Radio technology has advanced greatly in the last several years, and will advance more. When the FCC opened up the small “useless” band where microwave ovens operate to unlicenced use, it generated the greatest period of innovation in the history of radio. As my friend David Reed often points out, radio waves don’t interfere with one another out in the ether. Interference only happens at a receiver, usually due to bad design. I’m going to steal several of David’s ideas here and agree with him that a powerful agency founded on the idea that we absolutely must prevent interference is a bad idea.

My overly simple summary of a replacement regime is just this, “Don’t be selfish.” More broadly, this means, “don’t use more spectrum than you need,” both at the transmitting and receiving end. I think we could replace the FCC with a court that adjudicates problems of alleged interference. This special court would decide which party was being more selfish, and tell them to mend their ways. Unlike past regimes, the part 15 lesson suggests that sometimes it is the receiver who is being more spectrum selfish.

Here are some examples of using more spectrum than you need:

• Using radio when you could have readily used wires, particularly the internet. This includes mixed mode operations where you need radio at the endpoints, but could have used it just to reach wired nodes that did the long haul over wires.
• Using any more power than you need to reliably reach your receiver. Endpoints should talk back if they can, over wires or radio, so you know how much power you need to reach them.
• Using an omni antenna when you could have used a directional one.
• Using the wrong band — for example using a band that bounces and goes long distance when you had only short-distance, line of sight needs.
• Using old technology — for example not frequency hopping to share spectrum when you could have.
• Not being dynamic — if two transmitters who can’t otherwise avoid interfering exist, they should figure out how one of them will fairly switch to a different frequency (if hopping isn’t enough.)

As noted, some of these rules apply to the receiver, not just the transmitter. If a receiver uses an omni antenna when they could be directional, they will lose a claim of interference unless the transmitter is also being very selfish. If a receiver isn’t smart enough to frequency hop, or tell its transmitter what band or power to use, it could lose.

Since some noise is expected not just from smart transmitters, but from the real world and its ancient devices (microwave ovens included) receivers should be expected to tolerate a little interference. If they’re hypersensitive to interference and don’t have a good reason for it, it’s their fault, not necessarily the source’s.  read more »

Update: Several of the spam bounces of this sort that I got were traced to the same anti-spam system, and the operator says it was not intentional, and has been corrected. So it may not be quite as bad as it seemed quite yet.

I have a social list of people I invite to parties. Every time I mail to it, I feel the impact of spam and anti-spam. Always several people have given up on a mailbox. And I run into new spam filters blocking the mail.

Perhaps I’m an old timer, but I run my own mail server. It’s in my house. I read my mail on that actual machine, and because of that, mail is wicked-fast for me, as fast as instant messaging for many people. (In fact, I never adopted IM the way some people did because E-mail is as fast.)

They’re working to make this harder to do. Many ISPs won’t even let you send mail directly, or demand you make a special request to have the mail port open to you. I’m bothered by the first case, less so by the second, because indeed, zombie PCs send much of the spam we’re now getting.

Because I send mail from the system, I also web surf from it. And while it’s not a serious privacy protection, I decided I would not have a reverse-DNS record for my system. That way people would not see “templetons.com” in their web logs whenever I surfed. It’s not that you can’t use other techniques to find out that the address is mine, but that requires deliberate thought. Reverse DNS is automatic for many web logs.

Soon more and more sites would not take mail from a system without reverse DNS. Because I get my IP block from a small ISP, he does my reverse DNS, and I asked him to make one. He made one like many ISPs do, built from the IP numbers themselves. As in ip-nn-nn-nn.ispname.com.

But soon I saw bounces that said, “This reverse DNS looks like a dialup user, I won’t take your mail.” So I had him change it to a different string that doesn’t trumpet my name but doesn’t look like a standard anonymous reverse DNS.

But now I’m getting bounces just because the reverse DNS doesn’t match the name my mail server uses. There is no security in this, any spammer can program their mail server to use the reverse DNS name of the system they have taken over. But I guess some don’t, so another wall is thrown up, and those people won’t get invites to my parties.

This one is really stupid because it’s quite common for a single machine to have many names and serve many domains. To correct an earlier note, it is possible for an IP to have more than one PTR reverse DNS record, though I don’t know how many applications deal with that. And that screws these mailers. There is no need to look at reverse DNS at all.

Sigh.