We connect to the Internet through a proxy, and I checked Window/Preferences/General/Network Connections and the proxy host and port numbers are correct for HTTP and the other schemas.
How can I tell if this connection error is at my end?
I appreciate anyone looking into this, but it's working now.
I deleted my extracted juno directory and re-extracted it from the zip, with a different zip utility. The update site worked this time when attempting to install the SVN Team plugin.