Contacts vs Subscribers in OCS 2007 R2

In OCS 2007 R2 deployments where you have a large amount of users with large contact lists you may have users that experience the problem of seeing colleagues with unknown presence. Troubleshooting this may prove to be difficult because there is nothing wrong with the system, it is by design. The reason for this is that the Default Presence Policy has a set of limits and restrictions that affect presence. The following table describes the available presence policy settings:
By default, the Default Policy and Service: Medium presence policies are installed when you deploy Office Communications Server 2007 R2. The following table describes the specific settings of the two presence policies
So what does this mean?
  • CategorySubscriptions: Defines how many users are getting your presence information
    • Max: 3000 / 5 = 600. Additional users will see you as presence unknown
    • We divide by 5 because of each category that make up the presence document
      • contactCard
      • calendarData
      • Note
      • Services
      • State categories
    • The result of this is that 400 hundred out of thousand users how have you in their contact list will see presence unknown
    • Setting a large number here will have a significant impact on performance if the average user has a larger number of users subscribing to their presence
  • PromptedSubscribers: Maximum Number of Queued Presence Subscription Alerts
    • Max: 500
    • Determines the maximum number of prompts that can be queued up for a given user
      • An “acknowledgement prompt” is created when a subscriber subscribes to a users presence
      • Once the user acknowledges the subscription, the entry is moved
      • Most of the time there will only be a few entries in this table (assuming the user acknowledges the prompts and doesn’t just ignore them)
    • This table could get full in certain situations when users are imported into the system
    • Setting a larger number here has no real impact on performance
  • “Maximum contacts per user”: Maximum number of contacts per users contact list
    • Max 1000, default 200
    • If you have 1000 users and all those 1000 users have indeed 1000 contacts, then each user will get presence unknown for 400 contacts
Conclusion:
If you see users start getting presence unknown you should expand the numbers of CategorySubscriptions in the Default Policy for presence. If you still get issues with this you should help your customer reevaluate how they use the contact list in Communicator. One of the strengths with Communicator is that you don’t need to add the entire organization to you list because you are able to search up contacts you are not collaborating with on a daily basis and see their presence status.

As long as you have 1000 users and only a few have indeed 1000 contacts and the others have lots less so that no user gets more than 600 subscriptions, then nobody will get presence unknown. You could say to be on the safe side they should allow “Maximum contacts per user” only 600. But Microsoft decided to allow slightly more as the experience in practice is that not all users will indeed add contacts to the max but a few wants to, and that´s what they are making possible.

 
References:

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