(→Path Overkill: close loopholes)
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Latest revision as of 13:35, 26 March 2012
 Path Overkill
A path that specifies more hops than necessary for the area you're operating in can be considered an abusive path. An example of a path that's excessive or abusive almost everywhere is "WIDE1-1,WIDE3-3." This path can result in up to four "hops" - that is, it can be repeated up to four times. In virtually any area with APRS coverage, this is too much. In many areas, three hops is excessive.
One of the things about the APRS Internet System (APRS-IS) is that the same packet can get to the Internet by many routes, and the APRS-IS system keeps only one of them. The one it keeps is basically random - it keeps one of the many copies that arrive, and throws away the rest. While experimenting with high-hop-count paths one night, the copy that survived was one that had gone through the full four hops, and the results show exactly why this is abusive.
Example: The route part of the packet on when viewed as "raw packets" might look like this: WR6ABD,N6CP-1,WA6LDQ-3,WA6YLB-3*,WIDE3,qAo,KF6HJO
That means it had been digipeated by WR6ABD, N6CP-1, WA6LDQ-3, and WA6YLB-3 before finally being heard by the IGate KF6HJO. This does not mean the four-hop route was justified. The exact same data also got to APRS-IS in a single hop, because there is an IGate that can hear WR6ABD, the first digipeater this packet hit. And there are certainly many more digipeaters involved and other routes that this same data took to get to the Internet, too; this is just the one copy that survived. The point is that a path whose hop count is too high can "light up" a wide geographic area unnecessarily, using up time on the one APRS frequency and interfering with other APRS users hundreds of miles away.
The best advice is to specify a path that uses the minimum number of hops to accomplish your legitimate goals with the limited APRS resources in the area you are using it. Because each region's geographical and RF propagation characteristic is unique, it's best to check the Regional Information pages for localized info. Above all, please be considerate of your neighbors.