheLad wrote:

Delivery is the process of picking goods from a warehouse and packing ready for transport by a means, any means of freight forwarding eg air, truck, train, courier. The exact route the plane, truck or train takes isn't important to the delivery process, once the goods arrive at the destination
the delivery process is complete.
Lets say one of the ships sunk due to a storm out at sea, the delivery process can send another shipment via air to ensure a reliable service to the end customer.

Now replace the delivery process with the transport layer and the route taken with the network layer and maybe you will form a new conclusion.

What the hell!!...What you just explained is genius!!...lol...I'm a technical trainer and buddy I've got to steal that one..lol...I love this site!!!

VERY..well said.

Dowima

EdTheLad.... i found the book. and it says the same thing.
Transport is connecting processes, and network is connecting end-systems.

Now got another Q :
Does each process have thier own 4 lower layers{L4-L1} or are share and controlled by OS.

Dowima

this is the book's name : Computer Networking: A Top-Down Approach Featuring the Internet.

And this is true cuz in transport layer the addresses are ports.
So is that just theory? Or i'm just s bit confiused .

Pash

Dowima wrote:

EdTheLad.... i found the book. and it says the same thing.
Transport is connecting processes, and network is connecting end-systems.

Now got another Q :
Does each process have thier own 4 lower layers{L4-L1} or are share and controlled by OS.

Hi Dowima,

Don't use connecting when describing Transport, as ed said, Transport is "Delivery". Because if you say connecting, you are putting youself in one field when the game is on the other........for example what does UDP do? We all know what TCP does

Not sure I understand your question really unless im being slow as usual? Care to elaborate further?

Yes L4 does use ports to confirm a delivery "method". As darkuser points out, you can use the netstat command on any client/server (Windows or Linux) to see L3&L4 in bed together. Now whats L3&L4 port number combined again?

Edit: Not method sorry, I mean delivery distinction. Remember host's listen on multiple ports at the same time, there has to be a port to move onto the application layer.