NonStop S-Series Server Description Manual (G06.27+)

Principles of System Operation

HP NonStop S-Series Server Description Manual—520331-004

2-2

ServerNet Devices

Figure 2-1 illustrates the basis for ServerNet device identification, which in turn is the

basis for communication between ServerNet devices. A ServerNet device is some kind

of ServerNet hardware interface that connects a ServerNet link to a single processor or

to an I/O entity that usually controls an array of I/O devices.

In the case of a processor, that interface is a processor ServerNet interface.

In the case of I/O entities, ServerNet addressable controllers (SACs) are always

considered to be ServerNet devices. Thus, whenever a single SAC is connected to the

ServerNet hardware with its own dedicated ServerNet bus interface (SBI), the SAC is

the ServerNet device, not the SBI. Also, I/O devices, whether one per SAC or many

per SAC, are never considered to be ServerNet devices.

Sometimes, however, a single SBI can provide the ServerNet interface for several

SACs. In that case each SAC is a ServerNet device and, in addition, the SBI can have

its own individual ServerNet device identification; it becomes a ServerNet device, just

like a SAC. In the example in the lower right corner of Figure 2-1, there is only one link

to the ServerNet routers, even though in this case there are four ServerNet devices.

Note the distinction that ServerNet routers (in the middle of the diagram) are pass-

through switching circuits and are never referred to as ServerNet devices. To

emphasize this distinction, a true ServerNet device is sometimes termed a ServerNet

end device.