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Appendix A: Introduction to Serial Attached SCSI ● 64
How Do SAS Devices Communicate?
SAS devices communicate with each other through links. A link is a physical connection
between two phys.
As shown in the following figure, SAS devices contain ports (see page 65), ports contain phys,
and each phy contains one transmitter and one receiver—one transceiver. A phy can belong to
one port only.
What’s a Phy?
Phys are part of the physical communication connection between SAS devices. Each phy
contains a transceiver that sends data back and forth between SAS devices.
When a connection is formed between two end devices, a link is established from a phy in one
port to a phy in the other port. As shown in the figure above, a wide port can support multiple
independent links simultaneously.
Phys are internal, within SAS connectors (see page 65).
SAS cables physically connect one or more phys on one SAS device to one or more phys on
another SAS device.
Wide
Port
Wide
Port
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Narrow
Port
Phy
Receiver
Transmitter
Narrow
Port
SAS DeviceSAS Device
SAS Device
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Wide
Port
Wide
Port
SAS Device
link