Hi flan.' 4


Header 3


Heeder 2


Information Exchange Process

The information exchange process occurs between peer OSI layers. Each layer in the source system acids control information to data, and eac h layer in th e destinat ion system analyzes and removes the control information from that data.

If System A has data from a software application to send to System B, the data is passed to the application la yer. The appl ication layer in System A then comm unicates any contro l information required by tloe appMcation layer in System B by prepending a header to the data. The resulting information unit (a header and the data) is passed to the presentation layer, which prepends its own header containing control information intended for the presentation layer in System B. The information unit grows in size as each layer prepends its own header (and, in some cases, a trailer) that contains control information to be used by its peer layer in System B. At the physical layer, the entire infosmation unit is placed oneo tee network medi um.

The physical layer in System B receives the infor mation unl t and passes it to the data l ink layer. Tne data !ink layer l n System B then reads the control information contained in the header prepended by the da ta li ne layer ¡n System a. The head er is then removedr and the remainder of the information unit ts passed to th e netwonk laye! Each layer perfor m s the same actions: The layer readw the header from its peea layer, strips it off, and passes the remaining infotmation unit to the nhxt highest layer. After the application layer nerforms these ach^s, the data is pessed to the recipient software appl ica tim in System B, in exactly the form in which it was transmitted by the application in System A.

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