The server for MKDC online fluctuates on a regular basis but usually holds good enough to have an enjoyable online experience.

It is not uncommon for people with wirless internet to experience difficulties on PS3 due to the server sometimes.

If you are having continual difficulties that you feel are not your system or anything minor. I would suggsting contacting your Internet provider to do a connection test. If all is well, then it must be on their end.