Consider this: When you connect to your local node, using standard AX. It'll acknowledge that packet, then send you a connected packet which you must then acknowledge.
This same thing happens with each and every packet you, or the other station, send. If it's not received on the first transmission, APRS retransmits it, using a decaying time delay that is, the second packet is sent eight seconds after the first, the third fifteen seconds later, the fourth half a minute later, the fifth a minute later, the sixth two minutes later etc.
It makes more efficient use of the frequency. APRS uses several different kinds of digipeaters in order to propagate beyond their immediate area. A RELAY station the default setting are usually base stations, and are used to digipeat low-power portable and mo- bile stations. When setting up APRS for your location, you'd set your digipath based on the situation at that QTH and where you want your packets to go.
In using keyboard-to-keyboard communication the only comms that use "ACK's" you can also set alternate digipeater paths. Not only does this direct your message via the shortest possible route, but it also reduces QRM.
I call it a framework as it took the next decade for APRS to mature. A full time internet gateway developed, and digipeat and path protocols formalized. Those wild west days of APRS may be gone, but the Automated Packet Reporting System has become an established, functional, and quite useful mode for amateur radio operators- especially those interested in Emergency Communications.
So APRS works by transmitting unconnected packets containing a callsign, path, location, and other information.
When I say unconnected, I mean that an APRS packet is transmitted without the expectation that it will be received by another station. Back in the olden days of packet radio you would use your TNC to connect to another station, much like a computer and modem would connect to another computer over the phone lines. So with an unconnected packets of APRS any number of receiving stations can potentially pick up the message and retransmit or digipeat it.
This has the potential of conflict and these retransmitted packets can collide over the air, so a method of filtering and packet deprecation built into the digipeater firmware eliminatea duplicate packets. These are the path protocols. The purpose of a digipeater is to listen for a packet and retransmit it. Since digipeaters cover a wide area, they will automatically retransmit a packet with the WIDE designator.
The packet now expires. Of course multiple digipeaters could receive the packet and retransmit them but the callsign substitution feature of the protocol prevents that ping pong effect from happening. You never want to extend your packets out more than 3 hops as each hope introduces more chances for collision.
See also the original Commented Parser. APRS Satellites. Description , and Basic code , and mm-data. The concept, which dates back to the mid 's, is that all relevant information is transmitted immediately to everyone in the net and every station captures that information for consistent and standard display to all participants. Information was refreshed redundantly but at a decaying rate so that old information was updated less frequently than new info.
See the original APRS. The two images below should give you an idea of the kinds of information available to the mobile operator on his APRS radio.
Each station or object in the list has three more pages of information on it. The objects can show Repeater frequenceis in an area, meetings, nets, events, hamfests, echolink and IRLP nodes and frequencies, traffic speeds, accidents, emergency situations. And the attached GPS can show the location of each of these items. APRS is much more. See the Kenwood mobile display above. All of this while providing not only instantaneous operator-to-operator keyboard messaging capability for special events , but also an always-on Voice Alert backchannel between mobiles in simplex range.
Think of APRS as a signalling channel to reveal ALL amateur radio resources and live activities that are in range of the operator at any instant in time. In North America, In Europe, use National operating rules were standardized in the time frame under the New-N Paradigm to eliminate obsolete and inefficient routing. See the high density areas in the map to the right. Further, the APRS channel is a resource to inform everyone of nearby ham resources in range.
Please see the Local Info Initiative. Here is the live IGate list of over IGates that give connectivity throughout the world. Not only does this allow for global monitoring of local activity, it also allows the two-way point-to-point messaging between any two APRS users anywhere on the planet that has an APRS infrastructure.
0コメント