Black Box LGB2118A Manuel D’Utilisation
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Chapter 4: Basic Concepts and Management
Table 4-5. Ethernet parameters for half-duplex mode.
Parameter Value/LAN
10BASE
100BASE
1000BASE
Max. collision domain DTE to DTE
328 feet (100 m)
328 feet (100 m) for UTP
1351.7 feet (412 m) for fiber
328 feet (100 m) for UTP
1043.3 feet (316 m) for fiber
Max. collision domain with repeater
8202.1 feet (2500 m)
672.6 feet (205 m)
646.1 feet (200 m)
Slot time
512 bit times
512 bit times
512 bit times
Interframe gap
9.6 µs
0.96 µs
0.096 µs
Attempt Limit
16
16
16
Backoff Limit
10
10
10
Jam size
32 bits
32 bits
32 bits
Max. frame size
1518
1518
1518
Min. frame size
64
64
64
Burst limit
Not applicable
Not applicable
65536 bits
Figure 4-5. Full-duplex mode.
In full-duplex operation mode, both transmitting and receiving frames are processed simultaneously. This doubles the total
bandwidth. Full-duplex is much easier than half-duplex because it does not involve media contention, collision, retransmission
schedule, and padding bits for short frames. It functions according to the IEEE 802.3 specification. The minimum inter-frame gap
requirement between successive frames and frame formats is the same as that in the half-duplex operation.
bandwidth. Full-duplex is much easier than half-duplex because it does not involve media contention, collision, retransmission
schedule, and padding bits for short frames. It functions according to the IEEE 802.3 specification. The minimum inter-frame gap
requirement between successive frames and frame formats is the same as that in the half-duplex operation.
No collision will happen in full-duplex operation. What happens if the receiving device is busy and a frame is coming at the same
time? Can it use “backpressure” to tell the source device? A flow control function is introduced in full-duplex operation.
time? Can it use “backpressure” to tell the source device? A flow control function is introduced in full-duplex operation.
4.4 Flow Control
Flow control is a mechanism that tells the source device to stop sending frames for a specified period of time designated by a
target device until the PAUSE time expires. It does this by sending a PAUSE frame from the target device to the source device.
When the target is not busy and the PAUSE time is expired, it will send another PAUSE frame with zero time-to-wait to the source
device. After the source device receives the PAUSE frame, it will again transmit frames immediately. The PAUSE frame is identical in
the form of the MAC frame with a pause-time value and with a special destination MAC address 01-80-C2-00-00-01. As per the
specification, PAUSE operation can not be used to inhibit the transmission of a MAC control frame.
target device until the PAUSE time expires. It does this by sending a PAUSE frame from the target device to the source device.
When the target is not busy and the PAUSE time is expired, it will send another PAUSE frame with zero time-to-wait to the source
device. After the source device receives the PAUSE frame, it will again transmit frames immediately. The PAUSE frame is identical in
the form of the MAC frame with a pause-time value and with a special destination MAC address 01-80-C2-00-00-01. As per the
specification, PAUSE operation can not be used to inhibit the transmission of a MAC control frame.
Normally, in 10-Mbps and 100-Mbps Ethernet, only symmetric flow control is supported. However, the Gigabit Smart Switch Eco
Fanless supports not only symmetric, but also asymmetric flow control for the special application. In Gigabit Ethernet, both
symmetric flow control and asymmetric flow control are supported. Asymmetric flow control only allows transmitting a PAUSE
frame in one way from one side; the other side is not transmitted. Instead the switch receives and discards the flow control
information. Symmetric flow control allows both two ports to transmit PAUSE frames to each other simultaneously.
Fanless supports not only symmetric, but also asymmetric flow control for the special application. In Gigabit Ethernet, both
symmetric flow control and asymmetric flow control are supported. Asymmetric flow control only allows transmitting a PAUSE
frame in one way from one side; the other side is not transmitted. Instead the switch receives and discards the flow control
information. Symmetric flow control allows both two ports to transmit PAUSE frames to each other simultaneously.