A data center is not of much use if it is totally disconnected from the rest of the organization that it serves. Depending on the disaster recovery plan and the nature of the disaster itself, your user community might be located miles away from the backup site. In these cases, good connectivity is vital to restoring production.
Another kind of connectivity to keep in mind is that of telephone connectivity. You must ensure that there are sufficient telephone lines available to handle all verbal communication with your users. What might have been a simple shout over a cubicle wall may now entail a long-distance telephone conversation; so plan on more telephone connectivity than might at first appear necessary.