thx for the note. It's not necessarily related to realtime; the question is, how to connect to a service from
a) the user's client,
b) the DSP.
Let me explain a bit:
a) Think of a blog, where users can comment (or post) while they're offline (e.g. using Couchbase or CouchDB). As soon as they go online, the client starts synching with the server (using e.g. Couchbase Sync Gateway or PouchDB's synching mechanism). For this to happen, the client needs to connect to the sync gateway directly (or through a proxy). In that case the user would be connected to the DB twice (once through the DSP, and once through the Sync-Gateway).
b) The DSP collects 'live data' (e.g. Traffic data) and connects it's clients to this live data stream (either individually or in groups). Even if no user is logged in, collecting data proceeds.
It's a bit tricky to explain, but I hope you get the idea.
An additional note: Using the DSP as frontend for these kind of things, allows me to hide away the target systems IP and connection-credentials. This provides an extra layer of security. But when I need to forward the IP to the user's client, this advantage is gone.