[b]what's The differents between layer 3 and 4[/b]

aueddonline

Both layer 5 and 4 seem to have the ability to establish and terminate a connection so what's the difference

carveone

Session establishes and terminates connections in a broader sense. I hope

Layer 4 - Transport. Segments data into, um, segments. Does error recovery, flow control, and ensuring complete data transfer. Eg: TCP, which is connection oriented and UDP which isn't.

Layer 3 - Network (or Internet in tcpip parlance). Encapsulates the segments into packets. In essence, the network layer is responsible for end to end (source to destination) packet delivery. The Network layer performs network routing, flow control etc. Eg: IP

There's probably a wealth of info on wikipedia.

Conor.

mgeorge

The difference of 3 and 4 is 1 lol.... (Couldn't help my self ^_^)

But any who read what the guy said above me... i think he did
a good enough job explaining it all ^_^

persona

To make things easier for you, remember that layer 5 establish and terminates a connection, while layer 4 take control of SYN/ACK and windowing (flow control).

Well said carveone.

Cucumber

Layer4: Segmentation & Multiplexing
Layer3: End To End data delivery
Connecting Different Data Link Layers together
Logical Addressing
Routing

Layer 4 breaks Layer5 PDUs into smaller chunks (segmentation), also receives segments and handles them to different Layer5 protocols.
Segmentation must be done due to the MTU limitation of the Data Link Layer.
One single Layer4 protocol process on a device can segment outgoing Layer5 PDUs and can receive segments from different Layer5 sessions on remote devices, this is known as multiplexing. Multiplexing works thanks to Port numbers.

UDP does only those two stuff, segmenting and multiplexing. It does not even reassemble segments.
TCP happens to be a very nice protocol that also does Connection Oriented delivery, Reassembly, Error Correction, Flow Control and Sequencing. But none of these features are mandatory for Layer4 protocols. They are optional.

Layer3 is responsible for delivering data accross diferent types of networks, i.e. from an Ethernet network, passing through a FrameRelay Network and finally to a TokenRing network. It can do so thanks to logical addresing and Routing.

Connection Oriented data delivery, Error Correction, Flow Control, Sequencing and Reassembly are optional features that can get performed by different layers.
For instance, NFS is a layer5 protocol that does Reassembly and Sequencing among
many other things. Frame Relay is a Layer2 protocol that does Connection Oriented Data Delivery.

Kaminsky

An easy way to get it into your mind is that layer 5 forms the connection, layer 4 manages the flow of data and layer 3 does the most work going from A to B.

Session gets established and layer 4 takes over. Then layer 4 throws the data into layer 3 at the source and it jumps around layers 3,2,1.. hop.. then 1,2,3 from router to router to router until arrives at it's final destination and then the destination layer 3 pulls it up to layer 4 until the whole transmission sequence is received then it throws it up to layers 5,6,7. Transmission transferred.

This is a basic explanation that should help get whats going on in your head. As ever with this stuff, the more you learn the more complicated it gets.

aueddonline

thanks man that explains it, makes sence now, get confused anbout these damm layers!