Help On OSI Model.

can anyone explain me this
i am having hard time understanding this

PDU (protocol data units)
ENCAPSULATION PROCESS – PDU*
and the equiptment used on each device.
All 7 layers.
Egal

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ziggy

There is an unlimited amount of information on the Internet on this topic. I know I too had a hard time with this at first.

PDU (Protocol Data Unit) is the type of datagram that exists within certain Layers of the OSI Model. You really only need to be concerned with the encapsulation and PDU structure at the 1st four Layers

Layer 2 = Frame
Layer 3 = Packet
Layer 4 = Segment

DIG, DIG, and Dig some more, there is a lot of information on the Internet about the OSI model.
http://www.interfacebus.com/Design_OSI_Stack.html

Good Luck

johnnynodough

Heres the skinny,

A PDU is a chunk of control information ( a header and often a trailer) attached to the data as it traverses down the OSI model stack on its way to being transmitted as electrical signals on a wire, this is the encapsulation process.

Layer 5,6,7 - This is raw data from the application layer, with format and control information provided courtesy of the Session and Presentation layer. These are datagrams. - Gateways, client applications, server applications, some specialized multi layer swicthes.

Layer 4 - Here is where encapsulation really starts to happen, a PDU is attached to the datagram to create a segment. The PDU attached at this layer is a TCP or UDP header. - Gateways, layer 4 switches

Layer 3 - The Segment gets another PDU attached as part of the encapsulation process, here we get an IP header usually, although it can be any layer 3 protocol (IPX, Appletalk). The combination of the PDU at this layer and the segment from Layer 4 creates a Packet. Inside is a segment with a layer 3 PDU, a header - Routers operate at this layer, along with layer 3 switches.

Layer 2 - The frame gets one more PDU attached here, the layer 3 packet plus the PDU creates a frame - inside is a packet with a layer 2 header. - Switches and bridges operate at this layer.

Layer 1 - one final process, but instead of data encapsulation, modulation and encoding take place, as prescribed by the physical layer, i.e. +3.3 V is a 1, wavelengths are described, all electrical charechteristics are defined. - hubs

http://www.petri.co.il/osi_concepts.htm

Webmaster

And check here for some more info:

www.techexams.net/technotes/ccna/osimodel.shtml

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