User`s guide

Appendix A: Introduction to Serial Attached SCSI (SAS) ● 72
How Do SAS Devices Communicate?
SAS devices communicate with each other through links. A link is a
physical connection between two phys.
As shown below, SAS devices contain ports (see page 73), ports contain
phys (see below), 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 74).
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
Por
t
SAS DeviceSAS Device
SAS Device
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Phy
Receiver
Transmitter
Wide
Por
t
Wide
Por
t
SAS Device
link