Compaq AlphaServer ES45 Service Manual page 237

Figure 7–2 shows the data flow in the bypass modes. Note that the internal
system COM1 port is connected directly to the modem port.
NOTE: You can connect a serial terminal to the modem port in any of the
bypass modes.
The local terminal is still connected to the RMC and can still connect to the
RMC CLI to switch the COM1 mode if necessary.
Snoop Mode
In Snoop mode data partially bypasses the RMC. The data and control signals
are routed directly between the system COM1 port and the external modem
port, but the RMC taps into the data lines and listens passively for the RMC
escape sequence. If it detects the escape sequence, it connects to the RMC CLI.
The escape sequence is also passed to the system on the bypassed data lines. If
you decide to change the default escape sequence, be sure to choose a unique
sequence so that the system software does not interpret characters intended for
the RMC.
In Snoop mode the RMC is responsible for configuring the modem for dial-in as
well as dial-out alerts and for monitoring the modem connectivity.
Because data passes directly between the two UART ports, Snoop mode is
useful when you want to monitor the system but also ensure optimum COM1
performance.
Soft Bypass Mode
In Soft Bypass mode all data and control signals are routed directly between the
system COM1 port and the external modem port, and the RMC does not listen
to the traffic on the COM1 data lines. The RMC is responsible for configuring
the modem and monitoring the modem connectivity. If the RMC detects loss of
carrier or the system loses power, it switches automatically into Snoop mode. If
you have set up the dial-out alert feature, the RMC pages the operator if an
alert is detected and the modem line is not in use.
Soft Bypass mode is useful if management applications need the COM1 channel
to perform a binary download, because it ensures that RMC does not
accidentally interpret some binary data as the escape sequence.
Using the Remote Management Console 7-7