On Oct. 1, ComCast cable company will update its user agreement to say that users will be allowed 250 gigabytes of traffic per month, the company announced on its Web site.

Comcast floated the idea of a 250 gigabyte cap in May and mentioned then that it might charge users $15 for every 10 gigabytes they go over, but the overage fee was missing in Thursday's announcement.

Curbing the top users is necessary to keep the network fast and responsive for other users, Comcast has said.

Comcast stressed that the bandwidth cap is far above the median monthly usage of its customers, which 2 to 3 gigabytes.

Very few subscribers use more than 250 gigabytes, it said. A user could download 125 standard-definition movies, about four per day, before hitting the limit.

The cap is also above those of some other ISPs. Cox Communications' monthly caps vary from 5 gigabytes to 75 gigabytes depending the subscriber's plan. Time Warner Cable Inc. is testing caps between 5 gigabytes and 40 gigabytes in one market. Frontier Communications Co., a phone company, plans to start charging extra for use of more than 5 gigabytes per month.