unable to retrieve xmldsig schema

http://www.w3.org/TR/xmldsig-core/#sec-Schema specifies that the canonical location for the corresponding schema is: http://www.w3.org/TR/xmldsig-core/xmldsig-core-schema.xsd

Attempts to retrieve this document frequently time out with no response from the server for over 30 seconds.  Most other schema documents are provided promptly.

Peter