Alan Frayer, CNE, CNI, CIW CI, Net+, MCP

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Q. What are two functions of the Host to Host layer of the DOD Model?

A. Route packages between different hosts.
B. Provide interface to host layer.
C. Maintain data integrity between systems.
D. Ensure error free, sequencing of data.

I would normally jump on C and D, except D does not fit the bill as far as UDP is concerned, as UDP is connectionless and does not provide error correction or sequencing. I think that disqualifies D as an answer.

With C, just what do they mean by data integrity between systems? If they mean error checking, like TCP provides, then again we have the problem of UDP in the same layer.

A. Your instincts are good; C and D should be the correct answers.

Keep in mind that they are asking about the responsibilities of the layer. Layers do nothing except organize protocols. TCP and UDP can exist on the same layer because they both deal with the same subject: transporting data. The fact that they do so differently is inconsequential.

Host to Host is responsible for maintaining data integrity. Just because a protocol doesn’t do it doesn’t mean the responsibility doesn’t exist; it only means the protocol passes the buck.

Don’t get hung up on TCP vs UDP. Accept that they are on the same layer, and concentrate on the criteria the layer organizes protocols by.

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