1. A method for metering the usage, on a group of lines subject to a group user agreement, of the data processing capacity of a network, comprising: receiving usage reports from respective lines of the group; maintaining a total, over the group, of usage that has been reported by the lines and of outstanding usage quotas that have been granted to the lines; maintaining a comparison between the total outstanding group quota and a limit that depends on the total reported group usage, so as to detect violation events when said quota violates the limit; upon occurrence of at least some violation events, automatically selecting one or more lines for quota reallocation; and automatically transmitting an instruction to a processor serving each selected line, but to no processor serving any other line of the group, that causes a new quota to be negotiated for the served line.