The media access (MAC) protocol layer corresponds to the lowest-level protocol in the protocol stack concerned with actually transmitting bits across some physical transmission medium. The MAC layer is often further decomposed into a physical Layer 1 (hardware) and a data link Layer 2 (software). There are a number of choices available for the MAC physical layer of data transmission, among them, Token Ring, FDDI, and various flavors of Ethernet, all of which we discuss to some degree. However, we do not discuss more exotic MAC protocols such as ATM and SONET that are rarely encountered on Windows 2000 machines. In this section, we explore the major architectural features of the MAC physical layer and compare and contrast various implementations. As always, we focus on those features that have the most impact on network performance.
The Ethernet standard represents by far the most popular choice for the data link layer. Ethernet’s popularity is the result of several factors:
The simple nature of Ethernet makes it very inexpensive to build
hardware and software to support it, lowering the cost of all
Ethernet components. Ethernet interface cards are quite inexpensive.
In addition, the protocol does not require expensive wiring and
cabling. It supports both coax (sometimes denoted as
thicknet) and inexpensive twisted-pair wiring.
The advantage of using coax is that Ethernet segments can be
substantially longer, as Table 11-2 indicates.