Call blocking, please...

Michael Dillon michael at
Tue Jan 7 02:36:57 UTC 1997

Barry wants Sprint to block port 25 traffic from a Sprint customer
to his ISP.

On Mon, 6 Jan 1997, Sean Donelan wrote:

> The phone company equivalent of Barry's request is call blocking, "beep,
> boop, BEEP, The number you have dialed is blocked at the subscriber's
> request."  A major impetus for this feature was 'the' telephone company's
> desire to get out of the abuse and harrassment complaint handling business.
> The subscriber doesn't have to give a reason why they want the number
> blocked, they just ask the phone company to do it.  Due to the way SS7
> works, the blocked announcement (usually) comes from the telephone company
> at the origin's location.
> BBNPlanet installs firewalls and filters for all sorts of customers
> that don't want to recieve traffic from some sources.  You don't need
> a court order to install a firewall to block traffic, just the customer's
> request.  A traffic filter may be installed in any of several places, on
> the destination customer's equipment, on the provider's equipment serving
> the destination customer, at some intermediate point in the provider's
> network, or in the provider's equipment serving the source customer.  It
> could also be placed in the source customer's equipment, but in most of
> these cases we are dealing with an uncooperative source customer.
> There may be management reasons why an ISP doesn't want to fullfill a
> customer's or non-customer's request to stop forwarding bits to/at them.
> If you follow the rule used by the RBOC's managing the ATM NAP's, a PVC
> may be terminated at the request of *either* subscriber.  Their policies
> cause an occasional routing blackhole, but don't seem to have opened
> PacBell or Ameritech up to a lot of legal liability.  And since the telco's
> are extremely risk adverse, this is a pretty strong precedent.
> Maybe I'll add a section to my internet-draft on Responsible Internet
> Service Provider Guidelines.
>     - An ISP may stop forwarding traffic at the request of either the
>       source or destination.
>         - Traffic forwarding filters should be symetrical, unless otherwise
>           requested by *both* the source and destination.  This isn't exactly
>           what I want to say, the intent is to prevent people from using their
>           ISP as a shield while attacking a site that can't respond.  But
>           most networks use asymtrical filters, e.g. anyone can FTP out, not
> 	  in.  If you tell AOL you don't want mail from, you
>           shouldn't be able to mailbomb from AOL either.
> As always, a big concern is financial.  Who should pay for traffic forwarding
> filters?  The prudish person who wants to keep the traffic out?  Or the
> annoying person who wants to bother as many sites as possible?  So far the
> net has had a policy, the person keeping the traffic out has to pay for
> the firewall or cybernanny.
>     - An ISP may charge the requestor a $100 processing fee (indexed to
>       the CPI) to install or remove a traffic forwarding filter.  This
>       makes it profitable for an ISP to become a spammer's haven.
> -- 
> Sean Donelan, Data Research Associates, Inc, St. Louis, MO
>   Affiliation given for identification not representation

Michael Dillon                   -               Internet & ISP Consulting
Memra Software Inc.              -                  Fax: +1-604-546-3049             -               E-mail: michael at

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