Network Call Flow – c-Bridge

The c-Bridge is a DMR call routing platform that directs calls to the appropriate destinations. This functions as a point to multi-point router or similar to VLAN Trunking.

Talkgroups are the control points for the c-Bridge. They convey the voice traffic, the routing of that traffic and set timers for the duration of that voice path as well as hold-off some or all other traffic on that timeslot in use.

Talkgroups carry the voice traffic over the network as well as the routing information that tells the c-Bridge (Network or Conference Controller) who to send out that traffic and lastly with timers to help prioritize the traffic on that timeslot. A talkgroup may appear on or be distributed to just 1 repeater or to hundreds of repeater. The talkgroup name generally denotes the geography, language or purpose. A talkgroup may be programmed to ride on 1 of the 2 timeslots (voice paths). 2 simultaneous conversations are possible on each DMR repeater. For example, “Washington 1” is a talkgroup that goes out to every repeater in Washington on timeslot 1 and is always “on” or live all the time. This makes Washington 1 a great hailing talkgroup using the repeaters in the state of Washington.

graphic showing the 2 voice paths and their simultaneous capability
DMR Repeaters support 2 voice paths and its capability of 2 independent and simultaneous conversations (graphic by Retevis)
Above: Call Flow: Users may enter the network via fixed site repeaters or personal hotspots. Graphic by Steve, N9VW

PNW DMR –  c-Bridge Call Flows

The c-Bridge is a DMR call routing platform that directs calls to the appropriate destinations. This functions as a point to multi-point router. The c-Bridge is composed of three sections:

  1. Managers – The link layer definitions for each time slot for each connected repeater.
  2. Bridge_Groups – The definition of each Talk Group on each repeater.
  3. Super_Groups – The connection(s) for Talk Group between different Bridge_Groups.

A call is routed into the c-Bridge from the repeaters via a Manager and then forwarded to a Bridge Group. From there the Bridge Group routes the call up to the Super Group logic to determine which other repeaters the call should be routed to.

Note: The numbers that appear (ex: Wash 1-23) are what show up on Call Watch. These are just Bridge_Group identifiers, helpful in knowing where the call came from.

There are three basic calls indicated on the diagram as follows:

  • A call on Washington 1 is sent to the c-Bridge. In this case the call will be routed to all Washington repeaters as this is a state wide talk group.
  • A call on TAC 1 is sent to the c-Bridge.  In this case the call will be routed only to those sites that a user has ‘opened’ the talk group by press their PTT. This only brings up repeaters that are actively using TAC 1 at the time.
  • A call on Metro 2 is sent to the c-Bridge. In this case the call will be routed to the Local repeater that the call came in on or via several grouped repeaters as has been previously defined. NOTE: Local 1 only operates on a single repeater that the call originated on.

If you have questions or need a clarification, simply ask on the air, search messages or post to the IO Forum. Or, you may send your questions to: Support@PNWDigital.net

Now that you have made it to the end of this “Not-so-Quick-Start” page, proceed with more “light” reading on our PNWDigital.Net Talkgroups to get more involved in the complexities of the PNWDigital.Net network.

First Published: December 17, 2021 Last Updated: 1 year ago by Mike – NO7RF

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