Traditionally, mainframes expect all the physical units on a channel to be powered on before the channel is varied online. When a channel is varied online, the mainframe polls each of the units it expects to find on this channel. If a unit does not respond, an error message displays on the operator console.
To respond to the mainframe poll, the Barr channel device driver must know the subchannel address. Usually this information is not available until you start the corresponding SNA gateway connection and the connection reaches the pending state. However, you can use the Static subchannel addresses feature on the Adapter tab to predetermine which addresses the Barr channel device driver should respond to, so the driver can respond to the poll when the connection is inactive.
The Static subchannel addresses feature is particularly useful when you also use the Distributable link service feature. With a distributed link service, the corresponding SNA gateway connection can reside on another SNA gateway at a remote location. If you specify the static subchannel addresses, a channel can be varied online, without error messages, independently of the connection state at the remote location.
Subchannel addresses for each channel device must be unique. Verify that none of the statically configured addresses are being used by other devices on the channel.