Encapsulation

Phillies8607

This is a term I often hear with L2 protocols. But I'm not sure I fully understand the meaning behind it. It seems it is often used in conjunction with an L3PDU being put in an L2 frame with a header and trailer specific to the L2 protocol to be used on the sending device and the receiving device of a link. Is there anything I'm missing?? I'm not sure if what I'm saying makes sense lol. But it feels like there is more meaning to the word encapsulation beyond establishing header and trailers.

Welly_59

It works the other way around. Encapsulation occurs from layer 1 upwards. So a frame from layer 2 gets encapsulated by layer 3 and is then a packet. It leaves the existing data and headers in place and encloses it (encapsulates it) within the packet headers and trailers

GDaines

Phillies8607 wrote: »

This is a term I often hear with L2 protocols. But I'm not sure I fully understand the meaning behind it. It seems it is often used in conjunction with an L3PDU being put in an L2 frame with a header and trailer specific to the L2 protocol to be used on the sending device and the receiving device of a link. Is there anything I'm missing?? I'm not sure if what I'm saying makes sense lol. But it feels like there is more meaning to the word encapsulation beyond establishing header and trailers.

In general, encapsulation is the inclusion of one thing within another thing so that the included thing is not apparent. Decapsulation is the removal or the making apparent a thing previously encapsulated. (Description was taken from here).

From that I'd summize that data is encapsulated into a segment at layer4, then a packet at layer3, and a frame at layer2 before being sent as bits at layer1. At the receiving end decapsulation takes place stripping the additional information to finally leave the data.

Welly_59 wrote: »

It works the other way around. Encapsulation occurs from layer 1 upwards. So a frame from layer 2 gets encapsulated by layer 3 and is then a packet. It leaves the existing data and headers in place and encloses it (encapsulates it) within the packet headers and trailers

You would not add headers and trailers to data received which is destined for an application, they are part of the routing process and would be stripped off as it passes layers 2, 3 then 4.

james43026

GDaines wrote: »

In general, encapsulation is the inclusion of one thing within another thing so that the included thing is not apparent. Decapsulation is the removal or the making apparent a thing previously encapsulated. (Description was taken from here).

From that I'd summize that data is encapsulated into a segment at layer4, then a packet at layer3, and a frame at layer2 before being sent as bits at layer1. At the receiving end decapsulation takes place stripping the additional information to finally leave the data.



You would not add headers and trailers to data received which is destined for an application, they are part of the routing process and would be stripped off as it passes layers 2, 3 then 4.

This pretty much sums it up.

carterw65

Segment -> Packet -> Frame -> bits sent -> bits rec'd -> Frame -> Packet -> Segment. Each layer adds its header and trailer (if needed) and sends it to the next lower layer until it is broken up in bits by MTU size and sent out. On the other side the exact opposite happens; Each layer strips off the lower layer header and trailer, processes the information and sends it up to the next layer. Of course Layer 4 is responsible for the session and regulates the window size (windowing) based on any congestion on the link.

Remember though, we are usually talking about the OSI model which is cool for teaching the concepts, but is not actually in use except for, perhaps, a few networks most of us will never see. The TCP/IP stack is what is being used so you have to know which OSI layers correlate to the TCP/IP layers.

Hope that make sense. It is early! LOL

BuzzSaw

carterw65 wrote: »

Remember though, we are usually talking about the OSI model which is cool for teaching the concepts, but is not actually in use except for, perhaps, a few networks most of us will never see. The TCP/IP stack is what is being used so you have to know which OSI layers correlate to the TCP/IP layers.

Hope that make sense. It is early! LOL

Totally true - In fact there are people pushing to have the OSI material removed from some of the industry leading certs . . .

At anyrate: another way to look at it would be boxes in boxes. IF you buy, say a new computer from amazon. Amazon is packaging a box that was already packaged by a manufacturer. By the time UPS drops the box off to you, you have to "decap" it in the fact that you probably of 3 or 4 boxes to open to get all of the equipment and accessories out and available.

Overly simple clearly, but I've had to use that example to explain encap and decap to people before and it seems to work

If you want to add some more fun learning to this, take a look at AH and ESP for tunnel encryption