Methods, systems, and apparatus include computer programs encoded on a computer-readable storage medium for providing content. A method includes: receiving a first request for an advertisement to be presented in a slot on a web resource that is to be displayed by an access device; identifying an advertisement to serve; determining an amount of time required to deliver the advertisement to the access device including determining a connection speed; storing connection information including at least the connection speed; subsequent to the storing, receiving a second request for a second advertisement from the access device; using the stored connection information to determine one or more of an advertisement eligibility, an advertisement type, or an advertisement size, including selecting a second advertisement responsive to the second request that meets at least one of the determined eligibility, size or type; and providing the second advertisement responsive to the second request.