3Com 3C780 User Guide - Page 63

Data Flow Specifications

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Installing the Hub 2-23 Data Flow Specifications The FDDI standard specifies that data travels on the primary ring in a counterclockwise direction, and that data traveling on the secondary ring rotates clockwise. (Refer to Figure 3-1.) As you attach the hub to the ring and network devices to the hub, be aware of the data flow direction. Table 2-3 shows the four supported port types and the direction of data flow through each port. Figure 2-9 illustrates the various port types and the data flow direction allowed by the FDDI standard. Table 2-3. FDDI Port Types Port Data Flow Direction A Primary In/Secondary Out (PI/SO) B Primary Out/Secondary In (PO/SI) M Master (PO/PI) S Slave (PI/PO) Use Connects dual attachment devices to the trunk ring Connects dual attachment devices to the trunk ring Connects single attachment devices to the hub port; uses the primary ring only Connects single attachment devices to the hub; uses the rimary ring only Table 2-3 and Figure 2-9 show that the primary ring (solid line) enters the A port as Primary In (PI) and exits as Primary Out (PO) through port B. The secondary ring (dashed line) enters through port B as Secondary In (SI) and exits through port A as Secondary Out (SO). For both master (M) and slave (S) ports, the primary ring enters the port as PI and exits as PO. The secondary ring never connects to these two ports.

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2-23
Installing the Hub
Data Flow Specifications
The FDDI standard specifies that data travels on the primary ring in a
counterclockwise direction, and that data traveling on the secondary ring rotates
clockwise.
(Refer to Figure 3-1.)
As you attach the hub to the ring and network
devices to the hub, be aware of the data flow direction.
Table 2-3 shows the four supported port types and the direction of data flow
through each port.
Figure 2-9 illustrates the various port types and the data flow
direction allowed by the FDDI standard.
Table 2-3.
FDDI Port Types
Port
Data Flow Direction
Use
A
Primary In/Secondary Out
Connects dual attachment
(PI/SO)
devices to the trunk ring
B
Primary Out/Secondary In
Connects dual attachment
(PO/SI)
devices to the trunk ring
M
Master (PO/PI)
Connects single attachment
devices to the hub port; uses
the primary ring only
S
Slave (PI/PO)
Connects single attachment
devices to the hub; uses the
rimary ring only
Table 2-3 and Figure 2-9 show that the primary ring (solid line) enters the A
port as Primary In (PI) and exits as Primary Out (PO) through port B.
The
secondary ring (dashed line) enters through port B as Secondary In (SI) and
exits through port A as Secondary Out (SO).
For both master (M) and slave (S) ports, the primary ring enters the port as PI
and exits as PO.
The secondary ring never connects to these two ports.