BSP Developer's Guide

VxWorks 5.5
BSP Developer’s Guide
The MUX Is an Interface Joining the Data Link and Protocol Layers
One feature of the network stack is an API between the data link and network
protocol layers. This API multiplexes access to the networking hardware for
multiple network protocols. This interface is known as the MUX. Figure H-1 shows
the MUX in relationship to protocol and data link layers.
Figure H-1
The MUX Is the Interface Between the Data Link and Protocol Layers
Protocol Layer:
IP + ICMP
Streams
(custom
protocol)
MUX
Data Link Layer:
Ethernet
Backplane
CSLIP
(other)
At the protocol layer, VxWorks typically uses IP, although you can port and use
other protocols. At the data link layer, VxWorks typically uses Ethernet, although
VxWorks does support other physical media for data transmission. For example,
VxWorks supports the use of serial lines for long-distance connections. In more
closely coupled environments, VxWorks Internet protocols can also use the shared
memory on a common backplane as the physical medium. However, whatever the
medium, the network interface drivers all use the MUX to communicate with the
protocol layer.
NOTE: The data link layer is an abstraction. A network interface driver is code that
implements the functionality described by that abstraction. Likewise, the protocol
layer is an abstraction. The code that implements the functionality of the protocol
layer could be called a protocol interface driver. However, this document refers to
such code simply as “the protocol.”
The MUX Decouples Network Interface Drivers and Protocols
Under the BSD 4.3 model, VxWorks network drivers and protocols are tightly
coupled. Both the protocol and the network driver depend on an intimate
knowledge of each other’s data structures. Under the MUX-based model, network
drivers and protocols have no knowledge of each other’s internals. Network
interface drivers and protocols interact only indirectly—through the MUX.
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