Frame Realay Encapsulation Question

It is easy to confuse the two if you don't fully understand what each one does. I don't understand it as well as an SME of data-structure would.

LMI (link mgmt interface) only serves as keep-alive if after a certain period the node doesn't receive a request for an update from your router it declares your link down and sends notifications in the other direction to stop the remote from sending and it too declares that link down, very important for hosts that have two paths, telling the host to use the other path, and equally important for both adjacent nodes to know what to expect/send. Along the many hops in the cloud there will be many settings that aren't the same as the original host, such as DLCIs, but as long as ingress and eqress interfaces to adjacent nodes (facing one another) agree on what to send/expect, the data flows properly and the link stays up end to end.

Encapsulation only deals with how the router structures the packet's Protocol Header before it sends it out the interface. Every layer as you move down the OSI stack (as does each protocol stack prepares the data by appending or stripping appropriate bits in preparation of passing to the next layer in the OSI model) places it's own header and possibly footer on your data (encapsulation) as it prepares to convert the bit patterns for transmission, as you move back up the layer each layer must agree on just where that header or footer stops - leaving the next packet structure intact as it passes it up through the stack again. One step gets it wrong, the packet is discarded as the checksums are recalculated or if the packet length doesn't agree as predetermined by either a set standard or a setting within the packet itself.

You can see this if you capture packets with a packet analyzer such as wireshark or sniffer. You will see many headers that are added along the path and depending on where you capture the packets, you may or may not see certain headers on your data.

Thank you for the clear description; however, my confusion came from a learning source stating that only the router and the frame relay cloud is concerned with the LMI type while the DTE routers are only concerned with the encapsulation type. Is this true? Or do you have to match both LIM type and encapsulation type with the frame cloud?

Hey Skepticals, I wasn't pointing the finger, it is confusing at best! I have seen many posts and replies of yours and truly respect your opinions/knowledge. Unless you use it everyday, it is confusing.

IMHO, no one can know everything and I try never to remember what I can look up. I think the best way for anyone to survive this business is to use your resources to the best of your ability; this site is one of my resources.

For instance, I know very little about PCs and applications but a great deal of networking, TCP/IP and packet analysis. My background is telecom and mainly from the carrier side (AT&T) until lately (6yrs.) on the enterprise side as a customer/end user.

DTEs need to match encapsulation and LMI type with the next hop. If you have a true private build, many times it is the remote end (as in a lab situation, campus environment or private MAN.)

I didn't think you were pointing a finger. I just wanted to be as clear as I could.

My main confusion came from conflicting sources. One said one thing and the other said the opposite.

I appreciate your time and information. Thanks for helping out.