Comcast will challenge cord cutting and entice cord-nevers with an online video package of about a dozen television channels it will sell for $15 a month and likely exempt from its usage cap.

“Stream” will offer about 12 channels — almost all over the air stations including NBC, CBS, ABC, PBS, Fox, The CW, Telemundo, Univision — and HBO to Comcast’s broadband customers and deliver the package over Comcast’s privately managed IP network, which it considers separate from the public Internet. That will also allow Comcast to offer on-demand programming, cloud DVR storage and access to Streampix, Comcast’s movies-on-demand feature it largely abandoned a few years ago.

Comcast’s new no-contract video service will begin in Boston by the end of summer, quickly followed by launches in Chicago and Seattle. Comcast plans to expand the service nationwide by early 2016.

Stream will target millennials and others that have turned their backs on traditional cable television. It will also directly take aim at competing Sling TV, which sells streaming cable TV channels for about $20 a month.

But at first glance, Comcast may have one up on its competition.

Comcast will deliver Stream over the same network it uses for content delivery to game consoles that does not count against Comcast’s trialed usage caps. Watching competitor Sling TV does count against your Comcast usage allowance because it is delivered over the public Internet.

That advantage alone may not help Comcast overcome some of the harsh restrictions it will impose on Stream customers that could prove major turn-offs:

• Viewing must be done from a web browser, tablet, or phone. Stream will not be available on TV-connected platforms like Roku or Apple TV;
• Viewers must stay inside the home to access live streamed content;
• Customers must subscribe to Comcast High Speed Internet service to buy Stream;
• Only Comcast customers inside a Comcast service area can subscribe;
• There are no cable networks offered, except HBO, for now.

Customers will be able to sign up for Stream (and cancel it) over the web with no service technician visit needed. Customers can cancel anytime.