They may locate an end-device either directly (when the end-device is connected to it), via a routing table (a mapping of end-device IDs and the expander the link should be switched to downstream to route towards that ID), or when those methods fail, via subtractive routing: the link is routed to a single expander connected to a subtractive routing port.
If there is no expander connected to a subtractive port, the end-device cannot be reached.
SAS devices use these port identifiers to address communications to each other.
In addition, every SAS device has a SCSI device name, which identifies the SAS device uniquely in the world.
The components known as Serial Attached SCSI Expanders (SAS Expanders) facilitate communication between large numbers of SAS devices.
Expanders contain two or more external expander-ports.
Each expander device contains at least one SAS Management Protocol target port for management and may contain SAS devices itself.
For example, an expander may include a Serial SCSI Protocol target port for access to a peripheral device.
People sometimes call a SAS address a World Wide Name or WWN, because it is essentially the same thing as a WWN in Fibre Channel.In 2013, 12 Gbit/s followed in the SAS-3 specification.An initiator may connect directly to a target via one or more PHYs (such a connection is called a port whether it uses one or more PHYs, although the term wide port is sometimes used for a multi-PHY connection).This allows the connection of SATA drives to most SAS backplanes or controllers.The reverse, connecting SAS drives to SATA backplanes, is not possible.