intermod
Posts: 63
Joined: 10/23/2006
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A D-Star (DS) repeater site can be configured as one or more repeaters using a common controller. Optionally, the controller can then be connected to an Internet gateway (a PC equipped with Linux and special gateway software). The gateway provides connectivity to all other DS systems that have gateways.
For the following I will assume a gateway is included.
Functionally, it is point-to-point (PTP). When you operate through your repeater, it will only activate that repeater unless you specify another destination. When you specify a destination, it brings up one other repeater as well. That second repeater can be at the same site on a different band, or a repeater anywhere else in the nation, any band. The latter requires a gateway at both ends.
There are really only two calling methods - individual or a station call. You either set the destination callsign in your radio channel position to someone’s personal callsign (individual call), or to a repeater station's callsign (station call). In DS, a repeater callsign is never the same as a person's call; it is usually a club call, or a call that is unused.
But in either method, the call activates both the local and the destination repeater. Today, most users listen in "open squelch" (its equivalent in digital) so your message would be heard by all users on both ends. But, users can set their radios to only "unsquelch" when (1) a specific callsign is received, or (2) when a specific digital code is received (like DCS; there are 100). What is cool is that the callsign of the caller, and the digital code they are transmitting (if any) is always routed with the message – anywhere in the DS system. Try that with analog….
The real breakthrough is the individual call. When I set the destination field in my radio to your personal callsign, the site controller and gateway system will literally route each and every transmission to the repeater your were last registered on - so I don't need to know where you are. If it is busy, I will get a display message that my call was not completed. However, you must have "registered" on a repeater. You register by simply keying up once on your local system. Your callsign is then registered and entered into a national database along with the specific repeater you were on (probably its IP address). When you change to a new repeater, simply key-up momentarily and you will be registered there.
One interesting rub that makes it more challenging than IRLP or Echolink - audio in DS is pushed to remote repeaters by the unit transmitting; the reply message is not pulled back, however. That is, you can direct your message out of a remote repeater, but the reply message routing back to you from the oitehr user is not automatic; the user that responds must set their radio to your callsign, or to that of the repeater you are on. There are automated ways of doing this (call reversal button, or automatic caller source storage), but it is still clumsy at best. If they simply reply without setting up the correct destination (which is the local repeater you accessed), you will not hear a reply.
To directly answer your other questions – repeaters operate like conventional FDMA today; one repeater, one conversation. A DS site will usually consist of a UHF, VHF and 1200 MHz module; so up to three separate conversations can occur as usual (each can be linked to one other local repeater, or to one remote repeater through the gateway, or just be conducted on a single repeater).
Today, DS systems don’t “multicast” or simulcast audio across all three stations at the same site; each station is separate.
If station A only wants to only talk to and hear station B, and station C wants to only talk to and only hear station D, they would have to be on different repeaters like conventional. I am guessing that most users will eventually have dual-band DS radios, so that they can switch to a repeater in the alternate band and still have the same routing capability.
What is missing in DS today? IP multicasting and group calling like trunking. I would like to be able to activate three or more repeaters at once (my local VHF, and two others elsewhere in the US), and have replies route back to all others. While this is wasteful of spectrum, the spectrum is lightly used, so it may be better to provide this function since people are used to it.
This could be done using a “group callsign” or by using a multicast addressing scheme. But it can get complicated.
In the meantime, the closest thing we have to trunking, or conventional Project 25 (P25) is the digital code function; this code (like encoded CTCSS) is imbedded and transmitted with a voice message, and is repeated both locally and by the remote repeater. So groups of users can simply set their radios to unmute when they detect that code. But there are only 100 codes (00-99). Also – I understand that DS repeaters cannot be set to activate on a specific code – they simply pass them through. Kind of like a community repeater. This is very useful.
Hope this long-winded message helps.
Greg
N6LDJ
< Message edited by intermod -- 1/3/2007 10:28:54 PM >
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