EWS: Streaming Notifications vs Push Notifcations

Question

Microsoft Exchange introduced Streaming notifications as an alternative to pull/push notifications with Exchange 2010. Basic introduction on streaming can be found on this msdn article and blog

However, I cant figure out the actual advantage of streaming over push notifications. The only advantage mentioned in the blog is "..and you don’t have to create a listener application as for the push notifications." Apart from that, are there any other advantages and disadvantages? How do other factors like managing the subscription, re-subscription logic, scalability, max num of subscriptions, etc compare over push? Also, Streaming subscription has a maximum alive time of 30 mins and I would have to re-subscribe every 30 mins? Isnt that a disadvantage for a large number of subscriptions(my application has to manage 20K+ mailboxes)?

Any light on the comparison factors would be helpful.

Answer 1

The main reason for Streaming Notifications (SNs) is Exchange Online. You can't have EOL opening up an HTTP connection to an application potentially behind a firewall. Even within a corporate network there are firewall issues. I've had several cases where my app could not get Push Notifications (PNs) because of the firewall on its own server.

On the surface SNs would also seem to be more efficient because each notification is not opening up its own TCP connection, but rather they flow in on a single pipe. After doing some Wiresharking on this, I'm not really convinced this is so because it seems like under the covers they're doing Long Polling, so each notification coming in will cause a new HTTP call back up to Exchange.

The 30 minute max is no big deal, just reopen the connection in the handler and you're done--you don't have to actually re-subscribe. In fact, I am of the opinion that I want to lower that even more to say 3 minutes. You apparently cannot add new subscriptions or remove old ones except within the disconnect handler. (Try it, and you get errors.)

And yes, you don't have to code an HTTP handler, which is nice I guess.