Repost: MOTOTRBO Link

This post originally appeared on 3 July 2018. Around 18 November 2024, I made some small changes and added some (hopefully useful) information to this post.

MOTOTRBO Link allows repeaters in an IP Site Connect system to be connected via a backhaul link that uses repeaters. This feature is especially useful in areas where no site link via some other means (e.g. microwave) is not possible.

This feature is supported by all the SLR series repeaters. 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 control messaging.

All the repeaters can be monitored using RDAC - though the amount of information provided is limited when compared to an IP-linked system.

The repeaters themselves support IP Site Connect roaming beacons; NAI voice and data; control; phone patch; CWID and RAS.

Enhanced and single-CSBK GNSS; Transmit Interrupt; Repeater Call Monitoring; Digital Telephone Patch; Digital Voting; Confirmed Group Data and CSBK based data are however not supported.

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 Interim Sites.

In a MOTOTRBO Link system, radios will use the Standard Repeaters using the DMR air interface (just like a regular standalone/IPSC repeater). These repeaters transmit and receive voice calls over the air (just like a regular repeater) and pass voice streams to to the colocated Link Repeater(s) over IP.
The Link Repeaters receive the calls from the connected Stanard Repeater and forward this to the adjacent site' Link Repeater(s) through a seperate DMR link channel. The Link Repeater at the other end will receive this traffic and send it to the local Standard Repeater (if present) as well as the next site's site Link Repeater.

The frequency pairs can be reused if there is no overlap between sites and/or links. The Link Repeaters can also be in a different frequency range (TX RX 10-16).

It's also possible to have a hybrid system consisting of regular IP Site Connect repeaters and MOTOTRBO Link repeaters as shown in the diagram below. If you intend doing this, be aware that the Link Repeater(s) and Standard Repeater at a site use a combination of gratuitous ARP and IP local broadcast to manage communications. This means that you should use a where two or more Standard repeaters will be connected via ethernet.

To ensure bursts are properly synchronised, all colocated repeaters that make up the linked system, must make use of a sync cable. You would need to make this cable yourself using either single core shielded cable or twisted pair and some D25M plugs (or RJ45 if using a SLR1000). 

The pinout for the SLR5500 can be found here. I will post the SLR1000 pinout shortly.

One of the repeaters at the site will need to be configured as the GPIO Timing Master using CPS (tick in MOTOTRBO Link set). This repeater would also need to have one of its GPIO pins set to Site Slot Link Output (now try saying that when you've had one too many, eh!?). 

The other repeaters would need to have one GPIO set to Site Slot Link Input and GPIO Timing Master must be unticked.

You can find more information about MOTOTRBO link and some configuration details at https://cwh050.mywikis.wiki/wiki/MOTOTRBO_Link.