Startup and functions
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3.4
Frame switching
The MMS/MCS operates in store-and-forward mode. When receiving a data packet, the
switch analyzes the source and destination addresses. The switch stores up to 8000 MAC
addresses with an adjustable aging time of 10 to 825 seconds in its address table.
3.4.1
Store-and-forward
All data telegrams that are received by the switch are saved and their validity is checked.
Invalid or faulty data packets (> 1522 bytes or CRC errors) and fragments (< 64 bytes) are
rejected. Valid data telegrams are forwarded by the switch.
3.4.2
Multi-address function
The switch learns all the source addresses for each port. Only packets with:
–
Unknown source addresses
–
A source address for this port
–
A multicast/broadcast address
are forwarded to the destination address field via the relevant port. The switch can learn up
to 8000 addresses. This is important when more than one termination device is connected
to one or more ports. In this way, several independent subnetworks can be connected to
one switch.
3.4.3
Learning addresses
The switch independently learns the addresses for termination devices, which are
connected via a port, by evaluating the source addresses in the data telegram. When the
MMS/MCS receives a data telegram, it only forwards this data telegram to the port that
connects to the specified device (if the address could be learned beforehand).
The devices can learn up to 8000 addresses and store them in a table. The switch monitors
the age of the learned addresses. The switch automatically deletes address entries from its
address table that have exceeded a specific age (default: 40 seconds, adjustable from 10
to 825 seconds, aging time).
All learned entries are deleted on a restart.
A list of detected MAC addresses can be found in the MAC address table (see Section
""Diagnostics/MAC Address Table" menu" on page 4-40). The MAC address table can be
deleted via "Clear".
The aging time is set using the "dot1dTpAgingTime" MIB object
(OID 1.3.6.1.2.1.17.4.2). The available setting range is 10 - 825 seconds. For static
configuration, an aging time of 300 seconds is recommended.
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