Figure 1.6: The replacement of the binary interface in Figure 1.6 with 3 layers in an
oversimplified view of the internet: There is a TCP (transport control protocol) module
associated with each source/destination pair; this is responsible for end-to-end error
recovery and for slowing down the source when the network becomes congested. There
is an IP (internet protocol) module associated with each node in the network; these
modules work together to route data through the network and to reduce congestion.
Finally there is a DLC (data link control) module associated with each channel; this
accomplishes rate matching and error recovery on the channel. In network terminology,
the channel, with its encoder and decoder, is called the physical layer.