About the Radio | 49
Aprisa SRi User Manual 1.1.0
Bridge Mode with VLAN Aware
Ethernet VLAN Bridge / Switch Overview
The Aprisa SRi in Bridge mode of operation is a standard Ethernet Bridge based on IEEE 802.1d or VLAN
Bridge based on IEEE 802.1q/p which forward / switch Ethernet packet based on standard MAC addresses
and VLANs using FDB (forwarding database) table decisions. VLAN is short for Virtual LAN and is a virtual
separate network, within its own broadcast domain, but across the same physical network.
VLANs offer several important benefits such as improved network performance, increased security and
simplified network management.
The Aprisa SRi Bridge mode (see figure below), is the default mode of operation and it enables the switching
/ bridging of Ethernet VLAN tagged or untagged packets within the Aprisa SRi wireless network and in and
out to the external Industrial LAN network and RTUs devices connected to the Aprisa SRi wired Ethernet
ports or serial ports through the terminal server function.
Within the Aprisa SRi Bridge mode, each incoming Ethernet packet is inspected for the destination MAC
address (and VLAN) and looks up its FDB table for information on where to send the specific Ethernet frame.
If the FDB table doesn’t
contain the specific MAC address, it will flood the Ethernet frame out to all ports
in the broadcast domain and when using VLAN, the broadcast domain is narrowed to the specific VLAN used
in the packet (i.e. broadcast will be done only to the ports which configured with that specific VLAN).
The FDB table is used to store the MAC addresses that have been learnt and the ports associated with that
MAC address. If the destination MAC address is one of the RTUs, the packet is then forwarded to the wireless
ports and broadcast as a PMP wireless packet to all the remote radios. The appropriate remote then switches
the Ethernet packet and forwards it based on its FDB table (based on the MAC or VLAN & MAC) to the
appropriate Ethernet port to the RTU. The RTU can then interpret and process the Ethernet / IP data and
communication is established between the RTU and the initiating communication device.