Description of functions
User manual 58185_TREE M4/6-TX PN IP20_hdb_en_10
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4.1.3
Frame switching
Store-and-forward
mode
The switch operates using
store-and-forward
mode.
The switch analyzes the source and destination whenever it receives a data
packet. The switch can store up to 1024 MAC addresses in its address table,
with a retention time of 330 seconds.
Switching Fabric Unit
(SFU)
The SFU receives defect-free packets from the ports and forwards them to the
MAC address of the device for which they are intended for processing.
The SFU recognizes which packets have to be sent to which ports. It does this
by creating a table with the source addresses of the packets and the numbers
of the ports where the packets were received.
The SFU uses the generated table and the destination MAC addresses to de-
cide which packets have to be sent using which port.
Lookup Address Table
(LUT)
The internal lookup engine generates the LUT. It stores all source addresses
of incoming packets together with the port number of the switch. Up to 1024
address port numbers can be mapped in the LUT.
This must be done if multiple devices are connected to a port or multiple ports.
In such cases, different independent subnetworks can be connected using the
switch.
Finding addresses
Whenever a packet arrives, the switch searches for the destination address in
the LUT.
If the destination address is in the LUT, the number of the output port is for-
warded to the output port queue manager. The switch then forwards the pack-
et to the corresponding output port.
The switch forwards packets with a multicast or broadcast address to all ports
except the port where the packet was received.
Learning addresses
If the MAC address of the destination cannot be found in the LUT, the switch
switches to automatic learning mode.
Automatic learning mode:
The switch sends the packet to all ports.
When a device responds to this packet, the SFU learns its MAC address.
The SFU records the new MAC address and the port in the LUT.
The switch then transmits all future packets to the destination directly us-
ing this port only.
Address retention
The address retention process is continuously ongoing.
NOTE
The aging time of the entries is updated every time the LUT is accessed. En-
tries are removed from the LUT when the connection to a network node is
closed or the device is deactivated.
