DMRGateway is software developed by, Jonathan Naylor, the author of MMDVMHost
and ircDDBGateway to allow an MMDVM repeater or hotspot to
connect to multiple DMR networks and XLX servers. It does this by
translating DMR Talkgroups between MMDVMHost and the DMR
network or XLX server. Currently it supports two DMR networks –
Brandmeister and DMR+, and XLX reflectors. Talkgroup definitions
can be changed in the dmrgateway.ini file but defaults are TG 9 for
Brandmeister, TG 8 for DMR+, and TG 6 for XLX. XLX is often refered to
as DMR+ is not used as much. The DMR-MARC organistaion is taking steps
to allow DMR+ (XLX) to connect to its network.
D-Star transmissions only go to D-Star reflector -> Only heard by D-Star radios
DMR transmissions only go to Brandmeister Network -> Only heard by DMR radios
Transcoding overcomes this limitiation.
For transcoding, each XLX module needs an AMBE Server instance with a hardware AMBE chip. A XLX reflectors which is cross-connected to a XRF reflector requires an AMBE Server. If a repeater or hotspot is connected to such an XLX reflector, D-Star transmissions will be transcoded to DMR and vice versa.
This site explains the Gateway Scenario but, unfortunately, from a US perspective:
DMR Gateway will only pass traffic to the different networks if it's referenced in a rewrite rule in the .ini file.
TGRewrite allows you to translate one talk group ID to another, and to alter the time slot. TGRewrite can also be used to route a talk group and slot combination to a particular network. 'from' applies to DMR frames entering the Gateway via MMDVMHost (RF), and 'to' is where they are routed on the network side (Net). The rules apply to DMR frames traversing the gateway in both directions.
See this wiki for more dewtails: