Ethernet RF bridging
XLR PRO Radio Frequency (RF) Modem User Guide
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Ethernet RF bridging
Related parameters: BE, BA
The purpose of Ethernet RF bridging is to act as an Ethernet cable replacement. The MAC/PHY layer of the Ethernet
standard handles all Ethernet traffic. As a result, the XLR PRO does not have to have a valid IP address on the network
for bridging to work.
Ethernet packet handling
If the XLR PRO receives an Ethernet packet with a MAC address that does not match its own MAC address, and if you
enable Ethernet bridging, then the entire Ethernet packet is encapsulated inside of a radio frame and sent over the air
(OTA) to another XLR PRO.
The XLR PRO does not support fragmentation, so the unit sends the entire Ethernet packet in one OTA frame. This can
cause an issue at lower data rates. If the RF data rate (BR) is less than 3 (141kb/s), then full size Ethernet frames cannot
be transmitted. However, smaller frames can be transmitted at lower data rates. We do not recommend this for
typical Ethernet applications, but you could use it in some scenarios.
When the XLR PRO receives an RF bridging packet, it inspects the Ethernet MAC address of the packet. If the address
matches the Ethernet MAC address of the XLR PRO, then the XLR PRO handles the packet on board. Otherwise, it
forwards the frame over the Ethernet interface.
The MT and RR parameters do not apply to Ethernet bridging packets, but they do apply for all non-bridging traffic
(serial or IP socket mode). Serial data from serial or IP socket mode operates concurrently with Ethernet bridging. If
the XLR PRO sends serial and Ethernet traffic at the same time, the traffic encounters latency.
Precautions
The practical application of an Ethernet bridge is to span two Ethernet networks that are not otherwise connected. If
they are connected by another path, then a bridge loop allows multiple paths to the same node. When multiple paths
to the same node occur, then a broadcast storm can result in a saturated network, resulting in denial of service for
legitimate traffic. Typically, this is alleviated by a network switch that support the Spanning Tree Protocol (STP) to
detect and prevent such a network loop. The XLR PRO does not implement STP.
As a precaution, when using bridging, only connect one of the XLR PRO devices to the same Ethernet network to avoid
bridging loops. If you create multiple paths and you connect enterprise level switches with STP to the XLR PRO
devices, then the connected switch ports are shutdown.
When bridging two networks, if each has its own DHCP server, it can create many problems.
Enabling bridging
To enable bridging, set the bridging enable (BE) parameter to 1. This parameter is disabled by default due to the risk
of encountering a bridging loop during initial configuration.
64-bit addresses
Each radio has a unique factory-assigned IEEE 64-bit address. You can read the factory-assigned address with the SH
and SL commands. Addresses use the following form: 0x0013A2XXXXXXXXXX. The first six digits are the Digi
Organizationally Unique Identifier (OUI). The broadcast address is 0x000000000000FFFF.