25 pair Cat3 wire typically used on business RJ66 blocks for distributing phones. This case it looks like the possible main feed into the room for several lines. I would recommend replacement to a Cat 6 ethernet wire if at all possible. This will not work for internet purposes are any decent speeds.

It is useful for a read but it is outdated for trying to use as a test prep. You would definitely want the newest updated book to match the latest test.