No LOS, no problem!

Digital Repeater Backhaul allows IP Site Connect sites to be connected via a backhaul link that uses repeaters. This feature is especially useful in areas where no site link connectivity exists (e.g. Microwave).

This feature is supported by all the SLR series repeaters but not the (discontinued) MTR3000 or DR3000. Up to 14 backhaul chains are supported as well as up to 8 over the air hops per chain.

It supports all call types including Emergency call, All Call; Group Call; Individual Call; data and CSBK messaging.

All the repeaters in such a system can be monitored using RDAC - though the amount if information provided is limited when compared to IP-linked IPSC.
The repeaters support roaming beacons; NAI voice/data/control/phone; CWID and RAS. However, only standard GPS is supported - this means enhanced and single-CSBK GPS are not supported.

Transmit Interrupt; Repeater Call Monitoring; Digital Telephone Patch; Digital Voting; Confirmed Group Data and CSBK based data are also not supported in a Digital Repeater Backhaul system.

The sites at the beginning and end of a chain are known as the Origin and Terminating Site. The sites in between the the Origin and Terminating Sites are known as a Link Sites.

In a Digital Repeater Backhaul system, radios will talk (and listen to) to Drop Repeaters through regular DMR channels (just like a regular standalone/IPSC repeater). The Drop Repeaters repeat the calls over the air (just like a regular repeater) and send call streams to Link Repeater(s) over IP.

The Link Repeaters receive the calls from the connected Drop Repeater and forward this to the adjacent site/site's Link Repeater(s) through a seperate DMR link channel.

The Link Repeater(s) at the other end will receive the calls from over the air and send the call streams to its own Drop Repeater over IP.  and forward to adjacent site Link Repeater (except Origin & Terminating sites).

The frequency pairs (see above diagram) can be reused if there is no overlap between sites and/or links.

It's also possible to have a hybrid system consisting on regular IPSC repeaters and repeaters connected via a repeater backhaul - as shown in the diagram below.

Digital Repeater Backhaul makes an excellent substitute, or replacement, for EVX-link -  which was discontinued with the rebranding.