Why is the Azure Service Bus not influenced by firewalls and proxies?

Question

I'm wondering why the Windows Azure Service Bus works through NATs, firewalls, proxies. Microsoft mentions this fact often but they do not mentioned why this works.

I think each participant initiates connections, ok, but this isn't enough. Do they "misuse" some open ports, 80?

Thanks

Answer 1

without running Wireshark to be able to tell for sure, my guess be because the client (behind a nat/firewall) initiates connection and keeps calling server (always open) for more information.

let's explain more: as tis works slightly differently in windows sockets (and other socket systems for that matter):

1. client (C) initiates connection to the server (S) on port 80

2. server then responds to client: too many calls on 80, let's move the connection to next free socket at port 90000 + rnd() = 90001

3. Client socket manager counts unused sockets on client, and say finds C:90012 port

4. client calls server at S:90001 and the proper connection is initiated between C:90012 and S:90001

5. This is what's gonna be written into nat table on a nat/firewall box and gonna allow communication between C <-> S