Cognition and FDG 81triggers another request from the application layer, in the form of a ‘frame’
made up of some data and a header.
User program
REQUEST ACKNOWLEDGEMENT+ROUTINE
Application
layer
REQUEST ACKNOWLEDGEMENT+ROUTINE
Presentation
layer
Session
layer
... ... ...
Figure 1. An example using the OSI model
This request goes down to the next layer, where it is taken as the data of
a further packet with a new header; it then goes down to the next layer, and
so on. In the entire process down to the physical layer, where the flow of 1s
and 0s is transmitted along the communication lines, packets of a given
level are included as data in packets of the next level, creating a multilay-
ered structure that is very familiar to Functional Grammar researchers. This
is the encoding process. At the other end, the receiver of these packets
starts the process of unpacking the chunks of information received. At the
data-link layer a packet is obtained with a header and data. If the data has
some instruction that can be performed at this level, the process stops here;
but, if the data is a packet of a higher level, the unpacking process goes on
until it reaches the level at which the data contains instructions that can be
executed. In our analogy, the sender operating system would be the en-
coder of the linguistic message, and the receiver operating system the
decoder. Any request generated at a given level would need to be proc-