In its simplest form, snapshot replication is based on a model of one-way replication; that is, data is replicated from a Publisher to a Subscriber. However, Microsoft® SQL Server™ builds additional functionality into this model by allowing Subscribers to modify replicated data as well. The Immediate-updating Subscribers option provides latent transactional consistency to other Subscribers (it is immediate between the Subscriber doing the updating and the Publisher) without requiring that updates only be done at the publishing site. This option is set at the time the publication is created and allows a Subscriber to update the copy of its local data, as long as that update can be immediately reflected to the Publisher by using the two-phase commit protocol (2PC). 2PC is managed by Microsoft Distributed Transaction Coordinator (MS DTC). If the update can be performed using 2PC, then the Publisher propagates those changes to all other Subscribers according to the Distribution Agent schedule (or at the time of the next snapshot refresh, if it is a snapshot publication). Because the Subscriber making the update already has the data changes reflected locally, the user can continue working with the updated data secure in the guarantee that the Publisher data also reflects the change. There is no loss of transactional integrity.
For more information about the immediate-updating Subscribers option, see Option: Immediate-updating Subscribers (Transactional).