[Users] SER in production environment (reloaded)

Hello, I've already posted message on this topic, but some questions remain unanswered. My concerns are bout the pa module (presence). * Does it support RFC3857 to allow authorization management of subscriptions? * Any ideas if the presence server can be easily distributed on several machines? - What kind of database is used (to ensure having up-to-date data on each server) ? - How to determine which server sends the status change's notification to users? * How can one estimate the required bandwidth (5000 online users, with avg 40 users per contact list, is likely to generate many NOTIFY message) * Is it possible to performs computation before proceeding (to check account credit before giving access to a service) Regards, Luba Vincent