2.2. Transparent Bridge Architecture

In this section we look at how transparent bridges map into and provide the services for communication in the context of the OSI seven-layer reference model [IS094]. In addition, we consider how the insertion of transparent bridges between end stations affects the architectural invariants of the Data Link as seen by higher-layer protocols and applications within those stations. If abstract architecture bores you, you may safely skip this entire section with no loss of continuity.[]

[] If only we, the authors, could do the same.

Transparent bridges, dealing exclusively with globally unique MAC addresses, provide internetworking services at the Data Link layer of the OSI model.[] This is depicted in Figure 2-6. For simplicity, the figure shows only a two port bridge, although the architecture is the same regardless of the number of ports present.

[] Okay, to be absolutely precise, the service is provided at the MAC sublayer of the Data link layer.

Figure 2.6. Bridge architecture

Each port on the bridge comprises a MAC and Physical layer entity, which communicate with their peer entities in the end stations on the attached LANs. On any given port, all of the devices — both the end station(s) and the bridge port itself — must use the same MAC method (for example, Ethernet) and the same Physical layer data rate (for example, 10 Mb/s or 100 Mb/s). ...

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