Bridges (switches) provide the infrastructure that holds the pieces of a LAN together. Each bridge port connects to one of these pieces.
No standard terminology exists for the piece of a LAN that is connected to a bridge port. The term subLAN is used for this purpose in this book.
The LAN pieces (subLANs) look quite different depending on their internal technology. For example, subLAN A, in the upper-left corner of See figure 13.1, is a coax-based collision domain that includes two segments and a repeater. SubLAN B, in the upper-right corner, is a twisted-pair collision domain that is built around two hubs. Note that traffic moving between bridge 1 and bridge 2 must cross subLAN B.